Patent Publication Number: US-2021176692-A1

Title: A radio network node, a wireless device and methods therein for re-establishing a radio connection

Description:
BACKGROUND 
     In a typical wireless communication network, wireless devices, also known as wireless communication devices, mobile stations, stations (STAs) and/or User Equipments (UEs), communicate via a Local Area Network (LAN) such as a WiFi network or a Radio Access Network (RAN) to one or more Core Networks (CN). The RAN covers a geographical area which is divided into service areas or cell areas, which may also be referred to as a beam or a beam group, with each service area or cell area being served by a radio network node such as a radio access node e.g., a Wi-Fi access point or a Radio Base Station (RBS), which in some networks may also be denoted, for example, a NodeB, eNodeB (eNB), or gNB as denoted in 5G. A service area or cell area is a geographical area where radio coverage is provided by the radio network node. The radio network node communicates over an air interface operating on radio frequencies with the wireless device within range of the radio network node. 
     Specifications for the Evolved Packet System (EPS), also called a Fourth Generation (4G) network, have been completed within the 3rd Generation Partnership Project (3GPP) and this work continues in the coming 3GPP releases, for example to specify a Fifth Generation (5G) network also referred to as 5G New Radio (NR). The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access network, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a variant of a 3GPP radio access network wherein the radio network nodes are directly connected to the EPC core network rather than to RNCs used in 3G networks. In general, in E-UTRAN/LTE the functions of a 3G RNC are distributed between the radio network nodes, e.g. eNodeBs in LTE, and the core network. As such, the RAN of an EPS has an essentially “flat” architecture comprising radio network nodes connected directly to one or more core networks, i.e. they are not connected to RNCs. To compensate for that, the E-UTRAN specification defines a direct interface between the radio network nodes, this interface being denoted the X2 interface. 
     Multi-antenna techniques may significantly increase the data rates and reliability of a wireless communication system. The performance is in particular improved if both the transmitter and the receiver are equipped with multiple antennas, which results in a Multiple-Input Multiple-Output (MIMO) communication channel. Such systems and/or related techniques are commonly referred to as MIMO. 
     In addition to faster peak Internet connection speeds, 5G planning aims at higher capacity than current 4G, allowing higher number of mobile broadband users per area unit, and allowing consumption of higher or unlimited data quantities in gigabyte per month and user. This would make it feasible for a large portion of the population to stream high-definition media many hours per day with their mobile devices, when out of reach of Wi-Fi hotspots. 5G research and development also aims at improved support of machine to machine communication, also known as the Internet of things, aiming at lower cost, lower battery consumption and lower latency than 4G equipment. 
     1.1 Inter-RAT and Inter 5GC Working in LTE and NR 
     The 5G network in the 3GPP introduces both a new core network (5GC) and a new Radio Access Network (NR). The core network, 5GC, will however, also support other RATs than NR. It has been agreed that the LTE (or E-UTRA) RAT should also be connected to the 5GC. LTE base stations (eNBs) that are connected to the 5GC is called ng-eNB and is part of the NG-RAN which also consists of NR base stations called gNBs.  FIG. 1  schematically shows how the base stations are connected to each other and to the nodes in the 5GC. 
     Currently in an LTE (EUTRA) RAT connected to the 5GC (5G Core network) and in the NR RAT the state transitions schematically illustrated in  FIG. 2  are supported.  FIG. 2  schematically illustrates UE state machine and state transitions between NR/5GC, E-UTRA/EPC and E-UTRA/5GC. 
     As shown it is possible to move ongoing UE connection i.a. a UE is in an RRC_CONNECTED state between the two RATs using a handover procedure. 
     Additionally (not shown) it is possible for the network to move the UE to the other RAT by sending a Release message with re-direct information. When the UE is in an IDLE state or an INACTIVE state the cell reselection procedure will be used when transiting between the RATs. Within the RATs there is also an RRC Re-establishment procedure which may be triggered if the UE loses the radio connection, e.g. due to a Radio Link Failure (RLF) or at intra- or inter-RAT handover failure. The RRC re-establishment procedure is not supported between the RATs, instead the UE which e.g. experiences an RLF in one RAT will if it find a suitable cell in a different RAT performing a transition to the RRC_IDLE state and perform a new RRC connection setup (further elaborated in next section). 
     In NR and E-UTRA, i.e. LTE connected to 5GC, it has been introduced a new RRC state called an RRC_INACTIVE state. In this disclosure, the term NG-RAN refers to either NR or LTE connected to 5G Core network. 
     1.2 RRC Reestablishment in Both NR Rel-15 and LTE 
     In a NR RAT, if a UE in an RRC_CONNECTED state detects a radio link failure (RLF) on the Master Cell Group (MCG) in the NR and the LTE, or if the UE fails a handover, the UE selects a suitable cell and initiates an RRC reestablishment. The definition of a suitable cell in TS 38.300 is:
         A suitable cell is one for which the measured cell attributes satisfy the cell selection criteria; the cell Public Land Mobile Network (PLMN) is the selected PLMN, registered or an equivalent PLMN; the cell is not barred or reserved and the cell is not part of a tracking area which is in the list of “forbidden tracking areas for roaming”;       

     If the UE selects an NR cell, the UE stops a timer T 311  and initiates the re-establishment procedure by starting the timer T 301  and transmitting the re-establishment request. However, if the UE selects an inter-RAT cell, e.g. an LTE cell connected to EPC or an LTE cell connected to 5GC, the UE will transition to an IDLE state and perform NAS signalling which is less optimized than re-establishment. So, if the UE is in an RRC_CONNECTED state in the NR RAT it will enter the RRC_IDLE state and upper layers may trigger a new connection. For NR, that is specified in TS 38.331 in 5.3.7.3 as follows: 
     TS 38.331 section 5.3.7.3 Actions following cell selection while T 311  is running 
     Upon selecting a suitable NR cell, the UE shall: 
     1&gt; stop timer T 311 ; 
     1&gt; start timer T 301 ; 
     1&gt; initiate transmission of the RRCReestablishmentRequest message in accordance with 5.3.7.4 
     NOTE: This procedure applies also if the UE returns to the source PCell. 
     Upon selecting an inter-RAT cell, the UE shall: 
     1&gt; perform the actions upon going to RRC_IDLE as specified in 5.3.11, with release cause ‘RRC connection failure’; 
     The behaviour described above for NR, according to TS 38.300 and TS 38.331 is similar the one in LTE, given in TS 36.300 and TS 36.331, with few differences e.g. in the structure of the messages. During the reestablishment procedure in any of the RATs in the intra-RAT case, the UE prepares and transmits the RRCConnectionReestablishmentRequest in E-UTRA if failure happens declared in E-UTRA, or the RRCRestablishmentRequest in NR if failure happens in NR. 
     
       
         
           
               
             
               
                   
               
               
                 RRCConnectionReestablishmentRequest message 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 -- ASN1START 
                   
               
               
                 RRCConnectionReestablishmentRequest ::=  
                 SEQUENCE { 
               
               
                  criticalExtensions  
                 CHOICE { 
               
            
           
           
               
            
               
                   rrcConnectionReestablishmentRequest-r8 
               
            
           
           
               
               
            
               
                   
                  RRCConnectionReestablishmentRequest-r8-IEs, 
               
               
                   criticalExtensionsFuture  
                  SEQUENCE { } 
               
            
           
           
               
            
               
                  } 
               
               
                 } 
               
               
                 RRCConnectionReestablishmentRequest-r8-IEs ::= SEQUENCE { 
               
            
           
           
               
               
            
               
                  ue-Identity  
                 ReestabUE-Identity, 
               
               
                  reestablishmentCause  
                 ReestablishmentCause, 
               
               
                  spare  
                 BIT STRING (SIZE (2)) 
               
            
           
           
               
            
               
                 } 
               
            
           
           
               
               
            
               
                 ReestabUE-Identity ::=  
                 SEQUENCE { 
               
            
           
           
               
               
            
               
                  c-RNTI 
                 C-RNTI, 
               
               
                  physCellId 
                 PhysCellId, 
               
               
                  shortMAC-I 
                 ShortMAC-I 
               
            
           
           
               
            
               
                 } 
               
            
           
           
               
               
            
               
                 ReestablishmentCause ::= 
                 ENUMERATED { 
               
            
           
           
               
               
            
               
                   
                 reconfigurationFailure, handoverFailure, 
               
               
                   
                 otherFailure, spare1} 
               
            
           
           
               
            
               
                 -- ASN1STOP 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 RRCConnectionReestablishmentRequest field descriptions 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 physCellId 
               
               
                 The Physical Cell Identity of the PCell the UE was connected to prior 
               
               
                 to the failure. 
               
               
                 reestablishmentCause 
               
               
                 Indicates the failure cause that triggered the re-establishment procedure. 
               
               
                 eNB is not expected to reject a RRCConnectionReestablishmentRequest 
               
               
                 due to unknown cause value being used by the UE. 
               
               
                 ue-Identity 
               
               
                 UE identity included to retrieve UE context and to facilitate contention 
               
               
                 resolution by lower layers. 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 RRCReestablishmentRequest message 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 -- ASN1START 
               
               
                 -- TAG-RRCREESTABLISHMENTREQUEST-START 
               
            
           
           
               
               
            
               
                 RRCReestablishmentRequest ::=  
                 SEQUENCE { 
               
               
                  rrcReestablishmentRequest  
                   RRCReestablishmentRequest-IEs 
               
            
           
           
               
            
               
                 } 
               
            
           
           
               
               
            
               
                 RRCReestablishmentRequest-IEs ::=  
                  SEQUENCE { 
               
               
                  ue-Identity 
                    ReestabUE-Identity, 
               
               
                  reestablishmentCause 
                    ReestablishmentCause, 
               
               
                  spare 
                    BIT STRING (SIZE (1)) 
               
            
           
           
               
            
               
                 } 
               
            
           
           
               
               
            
               
                 ReestabUE-Identity ::= 
                   SEQUENCE { 
               
               
                  c-RNTI 
                    RNTI-Value, 
               
               
                  physCellId 
                    PhysCellId, 
               
               
                  shortMAC-I 
                    ShortMAC-I 
               
            
           
           
               
            
               
                 } 
               
            
           
           
               
               
            
               
                 ReestablishmentCause ::= 
                   ENUMERATED { 
               
               
                   
                    reconfigurationFailure,  
               
            
           
           
               
            
               
                 handoverFailure, otherFailure, spare1} 
               
               
                 -- TAG-RRCREESTABLISHMENTREQUEST-STOP 
               
               
                 -- ASN1STOP 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 RRCReestablishmentRequest field descriptions 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 physCellId 
               
               
                 The Physical Cell Identity of the PCell the UE was connected to prior 
               
               
                 to the failure. 
               
               
                 reestablishmentCause 
               
               
                 Indicates the failure cause that triggered the re-establishment procedure. 
               
               
                 gNB is not expected to reject a RRCReestablishmentRequest due to 
               
               
                 unknown cause value being used by the UE. 
               
               
                 ue-Identity 
               
               
                 UE identity included to retrieve UE context and to facilitate contention 
               
               
                 resolution by lower layers. 
               
               
                   
               
            
           
         
       
     
     In both LTE and NR, the different RRC Reestablishment messages contain a ue-Identity, which contain a security token, e.g. shortMAC-I, used to authenticate the UE in the serving node hosting the UE AS context, when the UE tries to re-establish the connection after the failure. 
     1.3 Message Authentication Code-Integrity 
     In LTE and NR, integrity protection of messages is performed in the Packet Data Convergence Protocol (PDCP) in both the network and the UE by computing a Message Authentication Code-Integrity (MAC-I) which is included in the PDCP header. When the receiver receives the PDCP packet it computes and verifies the MAC-I using the same inputs and algorithms as the transmitter so that each side may be authenticated. The derivations are specified in TS 33.401 and TS 33.501 for EPS and 5GS respectively, although the only difference is which algorithms are applied. For E-UTRA connected to either EPC or 5GC, the algorithms used are defined in TS 33.401, while for NR, the algorithms used are defined in TS 33.501: 
     Below is an excerpt from TS 33.501 v 15.1.0 (2018-06) for the derivation of the MAC-I: 
     The input parameters to the integrity algorithm are a 128-bit integrity key named KEY, a 32-bit COUNT, a 5-bit bearer identity called BEARER, the 1-bit direction of the transmission i.e. DIRECTION, and the message itself i.e. MESSAGE. The DIRECTION bit shall be 0 for uplink and 1 for downlink. The bit length of the MESSAGE is LENGTH. 
       FIG. 3  schematically illustrates the use of the NR Integrity Algorithm (NIA) to authenticate the integrity of messages. 
     Based on these input parameters the sender computes a 32-bit message authentication code (MAC-I/NAS-MAC) using the integrity algorithm NIA. The message authentication code is then appended to the message when sent. For integrity protection algorithms, the receiver computes the expected message authentication code (XMAC-I/XNAS-MAC) on the message received in the same way as the sender computed its message authentication code on the message sent and verifies the data integrity of the message by comparing it to the received message authentication code, i.e. MAC-I/NAS-MAC. 
     The integrity protection is always applied for control signaling, e.g. for RRC messages, and is configurable for user plane messages in NR. 
     SUMMARY 
     Embodiments disclosed herein relate to inter-RAT connection reestablishment i.e. when the UE being connected in one RAT, e.g. a first RAT, detects a failure and needs to reestablish in another RAT, e.g. a second RAT. The first and second RATs are different RAT. In prior art, it is not clear how the UE should calculate the security token, e.g. a MAC-I, of a target RAT, e.g. the second RAT, and how the UE should handle the input parameters when it has been connected in a cell from a different source RAT, e.g. the first RAT, since the input parameters used are different in the two RATs e.g. in terms of the number of bits, their exact meaning, etc. 
     An object of embodiments disclosed herein is therefore to overcome or at least ameliorate the drawbacks with the prior art. 
     According to an aspect of embodiments herein, the object is achieved by a method performed by a wireless device for re-establishing a radio connection in a wireless communications network comprising a first Radio Access Technology (RAT) and a second RAT being different from the first RAT. The wireless device is operating in a first cell served by a first radio network node operating in the first RAT. 
     When a connection failure with the first cell served by the first radio network node is detected, the wireless device performs a cell selection and selects a second cell served by a second radio network node operating in the second RAT. The second cell is known by the wireless device to be a candidate for reestablishment. 
     The wireless device determines a first set of parameters associated with the first cell. The first set of parameters comprises at least one parameter identifying the wireless device or the first cell. 
     The wireless device receives a second set of parameters associated with the second cell. The second set of parameters comprises at least one parameter identifying the wireless device or the second cell. 
     Further, the wireless device determines a security token based on the first and second sets of parameters, and transmits, to the second cell, a re-establishment request message comprising the security token. 
     According to another aspect of embodiments herein, the object is achieved by a wireless device for re-establishing a radio connection in a wireless communications network comprising a first Radio Access Technology (RAT) and a second RAT being different from the first RAT. The wireless device is configured to operate in a first cell served by a first radio network node operating in the first RAT. 
     The wireless device is configured to perform a cell selection and selects a second cell served by a second radio network node operating in the second RAT, when a connection failure with the first cell served by the first radio network node is detected. The second cell is known by the wireless device to be a candidate for reestablishment. 
     The wireless device is configured to determine a first set of parameters associated with the first cell. The first set of parameters comprises at least one parameter identifying the wireless device or the first cell. 
     The wireless device is configured to receive a second set of parameters associated with the second cell. The second set of parameters comprises at least one parameter identifying the wireless device or the second cell. 
     Further, the wireless device is configured to determine a security token based on the first and second sets of parameters, and to transmit, to the second cell, a re-establishment request message comprising the security token. 
     According to another aspect of embodiments herein, the object is achieved by a method performed by a first radio network node for assisting a wireless device in re-establishing a radio connection in a wireless communications network comprising a first RAT and a second RAT being different from the first RAT. The wireless device is operating in a first cell served by the first radio network node operating in the first RAT. 
     The first radio network node provides the wireless device with a first set of parameters associated with the first cell. The first set of parameters comprises at least one parameter identifying the wireless device or the first cell. 
     The first radio network node receives, from a second radio network node operating in the second RAT, a second set of parameters associated with a second cell served by the second radio network node. 
     Further, the first radio network node receives, from the second radio network node, a security token received by the second radio network node in a re-establishment request message from the wireless device when a failure of a radio connection with the first radio network node has been detected. 
     The first radio network node determines an expected security token based on the first and second sets of parameters and verifies the wireless device&#39;s identity by means of the received security token and the determined expected security token. 
     The first radio network node transmits, to the second radio network node, one or more configurations and/or parameters relating to the radio connection to be re-established, when the wireless device is verified as valid. 
     According to another aspect of embodiments herein, the object is achieved by a first radio network node for assisting a wireless device in re-establishing a radio connection in a wireless communications network comprising a first RAT and a second RAT being different from the first RAT. The wireless device is configured to operate in a first cell served by the first radio network node operating in the first RAT. 
     The first radio network node is configured to provide the wireless device with a first set of parameters associated with the first cell. The first set of parameters comprises at least one parameter identifying the wireless device or the first cell. 
     The first radio network node is configured to receive, from a second radio network node operating in the second RAT, a second set of parameters associated with a second cell served by the second radio network node. 
     Further, the first radio network node is configured to receive, from the second radio network node, a security token received by the second radio network node in a re-establishment request message from the wireless device when a failure of a radio connection with the first radio network node has been detected. 
     The first radio network node is configured to determine an expected security token based on the first and second sets of parameters and to verify the wireless device&#39;s identity by means of the received security token and the determined expected security token. 
     According to another aspect of embodiments herein, the object is achieved computer program comprises instructions, which when executed by at least one processor of the wireless device, cause the at least one processor of the wireless device to perform one or more of the actions described herein. 
     According to another aspect of embodiments herein, the object is achieved computer program comprises instructions, which when executed by at least one processor of the first radio network node, cause the at least one processor of the first radio network node to perform one or more of the actions described herein. 
     According to another aspect of embodiments herein, the object is achieved by a carrier comprising the respective computer program, wherein the carrier is one of an electronic signal, an optical signal, an electromagnetic signal, a magnetic signal, an electric signal, a radio signal, a microwave signal, or a computer-readable storage medium. 
     Since the wireless device determines the security token based on the first set of parameters associated with the first cell of the first RAT from which first cell a link failure is detected and based on the second set of parameters associated with the second cell of the second RAT being different from the first RAT, a connection may be re-established after a link failure based on the old configurations instead of being released and re-established from scratch. Thereby, the signaling needed to re-establish the connection after the link failure is reduced as is the time needed for resuming the connection. This results in an improved performance of the wireless communications network. 
     An advantage of some embodiments disclosed herein is that they enable the wireless device to be connected in one RAT, e.g. in LTE or NR, and then attempt to reestablish in the other RAT if the wireless device experiences a failure in the first RAT triggering re-establishment. Thanks to that, faster recovery is possible as the RRC reestablishment procedure is expected to be faster to execute than transition via the RRC_IDLE state which is the existing solution for the inter-RAT scenarios in Rel-15 specifications. For example, this is particularly likely since NR maybe deployed in quite high frequencies and relies on beamforming, where radio related failures may be more common than in current systems. Then, the wireless device could efficiently re-connect to LTE. 
     Another advantage of some embodiments disclosed herein is that it they provide for a secured solution for inter-RAT reestablishment. Without embodiments disclosed herein, the wireless device and the radio network node would not be able to calculate the security token required to authenticate the wireless device during an inter-RAT reestablishment procedure or during any procedure where the first RAT and re-establishment second RAT have different formatting for the security token calculation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Examples of embodiments herein are described in more detail with reference to attached drawings in which: 
         FIG. 1  is a schematic block diagram illustrating a 5G wireless communications network according to prior art; 
         FIG. 2  is a schematic block diagram illustrating a UE state machine and state transitions between an EUTRA access network and a NR access network according to prior art; 
         FIG. 3  is a schematic block diagram illustrating input parameters to and output parameter from an NR integrity algorithm NIA at a sender and a receiver, respectively, according to prior art; 
         FIG. 4A  is a combined signaling scheme and flowchart illustrating signaling for inter-RAT re-establishment when a UE detects a failure in NR while in an RRC_CONNECTED state and upon selecting a cell in LTE triggers an re-establishment; 
         FIG. 4B  is a combined signaling scheme and flowchart illustrating signaling for inter-RAT re-establishment when a UE detects a failure in LTE while in an RRC_CONNECTED state and upon selecting a cell in NR triggers an re-establishment; 
         FIG. 5  is a schematic block diagram illustrating embodiments of a wireless communications network; 
         FIG. 6  is a flowchart depicting embodiments of methods in a wireless device; 
         FIG. 7  is schematic block diagram illustrating embodiments of a wireless device; 
         FIG. 8A  is a flowchart depicting embodiments of methods in a first radio network node; 
         FIG. 8B  is schematic block diagram illustrating embodiments of a first radio network node; 
         FIG. 9A  is a flowchart depicting embodiments of methods in a second radio network node; 
         FIG. 9B  is schematic block diagram illustrating embodiments of a second radio network node; 
         FIG. 10  is a flowchart depicting embodiments of methods in a wireless device connected in LTE that detects a failure and re-establishes in LTE or NR, and when resuming in NR calculating an inter-RAT security token using NR format and procedures; 
         FIG. 11  is a flowchart depicting embodiments of methods in a wireless device connected in NR that detects a failure and re-establishes in NR or LTE, and when resuming in LTE calculating an inter-RAT security token using LTE format and procedures; 
         FIG. 12  is a flowchart depicting embodiments of methods in a wireless device connected in LTE detects a failure and re-establishes in LTE or NR, and when resuming in NR calculating an inter-RAT security token using LTE format and NR procedures; 
         FIG. 13  is a flowchart depicting embodiments of methods in a wireless device connected in NR that detects a failure and re-establishes in LTE or NR, and when resuming in LTE calculating an inter-RAT security token using NR format and LTE procedures; 
         FIG. 14  is a flowchart depicting embodiments of methods in a wireless device connected in LTE that detects a failure and re-establishes LTE or NR, and when resuming in NR calculating an inter-RAT security token using a new Information Element (IE) defined in NR format and using NR procedures; 
         FIG. 15  is a flowchart depicting embodiments of methods in a wireless device connected in NR that detects a failure and re-establishes NR or LTE, and when resuming in LTE calculating an inter-RAT security token using a new Information Element (IE) defined in LTE format and using LTE procedures; 
         FIG. 16  is a flowchart depicting embodiments of methods in a wireless device connected in LTE that detects a failure and re-establishes in LTE or NR, and when resuming in NR calculating an inter-RAT security token using a new Information Element (IE) defined in LTE format and using NR procedures; 
         FIG. 17  is a flowchart depicting embodiments of methods in a wireless device connected in NR that detects a failure and re-establishes NR or LTE, and when resuming in LTE calculating an inter-RAT security token using a new Information Element (IE) defined in NR format and using LTE procedures; 
         FIG. 18  schematically illustrates a telecommunication network connected via an intermediate network to a host computer; 
         FIG. 19  is a generalized block diagram of a host computer communicating via a base station with a user equipment over a partially wireless connection; and 
         FIGS. 20-23  are flowcharts illustrating methods implemented in a communication system including a host computer, a base station and a user equipment. 
     
    
    
     DETAILED DESCRIPTION 
     As a part of developing embodiments herein a problem will first be identified and discussed. 
     2.1 Inter-RAT Re-Establishment Between NR and eLTE 
     In both LTE and NR, when the UE detects a radio link failure it needs to select a suitable cell and, if that cell is in the same RAT, the UE initiates an RRC reestablishment procedure. However, if the cell the UE re-selects to is an inter-RAT cell, the UE will release the AS context and go to an RRC_IDLE state, possibly triggering NAS recovery with a new connection establishment. 
     The performance of the RRC re-establishment procedure is much better than the performance of a procedure going via the IDLE state. In LTE connected to the EPC, upon transmitting a re-establishment request like message, the network, e.g. the serving node hosting the UE AS Context, is able to verify the UE thanks to the security token short MAC-I. Then the UE receives a re-establishment message for the SRB1 setup and sends a complete message. Afterwards, the UE receives an RRC Reconfiguration. This may either occur upon the triggering of the RLF or upon the expiry of the timer T 304  during handover, i.e. during handover failure. In the re-establishment case the core network connection does not need to be teared down and both the UE and the network may be prepared in terms of security. 
     Despite these benefits in re-establishment, inter-RAT re-establishment in LTE towards other RATs, like UTRA or GSM, was not supported. That seemed quite complex and perhaps not feasible since other RATs, e.g. the UTRAN and the GSM; would always have different core networks. And, it would not be possible to identify the UE AS context and maintain the CN connection. 
     In NR, for release 15, inter-RAT re-establishment at least between NR and eLTE, i.e. when LTE is connected to 5GC, was considered and has quite some likelihood to be standardized in further NR releases. In NR and eLTE, inter-RAT re-establishment is feasible thanks to the fact that the same CN is used for both eLTE and NR. In other words both RATs are connected to the same core network. Also, many aspects are to certain extent harmonized across RATs such as security algorithms and overall framework, higher layers protocols (like PDCP), etc. Such a solution also becomes attractive as it is likely that a UE connected to an NR cell may experience sudden drop in radio conditions which may lead to RLF and/or handover (reconfiguration with sync) failures due to the higher frequencies of NR. Notice that LTE or eLTE here refers to the EUTRA radio interface. 
     In the context of some embodiments, the term inter-RAT re-establishment is mostly used when the UE detects a failure in a first RAT, e.g. in NR, while being in an RRC_CONNECTED state and, upon selecting a cell in a second RAT, e.g. in eLTE, triggers a re-establishment instead of going via an RRC_IDLE state, as shown in the  FIGS. 4A and 4B  below for the successful case. 
     By the term security token when used herein is meant a message authentication token or some secure signature which may only be generated by an UE that has access to the correct session keys. The generation of the security token may be done using a secure algorithm, e.g. secure hash, checksum, integrity protection algorithm or other. The security token may be a Message Authentication Code (MAC) or a part thereof. In this disclosure the terms security token and message authentication token may be used interchangeably. 
     Sometimes in this disclosure reference to the expiry of a timer is made. It should be understood that such a reference refers to the expiry of a time period. 
     An existing solution is the intra-RAT re-establishment procedure/messages in NR and eLTE. When the UE attempts the RRC Reestablishment, it transmits an RRC 
     Reestablishment Request message, which contains a security token, e.g. a shortMAC-I, used to authenticate the UE. 
     Some embodiments disclosed herein relate to inter-RAT connection reestablishment i.e. when the UE being connected in one RAT, e.g. a first RAT, detects a failure and needs to reestablish in another RAT, e.g. a second RAT. The first and second RATs are different RAT. In prior art, it is not clear how the UE calculates the security token, e.g. a MAC-I, of a target RAT, e.g. the second RAT, and how it handles input parameters when it has been connected in a cell from a different source RAT, e.g. the first RAT, since the input parameters used are different in the two RATs e.g. in terms of the number of bits, their exact meaning, etc. 
     For a NR re-establishment, the calculation of the security token according to TS 38.331 section 5.3.7.4 is shown below. 
     TS 38.331 5.3.7.4 Actions related to transmission of RRCReestablishmentRequest message 
     The UE shall set the contents of RRCReestablishmentRequest message as follows: 
     1&gt; set the ue-Identity as follows: 
     2&gt; set the c-RNTI to the C-RNTI used in the source PCell (reconfiguration with sync or mobility from NR failure) or used in the PCell in which the trigger for the re-establishment occurred (other cases); 
     2&gt; set the physCellId to the physical cell identity of the source PCell (reconfiguration with sync or mobility from NR failure) or of the PCell in which the trigger for the re-establishment occurred (other cases); 
     2&gt; set the shortMAC-I to the 16 least significant bits of the MAC-I calculated: 
     3&gt; over the ASN.1 encoded as per section 8 (i.e., a multiple of 8 bits) VarShortMAC-Input; 
     3&gt; with the K RRCint  key and integrity protection algorithm that was used in the source PCell (reconfiguration with sync or mobility from NR failure) or of the PCell in which the trigger for the re-establishment occurred (other cases); and 
     3&gt; with all input bits for COUNT, BEARER and DIRECTION set to binary ones; 
     2&gt; if the re-establishment procedure was initiated due to reconfiguration failure as specified in 5.3.5.8: 
     3&gt; set the reestablishmentCause to the value reconfigurationFailure; 
     2&gt; else if the re-establishment procedure was initiated due to reconfiguration with sync failure as specified in 5.3.5.8.3 (intra-NR handover failure) or 5.4.3.5 (inter-RAT mobility from NR failure): 
     3&gt; set the reestablishmentCause to the value handoverFailure; 
     2&gt; else: 
     3&gt; set the reestablishmentCause to the value otherFailure; 
     1&gt; restore the RRC configuration and security context from the stored UE AS context; 
     1&gt; restore the PDCP state and re-establish PDCP for SRB1; 
     1&gt; re-establish RLC for SRB1; 
     1&gt; resume SRB1; 
     1&gt; The UE shall submit the RRCReestablishmentRequest message to lower layers for transmission. 
     The UE variable in NR with the parameters to compute the security token for the re-establishment (e.g. short MAC-I) is shown below:
         VarShortMAC-Input       

     The UE variable VarShortMAC-Input specifies the input used to generate the shortMAC-I during RRC Connection Reestablishment procedure. 
     
       
         
           
               
             
               
                   
               
               
                 VarShortMAC-Input variable 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 -- ASN1START 
               
               
                   
                 -- TAG-VAR-SHORTMACINPUT-START 
               
            
           
           
               
               
               
            
               
                   
                 VarShortMAC-Input ::=  
                 SEQUENCE { 
               
               
                   
                  sourcePhysCellId 
                  PhysCellId, 
               
               
                   
                  targetCellIdentity 
                  CellIdentity, 
               
               
                   
                  source-c-RNTI 
                  RNTI-Value 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 -- TAG-VAR- SHORTMACINPUT-STOP 
               
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 VarShortMAC-Input field descriptions 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 targetCellIdentity 
               
               
                 Set to CellIdentity of the target cell i.e. the cell the UE is trying to 
               
               
                 reestablish the connection. 
               
               
                 source-c-RNTI 
               
               
                 Set to C-RNTI that the UE had in the PCell it was connected to prior to 
               
               
                 the reestablishment. 
               
               
                 sourcePhysCellId 
               
               
                 Set to the physical cell identity of the PCell the UE was connected to 
               
               
                 prior to the RRC connection. 
               
               
                   
               
            
           
         
       
     
     For the LTE re-establishment, the calculation of the security token according to TS 36.331 also in section 5.3.7.4 is shown below: 
     TS 36.331 5.3.7.4 Actions related to transmission of RRCConnectionReestablishmentRequest message 
     Except for NB-IoT, if the procedure was initiated due to radio link failure or handover failure, the UE shall:
         1&gt; set the reestablishmentCellId in the VarRLF-Report to the global cell identity of the selected cell;       

     The UE shall set the contents of RRCConnectionReestablishmentRequest message as follows:
         1&gt; except for a NB-IoT UE for which AS security has not been activated, set the ue-Identity as follows:
           2&gt; set the c-RNTI to the C-RNTI used in the source PCell (handover and mobility from E-UTRA failure) or used in the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; set the physCellId to the physical cell identity of the source PCell (handover and mobility from E-UTRA failure) or of the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; set the shortMAC-I to the 16 least significant bits of the MAC-I calculated:
               3&gt; over the ASN.1 encoded as per section 8 (i.e., a multiple of 8 bits) VarShortMAC-Input (or VarShortMAC-Input-NB in NB-IoT);   3&gt; with the KRR Cint  key and integrity protection algorithm that was used in the source PCell (handover and mobility from E-UTRA failure) or of the PCell in which the trigger for the re-establishment occurred (other cases); and   3&gt; with all input bits for COUNT, BEARER and DIRECTION set to binary ones;   
               
           1&gt; for a NB-IoT UE for which AS security has not been activated, set the ue-Identity as follows:
           2&gt; request upper layers for calculated ul-NAS-MAC and ul-NAS-Count using the cellIdentity of the PCell in which the trigger for the re-establishment occurred;   2&gt; set the s-TMSI to the S-TMSI provided by upper layers;   2&gt; set the ul-NAS-MAC to the ul-NAS-MAC value provided by upper layers;   2&gt; set the ul-NAS-Count to the ul-NAS-Count value provided by upper layers;   
           1&gt; set the reestablishmentCause as follows:
           2&gt; if the re-establishment procedure was initiated due to reconfiguration failure as specified in 5.3.5.5 (the UE is unable to comply with the reconfiguration):
               3&gt; set the reestablishmentCause to the value reconfigurationFailure;   
               2&gt; else if the re-establishment procedure was initiated due to handover failure as specified in 5.3.5.6 (intra-LTE handover failure) or 5.4.3.5 (inter-RAT mobility from EUTRA failure):
               3&gt; set the reestablishmentCause to the value handoverFailure;   
               2&gt; else:
               3&gt; set the reestablishmentCause to the value otherFailure;   
               
           1&gt; if the UE is a NB-IoT UE:
           2&gt; if the UE supports DL channel quality reporting and cqi-Reporting is present in SystemInformationBlockType2-NB:
               3&gt; set the cqi-NPDCCH to include the latest results of the downlink channel quality measurements of the serving cell as specified in TS 36.133 [16];
 
NOTE: The downlink channel quality measurements may use measurement period T 1  or T 2 , as defined in TS 36.133 [16]. In case period T 2  is used the RRC-MAC interactions are left to UE implementation.
   
               
           2&gt; set earlyContentionResolution to TRUE;       

     The UE shall submit the RRCConnectionReestablishmentRequest message to lower layers for transmission. 
     The UE variable in NR with the parameters to compute the security token for the re-establishment (e.g. short MAC-I) is shown below
         VarShortMAC-Input       

     The UE variable VarShortMAC-Input specifies the input used to generate the shortMAC-I. 
     
       
         
           
               
             
               
                   
               
               
                 VarShortMAC-Input UE variable 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 -- ASN1START 
               
            
           
           
               
               
               
            
               
                   
                 VarShortMAC-Input ::=  
                 SEQUENCE { 
               
               
                   
                  cellIdentity 
                  CellIdentity, 
               
               
                   
                  physCellId 
                  PhysCellId, 
               
               
                   
                  c-RNTI 
                  C-RNTI 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 VarShortMAC-Input field descriptions 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 cellIdentity 
               
               
                 Set to CellIdentity included in cellIdentity (without suffix) in SIB1 of 
               
               
                 the current cell. 
               
               
                 c-RNTI 
               
               
                 Set to C-RNTI that the UE had in the PCell it was connected to prior to 
               
               
                 the failure. 
               
               
                 physCellId 
               
               
                 Set to the physical cell identity of the PCell the UE was connected to 
               
               
                 prior to the failure. 
               
               
                   
               
            
           
         
       
     
     As shown above, in the case of LTE and NR, the input parameters used to calculate the MAC-I, e.g. exemplified in the UE variables VarShortMAC-Input in LTE TS 36.331, or in NR TS 38.331, are different and have different lengths and contains parameters related to both the source and the target cell. 
     Furthermore, it is not possible to simply use the parameters of one of the RATs, e.g. of the source RAT or of the target RAT, since the parameters are related to both the source cell and the target cell. For example, the CellIdentity in VarShortMAC-Input is associated with the current or target cell while the physCellId and the C-RNTI in VarShortMAC-Input are associated with the source cell. 
     For example, the following differences exist:
         targetCellIdentity: This is the CellIdentity of the target cell i.e. the cell the UE is trying to reestablish. In NR, that is defined as a bit string of 36 bits. In LTE, that is defined as a bit string of 28 bits.       

     source-C-RNTI: This is the C-RNTI that the UE had in the PCell it was connected to prior to the failure. In NR, that is defined as an integer between 0 and 65535, equivalent to a bit string of 16 bits. The same number of bits was defined in LTE. 
     sourcePhysCellId: Set to the physical cell identity of the PCell the UE was connected to prior to the failure. In NR, that is defined as an integer between 0 and 1007, coded as a bit string of 10 bits. In NR, that is defined as an integer between 0 and 503, coded as a bit string of 9 bits. 
     When a UE, e.g. a wireless device, reestablishes an RRC connection it must include a security token, e.g. a ShortMAC-I, in the RRC Reestablishment Request message and the network, e.g. a radio network node, calculates the same token to authenticate the UE. To calculate this security token, the UE and the network use input variables from the source cell and from the target cell. 
     If a UE is connected in one RAT, e.g. LTE or NR, and experiences an RLF or a handover failure and attempts to reestablish to another RAT, e.g. NR or LTE, the required input variables will be defined in the different RATs. The parameters will have different sizes and characteristics in the different RATs. 
     Some embodiments disclosed herein relate to how to convert parameters used to calculate the reestablishment security token from one RAT to another RAT, e.g. how to convert the source RAT parameter to the target RAT format or vice versa, or how to adapt the procedures to allow input parameters from different source and target RATs. 
     This may be achieved either by modifying the content of an existing message or introducing a new message and modifying the procedures. 
     Some embodiments herein focus on the handling of the security token used for authentication during RRC re-establishment, computed based on the MAC-I, in the case the source cell, e.g. the source radio network node serving the source cell, and the target cell, e.g. the target radio network node serving the target cell, have differences in the input parameters for the token calculation, such as in the case of inter-RAT re-establishment or any kind of inter-RAT radio link failure/re-establishment procedure. The method is then used when the UE detects a failure in one RAT and initiates re-establishment in another RAT. 
     Some embodiments herein provide multiple mechanisms at a UE and a network node for generating the short MAC-I, i.e. the security token used in re-establishment procedure, and similar cryptographic checksums in case of inter-RAT re-establishment procedures or more generally, in case both the source cell where UE is connected and detects radio link failure and the target cell where the UE tries to re-establish differs in the calculation of short MAC-I or its input parameters. Some embodiments herein comprise a UE that has detected radio link failure in one first source RAT and performs a re-establishment procedure in a second RAT, the method comprises one or more out of:
         Determining a first set of parameters associated to a first RAT, e.g. a source physical cell identity in first RAT, a source C-RNTI in first RAT. This may be triggered e.g. upon detecting a radio link failure, a handover failure, a beam failure, a reconfiguration with sync failure or any other failure or ordinary triggering leading to a re-establishment and/or initiating re-establishment;   Determining a second set of parameters associated to a second cell in a first RAT, e.g. to a target cell identity in first RAT. This may be done e.g. upon detection of radio link failure or before trying to re-establish in the first RAT;   Determining an updated version of one or multiple parameters from the first set of parameters associated to a first RAT, e.g. a source physical cell identity in first RAT, a source C-RNTI in first RAT. This may be done e.g. upon inter-RAT cell reselection, cell selection or before trying to re-establish in a second RAT. How these are determined is explained later in different embodiments.   Determining an updated version of one or multiple parameters in this second set of parameters associated to a second cell in a second RAT, e.g. to a target cell identity in the second RAT or any other parameters for replay attack avoidance or protocol discriminator. That may be done e.g. upon inter-RAT cell reselection or before trying to re-establish in the second RAT.   Upon re-establishing in a second RAT, after being connected and detecting a failure in a first RAT (or any other triggering to re-establishment procedure), using the first and/or second set of parameters, and/or updated version of the parameters to compute a security token to be included in the Re-establishment Request message in the second RAT.       

     Five exemplifying embodiments will be described in more detail below. These five exemplifying embodiments relate to: 
     Some first exemplifying embodiments. Convert source RAT parameter, e.g. C-RNTI and PCI, to a target RAT format by mapping, recalculating, truncating, or padding and use variables defined in the target RAT format to compute the security token. 
     Some second exemplifying embodiments. Convert target RAT parameters, e.g. Cell ID, to source RAT format by mapping, recalculating, truncating or padding and use variables defined in the source RAT format to compute the security token. 
     Some third exemplifying embodiments. Create new variable, e.g. a new Information Element (IE), allowing source parameters, e.g. C-RNTI and PCI, in source RAT format and target RAT parameters, e.g. Cell ID, in target RAT format. The new IE is defined in either the source RAT or in the target RAT. 
     Some fourth exemplifying embodiments. Create new variable or extend an existing variable to allow both RAT formats for all parameters, e.g. C-RNTI, PCI, and Cell ID, using e.g. a CHOICE structure. This variable may be used for both intra-RAT and inter-RAT calculation of the security token, e.g. the short MAC-I, during a failure and re-establishment procedure. The variable may be defined in only the LTE specification, only the NR specification, or in both LTE and NR specifications. 
     Some fifth exemplifying embodiments. Extend definition of existing variables to use dummy values in the target RAT format for the source parameters, e.g. for the C-RNTI and/or the PCI. 
     In addition, during handover, called re-configuration with sync in RRC specifications, the target gNB may be prepared with re-establishment information of the target cell and other neighboring cells in the HandoverPreparationInfo message. Since this message also comprises the security token, e.g. the short MAC-I, if the UE is provided with re-establishment information to inter RAT cells the short MAC-I would have to be calculated using any of the solutions described below. 
     It should be understood that one or more features from one or more exemplifying embodiments may be combined. 
     An object of embodiments herein is therefore to improve the performance of a wireless communications network for re-establishing a radio connection. 
     Embodiments herein may refer to Inter-RAT Checksum (MAC-I) calculation at RRC re-establishment, connection re-establishment, inactive state, RRC, security procedures. 
     An advantage of embodiments disclosed herein is that it enables a UE to be connected in one RAT, e.g. in LTE or NR, and then attempt to reestablish in the other RAT if it experiences a failure in the first RAT triggering re-establishment. Thanks to that, faster recovery is possible as the RRC reestablishment procedure is expected to be faster to execute than transition via the RRC_IDLE state which is the existing solution for the inter-RAT scenarios in Rel-15 specifications. That is particularly likely since NR maybe deployed in quite high frequencies and rely on beamforming, where radio related failures may be more common than in current systems. Then, the UE could efficiently re-connect to LTE. 
     Without embodiments disclosed herein, the UE and the network would not be able to calculate the security token required to authenticate the UE during an inter-RAT reestablishment procedure or during any procedure where source RAT and re-establishment target RAT have different formatting for the MAC-I calculation. Or, a secured solution for inter-RAT reestablishment would not be possible to use. 
     Embodiments herein are mostly exemplified with NR, LTE wireless devices but it may be applicable to other wireless devices which are served by other Radio Access Technologies such as CAT-M, NB-IoT, WiFi, or NR Carriers. 
     Embodiments herein relate to wireless communication networks in general. FIG. is a schematic overview depicting a wireless communications network  100 . The wireless communications network  100  may be referred to as a radio communications network. The wireless communications network  100  comprises one or more Radio Access Networks (RANs) and one or more Core Networks (CNs). The radio communications network  100  may use a number of different Radio Access Technologies (RATs), such as NB-IoT, CAT-M, Wi-Fi, eMTC, Long Term Evolution (LTE), LTE-Advanced, 5G, New Radio (NR), Wideband Code Division Multiple Access (WCDMA), Global System for Mobile communications/enhanced Data rate for GSM Evolution (GSM/EDGE), Worldwide Interoperability for Microwave Access (WiMax), or Ultra Mobile Broadband (UMB), just to mention a few possible implementations. Sometimes in this disclosure the wireless communications network  100  is referred to as just a network. 
     In the wireless communication network  100 , wireless devices e.g. a wireless device  120  also referred to as the first UE  120 , is operating in the wireless communications network  100 . One or more further wireless devices  122  also referred to as one or more second UEs  122  may operate in the wireless communications network  100 . As schematically illustrated in  FIG. 5 , the wireless device  120 , 122  may communicate with a network node, e.g. a network node  110 ,  112  which will be described below. 
     The wireless devices  120 ,  122  may each e.g. be a mobile station, a non-Access Point (non-AP) STA, a STA, a user equipment (UE) and/or a wireless terminals, an NB-IoT device, an eMTC device, Integrated Access Backhaul (IAB) node and a CAT-M device, a WiFi device, an LTE device and an NR device communicate via one or more Access Networks (AN), e.g. RAN, to one or more Core Networks (CN). It should be understood by the skilled in the art that “wireless device” is a non-limiting term which means any terminal, wireless communication terminal, user equipment, Device to Device (D2D) terminal, or node e.g. smart phone, laptop, mobile phone, sensor, relay, mobile tablets or even a small base station communicating within a cell. 
     In this disclosure, the terms wireless device, terminal and UE are used interchangeably. 
     Network nodes operate in the radio communications network  100 , such as a Radio Network Node (RNN)  110 , 112  also referred to as the first network node  110  and the second network node  112 , respectively, providing radio coverage over a respective geographical area, e.g. a service area  11  and a service area  12 , which may also be referred to as cells, beams or beam groups of a first Radio Access Technology (RAT), or a second RAT. The first and second RATs may be different RATs such as one of the RATs is a NR, 5G, LTE, Wi-Fi, NB-IoT, CAT-M, Wi-Fi, eMTC or similar, and the other RAT is another one of the NR, 5G, LTE, Wi-Fi, NB-IoT, CAT-M, Wi-Fi, eMTC or similar. The network node  110 , 112  may be a transmission and reception point e.g. a radio access network node such as a Wireless Local Area Network (WLAN) access point or an Access Point Station (AP STA), an access controller, a base station, e.g. a radio base station such as a NodeB, an evolved Node B (eNB, eNode B), a Next Generation Radio Access Network eNB (NG-RAN eNB, ng-eNB), a gNB, a base transceiver station, a radio remote unit, an Access Point Base Station, a base station router, a transmission arrangement of a radio base station, a stand-alone access point or any other network unit capable of communicating with a wireless device within the service area served by the network node  110 , 112  depending e.g. on the radio access technology and terminology used. The network node  110  may be referred to as a serving radio network node and communicates with the wireless device  120 ,  122  with Downlink (DL) transmissions to the wireless device  120 ,  122  and Uplink (UL) transmissions from the wireless device  120 ,  122 . 
     Further network nodes operate in the radio communications network  100 , such as a Mobility Network Node (MNN)  130  also referred to as a third network node  130 . The network node  130  may be a Mobility Management Entity (MME) which is a control node for an EPS access network, a Serving Gateway (SGW), and a Packet Data Network Gateway (PGW). An MME is amongst other responsible for tracking and paging procedure including retransmissions. Further the network node  130  may be an Access and Mobility Management Function (AMF) which is a control node for a 5GS access network, and a User Plane Function (UPF). Further, the network node  130  may be an Operation And Maintenance (OAM) node such as an Operation and Support System Radio and Core (OSS-RC) node or an Ericsson Network Management (ENM) node. 
     Further network nodes such as a location server  132  and a positioning server  134  operate in the radio communications network  100 . For example, the location server  30 , 132  may be an E-SMLC and the positioning server  134  may be an RTK server. The location server  132  and the positioning server  134  may communication with each other over a communications interface. 
     It should be understood that the positioning server  134  may be arranged external of the radio communications network  100  and in such a scenario the positioning server  134  may be referred to as an external positioning server  132  and the location server  132  and the positioning server  134  may communicate over an IP interface. 
     The positioning server  134  may sometimes herein be referred to as an RTK server or an RTK network provider. 
     Methods according to embodiments herein may be performed by any of the network node  110  such as e.g. an eNB, the wireless device  120 , e.g. the UE, the mobility network node  130 , the location server  132  and/or by the positioning server  134 . As an alternative, a Distributed Node (DN) and functionality, e.g. comprised in a cloud  140  as shown in  FIG. 5  may be used for performing or partly performing the methods. 
     In this disclosure, the first RAT is the RAT of the first radio network node  110  serving the wireless device  120  when operating in a first service area  11 , e.g. a first cell  11 , and the second RAT is the RAT of a second radio network node  112  serving a second cell  12 . Further, the wireless device  120  is suspended from a connection with the first radio network node  110  which connection is to be re-established by the second radio network node  112 . Sometimes in this disclosure, the term “source node/cell” is used instead of the term “first RAT/node/cell”, and the term “target RAT/node/cell” is used instead of the term “second RAT/node/cell”. Thus, it may for example be said that the wireless device  120  is suspended from a connection with the source radio network node  110  and that the target radio network node  112  is to re-establish the connection. 
     Actions of Some Embodiments Herein 
     Example embodiments of a flowchart depicting embodiments of a method performed by the wireless device  120 , 122 , e.g. to re-establish a connection, is depicted in  FIG. 6  and will be described more in detail in the following. Especially, embodiments herein relates to a method performed by a wireless device  120  for re-establishing a radio connection in a wireless communications network  100  comprising a first Radio Access Technology (RAT) and a second RAT, wherein the wireless device  120  operates in a first cell  11  served by a first radio network node  110  operating in the first RAT. The first and second RATs are different RATs. The method may comprise one or more of the following actions which actions may be taken in any suitable order. Further, it should be understood that one or more actions may be optional and that actions may be combined. 
     In Action  601 , when a connection failure with a first cell, e.g. with the first radio network node  110 , has been or is detected, the wireless device  120 , 122  performs a cell selection. 
     In Action  602 , the wireless device  120 , 122  selects a second cell  12  in the second RAT. The second cell  12  is known by the wireless device  120  to be a candidate for reestablishment. 
     In Action  603 , the wireless device  120 , 122  determines and/or receives a first set of parameters associated with the first cell  11  of the first RAT. As mentioned above, the first cell  11  is served by the first radio network node  110  operating in the first RAT. The first set of parameters comprises at least one parameter identifying the wireless device  120  or the first cell  11 . The first set of parameters may comprise a C-RNTI, an I-RNTI and a PCI. The C-RNTI and the I-RNTI identify the wireless device  120  and the PCI identifies the first cell  11 . 
     In Action  604 , the wireless device  120 , 122  determines and/or receives a second set of parameters associated with the second cell  12  of the second RAT. The second cell  12  is served by the second radio network node  112  operating in the second RAT. The second set of parameters comprises at least one parameter identifying the wireless device  120  or the second cell  12 . The second set of parameters may comprise a Cell ID or a PCI. The cell ID and the PCI identify the second cell  12 . 
     In Action  605 , the wireless device  120 , 122  may determine updated versions of first and second sets of parameters. Additionally or alternatively, in Action  605 A′, the wireless device  120  creates or uses a new variable or extends an existing variable. When a reference is made to a new variable in this disclosure it should be understood to refer to a variable that is new in relation to the variables defined in the current standard, and which variable for example may comprise parameters having a format of two or more different RATs. 
     The wireless device  120  may determine an updated version of one or more parameters of the first set of parameters or an updated version of one or more parameters of the second set of parameters. 
     In some embodiments, e.g. in some first exemplifying embodiments, the wireless device  120  determines the updated version of the one or more parameters of the first set of parameters by converting the one or more parameters of the first set of parameters to a format corresponding to the format of the one or more parameters of the second RAT. The wireless device  120  may perform this conversion by performing one or more out of: 
     mapping, recalculating, or truncating the one or more parameters of the first set of parameters to a shortened bit string when the first RAT is NR technology and the second RAT is LTE, and 
     mapping, recalculating or padding the one or more parameters of the first set of parameters to an extended bit string when the first RAT is LTE technology and the second RAT is NR. Further, the wireless device  120  may use the converted one or more parameters of the first set of parameters in one or more variables defined in the second RAT as input in calculating the security token for the second RAT. 
     In some embodiments, e.g. in some second exemplifying embodiments, the wireless device  120  determines the updated version of the one or more parameters of the second set of parameters comprises by converting the one or more parameters of the second set of parameters to a format corresponding to the format of the one or more parameters of the first set of parameters. The wireless device  120  may perform this conversion by performing one or more out of: 
     mapping, recalculating, or truncating the one or more parameters of the second set of parameters to a shortened bit string when the first RAT is LTE technology and the second RAT is NR, and 
     mapping, recalculating or padding the one or more parameters of the second set of parameters to an extended bit string when the first RAT is NR technology and the second RAT is LTE. Further, the wireless device  120  may use the converted one or more parameters of the second set of parameters in one or more variables defined in the first RAT as input in calculating the security token for the first RAT. 
     Thus, the wireless device  120  may convert the one or more parameters of the first set of parameters having a format of the first RAT into a format of the second RAT, and may convert the one or more parameters of the second set of parameters having a format of the second RAT into a format of the first RAT. For example, the C-RNTI has the formats: In LTE: 16 bit string and In NR: 16 bit integer, the PCI has the format: In LTE: 9 bit integer and In NR: 10 bit integer, and the Cell ID has the format: In LTE: 28 bit string and in NR: 36 bit string. 
     In some embodiments, e.g. in some third exemplifying embodiments, the wireless device  120  creates and/or uses a new variable comprising the one or more parameters of the first set of parameters in the format of the first RAT and comprising the one or more parameters of the second set of parameters in the format of the second RAT. The new variable may comprise parameters having formats of more than one RAT. 
     In some embodiments, e.g. in some fourth exemplifying embodiments, the wireless device  120  creates and/or uses a new variable or extending an existing variable to comprise the one or more parameters of the first set of parameters and the one or more parameters of the second set of parameters in both the format of the first RAT and in the format of the second RAT. The new variable may comprise parameters of only one format as in the legacy scenario or parameters of two or more formats according to embodiments disclosed herein. The new variable may be an extension of an existing variable. 
     In some embodiments, e.g. in some fifth exemplifying embodiments, the wireless device  120  extends and/or uses definition of existing variables to use one or more values, e.g. predefined values, in the second RAT format for the one or more parameters of the first set of parameters. In other words, the wireless device  120  may determine the updated version of the one or more parameters of the first set of parameters or the updated version of the one or more parameters of the second set of parameters, by extending definition of existing variables to use one or more values in the second RAT format in place of the one or more parameters of the first set of parameters. However, it should be understood that the value does not have to be predefined. It could also be values which are not associated with the first set of parameters. For instance, the network may signal that for inter-RAT re-establish, the first set of parameters should be 0, and in another cell, it should be 42 (or something else). 
     In some embodiments, e.g. in some sixth exemplifying embodiments, the wireless device  120  receives an instruction how to update the first and second sets of parameters. Thus, the wireless device  120  may receive an instruction how to convert the one or more parameters of the first set of parameters into a format corresponding to the format of the one or more parameters of the second set of parameters or how to convert the one or more parameters of the second set of parameters into a format corresponding to the format of the one or more parameters of the first set of parameters. For example, the instruction may be received from the first radio network node  110  during link failure and from the second radio network node during re-establishment. In the latter case, the instruction may be broadcasted from the second radio network node. In such embodiments, the wireless device updates the first and second sets of parameters in accordance with the instruction received. 
     In Action  606 , the wireless device  120 , 122  determines a security token based on first and second sets of parameters. 
     As mentioned above, the wireless device  120  may determine an updated version of one or more parameters of the first set of parameters or an updated version of one or more parameters of the second set of parameters. In such embodiments, the wireless device  120  may determine the security token by determining the security token based on at least one out of the first set of parameters and the updated version of the one or more parameters of the first set of parameters, and based on at least one out of the second set of parameters and the updated version of the one or more parameters of the second set of parameters. Thus, the security token may be determined based on at least the C-RNTI, and the PCI identifying the wireless device  120  and the first cell  11 , respectively, and the Cell ID identifying the second cell  12 . Further, one or more of the C-RNTI, PCI and Cell ID may be updated before the determination of the security token. Additionally or alternatively, the I-RNTI identifying the wireless device  120  and/or the PCI identifying the second cell  12  may also be used in the determination of the security token. 
     In some first exemplifying embodiments, the wireless device  120  uses the converted one or more parameters of the first set of parameters in one or more variables defined in the second RAT as input in calculation of the security token for the second RAT. 
     In some second exemplifying embodiments, the wireless device  120  uses the converted one or more parameters of the second set of parameters in one or more variables defined in the first RAT as input in calculation of the security token for the first RAT. 
     In some third and fourth exemplifying embodiments, the wireless device  120  uses the new variable as input in calculation of the security token for the second RAT. 
     In Action  607 , the wireless device  120 , 122 , transmits, to the second cell  12  served by the second radio network node  112 , a re-establishment request, e.g. a re-establishment request message, comprising the determined security token. 
     To perform the method actions e.g. for re-establishing a connection, the wireless device  120  may comprise the arrangement depicted in  FIG. 7 . The wireless device  120 , 122  may e.g. comprise a transmitting unit  701 , a receiving unit  702 , a determining unit  703 , an updating unit  704 , a selecting unit  705 , a creating unit  706 , and a performing unit  707  As previously mentioned, the wireless device  120  and the first radio network node  110  are configured to operate in the wireless communications network  100 . The wireless device  120  is configured to perform, e.g. by means of the one or more units, one or more of the actions performed by the wireless device  120  and described herein. 
     The wireless device  120  is configured to transmit, e.g. by means of the transmitting unit  701 , a signal, message or information to one or more nodes operating in the communications network  100 . The transmitting unit  701  may be implemented by or arranged in communication with a processor  709  of the wireless device  120 . The processor  708  will be described in more detail below. 
     The wireless device  120 , 122 , is configured to transmit, to the second cell  12  served by the second radio network node  112 , a re-establishment request, e.g. a re-establishment request message, comprising a determined security token. 
     The wireless device  120  is configured to receive, e.g. by means of the receiving unit  702 , a signal, message or information from one or more nodes operating in the communications network  100 . The receiving unit  702  may be implemented by or arranged in communication with the processor  709  of the wireless device  120 . 
     The wireless device  120 , 122  is configured to receive a first set of parameters associated with the first cell  11 . The first set of parameters comprises at least one parameter identifying the wireless device  120  or the first cell  11 . 
     Further, the wireless device  12  is configured to receive a second set of parameters associated with the second cell  12 . The second set of parameters comprises at least one parameter identifying the wireless device  120  or the second cell  12 . 
     In some embodiments, the wireless device  120  is configured to receive, from the first radio network node  110  or the second radio network node  112 , an instruction how to convert the one or more parameters of the first set of parameters into a format corresponding to the format of the one or more parameters of the second RAT or how to convert the one or more parameters of the second set of parameters into a format corresponding to the format of the one or more parameters of the first RAT. 
     The wireless device  120  is configured to determine, e.g. by means of the determining unit  703 , security token. The determining unit  703  may be implemented by or arranged in communication with the processor  709  of the wireless device  120 . 
     The wireless device  120 , 122  is configured to determine the first set of parameters associated with the first cell  11 . The first set of parameters associated with the first cell  11  has been received by the wireless device  120  when connected to the first cell  11 . The received first set of parameters may be stored in a memory. Upon a failure, e.g. a failure of the connection with the first cell  11 , the wireless device  120  determines the first set of parameters. For example, the wireless device  120  may retrieve the first set of parameters from the memory. 
     Further, the wireless device  120  is configured to determine the security token based on the first and second sets of parameters. 
     The first set of parameters may comprise one or more out of: a C-RNTI or an I-RNTI identifying the wireless device  120  and a PCI identifying the first cell  11 . The second set of parameters may comprise a Cell ID or a PCI identifying the second cell  12 . 
     In some embodiments, the wireless device  120  is configured to determine an updated version of one or more parameters of the first set of parameters or an updated version of one or more parameters of the second set of parameters. In such embodiments, the wireless device  120  is configured to determine the security token based on at least one out of the first set of parameters and the updated version of the one or more parameters of the first set of parameters, and based on at least one out of the second set of parameters and the updated version of the one or more parameters of the second set of parameters. 
     In some embodiments, e.g. in some first exemplifying embodiments, the wireless device  120  is configured to determine the updated version of the one or more parameters of the first set of parameters by converting the one or more parameters of the first set of parameters to a format corresponding to the format of the one or more parameters of the second RAT by performing one or more out of:
         mapping, recalculating or truncating the one or more parameters of the first set of parameters to a shortened bit string when the first RAT is 5G New Radio, NR, technology and the second RAT is Long Term Evolution, LTE, technology, and   mapping, recalculating or padding the one or more parameters of the first set of parameters to an extended bit string when the first RAT is LTE and the second RAT is NR.       

     Further, in some first exemplifying embodiments, the wireless device  120  is configured to determine the security token by using the converted one or more parameters of the first set of parameters in one or more variables defined in the second RAT as input in calculation of the security token for the second RAT. 
     In some embodiments, e.g. in some second exemplifying embodiments, the wireless device  120  is configured to determine the updated version of the one or more parameters of the second set of parameters by converting the one or more parameters of the second set of parameters to a format corresponding to the format of the one or more parameters of the first set of parameters by performing one or more out of:
         mapping, recalculating or truncating the one or more parameters of the second set of parameters to a shortened bit string when the first RAT is LTE technology and the second RAT is NR technology, and   mapping, recalculating or padding the one or more parameters of the second set of parameters to an extended bit string when the first RAT NR technology and the second RAT is LTE.       

     Further, in some second exemplifying embodiments, the wireless device  120  is configured to determine the security token by using the converted one or more parameters of the second set of parameters in one or more variables defined in the first RAT as input in calculation of the security token for the first RAT. 
     In some embodiments, e.g. in some third and fourth exemplifying embodiments, the wireless device  120  is configured to determine the security token by using the new variable as input in calculation of the security token for the second RAT. 
     In some embodiments, e.g. in some fifth exemplifying embodiments, the wireless device  120  is configured to determine the updated version of the one or more parameters of the first set of parameters or the updated version of the one or more parameters of the second set of parameters by extending definition of existing variables to use one or more values in the second RAT format in place of the one or more parameters of the first set of parameters. 
     The first wireless device  120  may be configured to update, e.g. by means of the updating unit  704 , one or more parameters of the first set of parameters and/or one or more parameters of the second set of parameters. The updating unit  704  may be implemented by or arranged in communication with the processor  709  of the first wireless device  120 . 
     Thus, the wireless device  120 , 122  may be configured to update the one or more parameters of the first set of parameters and/or the one or more parameters of the second set of parameters as described herein. 
     The wireless device  120  is configured to select, e.g. by means of the selecting unit  705 , a cell. The selecting unit  705  may be implemented by or arranged in communication with the processor  709  of the wireless device  120 . 
     The wireless device  120 , 122  is configured to select a second cell  12  served by the second radio network node  112  operating in the second RAT. The second cell  12  is known by the wireless device  120  to be a candidate for reestablishment. 
     The wireless device  120  is configured to create, e.g. by means of the creating unit  706 , a new variable or a new IE. The creating unit  706  may be implemented by or arranged in communication with the processor  709  of the wireless device  120 . 
     In some embodiments, e.g. in some third exemplifying embodiments, the wireless device  120 , 122  is configured to creating a new variable comprising the one or more parameters of the first set of parameters in the format of the first RAT and comprising the one or more parameters of the second set of parameters in the format of the second RAT. 
     In some embodiments, e.g. in some fourth exemplifying embodiments, the new variable is an extension of an existing variable. 
     The wireless device  120  is configured to perform, e.g. by means of the performing unit  707 , a cell selection. The performing unit  707  may be implemented by or arranged in communication with the processor  709  of the wireless device  120 . 
     The wireless device  120 , 122  is configured to perform a cell selection when a connection failure with the first cell  11  served by the first radio network node  110  is or has been detected. 
     Those skilled in the art will also appreciate that the units in the wireless device  120 , 122  described above may refer to a combination of analog and digital circuits, and/or one or more processors configured with software and/or firmware, e.g. stored in the wireless device  120 ,  122 , that when executed by the respective one or more processors such as the processors described above. One or more of these processors, as well as the other digital hardware, may be included in a single Application-Specific Integrated Circuitry (ASIC), or several processors and various digital hardware may be distributed among several separate components, whether individually packaged or assembled into a System-on-a-Chip (SoC). 
     The wireless device  120 , 122  may comprise an input and output interface  708  configured to communicate with one or more network nodes, e.g. with the first and second radio network nodes  110 , 112  and the location server  132 . The input and output interface may comprise a wireless receiver (not shown) and a wireless transmitter (not shown). 
     The embodiments herein may be implemented through a respective processor or one or more processors, such as the processor  709  of a processing circuitry in wireless device  120 , 122  depicted in  FIG. 7 , together with respective computer program code for performing the functions and actions of the embodiments herein. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing the embodiments herein when being loaded into the wireless device  120 , 122 . One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code may furthermore be provided as pure program code on a server and downloaded to the wireless device  120 , 122 . 
     The wireless device  120 , 122  may further comprise a memory  710  comprising one or more memory units. The memory comprises instructions executable by the processor in the wireless device  120 . 
     The memory is arranged to be used to store e.g. data, configurations, and applications to perform the methods herein when being executed in the wireless device  120 , 122 . 
     Some embodiments of the wireless device  120 , 122  may comprise: 
     a radio circuitry configured to determine/receive first and second sets of parameters according to the determined by a processing unit, and to transmit a re-establishment request; 
     a storage, configured to store first and second sets of parameters; 
     the processing unit configured to determine a security token based on first and second sets of parameters. 
     Example embodiments of a flowchart depicting embodiments of a method performed by the first radio network node  110  for assisting a wireless device  120 , 122  in re-establishing a radio connection in a wireless communications network  100  is depicted in  FIG. 8A  and will be described more in detail in the following. As previously mentioned the wireless communications network  100  comprises a first RAT and a second RAT being different from the first RAT. The wireless device  120  operates in a first cell  11  served by the first radio network node  110  operating in the first RAT. The method may comprise one or more of the following actions which actions may be taken in any suitable order. Further, it should be understood that one or more actions may be optional and that actions may be combined. 
     In Action  801 A, the first radio network node  110  provides the wireless device  120 , 122  with a first set of parameters associated with the first cell  11  of the first RAT. For example, the first radio network node  110  may transmit the first set of parameters to the wireless device  120 . The first set of parameters may comprise C-RNTI or the I-RNTI identifying the wireless device  120  and the PCI identifying the first cell  11 . 
     In Action  801 A′, the first radio network node  110  may provide the wireless device with an instruction how to convert parameters into another format. For example, the first radio network node  110  may transmit the instruction to the wireless device  120 . 
     Thus, the first radio network node  110  may provide the wireless device  120  with an instruction how to convert one or more parameters of a first set of parameters associated with the first cell  11  into a format corresponding to the format of the one or more parameters of the second set of parameters or how to convert the one or more parameters of the second set of parameters into a format corresponding to the format of the one or more parameters of the first set of parameters. 
     In Action  802 A, the first radio network node  110  receives from the second radio network node  112  operating in the second RAT, a second set of parameters associated with a second cell  12  of the second RAT. As previously mentioned, the second cell  12  is served by the second radio network node  112 . The second set of parameters may comprise the Cell ID or the PCI identifying the second cell  12 . 
     In Action  803 A, the first radio network node  110  receives from the second radio network node  112  a security token. The security token is received by the second radio network node  112  in a re-establishment request message transmitted from the wireless device  120  when a connection failure with the first radio network node  110  is or has been detected. 
     In Action  804 A, the first radio network node  110  determines an expected security token based on the first and second sets of parameters. 
     In some embodiments, the first radio network node  110  determines an updated version of one or more parameters of the first set of parameters or an updated version of one or more parameters of the second set of parameters. In such embodiments the first radio network node  110  determines the security token based on at least one out of: the first set of parameters and the updated version of the one or more parameters of the first set of parameters, and based on at least one out of: the second set of parameters and the updated version of the one or more parameters of the second set of parameters. 
     In some embodiments, e.g. in some first exemplifying embodiments, the first radio network node  110  determines the updated version of the one or more parameters of the first set of parameters by converting the one or more parameters of the first set of parameters to a format corresponding to the format of the one or more parameters of the second RAT. The first radio network node  110  may perform the conversion by performing one or more out of: 
     mapping, recalculating or truncating the one or more parameters of the first set of parameters to a shortened bit string when the first RAT is 5G NR technology and the second RAT LTE technology, and 
     mapping, recalculating or padding the one or more parameters of the first set of parameters to an extended bit string when the first RAT is LTE and the second RAT is NR. 
     Further, in some first exemplifying embodiments, the first radio network node  110  determines the security token by using the converted one or more parameters of the first set of parameters in one or more variables defined in the second RAT as input in calculation of the security token for the second RAT. 
     In some embodiments, e.g. in some second exemplifying embodiments, the first radio network node  110  determines the updated version of the one or more parameters of the second set of parameters by converting the one or more parameters of the second set of parameters to a format corresponding to the format of the one or more parameters of the first set of parameters. The first radio network node  110  may perform the conversion by performing one or more out of: 
     mapping, recalculating or truncating the one or more parameters of the second set of parameters to a shortened bit string when the first RAT is LTE technology and the second RAT is NR technology, and 
     mapping, recalculating or padding the one or more parameters of the second set of parameters to an extended bit string when the first RAT NR technology and the second RAT is LTE. 
     Further, in some second exemplifying embodiments, the first radio network node  110  determines the security token by using the converted one or more parameters of the second set of parameters in one or more variables defined in the first RAT as input in calculation of the security token for the first RAT. 
     In some embodiments, e.g. in some third exemplifying embodiments, the first radio network node  110  creates a new variable comprising the one or more parameters of the first set of parameters in the format of the first RAT and comprising the one or more parameters of the second set of parameters in the format of the second RAT. 
     In some embodiments, e.g. in some fourth embodiments, the new variable is an extension of an existing variable. 
     In some third and fourth exemplifying embodiments, the first radio network node  110  determines the security token by using the new variable as input in calculation of the security token for the second RAT. 
     In some embodiments, e.g. in some fifth embodiments, the first radio network node  110  determines the updated version of the one or more parameters of the first set of parameters or the updated version of the one or more parameters of the second set of parameters by extending definition of existing variables to use one or more values in the second RAT format in place of the one or more parameters of the first set of parameters. 
     In Action  805 A, the first radio network node  110  verifies the wireless device  120 , 122  based on the received security token and the determined expected security tokens. For example, based on the received and the determined expected security tokens the first radio network node  110  verifies an identity of the wireless device and whether or not the wireless device is valid. 
     In Action  806 A, e.g. when the wireless device  120  is verified as valid, the first radio network node  110  transmits, to the second radio network node  112 , one or more configurations and/or parameters relating to the radio connection to be re-established. The one or more configurations and/or parameters relating to the radio connection to be re-established may sometimes herein be referred to as UE context. 
     To perform the method actions e.g. for assisting a wireless device  120 , 122  in resuming a radio connection in a wireless communications network  100 , the first radio network node  110  may comprise the arrangement depicted in  FIG. 8B . The first radio network node  110  may e.g. comprise a transmitting unit  801 , a receiving unit  802 , a providing unit  803 , a determining unit  804 , and a verifying unit  805 . As previously mentioned, the wireless device  120  and the first radio network node  110  are configured to operate in the wireless communications network  100 . The first radio network node  110  is configured to perform, e.g. by means of the one or more units, one or more of the actions performed by the first radio network node  110  and described herein. 
     The first radio network node  110  is configured to transmit, e.g. by means of the transmitting unit  801 , a signal, message or information to one or more nodes operating in the communications network  100 . The transmitting unit  801  may be implemented by or arranged in communication with a processor  807  of the first radio network node  110 . The processor  807  will be described in more detail below. 
     The first radio network node  110  is configured to transmit, to the second radio network node  112 , one or more configurations and/or parameters relating to the radio connection to be re-established when the wireless device  120  is verified as valid. 
     The first radio network node  110  is configured to receive, e.g. by means of the receiving unit  802 , a signal, message or information from one or more nodes operating in the communications network  100 . The receiving unit  802  may be implemented by or arranged in communication with the processor  807  of the first radio network node  110 . 
     The first radio network node  110  is configured to receive, from the second radio network node  112  operating in the second RAT, a second set of parameters associated with the second cell  12  of the second RAT. As previously mentioned, the second cell  12  is served by the second radio network node  112 . The second set of parameters may comprise the Cell ID or the PCI identifying the second cell  12 . 
     Further, the first radio network node  110  is configured to receive from the second radio network node  112  a security token. As previously mentioned, the security token is received by the second radio network node  112  in a re-establishment request message transmitted from the wireless device  120  when a connection failure with the first radio network node  110  is or has been detected. 
     The first radio network node  110  is configured to provide, e.g. by means of the providing unit  803 , a signal, message or information to one or more nodes operating in the communications network  100 . The providing unit  803  may be implemented by or arranged in communication with the processor  807  of the first radio network node  110 . 
     In some embodiments, the first radio network node  110  is configured to provide the wireless device  120  with an instruction how to convert parameters into another format. For example, the first radio network node  110  may transmit the instruction to the wireless device  120 . Thus, the first radio network node  110  may be configured to provide the wireless device  120  with an instruction how to convert one or more parameters of a first set of parameters associated with the first cell  11  into a format corresponding to the format of the one or more parameters of the second set of parameters or how to convert the one or more parameters of the second set of parameters into a format corresponding to the format of the one or more parameters of the first set of parameters. 
     The first radio network node  110  is configured to determine, e.g. by means of the determining unit  804 , a security token. The determining unit  804  may be implemented by or arranged in communication with the processor  807  of the first radio network node  110 . 
     The first radio network node  110  is configured to determine an expected security token based on the first and second sets of parameters. 
     In some embodiments, the first radio network node  110  is configured to determine an updated version of one or more parameters of the first set of parameters or an updated version of one or more parameters of the second set of parameters. In such embodiments, the first radio network node  110  is configured to determine the security token based on at least one out of: the first set of parameters and the updated version of the one or more parameters of the first set of parameters, and based on at least one out of: the second set of parameters and the updated version of the one or more parameters of the second set of parameters. 
     In some embodiments, e.g. in some first exemplifying embodiments, the first radio network node  110  is configured to determine the updated version of the one or more parameters of the first set of parameters by converting the one or more parameters of the first set of parameters to a format corresponding to the format of the one or more parameters of the second RAT. The first radio network node  110  may be configured to perform the conversion by performing one or more out of: 
     mapping, recalculating or truncating the one or more parameters of the first set of parameters to a shortened bit string when the first RAT is 5G NR technology and the second RAT LTE technology, and 
     mapping, recalculating or padding the one or more parameters of the first set of parameters to an extended bit string when the first RAT is LTE and the second RAT is NR. 
     Further, in some first exemplifying embodiments, the first radio network node  110  is configured to determine the security token by using the converted one or more parameters of the first set of parameters in one or more variables defined in the second RAT as input in calculation of the security token for the second RAT. 
     In some embodiments, e.g. in some second exemplifying embodiments, the first radio network node  110  is configured to determine the updated version of the one or more parameters of the second set of parameters by converting the one or more parameters of the second set of parameters to a format corresponding to the format of the one or more parameters of the first set of parameters. The first radio network node  110  may be configured to perform the conversion by performing one or more out of: 
     mapping, recalculating or truncating the one or more parameters of the second set of parameters to a shortened bit string when the first RAT is LTE technology and the second RAT is NR technology, and 
     mapping, recalculating or padding the one or more parameters of the second set of parameters to an extended bit string when the first RAT NR technology and the second RAT is LTE. 
     Further, in some second exemplifying embodiments, the first radio network node  110  is configured to determine the security token by using the converted one or more parameters of the second set of parameters in one or more variables defined in the first RAT as input in calculation of the security token for the first RAT. 
     In some embodiments, e.g. in some third exemplifying embodiments, the first radio network node  110  is configured to create a new variable comprising the one or more parameters of the first set of parameters in the format of the first RAT and comprising the one or more parameters of the second set of parameters in the format of the second RAT. 
     In some embodiments, e.g. in some fourth embodiments, the new variable is an extension of an existing variable. 
     In some third and fourth exemplifying embodiments, the first radio network node  110  is configured to determine the security token by using the new variable as input in calculation of the security token for the second RAT. 
     In some embodiments, e.g. in some fifth embodiments, the first radio network node  110  is configured to determine the updated version of the one or more parameters of the first set of parameters or the updated version of the one or more parameters of the second set of parameters by extending definition of existing variables to use one or more values in the second RAT format in place of the one or more parameters of the first set of parameters. 
     The first radio network node  110  is configured to verify, e.g. by means of the verifying unit  805 , a wireless device  120 . The verifying unit  805  may be implemented by or arranged in communication with the processor  807  of the first radio network node  110 . 
     The first radio network node  110  is configured to verify the wireless device  120 , 122  based on the received security token and the determined expected security tokens. For example, the first radio network node  110  is configured to verify an identity of the wireless device and whether or not the wireless device is valid based on the received and the determined expected security tokens. 
     Those skilled in the art will also appreciate that the units in the first radio network node  110  described above may refer to a combination of analog and digital circuits, and/or one or more processors configured with software and/or firmware, e.g. stored in the network node  110  that when executed by the respective one or more processors such as the processors described above. One or more of these processors, as well as the other digital hardware, may be included in a single Application-Specific Integrated Circuitry (ASIC), or several processors and various digital hardware may be distributed among several separate components, whether individually packaged or assembled into a System-on-a-Chip (SoC). 
     The radio network node  110  may comprise an input and output interface  806  configured to communicate with one or more out of the wireless device  120 ,  122 , the second radio network node  112 , the network node  130 , and the location server  132 . The input and output interface may comprise a wireless receiver (not shown) and a wireless transmitter (not shown). 
     The embodiments herein may be implemented through a respective processor or one or more processors, such as the processor  807  of a processing circuitry in network node  110  depicted in  FIG. 8B , together with respective computer program code for performing functions and actions of the embodiments herein. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing the embodiments herein when being loaded into the network node  110 . One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code may furthermore be provided as pure program code on a server and downloaded to the network node  110 . 
     The network node  110  may further comprise a memory  808  comprising one or more memory units. The memory comprises instructions executable by the processor in the network node  110 . 
     The memory is arranged to be used to store e.g. data, configurations, and applications to perform the methods herein when being executed in the network node  110 . For example, the memory may comprise the buffer having the buffer size referred to herein. 
     Some embodiments of the first radio network node  110  may comprise: 
     a communication circuitry configured to provide wireless device with first set of parameters, possibly also with an instruction how to update parameters, receive a security token from second radio network node, and to transmit configurations 
     a storage configured to store set of parameters and security tokens, 
     a processing unit configured to determine an expected security token and 
     a radio circuitry configured to transmit configurations to second radio network node. 
     Example embodiments of a flowchart depicting embodiments of a method performed by the second radio network node  112  for assisting a wireless device  120 , 122  in re-establishing a radio connection in a wireless communications network  100  is depicted in  FIG. 9A  and will be described more in detail in the following. As previously mentioned the wireless communications network  100  comprises a first RAT and a second RAT. The wireless device  120  operates in a first cell  11  served by the first radio network node  110  operating in the first RAT The method may comprise one or more of the following actions which actions may be taken in any suitable order. Further, it should be understood that one or more actions may be optional and that actions may be combined. 
     In Action  901 A, the second radio network node  112  provides the wireless device with a second set of parameters associated with a second cell  12  of second RAT. 
     In Action  901 A′, the second radio network node  112  may provide the wireless device with an instruction how to convert parameters into another format. 
     In Action  902 A, the second radio network node  112  receives a re-establishing request from the wireless device, which re-establishing request comprises a security token. 
     In Action  903 A, the second radio network node  112  transmits to the first radio network node  110 , the second set of parameters associated with a second cell  12  of second RAT. 
     In Action  904 A, the second radio network node  112  transmits the received security token to the first radio network node  110 . This may be performed by the second network node  112  when transmitting, to the first radio network node  110 , a message requesting the parameters and/or configurations in Action  806 A above, which parameters and/or configurations are to be used when re-establishing the connection with the wireless device  120 . 
     In Action  905 A, the second radio network node  112  receives, from the first radio network node  110 , one or more configurations and/or parameters relating to the radio connection to be re-established. 
     In Action  906 A, the second radio network node  112  re-establishes the connection with the wireless device  120 . 
     To perform the method actions e.g. for assisting a wireless device  120 , 122  in resuming a radio connection in a wireless communications network  100 , the second radio network node  112  may comprise the arrangement depicted in  FIG. 9B . The second radio network node  112  may e.g. comprise a transmitting unit  901 , a receiving unit  902 , a providing unit  903 , a determining unit  904 , broadcasting unit  905  and a re-establishing unit  906 . 
     Those skilled in the art will also appreciate that the units in the second radio network node  112  described above may refer to a combination of analog and digital circuits, and/or one or more processors configured with software and/or firmware, e.g. stored in the network node  112  that when executed by the respective one or more processors such as the processors described above. One or more of these processors, as well as the other digital hardware, may be included in a single Application-Specific Integrated Circuitry (ASIC), or several processors and various digital hardware may be distributed among several separate components, whether individually packaged or assembled into a System-on-a-Chip (SoC). 
     The second radio network node  112  may comprise an input and output interface  907  configured to communicate with one or more out of the wireless device  120 ,  122 , the first radio network node  110 , the network node  130 , and the location server  132 . The input and output interface may comprise a wireless receiver (not shown) and a wireless transmitter (not shown). 
     The embodiments herein may be implemented through a respective processor or one or more processors, such as the processor  908  of a processing circuitry in network node  112  depicted in  FIG. 9B , together with respective computer program code for performing functions and actions of the embodiments herein. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing the embodiments herein when being loaded into the network node  112 . One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code may furthermore be provided as pure program code on a server and downloaded to the network node  112 . 
     The network node  112  may further comprise a memory  909  comprising one or more memory units. The memory comprises instructions executable by the processor in the network node  112 . 
     The memory is arranged to be used to store e.g. data, configurations, and applications to perform the methods herein when being executed in the network node  112 . For example, the memory may comprise the buffer having the buffer size referred to herein. 
     Some embodiments of the second radio network node  112  may comprise: 
     a communication circuitry configured to provide the wireless device with second set of parameters, possibly also with an instruction how to update parameters, receive a security token from wireless device and to transmit the security token to the first radio network node, and to receive one or more configurations and/or parameters to re-establish a connection with the wireless device. 
     a storage configured to store set of parameters and security tokens, 
     a processing unit and 
     a radio circuitry configured to receive configurations from the first radio network node and to re-establish radio connection with the wireless device. 
     In some embodiments, a respective computer program  810 ,  910  comprises instructions, which when executed by the respective at least one processor, cause the at least one processor of the network node  110 , 112  to perform one or more of the actions described herein. 
     In some embodiments, a respective computer program  712  comprises instructions, which when executed by the respective at least one processor, cause the at least one processor of the wireless device  120 , 122  to perform the actions described herein. 
     In some embodiments, a respective carrier  713 ,  811 ,  911  comprises the respective computer program, wherein the carrier is one of an electronic signal, an optical signal, an electromagnetic signal, a magnetic signal, an electric signal, a radio signal, a microwave signal, or a computer-readable storage medium. 
     Below a more detailed description will follow. 
     Embodiments disclosed herein may be separated into different parts which will be described in more detail below. 
     Some example Embodiments numbered 1-12 are described below. 
     The following embodiments refer among other things to  FIG. 5 ,  FIG. 6 , and  FIG. 7 . 
     Embodiment 1. A method performed by a wireless device ( 120 ) for re-establishing a radio connection in a wireless communications network ( 100 ) comprising a first Radio Access Technology, RAT, and a second RAT, wherein the wireless device ( 120 ) operates in a first cell ( 11 ) served by a first radio network node ( 110 ) operating in the first RAT, and wherein the method comprises: 
     when a connection failure with the first radio network node ( 110 ) has been detected,
         performing ( 601 ), e.g. by means of a performing unit, cell selection and selecting, e.g. by means of a selecting unit, ( 602 ) a second cell in second RAT, known by the wireless device ( 120 ) to be a candidate for reestablishment;   determining ( 603 ), e.g. by means of a determining unit, a first set of parameters associated with the first cell ( 11 ) served by the first radio network node ( 110 ) operating in the first RAT, wherein the first set of parameters comprises at least one parameter identifying the wireless device ( 120 ) or the first cell ( 11 );   determining ( 604 ), e.g. by means of the determining unit, a second set of parameters associated with the second cell ( 12 ) served by a second radio network node ( 112 ) operating in the second RAT, wherein the second set of parameters comprises at least one parameter identifying the wireless device ( 120 ) or the second cell ( 12 );   based on first and second sets of parameters; determining ( 606 ), e.g. by means of the determining unit, a security token; and   transmitting ( 607 ), e.g. by means of a transmitting unit, to the second radio network node ( 112 ), a re-establishment request message comprising the security token.       

     The first set of parameters may comprise C-RNTI and/or PCI, and the second set of parameters may comprise Cell ID. 
     Embodiment 2. The method of embodiment 1, further comprising:
         determining ( 605 ) an updated version of one or more parameters of the first set of parameters or an updated version of one or more parameters of the second set of parameters; and wherein the determining ( 606 ) of the security token comprises:   determining the security token based on at least one out of the first set of parameters and the updated version of the one or more parameters of the first set of parameters, and based on at least one out of the second set of parameters and the updated version of the one or more parameters of the second set of parameters.       

     Embodiment 3. The method of embodiment 2, wherein the determining ( 605 ) of the updated version of the one or more parameters of the first set of parameters comprises:
         converting the one or more parameters of the first set of parameters to a format corresponding to the format of the one or more parameters of the second RAT, e.g. by mapping, recalculating, truncating or padding, and by using one or more variables defined in the second RAT.       

     This may for example relate to some first exemplifying embodiments. 
     Embodiment 4. The method of embodiment 2 or 3, wherein the determining ( 605 ) of the updated version of the one or more parameters of the second set of parameters comprises:
         converting the one or more parameters of the second set of parameters to a format corresponding to the format of the one or more parameters of the first set of parameters, e.g. by mapping, recalculating, truncating or padding, and by using one or more variables defined in the first RAT.       

     This may for example relate to some second exemplifying embodiments. 
     Embodiment 5. The method of embodiment 1, further comprising:
         creating/using ( 605 ) a new variable comprising the one or more parameters of the first set of parameters in the format of the first RAT and comprising the one or more parameters of the second set of parameters in the format of the second RAT.       

     This may for example relate to some third exemplifying embodiments. 
     Embodiment 6. The method of embodiment 1, further comprising:
         creating/using ( 605 ) a new variable or extending an existing variable to comprise the one or more parameters of the first set of parameters and the one or more parameters of the second set of parameters in both the format of the first RAT and in the format of the second RAT.       

     This may for example relate to some fourth exemplifying embodiments. 
     Embodiment 7. The method of embodiment 2, wherein the determining ( 605 ) of the updated version of the one or more parameters of the first set of parameters or the updated version of the one or more parameters of the second set of parameters comprises:
         extending definition of existing variables to use one or more values, e.g. predefined values, in the second RAT format for the one or more parameters of the first set of parameters.       

     It should be understood that the value does not have to be predefined. It could also be values which are not associated with the first set of parameters. For instance, the network may signal that for inter-RAT re-establishment, the first set of parameters should be 0, and in another cell, it should be 42 (or something else). 
     This may for example relate to some fifth exemplifying embodiments. 
     Embodiment 8. The method of embodiment 2, wherein the determining ( 605 ) of the updated version of the one or more parameters of the first set of parameters or the updated version of the one or more parameters of the second set of parameters comprises:
         receiving, from the first radio network node ( 110 ) or the second radio network node ( 112 ), an instruction how to convert the one or more parameters of the first set of parameters into a format corresponding to the format of the one or more parameters of the second RAT or how to convert the one or more parameters of the second set of parameters into a format corresponding to the format of the one or more parameters of the first RAT.       

     The wireless device may receive the instruction from the first radio network node during suspension and from the second radio network node during re-establishment. In the latter case, the instruction may be broadcasted from the second radio network node. 
     This may for example relate to some sixth exemplifying embodiments. 
     The following embodiments refer among other things to  FIG. 5 ,  FIGS. 8A,8B  and  FIGS. 9A,9B . 
     Embodiment 9. A method performed by a first radio network node ( 110 ) for assisting a wireless device ( 120 ) in re-establishing a radio connection in a wireless communications network ( 100 ) comprising a first Radio Access Technology, RAT, and a second RAT, wherein the wireless device ( 120 ) operates in a first cell ( 11 ) served by the first radio network node ( 110 ) operating in the first RAT, and wherein the method comprises:
         providing ( 801 A), e.g. by means of a providing unit, the wireless device ( 120 ) with a first set of parameters associated with the first cell ( 11 ) served by the first radio network node ( 120 ) operating in the first RAT, wherein the first set of parameters comprises at least one parameter identifying the wireless device ( 120 ) or the first cell ( 11 ),   receiving ( 802 A), e.g. by means of a receiving unit, from a second radio network node ( 112 ) operating in the second RAT, a second set of parameters associated with a second cell ( 12 ) served by the second radio network node ( 112 );   receiving ( 803 A), e.g. by means of the receiving unit, from the second radio network node ( 112 ), a security token received in a re-establishment request message from the wireless device ( 120 ) when a failure of a radio connection with the first radio network node ( 110 ) has been detected;   based on first and second sets of parameters; determining ( 804 A), e.g. by means of a determining unit, an expected security token; and   by means of the received security token and the determined expected security token, verifying ( 805 A), e.g. by means of a verifying unit, the wireless device&#39;s ( 120 ) identity;   transmitting ( 806 A), e.g. by means of the transmitting unit, to second radio network node ( 112 ), one or more configurations and/or parameters relating to the radio connection to be re-established.       

     The first radio network node  110  may also receive the UE identity in the re-establishment request message. 
     Embodiment 10. The method of embodiment 9, further comprising:
         providing ( 801 A) the wireless device ( 120 ) with an instruction how to convert one or more parameters of a first set of parameters associated with the first cell ( 11 ) into a format corresponding to the format of the one or more parameters of the second set of parameters or how to convert the one or more parameters of the second set of parameters into a format corresponding to the format of the one or more parameters of the first set of parameters.       

     Embodiment 11. A method performed by a second radio network node ( 112 ) for assisting a wireless device ( 120 ) in re-establishing a radio connection in a wireless communications network ( 100 ) comprising a first Radio Access Technology, RAT, and a second RAT, wherein the wireless device ( 120 ) operates in a first cell ( 11 ) served by a first radio network node ( 110 ) operating in the first RAT, wherein the second radio network node ( 112 ) operates in the second RAT, and wherein the method comprises:
         providing ( 901 A), e.g. by means of a providing unit, the wireless device ( 120 ) with a second set of parameters associated with a second cell ( 12 ) served by the second radio network node ( 122 ) operating in the second RAT, wherein the second set of parameters comprises at least one parameter identifying the wireless device ( 120 ) or the second cell ( 12 );   receiving ( 902 A), e.g. by means of a receiving unit, a re-establishment request message comprising a security token, which re-establishment request message is transmitted by the wireless device ( 120 ) when a failure of a radio connection with the first radio network node ( 110 ) has been detected;   transmitting ( 903 A), e.g. by means of a transmitting unit, to the first radio network node ( 110 ), a second set of parameters associated with a second cell ( 12 ) served by the second radio network node ( 112 );   transmitting ( 904 A), e.g. by means of a transmitting unit, the security token to the first radio network node ( 110 );   receiving ( 905 A), e.g. by means of a receiving unit, from the first radio network node ( 110 ), one or more configurations and/or parameters relating to the radio connection to be re-established; and   re-establishing ( 906 A) e.g. by means of a re-establishing unit, the connection with the wireless device ( 120 ).       

     Embodiment 12. The method of embodiment 11, further comprising:
         providing ( 901 A) the wireless device ( 120 ) with an instruction how to convert one or more parameters of a first set of parameters associated with the first cell ( 11 ) into a format corresponding to the format of the one or more parameters of the second set of parameters or how to convert the one or more parameters of the second set of parameters into a format corresponding to the format of the one or more parameters of the first RAT.       

     2.1 Introduction 
     The following alternative sub-mechanism are proposed, mainly concerning the way the input parameters are determined. Thus, the following sections relate to the determination of the input parameters used in calculating the security token. 
     It should be understood that a reference to the UE in this disclosure is a reference to a wireless device  120 , 122 , a reference to a first/source cell is a reference to the first cell  11  served by the first radio network node  110 , and a reference to a second/target cell is a reference to the second cell  12  served by the second radio network node  112 . Thus, the first radio network node  110  may also be referred to as a source radio network node or just a source network node, and the second radio network node as a target radio network node or just a target network node. Furthermore, a reference to a source eNB or source gNB is be a reference to the first radio network node  110  and a reference to a target eNB or target gNB is be a reference to the second radio network node  112 . 
     Some First Exemplifying Embodiments 
     In this case the UE, e.g. the wireless device  120 , 122 , converts source related parameters associated to a first RAT, e.g. the first set of parameters described above, to equivalent or mapped input parameters for the token calculation on the second RAT, before reestablishing the RRC connection after failure. In other words, the wireless device converts the one or more parameters of the first set of parameters to a format corresponding to the format of the one or more parameters of the second set of parameters. As previously described, the conversion may be performed by performing one or more out of mapping, re-calculating, truncating, or padding of the one or more parameters of the first set of parameters as described above. This may be implemented in the specifications by describing, e.g. in field descriptions, the adaptation in terms of a UE variable in the second RAT for the case when the UE has been connected in another RAT, e.g. by updating the description of parameters in the UE variable VarShortMAC-Input or similar UE variable of the second RAT. In this case, the parameters like the C-RNTI and Physical Cell ID (PCI) are taken from the source RAT and stored along with the Cell identity of the target RAT into the UE variable to calculate the security token, i.e., Short MAC-I. To use the source PCI in the target RAT variable, the method proposes some embodiments wherein the UE uses either padded (if target RAT is NR) or truncated (if target RAT is LTE) input parameters with different number of bits in different RATs so that the same equation and/or function per RAT for the security token calculation may be used. Padding may be performed with a predefined sequence of 0&#39;s and/or 1&#39;s in order to extend the bit string of parameters of the first set of parameters, while truncation could involve removing some bits, e.g. one or more Most Significant Bits (MSB) or one or more Least Significant Bits (LSB), from the information element in order to shorten in order to extend the bit string of parameters of the first set of parameters. However, it should be understood that other mapping or re-calculation of the one or more parameters of the first set of parameters may be performed in order to obtain a bit string of the first set of parameters that matches the bit string of corresponding parameters of the other RAT. Thereby, the same equation and/or function per RAT for the security token calculation may be used. The calculated security token, e.g. the short MAC-I, is then transmitted in the RRC Reestablishment Request message to the second radio network node  112 . Corresponding procedures are performed in the network node, e.g. in the first radio network node  110 , to calculate the Reestablishment XMAC-I, i.e. the expected security token, used to verify the received Reestablishment Short MAC-I and thereby also to verify the wireless device  120 . 
     Advantage with some first exemplifying embodiments is that there is no need to truncate input parameters like the Cell ID parameter which makes the Cell ID unique, thereby avoiding the risk that different target cells would generate the same Short MAC-I. 
     Another advantage is that one would not need to design an additional MAC-I calculation having source inputs with different number of bits and consequently having to implement this additional function in the UE and in the network for the case the UE reestablishes in a different RAT than the source RAT. 
     Some Second Exemplifying Embodiments 
     In some second exemplifying embodiments, the source coding for the input parameter is used for calculating, the security token, e.g. the Reestablishment Short MAC-I. In this case the UE converts target related parameters associated to a second RAT to equivalent or mapped input parameters for the token calculation of the second RAT i.e. to be used in the VarShortMAC-Input (or similar parameter) of the first RAT. In other words, the wireless device converts the one or more parameters of the second set of parameters to a format corresponding to the format of the one or more parameters of the first set of parameters. As previously described, the conversion may be performed by performing one or more out of mapping, re-calculating, truncating, or padding of the one or more parameters of the second set of parameters as described above. 
     More concretely the parameter Cell Identity which is the target cell ID is used along with the C-RNTI and Physical Cell ID (PCI) of the source RAT into the parameter VarShortMAC-Input, or similar parameter to calculate the Reestablishment Short MAC-I (ShortMAC-I or similar, e.g. the security token. To use the Cell ID in the source RAT parameters, padding (LTE to NR) or truncation (NR to LTE) may be used. Padding may be performed with a predefined sequence of 0&#39;s and/or 1&#39;s in order to extend the bit string of parameters of the second set of parameters, or calculating a sequence of 0&#39;s and 1&#39;s based on information known to both the UE and the network e.g. the rest of the Cell ID, the Reestablishment causes, the I-RNTI, a constant value, etc. Truncation may involve removing some bits, e.g. MSB or LSB, from the information element and thereby to shorten the bit sting of parameters of the second set of parameters. However, it should be understood that other mapping or re-calculation of the one or more parameters of the first set of parameters may be performed in order to obtain a bit string of the first set of parameters that matches the bit string of corresponding parameters of the other RAT. Thereby, the same equation and/or function per RAT for the security token calculation may be used. For example, the truncation could also be performed by calculating a bit string with the shorter length using at least the full length of the parameter (e.g. Cell ID of the target cell) as input. Other parameters used as input to calculate the shorter value may be e.g. a constant, Reestablishment cause, the I-RNTI. 
     The short MAC-I, i.e. the security token, is then transmitted in the RRC Reestablishment Request message, e.g. to the second radio network node  112 . Part of that solution could comprise the introduction of an additional input parameter, sort of an inter-RAT discriminator so that the Reestablishment short MAC-I computed based on padded or truncated parameters will not be the same as another intra-RAT version of that Reestablishment short MAC-I with same values, just as coincidence. Corresponding procedures are performed in the network node calculating the Reestablishment MAC-I used to verify the received Reestablishment short MAC-I. 
     Advantage with some second exemplifying embodiments is that the calculation of the security token, e.g. the Short MAC-I or similar checksum, is done using the source format, which most likely limits the impact on the source node, i.e. the first radio network node  110  being the node in the network which verifies the Short MAC-I provided by the UE, i.e. the wireless device  120 . 
     Some Third Exemplifying Embodiments 
     In some embodiments, one or more new input variables are created in both RATs, e.g. in both LTE and NR, which may take the parameters C-RNTI and PCI from the source RAT and Cell ID of the target RAT and use this to calculate a security token, e.g. a MAC-I, in the target RAT. This variable could either be defined in the specifications of the source RAT (solution 3.1) or in the specifications of the target RAT (solution 3.2). 
     As previously described, the wireless device  120  may create a new variable comprising one or more parameters of the first set of parameters in the format of the first RAT and comprising one or more parameters of the second set of parameters in the format of the second RAT. Further, the wireless device  120  may use the new variable as input in calculation of the security token for the second RAT. 
     Advantage with some third exemplifying embodiments is that no information is lost (truncated) in the security token calculation, e.g. the Reestablishment Short MAC-I calculation, which reduces the (already small) risk of the same Short MAC-I being generated for a UE attempting to Reestablish in more than one cell. 
     Some Fourth Exemplifying Embodiments 
     In some embodiments, one or more new input variables are created in only one of the RATs (i.e. only in LTE or only in NR) or in both RATs. This new IE may be an extension of an existing IE, using a CHOICE structure to be used for both inter-RAT failure/Reestablishment as well as intra-RAT reestablishment. In solution 4.1 both the VarShortMAC-Input or similar in LTE and in NR are updated or introduced. These variables are used whenever the target RAT matches the specification, i.e. the LTE VarShortMAC-Input is used if target RAT is LTE regardless of whether the source RAT is LTE or NR and the NR VarShortMAC-Input is used if the target RAT is NR regardless of whether the source RAT is LTE or NR. In solution 4.2, only the variable VarShortMAC-Input or similar in LTE is updated and is used for reestablishment from LTE to LTE, from LTE to NR, or from NR to LTE. In case of failure/reestablishment from NR to NR, the variables defined in NR specification is used, e.g. the unmodified VarShortMAC-Input, or similar. In solution 4.3, only the variable VarShortMAC-Input or similar in NR is updated and is used for failure/Reestablishment from NR to NR, from LTE to NR, or from NR to LTE. In case of failure/Reestablishment from LTE to LTE, the unmodified variable VarShortMAC-Input or similar is used. 
     Advantage with some fourth embodiments is that no information is lost, e.g. truncated in the security token calculation, e.g. the Reestablishment Short MAC-I calculation, which reduces the (already small) risk of the same Short MAC-I being generate for a UE attempting to reestablish in more than one cell. 
     Some Fifth Exemplifying Embodiments 
     In some embodiments, the existing variables are updated to use dummy variables in place of the source parameters, e.g. in place of one or more parameters of the first set of parameters. For instance, the PCI may use a value outside the range of the defined identities compared to normal intra-RAT reestablishment, e.g. if the UE connected and detects failure in LTE and reestablishes in NR, the PCI may be set to e.g. 1023 (maximum PCI is 1007, but 10 bit coding allows values up to 1023) and if UE is connected and detects failure in NR and reestablishes in LTE, the PCI may be set to e.g. 511 (maximum PCI is 503 but 8 bit coding allows value up to 512). As described above, the wireless device  120  may extend definition of existing variables to use one or more values in the second RAT format in place of the one or more parameters of the first set of parameters. 
     Advantage with some fifth exemplifying embodiments is that no new variables need to be introduced. 
     In the previous description, the term Cell Identity refers to any type of cell identifier associated to the target cell, typically broadcasted by system information, e.g., PCI, cell global identity, etc. 
     In this description, the first RAT may either be LTE or NR. Also, the second RAT may either be LTE or NR. However, this does not preclude the application of some embodiments disclosed herein between other RATs employing similar procedures to authenticate the UEs. 
     The method also comprises mechanisms in a source network node, e.g. the first radio network node  110 , associated to the first RAT and in a target network node, e.g. the second radio network node  112  associated to the second RAT, the method comprising:
         The target network node of the second RAT, e.g. the second radio network node  112 , upon receiving a reestablishment request from the UE, e.g. the wireless device  120 , and identifying that request as an inter-RAT reestablishment procedure (e.g. by the identifier that contains network related information), triggering an inter-RAT fetching of the UE AS context by sending some kind of context request message to a source network node of the first RAT, e.g. to the first radio network node  110 , and including in that request message target cell parameters such as a target identity of that second RAT, and possibly other parameters e.g. for replay attack avoidance and/or protocol discriminator, in which second RAT the UE is trying to reestablish and in which second RAT the parameter(s) in target (e.g. a cell identity) has possibly a different number of bits compared to the parameter in the first RAT.   The source network node of the first RAT, e.g. the first radio network node  110 , receiving the context fetching request message including one or multiple inter-RAT target cell parameter(s) as described above and, using these parameters and other source parameters from the AS UE context associated to that UE, such as the source C-RNTI and the source PCI, computing the security token, e.g. the Reestablishment       

     Short MAC-I, so the UE may be verified as a valid UE. The way the Reestablishment Short MAC-I is computed, using source parameters of a first RAT and also target parameters of the second RAT follows the same rule the UE follows i.e. according to any of the described sub-methods of the embodiments described herein. Then, if the UE is verified, the source network node provides the UE AS context to the target network node of the second RAT;
         The target network node of the second RAT, upon receiving a message with the AS context for that UE, may decide to Reestablish or, Setup a new RRC Connection or Release the connection;       

     2.2. Disclaimers 
     A scenario described is the one where the UE in an RRC_CONNECTED state in one RAT, i.e. the source RAT, detects radio link failure and upon performing cell reselection/selection to another RAT, i.e. the target RAT, remains in the RRC_CONNECTED state. When the UE tries to reestablish, it needs to handle the fact that the security token, e.g. the Short MAC-I, in the target RAT has different inputs in order to compute the token as compared to the inputs used to compute the security token as used in the source RAT. 
     However, the methods described herein are applicable to any other scenario where there are differences between the input parameters and overall procedure handling between the source RAT, wherein the UE is connected and is detecting a radio link failure, and the target RAT, i.e. where the UE tries to reestablish. For example, this may be the case when the source and target RATs have different software version, e.g. in case one has been upgraded but not the other, when the source and target RATs are from different releases, etc. Some embodiments also cover the scenario where the UE performs resume due to a RAN area update, i.e. the UE enters an inter-RAT cell that does not belong to its configured RAN area. 
     Also, in most cases the inter-RAT mobility between LTE and NR is described. However, it should be understood that the source and target RATs may be any RATs where the handling of security token calculation and/or input parameters for the calculation differ. 
     Also, herein the cases where two RATs, i.e. the source RAT and target RAT, are connected to the same core network are described. In particular, embodiments herein relate to NR and LTE connected to 5GC. 
     However, the embodiments described herein may work in any other context even if the RATs are not connected to the same core network CN, as long as context fetching and security algorithm harmonization are supported across different CNs. 
     It is also important to note that some embodiments described the adaptation method using as examples the existing input parameters for the token calculation as described in TS 36.331 and TS 38.331. However, the embodiments disclosed are applicable to any parameters possibly introduced in the future in either of the RATs or even both e.g. new parameters like protocol discriminator and/or parameters for replay attack avoidance like radio specific parameters, or even parameters computed as a function of any of these existing parameters. 
     Embodiments herein are described in scenarios involving inter-RAT failure and reestablishment between E-UTRA and NR. However, if any other RAT would interwork (e.g. IEEE 801.11, Bluetooth, or any future RAT) with either E-UTRA or NR, and require the calculation of a security token, it should be understood that the embodiments described herein may be used to adapt the input parameters of different RATs. 
     Whenever in this document the terms NR messages, parameters, security token, procedures or similar are mentioned, they referred to those specified in the NR specifications, specifically the 3GPP NR RRC specification TS 38.331. 
     Likewise, whenever the terms LTE messages, parameters, security tokens, procedures or similar are mentioned, they refer to those specified in the E-UTRA (LTE) specifications, specifically the 3GPP E-UTRA RRC specification TS 36.331. 
     In this disclosure it is shown how to calculate the security token, e.g. the ShortMAC-I, when reestablishing in another RAT. The ShortMAC-I is used as example of the E-UTRA or NR Short MAC-I, or more generally the security token used in the other RAT. 
     When a UE attempts to reestablish its connection in either LTE or NR, the UE must include a 16 bit security token, e.g. the ShortMAC-I, in the message. 
     Note that in some embodiments disclosed herein it is assumed that as in LTE and NR, the output number of the bits of the MAC-I is the same. However, the function may be applied to the case the number of bits in the source RAT and the target RAT are different too. 
     To derive the security token, the UE, e.g. the wireless device  120 , and network, e.g. the first radio network node  110 , use the parameters in the VarShortMAC-Input or similar, defined in both LTE and NR separately. 
     2.3 Short MAC-I for RRC Reestablishment in LTE and NR 
     In LTE and NR, a secure checksum or hash or authentication token is used to verify the UE context in case of RRC Reestablishment. This checksum is called ShortMAC-I, or similarly. In this disclosure the ReestablishmentMAC-I, the shortMAC-I and the ShortReestablishmentMAC-I re also referred to as the security token and the terms may be used interchangeably. Below is a description how it is calculated using the integrity protection algorithm and key that the UE has been configured for RRC integrity protection. 
     TS 38.331 5.3.1 ShortMAC-I in NR 
     In TS 38.331 section 5.3.7.4, the ShortMAC-I, i.e. the security token, is calculated as: 
     The UE shall set the contents of RRCReestablishmentRequest message as follows:
         1&gt; set the ue-Identity as follows:
           2&gt; set the c-RNTI to the C-RNTI used in the source PCell (reconfiguration with sync or mobility from NR failure) or used in the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; set the physCellId to the physical cell identity of the source PCell (reconfiguration with sync or mobility from NR failure) or of the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; set the shortMAC-I to the 16 least significant bits of the MAC-I calculated:
               3&gt; over the ASN.1 encoded as per section 8 (i.e., a multiple of 8 bits) VarShortMAC-Input;   3&gt; with the KRR Cint  key and integrity protection algorithm that was used in the source PCell (reconfiguration with sync or mobility from NR failure) or of the PCell in which the trigger for the re-establishment occurred (other cases); and   3&gt; with all input bits for COUNT, BEARER and DIRECTION set to binary ones;   
               
               

     Although VarShortMAC-Input hasn&#39;t been defined yet, it is proposed to design it as (R2-1812169): 
     
       
         
           
               
             
               
                   
               
               
                 VarShortMAC-Input variable 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 -- ASN1START 
               
               
                   
                 -- TAG-VAR-SHORTMACINPUT-START 
               
            
           
           
               
               
               
            
               
                   
                 VarShortMAC-Input ::=  
                 SEQUENCE { 
               
               
                   
                  sourcePhysCellId 
                  PhysCellId, 
               
               
                   
                  targetCellIdentity 
                  CellIdentity, 
               
               
                   
                  source-C-RNTI 
                  RNTI-Value 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 -- TAG-VAR- SHORTMACINPUT-STOP 
               
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 VarShortMAC-Input field descriptions 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 targetCellIdentity 
               
               
                 Set to CellIdentity of the target cell i.e. the cell the UE is trying to 
               
               
                 reestablish the connection. 
               
               
                 source-C-RNTI 
               
               
                 Set to C-RNTI that the UE had in the PCell it was connected to prior to 
               
               
                 the reestablishment. 
               
               
                 sourcePhysCellId 
               
               
                 Set to the physical cell identity of the PCell the UE was connected to 
               
               
                 prior to the RRC connection. 
               
               
                   
               
            
           
         
       
     
     2.3.2. ShortMAC-I in LTE 
     In LTE/EPC (TS 36.331 section 5.3.3.3a), the ShortMAC-I, i.e. the security token, is calculated as: 
     The UE shall set the contents of RRCConnectionReestablishmentRequest message as follows:
         1&gt; except for a NB-IoT UE for which AS security has not been activated, set the ue-Identity as follows:
           2&gt; set the c-RNTI to the C-RNTI used in the source PCell (handover and mobility from E-UTRA failure) or used in the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; set the physCellId to the physical cell identity of the source PCell (handover and mobility from E-UTRA failure) or of the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; set the shortMAC-I to the 16 least significant bits of the MAC-I calculated:
               3&gt; over the ASN.1 encoded as per section 8 (i.e., a multiple of 8 bits) VarShortMAC-Input (or VarShortMAC-Input-NB in NB-IoT);   3&gt; with the KRR Cint  key and integrity protection algorithm that was used in the source PCell (handover and mobility from E-UTRA failure) or of the PCell in which the trigger for the re-establishment occurred (other cases); and   3&gt; with all input bits for COUNT, BEARER and DIRECTION set to binary ones;
 
Where VarShortMAC-Input is defined as:
   
               
               

     
       
         
           
               
             
               
                   
               
               
                 VarShortMAC-Input UE variable 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 -- ASN1START 
               
            
           
           
               
               
               
            
               
                   
                 VarShortMAC-Input ::=  
                 SEQUENCE { 
               
               
                   
                  cellIdentity 
                  CellIdentity, 
               
               
                   
                  physCellId 
                  PhysCellId, 
               
               
                   
                  c-RNTI 
                  C-RNTI 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 VarShorMAC-Input field descriptions 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 cellIdentity 
               
               
                 Set to CellIdentity included in cellIdentity (without suffix) in SIB1 of 
               
               
                 the current cell. 
               
               
                 c-RNTI 
               
               
                 Set to C-RNTI that the UE had in the PCell it was connected to prior to 
               
               
                 the failure. 
               
               
                 physCellId 
               
               
                 Set to the physical cell identity of the PCell the UE was connected to prior 
               
               
                 to the failure. 
               
               
                   
               
            
           
         
       
     
     2.4 Input Parameters for Calculation of Security Token in RRC Reestablishment 
     The calculations of the security token to be included in the RRC Reestablishment Request message use three different parameters: Physical cell ID (PCI) of the source cell, C-RNTI (Cell-Random Network Temporary Identity) of the source cell, and the Cell identity (CID) of the target cell. The following sections describe how these parameters are specified in LTE and NR. 
     In addition, the calculations of the security token rely on an integrity protection algorithm, which uses the parameters described as input. Since the LTE and the NR have separate configurations of the algorithms, the usage of the algorithms need to be coordinated. In LTE the UE may be configured with the E-UTRA Integrity Algorithms (EIA) EIA 0 -EIA 3 , while in the NR the UE may be configured with the NR Integrity Algorithms (NIA) NIA 0 -NIA 3 . Currently, in Rel-15, the NR algorithms NIA 0 -NIA 3  are identical to the corresponding E-UTRA algorithms EIA 0 -EIA 3 , however, the specifications allow introduction of separate algorithms in NR and/or LTE which may differ in future releases. If the UE was configured with an integrity protection algorithm in LTE which has an equivalent, e.g. identical, algorithm supported in NR, i.e. currently EIA 0 -EIA 3 , the UE could e.g. select the corresponding NR algorithm to calculate the MAC-I and vice versa in the other direction. 
     If the UE is configured with an integrity protection algorithm in the first RAT, which is not supported in the second RAT the UE could
         In one embodiment, abort the inter-RAT RRC Reestablishment procedure, delete its AS context, transition to the RRC_IDLE state and perform a NAS recovery.   In another embodiment, the UE selects a predefined integrity protection algorithm which both the first and the second RATs support (e.g. eia 0 /nia 0 , or eia 3 /nia 3 , or any of the other algorithms which are identical in LTE and NR).       

     2.4.1.1. PhysCellId 
     To calculate the short MAC-I during RRC reestablishment, the physical cell identity of the source cell is required. Both the LTE specification (TS 36.331) and the NR specification (TS 38.331), define the LTE and NR PC&#39;s as below. 
     The LTE PCI in LTE is defined as (TS 36.331 v15.2.0, 2018-06):
         PhysCellId (LTE)       

     The IE PhysCellId is used to indicate the physical layer identity of the cell, as defined in TS 36.211 [21]. 
     
       
         
           
               
             
               
                   
               
               
                 PhysCellId information element 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 -- ASN1START 
               
            
           
           
               
               
               
            
               
                   
                 PhysCellId ::=  
                 INTEGER (0..503) 
               
            
           
           
               
               
            
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     While the PCI in NR is defined as:
         PhysCellId (NR)       

     The PhysCellId identifies the physical cell identity (PCI). 
     
       
         
           
               
             
               
                   
               
               
                 PhysCellId information element 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 -- ASN1START 
               
               
                   
                 -- TAG-PHYS-CELL-ID-START 
               
            
           
           
               
               
               
            
               
                   
                 PhysCellId ::=  
                 INTEGER (0..1007) 
               
            
           
           
               
               
            
               
                   
                 -- TAG-PHYS-CELL-ID-STOP 
               
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     Notably, the size of the PCI differs in LTE and NR, where the LTE PCI is coded as 9 bits and the NR PCI is coded as 10 bits. 
     In addition, LTE also defines the NR PCI as:
         PhysCellIdNR       

     The IE PhysCellIdNR indicates the physical layer identity (PCI) of an NR cell. 
     
       
         
           
               
             
               
                   
               
               
                 PhysCellIdNR information element 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 -- ASN1START 
               
            
           
           
               
               
               
            
               
                   
                 PhysCellIdNR-r15 ::=  
                 INTEGER (0.. 1007) 
               
            
           
           
               
               
            
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     And NR defines the LTE PCI as:
         EUTRA-PhysCellId       

     The IE EUTRA-PhysCellId is used to indicate the physical layer identity of the cell, as defined in TS 36.211 [21]. 
     
       
         
           
               
             
               
                   
               
               
                 EUTRA-PhysCellId information element 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 -- ASN1START 
               
               
                   
                 -- TAG-EUTRA-PHYS-CELL-ID-START 
               
            
           
           
               
               
               
            
               
                   
                 EUTRA-PhysCellId ::=  
                 INTEGER (0..503) 
               
            
           
           
               
               
            
               
                   
                 -- TAG-EUTRA-PHYS-CELL-ID-STOP 
               
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     2.4.1.2. C-RNTI 
     Both the LTE and NR VarShortMAC-Input contain the source C-RNTI, to tie the calculations of the Reestablishment Short MAC-I to the source cell. 
     The C-RNTI in LTE is defined as (TS 36.331 v15.2.0, 2018-06): 
     
       
         
           
               
             
               
                   
               
               
                 C-RNTI information element 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 -- ASN1START 
               
            
           
           
               
               
               
            
               
                   
                 C-RNTI ::=  
                 BIT STRING (SIZE (16) ) 
               
            
           
           
               
               
            
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     While the C-RNTI in NR is defined as RNTI-Value: 
     
       
         
           
               
             
               
                   
               
               
                 RNTI-Value information element 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 -- ASNISTART 
               
               
                   
                 -- TAG-RNTI-VALUE-START 
               
            
           
           
               
               
               
            
               
                   
                 RNTI-Value ::=  
                 INTEGER (0..65535) 
               
            
           
           
               
               
            
               
                   
                 -- TAG-RNTI-VALUE-STOP 
               
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     As may be noted, both the LTE and NR C-RNTI are equal in length (16 bit, the integers 0 to 65535 are coded as 16 bits as 65536 is written with 16 digits in binary form, i.e. log 2(65536)=16). 
     Even though the LTE C-RNTI and the NR C-RNTI have the same length, they are specified in separate specifications and cannot be used interchangeably. 
     2.4.1.3 Cell Identity 
     To calculate the short MAC-I during RRC reestablishment, the cell identity of the target cell is needed. However, only the cell identity belonging to the same RAT is defined in LTE and NR. 
     The Cell Identity is defined in LTE as:
         CellIdentity       

     The IE CellIdentity is used to unambiguously identify a cell within a PLMN. 
     
       
         
           
               
             
               
                   
               
               
                 CellIdentity information element 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 -- ASN1START 
               
            
           
           
               
               
               
            
               
                   
                 CellIdentity ::=  
                 BIT STRING (SIZE (28)) 
               
            
           
           
               
               
            
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     While the Cell Identity is defined in NR as:
         CellIdentity (NR)       

     The IE CellIdentity is used to unambiguously identify a cell within a PLMN. 
     
       
         
           
               
             
               
                   
               
               
                 CellIdentity information element 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 -- ASN1START 
               
            
           
           
               
               
               
            
               
                   
                 CellIdentity ::=  
                 BIT STRING (SIZE (36)) 
               
            
           
           
               
               
            
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     As may be noted, both the LTE and NR cell identity are defined as bit strings, however with different lengths. In LTE the Cell identity is 28 bits, and in NR the cell identity is 36 bits. 
     2.5 Some First Exemplifying Embodiments: Use Input Parameter Format of the Target System and Convert Source System Parameters 
     In some embodiments, the definitions of the LTE VarShortMAC-Input, or similar parameter used when the target RAT is LTE and the NR VarShortMAC-Input or similar parameter used when the target RAT is NR are extended or modified to allow parameters from another RAT. 
     In either direction of the inter-RAT RRC Reestablishment procedure, the problem lies in using parameters from the source RAT in procedures of the target RAT, namely the PCI and the C-RNTI. 
     2.5.1. Failure in LTE and Reestablishment in NR: Calculate and Use NR ShortMAC-I Using LTE PCI and C-RNTI and NR Cell Identity as Input 
     If the UE, e.g. the wireless device  120 , is connected to an LTE cell, e.g. the first cell  11 , and detects and attempts to reestablish the connection in an NR cell, the UE and network would need to calculate the NR Reestablishment ShortMAC-I, e.g. the security token, using the NR VarShortMAC-Input. The NR VarShortMAC-Input contain the source PCI, the source RNTI and the target Cell identity. The target Cell identity is obtained from the SystemInformationBlockType1 (SIB1) which is broadcast by the target cell, e.g. the second cell  12 . 
     However, the source PCI and the source RNTI were obtained in another RAT (i.e. in the first RAT being LTE in this example) and have different characteristics compared to corresponding parameters in NR. 
     For the parameter C-RNTI, the VarShortMAC-Input may directly convert the source LTE C-RNTI as it consists of the same number of bits as the NR C-RNTI. 
     To employ the LTE PCI in the calculations of the NR ShortMAC-I, e.g. the security token for NR, the length of the parameter must be adjusted. The simplest way to do this is to add a dummy value (e.g. a single leading ‘0’) to the LTE PCI and use this modified value in the NR VarShortMAC-Input, e.g. to be used as input in the calculation of the security token. Naturally any other method to increase the length of the LTE PCI with one bit is equally applicable, e.g. a single trailing ‘0’ or ‘1’ or adding a bit at any other place in the bit string. In other words, the bit string may be extended in any other suitable way, e.g. by mapping, recalculating, or padding as previously described. This added bit could also be calculated based on e.g. the content of the bits in the LTE PCI. 
     If the UE was configured with an integrity protection algorithm in LTE which is not supported in NR, e.g. by a hypothetical future EIA 4 , different from any algorithm in NR, the UE could either:
         Abort the reestablishment procedure and fallback to RRC Setup, or   Use a predefined fallback algorithm which is supported in both LTE and NR (e.g. any of the algorithms NIA 0 -NIA 3 )       

     The calculation of the NR ShortMAC-I, i.e. the security token, is performed by both the UE, i.e. the wireless device  120 , and the network, i.e. the first and/or second radio network node  110 , 112 . The network node performing the calculation of the ShortMAC-I could either be the target node, e.g. the second radio network node  112 , which receives the RRCReestablishmentRequest message or the source node, e.g. the first radio network node  110 , to which the UE was connected to prior to the failure, or another network entity. 
     Since the calculation of the ShortMAC-I utilizes the security keys and the integrity protection algorithms stored in the UE context, one solution would be that the source node, i.e. the first radio network node  110 , calculates the ShortMAC-I, i.e. the security token, when it receives a context relocation request message (e.g. the RETRIEVE UE CONTEXT REQUEST message as defined in XNAP TS 38.423 v.15.0.0). This message would contain both the ShortMAC-I calculated by the UE, as well as the NR Cell Identity. 
     Retrieve UE Context Request 
     A retrieve UE context request message is sent by the new NG-RAN node, e.g. the second radio network node  112 , to request the old NG-RAN node, e.g. the first radio network node  110 , to transfer the UE Context to the new NG-RAN. 
     Direction: new NG-RAN node→old NG-RAN node. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 IE type and 
                 Semantics 
                   
                 Assigned 
               
               
                 IE/Group Name 
                 Presence 
                 Range 
                 reference 
                 description 
                 Criticality 
                 Criticality 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Message Type 
                 M 
                   
                 9.2.3.1 
                   
                 YES 
                 ignore 
               
               
                 New NG-RAN 
                 M 
                   
                 NG-RAN node 
                 Allocated at the 
                 YES 
                 reject 
               
               
                 node UE XnAP ID 
                   
                   
                 UE XnAP ID 
                 new NG-RAN 
                   
                   
               
               
                 reference 
                   
                   
                 9.2.3.16 
                 node 
                   
                   
               
               
                 UE Context ID 
                 M 
                   
                 9.2.3.40 
                   
                 YES 
                 reject 
               
               
                 Integrity protection 
                 M 
                   
                 BIT STRING 
                 ShortMAC-I either 
                 YES 
                 reject 
               
               
                   
                   
                   
                 (SIZE (16)) 
                 contained in the 
                   
                   
               
               
                   
                   
                   
                   
                 RRCConnection 
                   
                   
               
               
                   
                   
                   
                   
                 ResumeRequest 
                   
                   
               
               
                   
                   
                   
                   
                 message as 
                   
                   
               
               
                   
                   
                   
                   
                 defined in TS 
                   
                   
               
               
                   
                   
                   
                   
                 38.331 [10]) 
                   
                   
               
               
                   
                   
                   
                   
                 or in the 
                   
                   
               
               
                   
                   
                   
                   
                 RRCConnection 
                   
                   
               
               
                   
                   
                   
                   
                 ResumeRequest 
                   
                   
               
               
                   
                   
                   
                   
                 message as 
                   
                   
               
               
                   
                   
                   
                   
                 defined in TS 
                   
                   
               
               
                   
                   
                   
                   
                 36.331 [14]) 
                   
                   
               
               
                 New Cell Identifier 
                 M 
                   
                 NG-RAN Cell 
                 The Cell Identifier 
                 YES 
                 reject 
               
               
                   
                   
                   
                 Identity 
                 of the cell where 
                   
                   
               
               
                   
                   
                   
                 9.2.2.9 
                 the RRC 
                   
                   
               
               
                   
                   
                   
                   
                 connection has 
                   
                   
               
               
                   
                   
                   
                   
                 been requested to 
                   
                   
               
               
                   
                   
                   
                   
                 be resumed or to 
                   
                   
               
               
                   
                   
                   
                   
                 be re-established. 
               
               
                   
               
            
           
         
       
     
     The source eNB, e.g. the first radio network node  110 , already knows the source PCI and C-RNTI from the UE context. However, since the source PCI is shorter than the parameter required in the VarShortMAC-Input, the source PCI must be padded with e.g. one binary ‘0’. When the source eNB has calculated the ShortMAC-I, it compares the value with the received ShortMAC-I value which the UE calculated. 
     An alternative solution is that the source eNB provides the security algorithms, the source PCI and source C-RNTI to the target gNB, e.g. the second radio network node  112 , when the UE has sent the RRCConnectionReestablishmentRequest. The target gNB, then calculates the ShortMAC-I in the same way as the UE did by padding the LTE PCI, using the LTE C-RNTI and the NR Cell Identity, which it then compares with the ShortMAC-I, the UE calculated and transmitted to the network. By comparing the security token, e.g. the ShortMAC-I, calculated by the second radio network node  112  and the security token, e.g. the ShortMAC-I, calculated by the wireless device  120 , the second radio network node  112  is able to verify the wireless device  120  as valid. 
     The procedures of section 5.3.7.3 in TS 36.331 and section 5.3.7.4 in TS 38.331 may be extended (changes highlighted by underlining) to e.g. 
     2.5.1.1. Updates of TS 36.331 
     TS 36.331 5.3.7.3 Actions following cell selection while T 311  is running 
     Upon selecting a suitable E-UTRA cell, the UE shall:
         1&gt; stop timer T 311 ;   1&gt; start timer T 301 ;   1&gt; apply the timeAlignmentTimerCommon included in SystemInformationBlockType2;   1&gt; if the UE is a NB-IoT UE supporting RRC connection re-establishment for the Control Plane CIoT EPS optimisation and AS security has not been activated; and   1&gt; if cp-reestablishment is not included in SystemInformationBlockType2-NB:
           2&gt; perform the actions upon leaving RRC_CONNECTED as specified in 5.3.12, with release cause ‘RRC connection failure’;   
           1&gt; else:
           2&gt; initiate transmission of the RRCConnectionReestablishmentRequest message in accordance with 5.3.7.4;   
               

     NOTE: This procedure applies also if the UE returns to the source PCell. 
     Upon selecting an inter-RAT cell, the UE shall:
         1&gt; if the target cell is an NR cell and the previously configured integrity protection algorithms are available to configure in the target system:
           2&gt; stop timer T 311 ;   2&gt; start timer T 301 ;   2&gt; apply the timeAlignmentTimerCommon included in SystemInformationBlockType2;   2&gt; initiate transmission of the RRCReestablishmentRequest message in accordance with TS 38.331 section 5.3.7.4;   
           1&gt; else:
           2&gt; if the selected cell is a UTRA cell, and if the UE supports Radio Link Failure Report for Inter-RAT MRO, include selectedUTRA-CellId in the VarRLF-Report and set it to the physical cell identity and carrier frequency of the selected UTRA cell;   2&gt; perform the actions upon leaving RRC_CONNECTED as specified in 5.3.12, with release cause ‘RRC connection failure’;   
               

     2.5.1.2. Updates of TS 38.331 
     TS 38.331 5.3.7.4 Actions related to transmission of RRCReestablishmentRequest message 
     The UE shall set the contents of RRCReestablishmentRequest message as follows:
         1&gt; set the ue-Identity as follows:
           2&gt; set the c-RNTI to the C-RNTI used in the source PCell (reconfiguration with sync or mobility from NR failure) or used in the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; set the physCellId to the physical cell identity of the source PCell (reconfiguration with sync or mobility from NR failure) or of the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; set the shortMAC-I to the 16 least significant bits of the MAC-I calculated:
               3&gt; over the ASN.1 encoded as per section 8 (i.e., a multiple of 8 bits) VarShortMAC-Input;   3&gt; with the KRR Cint  key and integrity protection algorithm that was used in the source PCell (reconfiguration with sync or mobility from NR failure) or of the PCell in which the trigger for the re-establishment occurred (other cases); and   3&gt; with all input bits for COUNT, BEARER and DIRECTION set to binary ones;   
               NOTE: If the Source RAT was E-UTRA, use the previous E-UTRA KRR Cint  key as NR KRR Cint  key and use integrity protection algorithm matching the previously configured E-UTRA integrity protection algorithm.   
           1&gt; set the reestablishmentCause as follows:
           2&gt; if the re-establishment procedure was initiated due to reconfiguration failure as specified in 5.3.5.8.2:
               3&gt; set the reestablishmentCause to the value reconfigurationFailure;   
               2&gt; else if the re-establishment procedure was initiated due to reconfiguration with sync failure as specified in 5.3.5.8.3 (intra-NR handover failure) or 5.4.3.5 (inter-RAT mobility from NR failure):
               3&gt; set the reestablishmentCause to the value handoverFailure;   
               2&gt; else:
               3&gt; set the reestablishmentCause to the value otherFailure;   
               
           1&gt; restore the RRC configuration and security context from the stored UE AS context;   1&gt; restore the PDCP state and re-establish PDCP for SRB1;   1&gt; re-establish RLC for SRB1;   1&gt; resume SRB1;   1&gt; The UE shall submit the RRCReestablishmentRequest message to lower layers for transmission.       

     UE Variables
         VarShortMAC-Input       

     The UE variable VarShortMAC-Input specifies the input used to generate the ShortMAC-I during RRC Connection Reestablishment procedure. 
     
       
         
           
               
             
               
                   
               
               
                 VarShortMAC-Input variable 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 -- ASN1START 
               
               
                   
                 -- TAG-VAR-SHORTMACINPUT-START 
               
            
           
           
               
               
               
            
               
                   
                 VarShortMAC-Input ::=  
                 SEQUENCE { 
               
               
                   
                  sourcePhysCellId 
                  PhysCellId, 
               
               
                   
                  targetCellIdentity 
                  CellIdentity, 
               
               
                   
                  source-C-RNTI 
                  RNTI-Value 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 -- TAG-VAR- SHORTMACINPUT-STOP 
               
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 VarShortMAC-Input field descriptions 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 targetCellIdentity 
               
               
                 Set to CellIdentity of the target cell i.e. the cell the UE is trying to 
               
               
                 reestablish the connection. 
               
               
                 source-C-RNTI 
               
               
                 Set to C-RNTI that the UE had in the PCell it was connected to prior to 
               
               
                 the reestablishment. If the source cell was an E-UTRA cell, this field 
               
               
                 contain the source cell E-UTRA C-RNTI 
               
               
                 sourcePhysCellId 
               
               
                 Set to the physical cell identity of the PCell the UE was connected to 
               
               
                 prior to the RRC connection. If the source cell was an E-UTRA cell, the 
               
               
                 1 MSB of this field contain a binary ‘0’ and the 9 LSB of this field 
               
               
                 contain the source cell eutra-PhysCellId 
               
               
                   
               
            
           
         
       
     
       FIG. 10  schematically illustrated an example diagram for how a UE, e.g. the wireless device  120 , decides how to calculate the security checksum, i.e. the security token, during inter-RAT or intra-RAT reestablishment from LTE to LTE or NR. The diagram depicts one embodiment and should not be considered limiting to alternative solutions. 
     In Action  1001 , the wireless device  120  is connected to a first cell  11  being an LTE cell, and in Action  1002 , the wireless device  120  detects a radio link failure (RLF). In Action  1003  the wireless device  120  initiates an RRC reestablishment procedure and selects a suitable target cell, e.g. the second cell  12 . In Action  1004 , the wireless device  120  checks whether or not the target cell, i.e. the second cell  12 , belongs to the same RAT as the source cell, i.e. the first cell  11 . In other words, and in case the source cell is an LTE cell, the wireless device  120  checks whether or not the target cell is also an LTE cell. 
     In an intra-RAT procedure, i.e. when then the target cell is also an LTE cell, the wireless device  120  performs Actions  1005  and  1006 . In Actions  1005 , the wireless device  120  calculates the LTE security token, e.g. the ShortMAC-I, using the source PhysCellID, the source C-RNTI and the target cell identity in the LTE varShortMAC-Input. In Action  1006 , the wireless device  120  transmits an RRCConnectionReestablishmentRequest to the network node, e.g. to the first radio network node  110  and/or to the second radio network node  112 . The RRCConnectionReestablishmentRequest comprises the calculated security token. 
     In an inter-RAT procedure, i.e. when then the target cell is not in the same RAT as the source cell, e.g. when the source cell is an LTE cell and the target cell is a NR cell, the wireless device  120  performs Actions  1007 ,  1008 , and  1009 . In Action  1007 , the wireless device  120  concatenates one binary “0” with the source E-UTRA-PhysCellID and uses that as the PhysCellID, uses source E-UTRA C-RNTI, and uses target cell identity in NR VarShortMAC-Input. In Action  1008 , the wireless device  120  calculates the security token in NR, e.g. the NR ShortMAC-I, using the NR VarShortMAC-Input. Thus, the wireless device  120  calculates the security token using NR format and NR procedures. In Action  1009 , the wireless device  120  transmits an RRCReestablishmentRequest to the network node, e.g. to the second radio network node  112 . The RRCReestablishmentRequest comprises the calculated security token. 
     2.5.2. Failure in NR and Reestablishment LTE: Calculate and Use ShortMAC-I in LTE Using NR PCI and C-RNTI and LTE Cell Identity as Input 
     If the UE, e.g. the wireless device  120 , is connected to the first RAT being NR and detects failure and then reestablishes the connection in the second RAT being LTE, the UE and network would need to calculate the security token, e.g. the LTE ShortMAC-I, using the LTE VarShortMAC-Input or similar variable. The VarShortMAC-Input contain the source PCI, the source C-RNTI and the target Cell identity. The target Cell identity is obtained from the SystemInformationBlockType1 (SIB1) which is broadcast by the target cell, e.g. the second cell  12 . 
     However, the source PCI and source C-RNTI were obtained in another RAT, i.e. the first RAT being NR, and have different characteristics compared to corresponding parameters in the second RAT being LTE. 
     For the source C-RNTI, the UE stores the NR C-RNTI of the last serving cell, e.g. the first cell  11 , and since the LTE and NR C-RNTI have equal length, the LTE VarShortMAC-Input (or similar) may directly convert the NR C-RNTI as input. 
     To employ the NR PCI in the calculations of the security token, e.g. the LTE ShortMAC-I, the length of the parameter must be adjusted. The simplest way to do this is to truncate the value to either the 9 least significant bits (LSB) or the 9 most significant bits (MSB) and use this truncated value in the LTE VarShortMAC-Input (or similar variable). However, any other mapping of the 10 bit NR PCI to 9 bits to be used in the LTE PCI parameter would be equally possible. 
     If the UE was configured with an integrity protection algorithm in NR which is not supported in LTE (e.g. a hypothetical future NIA 4 , different from any algorithm in LTE), the UE could either:
         Abort the reestablishment procedure and fallback to RRC_IDLE   Use a predefined fallback algorithm which is supported in both LTE and NR (e.g. any of the algorithms EIA 0 -EIA 3 )       

     The calculation of the security token, e.g. the ShortMAC-I, is performed by both the UE, i.e. the wireless device  120 , and the network, i.e. the first and/or second radio network node  110 , 112 . The network node performing the calculation of the ShortMAC-I could either be the target node (gNB), i.e. the second radio network node  112 , which receives the RRCReestablishmentRequest message or the source node (eNB), i.e. the first radio network node  110 , in which the UE was connected to prior to the failure, or another network entity. 
     Since the calculation of the ShortMAC-I utilizes the security keys and the integrity protection algorithms stored in the UE context, one solution would be that the source node (gNB) calculates the ShortMAC-I, when it receives a context relocation request message (e.g. the RETRIEVE UE CONTEXT REQUEST message as defined in XNAP TS 38.423). This message would contain both the ShortMAC-I calculated by the UE, as well as the target LTE Cell Identity. Since the source node (gNB) already know the PCI and C-RNTI of the UE from the UE context, it may calculate the ShortMAC-I using the format of the target cell. Since the source PCI is longer than what fits in the target Var-ShortMAC-Input, the PCI must be truncated. When the source gNB has calculated the ShortMAC-I it compares it with the ShortMAC-I it has received from the UE to verify the UE identity. 
     Below are proposed changes to section 5.3.7.3 in TS 38.331 and section 5.3.7.4 in TS 36.331 to support inter-RAT reestablishment. The text relating to the proposed updates are shown as underlined. 
     2.5.2.1. Updates of TS 38.331 
     TS 38.331 5.3.7.3 Actions following cell selection while T 311  is running 
     Upon selecting a suitable NR cell, the UE shall:
         1&gt; stop timer T 311 ;   1&gt; start timer T 301 ;   1&gt; apply the timeAlignmentTimerCommon included in SIB1;   1&gt; initiate transmission of the RRCReestablishmentRequest message in accordance with 5.3.7.4;       

     NOTE: This procedure applies also if the UE returns to the source PCell. 
     Upon selecting an inter-RAT cell, the UE shall:
         1&gt; if the target cell is an E-UTRA cell and the previously configured integrity protection algorithms are available to configure in the target system:
           2&gt; stop timer T 311 ;   2&gt; start timer T 301 ;   2&gt; apply the timeAlignmentTimerCommon included in SIB1;   2&gt; initiate transmission of the RRCConnectionReestablishmentRequest message in accordance with TS 36.331 section 5.3.7.4;   
           1&gt; else:
           2&gt; perform the actions upon going to RRC_IDLE as specified in 5.3.11, with release cause ‘RRC connection failure’;   
               

     2.5.2.2. Updates of TS 36.331 
     TS 36.331 5.3.7.4 Actions related to transmission of RRCConnectionReestablishmentRequest message 
     Except for NB-IoT, if the procedure was initiated due to radio link failure or handover failure, the UE shall:
         1&gt; set the reestablishmentCellId in the VarRLF-Report to the global cell identity of the selected cell;
 
The UE shall set the contents of RRCConnectionReestablishmentRequest message as follows
   1&gt; except for a NB-IoT UE for which AS security has not been activated, set the ue-Identity as follows:
           2&gt; set the c-RNTI to the C-RNTI used in the source PCell (handover and mobility from E-UTRA failure) or used in the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; set the physCellId to the physical cell identity of the source PCell (handover and mobility from E-UTRA failure) or of the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; set the shortMAC-I to the 16 least significant bits of the MAC-I calculated:
               3&gt; over the ASN.1 encoded as per section 8 (i.e., a multiple of 8 bits) VarShortMAC-Input (or VarShortMAC-Input-NB in NB-IoT);   3&gt; with the KRR Cint  key and integrity protection algorithm that was used in the source PCell (handover and mobility from E-UTRA failure) or of the PCell in which the trigger for the re-establishment occurred (other cases); and   3&gt; with all input bits for COUNT, BEARER and DIRECTION set to binary ones;   
               NOTE: If the Source RAT was NR, use the previous NR KRR Cint  key as E-UTRA KRR Cint  key and use integrity protection algorithm matching the previously configured NR integrity protection algorithm.   
           1&gt; for a NB-IoT UE for which AS security has not been activated, set the ue-Identity as follows:
           2&gt; request upper layers for calculated ul-NAS-MAC and ul-NAS-Count using the cellIdentity of the PCell in which the trigger for the re-establishment occurred;   2&gt; set the s-TMSI to the S-TMSI provided by upper layers;   2&gt; set the ul-NAS-MAC to the ul-NAS-MAC value provided by upper layers;   2&gt; set the ul-NAS-Count to the ul-NAS-Count value provided by upper layers;   
           1&gt; set the reestablishmentCause as follows:
           2&gt; if the re-establishment procedure was initiated due to reconfiguration failure as specified in 5.3.5.5 (the UE is unable to comply with the reconfiguration):
               3&gt; set the reestablishmentCause to the value reconfigurationFailure;   
               2&gt; else if the re-establishment procedure was initiated due to handover failure as specified in 5.3.5.6 (intra-LTE handover failure) or 5.4.3.5 (inter-RAT mobility from EUTRA failure):
               3&gt; set the reestablishmentCause to the value handoverFailure;   
               2&gt; else:
               3&gt; set the reestablishmentCause to the value otherFailure;   
               
           1&gt; if the UE is a NB-IoT UE:
           2&gt; if the UE supports DL channel quality reporting and cqi-Reporting is present in SystemInformationBlockType2-NB:
               3&gt; set the cqi-NPDCCH to include the latest results of the downlink channel quality measurements of the serving cell as specified in TS 36.133 [16];
 
NOTE: The downlink channel quality measurements may use measurement period T 1  or T 2 , as defined in TS 36.133 [16]. In case period T 2  is used the RRC-MAC interactions are left to UE implementation.
   
               
           2&gt; set earlyContentionResolution to TRUE;       

     The UE shall submit the RRCConnectionReestablishmentRequest message to lower layers for transmission. 
     Where VarShortMAC-Input is defined as: 
     UE Variables 
     The UE variable VarShortMAC-Input specifies the input used to generate the shortMAC-I. 
     
       
         
           
               
             
               
                   
               
               
                 VarShortMAC-Input UE variable 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 -- ASN1START 
               
            
           
           
               
               
               
            
               
                   
                 VarShortMAC-Input ::= 
                 SEQUENCE { 
               
               
                   
                  cellIdentity 
                  CellIdentity, 
               
               
                   
                  physCellId 
                  PhysCellId, 
               
               
                   
                  c-RNTI 
                  C-RNTI 
               
               
                   
                 } 
                   
               
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 VarShortMAC-Input field descriptions 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 cellIdentity 
               
               
                 Set to CellIdentity included in cellIdentity (without suffix) in SIB1 of 
               
               
                 the current cell. 
               
               
                 c-RNTI 
               
               
                 Set to C-RNTI that the UE had in the PCell it was connected to prior to 
               
               
                 the failure. If the source cell was an NR cell, this field contain the 
               
               
                 source cell NR C-RNTI 
               
               
                 physCellId 
               
               
                 Set to the physical cell identity of the PCell the UE was connected to prior 
               
               
                 to the failure. If the source cell was an NR cell, this field contain the 9 
               
               
                 LSB of the source cell PhysCellIdNR 
               
               
                   
               
            
           
         
       
     
       FIG. 11  schematically illustrates an example diagram for how a UE, e.g. the wireless device  120 , decides how to calculate the security checksum, i.e. the security token, during inter-RAT or intra-RAT Reestablishment from NR to NR or LTE. The diagram depicts one embodiment and should not be considered limiting to alternative solutions. 
     In Action  1101 , the wireless device  120  is connected to a first cell  11  being a NR cell, and in Action  1102 , the wireless device  120  detects a RLF. In Action  1103  the wireless device  120  initiates an RRC reestablishment procedure and selects a suitable target cell, e.g. the second cell  12 . In Action  1104 , the wireless device  120  checks whether or not the target cell, i.e. the second cell  12 , belongs to the same RAT as the source cell, i.e. the first cell  11 . In other words, and in case the source cell is a NR cell, the wireless device  120  checks whether or not the target cell is also a NR cell. 
     In an intra-RAT procedure, i.e. when then the target cell is also a NR cell, the wireless device  120  performs Actions  1105  and  1106 . In Action  1105 , the wireless device  120  calculates the security token, e.g. the ShortMAC-I, using the source PhysCellID, the source C-RNTI and the target cell identity in the LTE varShortMAC-Input. In Action  1106 , the wireless device  120  transmits an RRCReestablishmentRequest to the network node, e.g. to the first radio network node  110  and/or to the second radio network node  112 . The RRCReestablishmentRequest comprises the calculated security token. 
     In an inter-RAT procedure, i.e. when then the target cell is not in the same RAT as the source cell, e.g. when the source cell is a NR cell and the target cell is an LTE cell, the wireless device  120  performs Actions  1107 ,  1108 , and  1109 . In Action  1107 , the wireless device  120  truncates source PhysCellIdNR to 9 bits and uses that as the PhysCellID, uses source NR C-RNTI as C-RNTI, and uses target cell identity in VarShortMAC-Input. In Action  1108 , the wireless device  120  calculates the security token in LTE, e.g. the LTE ShortMAC-I, using the LTE VarShortMAC-Input. Thus, the wireless device  120  calculates the security token using LTE format and LTE procedures. In Action  1109 , the wireless device  120  transmits an RRCConnectionReestablishmentRequest to the network node, e.g. to the second radio network node  112 . The RRCConenctionReestablishmentRequest comprises the calculated security token. 
     2.6 Some Second Exemplifying Embodiments: Use Input Parameter Format of the Source System and Convert Target System Parameters 
     In some embodiments, the source RAT parameters/variable (e.g. VarShortMAC-Input in LTE or NR) are used as input to the calculations of the source RAT security token, e.g. the ShortMAC-I or similar. These parameters/variables are extended or modified to allow parameters from target RAT, e.g. from the second RAT. In this disclosure, the source RAT parameters are also referred to as the first set of parameters, and the target RAT parameters are referred to as the second set of parameters. 
     In either direction of the inter-RAT RRC Reestablishment, the problem lies in using parameters from the target RAT in fields/procedures of the source RAT, namely the Cell Identity. 
     In LTE the (target) Cell Identity is currently 28 bits while in NR it is currently 36 bits. 
     When the network calculates the integrity checksum, i.e. the security token, it is done in the source node (eNB or gNB), i.e. the first radio network node  110 , when it receives e.g. a context relocation request message (e.g. the RETRIEVE UE CONTEXT REQUEST message as defined in XNAP TS 38.423). This message would contain both the ShortMAC-I calculated by the UE, as well as the target Cell Identity. The source node then pads or truncates the target cell identity to match the required size of the source variable. 
     In case of failure in NR and reestablishment in LTE, the target CellIdentity is e.g. padded from 28 bits to 36 bits, with 8 binary ‘0’s in the beginning. Thus, the bit string is extended. 
     If the failure/reestablishment is from LTE to NR, the target CellIdentity is e.g. truncated to the 28 LSB. Thus, the bit string is shortened. 
     Since the source node, e.g. the first radio network node  110 , calculates the integrity checksum, i.e. the security token, with the source format of the variables, the source integrity protection algorithms may be used. 
     2.6.1. Failure in LTE and Reestablishment in NR: Calculate and Use LTE Var-ShortMAC-Input Using LTE PCI and C-RNTI and NR Cell Identity as Input to Calculate NR ShortMAC-I 
     If the UE detects failure in LTE and attempt to reestablish the connection in NR, the UE and network would calculate the NR ShortMAC-I or similar using the LTE VarShortMAC-Input or similar, i.e. even though the UE reestablishes in NR, it calculates the integrity checksum using the LTE variables. The VarShortMAC-Input contain source PCI, source RNTI and target Cell identity. The target Cell identity is obtained by the UE from the SystemInformationBlockType1 (SIB1) which is broadcast by the target cell. 
     Since the UE and network calculate the NR ShortMAC-I using the source RAT format (i.e. LTE) of the input variables, the source PCI and source RNTI are already in the correct format. However, the target Cell Identity will be 36 bits, whereas the VarShortMAC-I requires a Cell Identity of 28 bits. 
     To use the target NR Cell Identity as cell identity in the Var-ShortMAC-Input, the UE and network may truncate the NR Cell Identity to e.g. the 28 least significant bits (LSB). Naturally, any other predefined truncation or other mapping of the NR cell identity would work as well. Thus, the bit string may be shortened by truncation or mapping or by recalculation as previously described. 
     Since the UE calculates the integrity checksum using variables input from the source system, the source integrity protection algorithms are also used. If the target system supports the same integrity protection algorithms, the UE may also use the corresponding NR integrity protection algorithm. 
     2.6.1.1. Updates of TS 38.331 
     The procedures of section 5.3.13.3 in TS 38.331 may be extended so that if the source cell is an NR cell, the ShortMAC-I is calculated over the NR VarShortMAC-Input but if the source cell is an E-UTRA cell, the UE calculates the ShortMAC-I over the LTE VarShortMAC-Input as defined in TS 36.331 e.g.: 
     TS 36.331 5.3.7.4 Actions related to transmission of RRCReestablishmentRequest message 
     The UE shall set the contents of RRCReestablishmentRequest message as follows:
         1&gt; set the ue-Identity as follows:
           2&gt; set the c-RNTI to the C-RNTI used in the source PCell (reconfiguration with sync or mobility from NR failure) or used in the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; set the physCellId to the physical cell identity of the source PCell (reconfiguration with sync or mobility from NR failure) or of the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; if the source cell is an NR cell:
               2&gt; set the shortMAC-I to the 16 least significant bits of the MAC-I calculated:   4&gt; over the ASN.1 encoded as per section 8 (i.e., a multiple of 8 bits) VarShortMAC-Input;   4&gt; with the KRR Cint  key and integrity protection algorithm that was used in the source PCell (reconfiguration with sync or mobility from NR failure) or of the PCell in which the trigger for the re-establishment occurred (other cases); and   4&gt; with all input bits for COUNT, BEARER and DIRECTION set to binary ones;   
               
           1&gt; else (source cell is an E-UTRA cell):
           2&gt; set the shortMAC-I to the 16 least significant bits of the MAC-I calculated:
               3&gt; truncate the target cellIdentity to the 28 LSB and use as input to VarShortMAC-Input as defined in TS 36.331;   3&gt; over the ASN.1 encoded as per section 8 (i.e., a multiple of 8 bits) VarShortMAC-Input as defined in TS 36.331;   3&gt; with the E-UTRA KRR Cint  key and NR integrity protection algorithm corresponding to the E-UTRA integrity protection algorithm that was used in the source PCell (reconfiguration with sync or mobility from NR failure) or of the PCell in which the trigger for the re-establishment occurred (other cases); and   3&gt; with all input bits for COUNT, BEARER and DIRECTION set to binary ones;   
               
           1&gt; set the reestablishmentCause as follows:
           2&gt; if the re-establishment procedure was initiated due to reconfiguration failure as specified in 5.3.5.8.2:
               3&gt; set the reestablishmentCause to the value reconfigurationFailure;   
               2&gt; else if the re-establishment procedure was initiated due to reconfiguration with sync failure as specified in 5.3.5.8.3 (intra-NR handover failure) or 5.4.3.5 (inter-RAT mobility from NR failure):
               3&gt; set the reestablishmentCause to the value handoverFailure;   
               2&gt; else:
               3&gt; set the reestablishmentCause to the value otherFailure;   
               
           1&gt; restore the RRC configuration and security context from the stored UE AS context;   1&gt; restore the PDCP state and re-establish PDCP for SRB1;   1&gt; re-establish RLC for SRB1;   1&gt; resume SRB1;   1&gt; The UE shall submit the RRCReestablishmentRequest message to lower layers for transmission.       

     2.6.1.2. Updates of TS 36.331 
     TS 36.331 5.3.7.3 Actions following cell selection while T 311  is running 
     Upon selecting a suitable E-UTRA cell, the UE shall:
         1&gt; stop timer T 311 ;   1&gt; start timer T 301 ;   1&gt; apply the timeAlignmentTimerCommon included in SystemInformationBlockType2;   1&gt; if the UE is a NB-IoT UE supporting RRC connection re-establishment for the Control Plane CIoT EPS optimisation and AS security has not been activated; and   1&gt; if cp-reestablishment is not included in SystemInformationBlockType2-NB:
           2&gt; perform the actions upon leaving RRC_CONNECTED as specified in 5.3.12, with release cause ‘RRC connection failure’;   
           1&gt; else:
           2&gt; initiate transmission of the RRCConnectionReestablishmentRequest message in accordance with 5.3.7.4;
 
NOTE: This procedure applies also if the UE returns to the source PCell.
   
               

     Upon selecting an inter-RAT cell, the UE shall:
         1&gt; if the target cell is an NR cell and the previously configured integrity protection algorithms are available to configure in the target system:
           2&gt; stop timer T 311 ;   2&gt; start timer T 301 ;   2&gt; apply the timeAlignmentTimerCommon included in SystemInformationBlockType2;   2&gt; initiate transmission of the RRCReestablishmentRequest message in accordance with TS 38.331 section 5.3.7.4;   
           1&gt; else:
           2&gt; if the selected cell is a UTRA cell, and if the UE supports Radio Link Failure Report for Inter-RAT MRO, include selectedUTRA-CellId in the VarRLF-Report and set it to the physical cell identity and carrier frequency of the selected UTRA cell;   2&gt; perform the actions upon leaving RRC_CONNECTED as specified in 5.3.12, with release cause ‘RRC connection failure’;
 
In addition, the VarShortMAC-Input must be updated to allow a truncated NR cellIdentity to be used as cellIdentity.
   
               

     UE Variables 
     The UE variable VarShortMAC-Input specifies the input used to generate the security token ShortMAC-I. In case of inter-RAT RRC Reestablishment from E-UTRA to NR, the VarShortMAC-Input is used to generate the ShortMAC-I as specified in TS 38.331. 
     
       
         
           
               
             
               
                   
               
               
                 VarShortMAC-Input UE variable 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 -- ASN1START 
               
            
           
           
               
               
               
            
               
                   
                 VarShortMAC-Input ::= 
                 SEQUENCE { 
               
               
                   
                  cellIdentity 
                  CellIdentity, 
               
               
                   
                  physCellId 
                  PhysCellId, 
               
               
                   
                  c-RNTI 
                  C-RNTI 
               
               
                   
                 } 
                   
               
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 VarShortMAC-Input field descriptions 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 cellIdentity 
               
               
                 Set to CellIdentity included in cellIdentity (without suffix) in SIB1 of 
               
               
                 the current cell. If the source cell was an E-UTRA cell and the target cell 
               
               
                 is an NR cell, this field contain the 28 LSB of the target NR cell identity. 
               
               
                 c-RNTI 
               
               
                 Set to C-RNTI that the UE had in the PCell it was connected to prior to 
               
               
                 the failure. 
               
               
                 physCellId 
               
               
                 Set to the physical cell identity of the PCell the UE was connected to 
               
               
                 prior to the failure. 
               
               
                   
               
            
           
         
       
     
       FIG. 12  schematically illustrates an example diagram for how a UE, e.g. the wireless device  120 , decides how to calculate the security checksum during inter-RAT or intra-RAT Reestablishment from LTE to LTE or NR. The diagram depicts one embodiment and should not be considered limiting to alternative solutions. 
     In Action  1201 , the wireless device  120  is connected to a first cell  11  being an LTE cell, and in Action  1202 , the wireless device  120  detects a RLF. In Action  1203  the wireless device  120  initiates an RRC reestablishment procedure and selects a suitable target cell, e.g. the second cell  12 . In Action  1204 , the wireless device  120  checks whether or not the target cell, i.e. the second cell  12 , belongs to the same RAT as the source cell, i.e. the first cell  11 . In other words, and in case the source cell is an LTE cell, the wireless device  120  checks whether or not the target cell is also an LTE cell. 
     In an intra-RAT procedure, i.e. when then the target cell is also an LTE cell, the wireless device  120  performs Actions  1205  and  1206 . In Actions  1205 , the wireless device  120  calculates the LTE security token, e.g. the ShortMAC-I, using the source PhysCellID, the source C-RNTI and the target cell identity in the LTE varShortMAC-Input. In Action  1206 , the wireless device  120  transmits an RRCConnectionReestablishmentRequest to the network node, e.g. to the first radio network node  110  and/or to the second radio network node  112 . The RRCConnectionReestablishmentRequest comprises the calculated security token. 
     In an inter-RAT procedure, i.e. when then the target cell is not in the same RAT as the source cell, e.g. when the source cell is an LTE cell and the target cell is a NR cell, the wireless device  120  performs Actions  1207 ,  1208 , and  1209 . In Action  1207 , the wireless device  120  uses source PhysCellID, uses source E-UTRA C-RNTI as C-RNTI and truncates target NR cell identity to 28 LSB and use it as cellIdentity in LTE VarShortMAC-Input. In Action  1208 , the wireless device  120  calculates the security token in NR, e.g. the NR ShortMAC-I, using the LTE VarShortMAC-Input. Thus, the wireless device  120  calculates the security token using LTE format and NR procedures. In Action  1209 , the wireless device  120  transmits an RRCReestablishmentRequest to the network node, e.g. to the second radio network node  112 . The RRCReestablishmentRequest comprises the calculated security token. 
     2.6.2. Failure in NR and Reestablishment in LTE: Calculate and Use NR ShortMAC-Input Using NR PCI and C-RNTI and LTE Cell Identity as Input to Calculate LTE ShortMAC-I 
     If the UE is connected to an NR cell and detects failure and the attempts to reestablish the connection in an LTE cell, the UE and network would calculate the LTE ShortMAC-I (or similar) using the (NR) VarShortMAC-Input (or similar). The NR VarShortMAC-Input contain source PCI, source C-RNTI and target Cell identity′. The target Cell identity is obtained from the SystemInformationBlockType1 (SIB1) which is broadcast by the target cell. 
     Since the UE and network calculate the LTE ShortMAC-I using the source RAT format (i.e. NR) of the input variables, the source PCI and source RNTI are already in the correct format. However, the target Cell Identity will be 28 bits, whereas the VarShortMAC-Input requires a Cell Identity of 36 bits. 
     To use the target LTE Cell Identity as cell identity in the VarShortMAC-Input, the UE and network may e.g. concatenate the LTE Cell Identity with 8 leading binary ‘0’s. 
     Naturally, any other predefined 8 bit constant may be added to the 28 bit LTE cell identity. Alternatively, the added bits may be calculated based on some parameter (e.g. the 28 bit LTE cell identity). 
     Since the UE calculates the integrity checksum using inputs from the source system, the source integrity protection algorithms are also used. If the target system supports the same integrity protection algorithms, the UE may also use the corresponding LTE integrity protection algorithm. 
     2.6.2.1 Updates of TS 36.331 
     The procedures of section 5.3.7.4 in TS 36.331 may be extended to e.g.: 
     TS 36.331 5.3.7.4 Actions related to transmission of RRCConnectionReestablishmentRequest message 
     Except for NB-IoT, if the procedure was initiated due to radio link failure or handover failure, the UE shall:
         1&gt; set the reestablishmentCellId in the VarRLF-Report to the global cell identity of the selected cell;
 
The UE shall set the contents of RRCConnectionReestablishmentRequest message as follows:
   1&gt; except for a NB-IoT UE for which AS security has not been activated, set the ue-Identity as follows:
           2&gt; set the c-RNTI to the C-RNTI used in the source PCell (handover and mobility from E-UTRA failure) or used in the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; set the physCellId to the physical cell identity of the source PCell (handover and mobility from E-UTRA failure) or of the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; if source cell is an E-UTRA cell:
               3&gt; set the shortMAC-I to the 16 least significant bits of the MAC-I calculated:   4&gt; over the ASN.1 encoded as per section 8 (i.e., a multiple of 8 bits) VarShortMAC-Input (or VarShortMAC-Input-NB in NB-IoT);   4&gt; with the KRR Cint  key and integrity protection algorithm that was used in the source PCell (handover and mobility from E-UTRA failure) or of the PCell in which the trigger for the re-establishment occurred (other cases); and   4&gt; with all input bits for COUNT, BEARER and DIRECTION set to binary ones;   
               2&gt; else:
               3&gt; set the shortMAC-I to the 16 least significant bits of the MAC-I calculated:   4&gt; prepend the target cellIdentity with 8 binary ‘0’s and use as input to targetCellIdentity in the VarShortMAC-Input as defined in TS 38.331;   4&gt; over the ASN.1 encoded as per section 8 (i.e., a multiple of 8 bits) VarShortMAC-Input as defined in TS 38.331;   4&gt; with the NR KRR Cint  key and E-UTRA integrity protection algorithm corresponding to the integrity protection algorithm that was used in the source PCell (handover and mobility from E-UTRA failure) or of the PCell in which the trigger for the re-establishment occurred (other cases); and   4&gt; with all input bits for COUNT, BEARER and DIRECTION set to binary ones;   
               
           1&gt; for a NB-IoT UE for which AS security has not been activated, set the ue-Identity as follows:
           2&gt; request upper layers for calculated ul-NAS-MAC and ul-NAS-Count using the cellIdentity of the PCell in which the trigger for the re-establishment occurred;   2&gt; set the s-TMSI to the S-TMSI provided by upper layers;   2&gt; set the ul-NAS-MAC to the ul-NAS-MAC value provided by upper layers;   2&gt; set the ul-NAS-Count to the ul-NAS-Count value provided by upper layers;   
           1&gt; set the reestablishmentCause as follows:
           2&gt; if the re-establishment procedure was initiated due to reconfiguration failure as specified in 5.3.5.5 (the UE is unable to comply with the reconfiguration):
               3&gt; set the reestablishmentCause to the value reconfigurationFailure;   
               2&gt; else if the re-establishment procedure was initiated due to handover failure as specified in 5.3.5.6 (intra-LTE handover failure) or 5.4.3.5 (inter-RAT mobility from EUTRA failure):
               3&gt; set the reestablishmentCause to the value handoverFailure;   
               2&gt; else:
               3&gt; set the reestablishmentCause to the value otherFailure;   
               
           1&gt; if the UE is a NB-IoT UE:
           2&gt; if the UE supports DL channel quality reporting and cqi-Reporting is present in SystemInformationBlockType2-NB:
               3&gt; set the cqi-NPDCCH to include the latest results of the downlink channel quality measurements of the serving cell as specified in TS 36.133 [16];   
               
           NOTE: The downlink channel quality measurements may use measurement period T 1  or T 2 , as defined in TS 36.133 [16]. In case period T 2  is used the RRC-MAC interactions are left to UE implementation.
           2&gt; set earlyContentionResolution to TRUE;   
               

     The UE shall submit the RRCConnectionReestablishmentRequest message to lower layers for transmission. 
     2.6.2.2 Updates of TS 38.331 
     The procedures in TS 38.33 section 5.3.7.3 need to be updated to handle the case of inter-RAT reestablishment. 
     TS 38.331 5.3.7.3 Actions following cell selection while T 311  is running 
     Upon selecting a suitable NR cell, the UE shall:
         1&gt; stop timer T 311 ;   1&gt; start timer T 301 ;   1&gt; apply the timeAlignmentTimerCommon included in SIB1;   1&gt; initiate transmission of the RRCReestablishmentRequest message in accordance with 5.3.7.4;       

     NOTE: This procedure applies also if the UE returns to the source PCell. 
     Upon selecting an inter-RAT cell, the UE shall:
         1&gt; if the target cell is an E-UTRA cell and the previously configured integrity protection algorithms are available to configure in the target system:
           2&gt; stop timer T 311 ;   2&gt; start timer T 301 ;   2&gt; apply the timeAlignmentTimerCommon included in SIB1;   2&gt; initiate transmission of the RRCConnectionReestablishmentRequest message in accordance with TS 36.331 section 5.3.7.4;   
           1&gt; else:
           2&gt; perform the actions upon going to RRC_IDLE as specified in 5.3.11, with release cause ‘RRC connection failure’;   
               

     The definition of VarShortMAC-Input need to be updated to allow using a padded LTE CellIdentity as targetCellIdentity in NR
         VarShortMAC-Input       

     The UE variable VarShortMAC-Input specifies the input used to generate the shortMAC-I. 
     
       
         
           
               
             
               
                   
               
               
                 VarShortMAC-Input UE variable 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 -- ASN1START 
               
            
           
           
               
               
               
            
               
                   
                 VarShortMAC-Input ::= 
                 SEQUENCE { 
               
               
                   
                  cellIdentity 
                  CellIdentity, 
               
               
                   
                  physCellId 
                  PhysCellId, 
               
               
                   
                  c-RNTI 
                  C-RNTI 
               
               
                   
                 } 
                   
               
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 VarShortMAC-Input field descriptions 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 cellIdentity 
               
               
                 Set to CellIdentity included in cellIdentity (without suffix) in SIB1 of the 
               
               
                 current cell. If the source cell was an NR cell and the target cell is an 
               
               
                 E-UTRA cell, the 8 MSB of this field are set to ‘0’ and the 28 LSB 
               
               
                 contain the target E-UTRA cell identity. 
               
               
                 c-RNTI 
               
               
                 Set to C-RNTI that the UE had in the PCell it was connected to prior 
               
               
                 to the failure. 
               
               
                 physCellId 
               
               
                 Set to the physical cell identity of the PCell the UE was connected to 
               
               
                 prior to the failure. 
               
               
                   
               
            
           
         
       
     
       FIG. 13  schematically illustrates an example diagram for how a UE, e.g. the wireless device  120 , decides how to calculate the security checksum during inter-RAT or intra-RAT Reestablishment from NR to NR or LTE. The diagram depicts one embodiment and should not be considered limiting to alternative solutions. 
     In Action  1301 , the wireless device  120  is connected to a first cell  11  being a NR cell, and in Action  1302 , the wireless device  120  detects a RLF. In Action  1303  the wireless device  120  initiates an RRC reestablishment procedure and selects a suitable target cell, e.g. the second cell  12 . In Action  1304 , the wireless device  120  checks whether or not the target cell, i.e. the second cell  12 , belongs to the same RAT as the source cell, i.e. the first cell  11 . In other words, and in case the source cell is a NR cell, the wireless device  120  checks whether or not the target cell is also a NR cell. 
     In an intra-RAT procedure, i.e. when then the target cell is also a NR cell, the wireless device  120  performs Actions  1305  and  1306 . In Action  1305 , the wireless device  120  calculates the NR security token, e.g. the ShortMAC-I, using the source PhysCellID, the source C-RNTI and the target cell identity in the NR varShortMAC-Input. In Action  1306 , the wireless device  120  transmits an RRCReestablishmentRequest to the network node, e.g. to the first radio network node  110  and/or to the second radio network node  112 . The RRCReestablishmentRequest comprises the calculated security token. 
     In an inter-RAT procedure, i.e. when then the target cell is not in the same RAT as the source cell, e.g. when the source cell is a NR cell and the target cell is an LTE cell, the wireless device  120  performs Actions  1307 ,  1308 , and  1309 . In Action  1307 , the wireless device  120  uses NR PhysCellID and source C-RNTI, and concatenates 8 binary ‘0’s to target cell identity and use in NR VarShortMAC-Input. In Action  1308 , the wireless device  120  calculates the security token in LTE, e.g. the LTE ShortMAC-I, using the NR VarShortMAC-Input. Thus, the wireless device  120  calculates the security token using NR format and LTE procedures. In Action  1309 , the wireless device  120  transmits an RRCConnectionReestablishmentRequest to the network node, e.g. to the second radio network node  112 . The RRCConnectionReestablishmentRequest comprises the calculated security token. 
     2.7. Some Third Exemplifying Embodiments: Create New IE and Update Procedures for RRC Reestablishment 
     In some embodiments, the LTE and NR specifications are extended to introduce new IEs used to calculate the security token ShortMAC-I and update the procedures accordingly. In all of these embodiments, the same principle as in some first and second exemplifying embodiments may be applied, i.e. the procedures and ASN.1 definition are defined in the target RAT specification (as in some first exemplifying embodiments), or the procedures are defined in the target RAT specification and the ASN.1 definition is defined in the source RAT specification (as some second exemplifying embodiments). 
     2.7.1. Solution 3.1: Define New IE (e.g. VarinterRAT-ShortMAC-Input) in Target RAT and Define Procedures to Calculate Security Token in Target RAT 
     2.7.1.1. Failure in LTE and Reestablishment in NR: 
     If the UE is connected to an LTE cell and detects failure and attempts to reestablish in an NR cell, the UE and network could calculate the Reestablishment ShortMAC-I using the source C-RNTI and source PCI (i.e. LTE) along with the target Cell identity (i.e. NR) in a newly defined IE. 
     The embodiments described here use the IE name VarInterRAT-ShortMAC-Input as an example, but the solution would work equally well with another parameter name. 
     2.7.1.1.1. Updates of TS 36.331 
     TS 36.331 5.3.7.3 Actions following cell selection while T 311  is running 
     Upon selecting a suitable E-UTRA cell, the UE shall:
         1&gt; stop timer T 311 ;   1&gt; start timer T 301 ;   1&gt; apply the timeAlignmentTimerCommon included in SystemInformationBlockType2;   1&gt; if the UE is a NB-IoT UE supporting RRC connection re-establishment for the Control Plane CIoT EPS optimisation and AS security has not been activated; and   1&gt; if cp-reestablishment is not included in SystemInformationBlockType2-NB:
           2&gt; perform the actions upon leaving RRC_CONNECTED as specified in 5.3.12, with release cause ‘RRC connection failure’;   
           1&gt; else:
           2&gt; initiate transmission of the RRCConnectionReestablishmentRequest message in accordance with 5.3.7.4;   
               

     NOTE: This procedure applies also if the UE returns to the source PCell. 
     Upon selecting an inter-RAT cell, the UE shall:
         1&gt; if the target cell is an NR cell and the previously configured integrity protection algorithms are available to configure in the target system:
           2&gt; stop timer T 311 ;   2&gt; start timer T 301 ;   2&gt; apply the timeAlignmentTimerCommon included in SystemInformationBlockType2;   2&gt; initiate transmission of the RRCReestablishmentRequest message in accordance with TS 38.331 section 5.3.7.4;   
           1&gt; else:
           2&gt; if the selected cell is a UTRA cell, and if the UE supports Radio Link Failure Report for Inter-RAT MRO, include selectedUTRA-CellId in the VarRLF-Report and set it to the physical cell identity and carrier frequency of the selected UTRA cell;   2&gt; perform the actions upon leaving RRC_CONNECTED as specified in 5.3.12, with release cause ‘RRC connection failure’;   
               

     2.7.1.1.2. Updates of TS 38.331
         VarinterRAT-ShortMAC-Input       

     The UE variable VarinterRAT-ShortMAC-Input specifies the input used to generate the ShortMAC-I during inter-RAT RRC Connection Reestablishment procedure when the UE was experienced failure in E-UTRA. 
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 -- ASN1START 
               
               
                   
                 -- TAG-VAR-INTER-RAT-SHORT-MAC-INPUT-START 
               
            
           
           
               
               
               
            
               
                   
                 VarInterRAT-ShortMAC-Input ::= 
                 SEQUENCE { 
               
               
                   
                  sourcePhysCellId 
                  EUTRA-PhysCellId, 
               
               
                   
                  targetCellIdentity 
                  CellIdentity, 
               
               
                   
                  source-C-RNTI 
                  BIT STRING (SIZE (16)) 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 -- TAG-VAR-INTER-RAT-SHORT-MAC-INPUT-STOP 
               
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
                             VarInterRAT-ShortMAC-Input field descriptions                                    targetCellIdentity       Set to CellIdentity of the target cell i.e. the cell the UE is trying to       reestablish the connection.       source-C-RNTI       Set to E-UTRA C-RNTI that the UE had in the PCell it was connected to       prior to suspension of the RRC connection.       sourcePhysCellId       Set to the E-UTRA physical cell identity of the PCell the UE was       connected to prior to suspension of the RRC connection.                    
The procedures in TS 38.331 may be updated to e.g.:
 
TS 38.331 5.3.7.4 Actions related to transmission of RRCReestablishmentRequest message
 
The UE shall set the contents of RRCReestablishmentRequest message as follows:
         1&gt; set the ue-Identity as follows:
           2&gt; set the c-RNTI to the C-RNTI used in the source PCell (reconfiguration with sync or mobility from NR failure) or used in the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; set the physCellId to the physical cell identity of the source PCell (reconfiguration with sync or mobility from NR failure) or of the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; if the source cell is an NR cell:
               2&gt; set the shortMAC-I to the 16 least significant bits of the MAC-I calculated:   4&gt; over the ASN.1 encoded as per section 8 (i.e., a multiple of 8 bits) VarShortMAC-Input;   4&gt; with the KRR Cint  key and integrity protection algorithm that was used in the source PCell (reconfiguration with sync or mobility from NR failure) or of the PCell in which the trigger for the re-establishment occurred (other cases); and   4&gt; with all input bits for COUNT, BEARER and DIRECTION set to binary ones;   
               
           1&gt; else (source cell is an E-UTRA cell):
           2&gt; set the shortMAC-I to the 16 least significant bits of the MAC-I calculated:
               3&gt; over the ASN.1 encoded as per section 8 (i.e., a multiple of 8 bits) VarInterRAT-ShortMAC-Input;   3&gt; with the previously configured E-UTRA KRR Cint  key and the NR integrity protection algorithms corresponding to the previously configured integrity protection algorithm; and   3&gt; with all input bits for COUNT, BEARER and DIRECTION set to binary ones;   
               
           1&gt; set the reestablishmentCause as follows:
           2&gt; if the re-establishment procedure was initiated due to reconfiguration failure as specified in 5.3.5.8.2:
               3&gt; set the reestablishmentCause to the value reconfigurationFailure;   
               2&gt; else if the re-establishment procedure was initiated due to reconfiguration with sync failure as specified in 5.3.5.8.3 (intra-NR handover failure) or 5.4.3.5 (inter-RAT mobility from NR failure):
               3&gt; set the reestablishmentCause to the value handoverFailure;   
               2&gt; else:
               3&gt; set the reestablishmentCause to the value otherFailure;   
               
           1&gt; restore the RRC configuration and security context from the stored UE AS context;   1&gt; restore the PDCP state and re-establish PDCP for SRB1;   1&gt; re-establish RLC for SRB1;   1&gt; resume SRB1;   1&gt; The UE shall submit the RRCReestablishmentRequest message to lower layers for transmission.
 
 FIG. 14  schematically illustrates an example diagram of how the procedure may be done. In  FIG. 14  actions performed by the wireless device  120  being connected to an LTE cell and when detecting failure are shown. In this example, the wireless device  120  initiates RRC Reestablishment towards LTE or NR. Further, the wireless device  120  calculates the inter-RAT integrity checksum using a new IE defined in NR format and use NR procedures.
       

     In Action  1401 , the wireless device  120  is connected to a first cell  11  being an LTE cell, and in Action  1402 , the wireless device  120  detects an RLF. In Action  1403  the wireless device  120  initiates an RRC reestablishment procedure and selects a suitable target cell, e.g. the second cell  12 . In Action  1404 , the wireless device  120  checks whether or not the target cell, i.e. the second cell  12 , belongs to the same RAT as the source cell, i.e. the first cell  11 . In other words, and in case the source cell is an LTE cell, the wireless device  120  checks whether or not the target cell is also an LTE cell. 
     In an intra-RAT procedure, i.e. when then the target cell is also an LTE cell, the wireless device  120  performs Actions  1405  and  1406 . In Actions  1405 , the wireless device  120  calculates the LTE security token, e.g. the ShortMAC-I, using the source PhysCellID, the source C-RNTI and the target cell identity in the LTE varShortMAC-Input. In Action  1406 , the wireless device  120  transmits an RRCConnectionReestablishmentRequest to the network node, e.g. to the first radio network node  110  and/or to the second radio network node  112 . The RRCConnectionReestablishmentRequest comprises the calculated security token. 
     In an inter-RAT procedure, i.e. when then the target cell is not in the same RAT as the source cell, e.g. when the source cell is an LTE cell and the target cell is a NR cell, the wireless device  120  performs Actions  1407 ,  1408 , and  1409 . In Action  1407 , the wireless device  120  uses source E-UTRA-PhysCellID, source E-UTRA C-RNTI, and target cell identity in NR VarInter-RAT-ShortMAC-Input. In Action  1408 , the wireless device  120  calculates the security token in NR, e.g. the NR ShortMAC-I, using the NR VarInter-RAT-ShortMAC-Input. Thus, the wireless device  120  calculates the security token using NR format and NR procedures. In Action  1409 , the wireless device  120  transmits an RRCReestablishmentRequest to the network node, e.g. to the second radio network node  112 . The RRCReestablishmentRequest comprises the calculated security token. 
     2.7.1.2. Failure in NR and Reestablishment in LTE 
     If the UE is connected to an NR cell and detects failure and attempts to reestablish in LTE, the UE and network could calculate the Reestablishment ShortMAC-I using the source C-RNTI and source PCI along with the target Cell identity. 
     2.7.1.2.1. Updates of TS 38.331 
     The procedures in section 5.3.7.3 need to be updated to handle the case of inter-RAT reestablishment. 
     TS 38.331 5.3.7.3 Actions following cell selection while T 311  is running 
     Upon selecting a suitable NR cell, the UE shall:
         1&gt; stop timer T 311 ;   1&gt; start timer T 301 ;   1&gt; apply the timeAlignmentTimerCommon included in SIB1;   1&gt; initiate transmission of the RRCReestablishmentRequest message in accordance with 5.3.7.4; NOTE: This procedure applies also if the UE returns to the source PCell.
 
Upon selecting an inter-RAT cell, the UE shall:
   1&gt; if the target cell is an E-UTRA cell and the previously configured integrity protection algorithms are available to configure in the target system:
           2&gt; stop timer T 311 ;   2&gt; start timer T 301 ;   2&gt; apply the timeAlignmentTimerCommon included in SIB1;   2&gt; initiate transmission of the RRCConnectionReestablishmentRequest message in accordance with TS 36.331 section 5.3.7.4;   
           1&gt; else:
           2&gt; perform the actions upon going to RRC_IDLE as specified in 5.3.11, with release cause ‘RRC connection failure’;   
               

     2.7.1.2.1. Updates of TS 36.331
         VarInterRAT-ShortMAC-Input       

     The UE variable VarinterRAT-ShortMAC-Input specifies the input used to generate the ShortMAC-I during inter-RAT RRC Connection Reestablishment procedure when the UE experienced failure in NR. 
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 -- ASN1START 
               
               
                   
                 -- TAG-VAR-INTER-RAT-SHORT-MAC-INPUT-START 
               
            
           
           
               
               
               
            
               
                   
                 VarInterRAT-ShortMAC-Input ::= 
                 SEQUENCE { 
               
               
                   
                  sourcePhysCellId 
                  EUTRA-PhysCellId, 
               
               
                   
                  targetCellIdentity 
                  CellIdentity, 
               
               
                   
                  source-C-RNTI 
                  BIT STRING (SIZE (16)) 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 -- TAG-VAR-INTER-RAT-SHORT-MAC-INPUT-STOP 
               
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 VarInterRAT-ShortMAC-Input field descriptions 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 targetCellIdentity 
               
               
                 Set to CellIdentity of the target cell i.e. the cell the UE is trying to 
               
               
                 reestablish the connection. 
               
               
                 source-C-RNTI 
               
               
                 Set to NR C-RNTI that the UE had in the PCell it was connected to prior 
               
               
                 to suspension of the RRC connection. 
               
               
                 sourcePhysCellId 
               
               
                 Set to the NR physical cell identity of the PCell the UE was connected 
               
               
                 to prior to suspension of the RRC connection. 
               
               
                   
               
            
           
         
       
     
     The procedures of section 5.3.7.4 in TS 36.331 may be extended to e.g.: 
     TS 36.331 5.3.7.4 Actions related to transmission of RRCConnectionReestablishmentRequest message 
     Except for NB-IoT, if the procedure was initiated due to radio link failure or handover failure, the UE shall:
         1&gt; set the reestablishmentCellId in the VarRLF-Report to the global cell identity of the selected cell;
 
The UE shall set the contents of RRCConnectionReestablishmentRequest message as follows:
   1&gt; except for a NB-IoT UE for which AS security has not been activated, set the ue-Identity as follows:
           2&gt; set the c-RNTI to the C-RNTI used in the source PCell (handover and mobility from E-UTRA failure) or used in the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; set the physCellId to the physical cell identity of the source PCell (handover and mobility from E-UTRA failure) or of the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; if source cell is an E-UTRA cell:
               3&gt; set the shortMAC-I to the 16 least significant bits of the MAC-I calculated:   4&gt; over the ASN.1 encoded as per section 8 (i.e., a multiple of 8 bits) VarShortMAC-Input (or VarShortMAC-Input-NB in NB-IoT);   4&gt; with the KRR Cint  key and integrity protection algorithm that was used in the source PCell (handover and mobility from E-UTRA failure) or of the PCell in which the trigger for the re-establishment occurred (other cases); and   4&gt; with all input bits for COUNT, BEARER and DIRECTION set to binary ones;   
               2&gt; else:
               3&gt; set the shortMAC-I to the 16 least significant bits of the MAC-I calculated:   4&gt; over the ASN.1 encoded as per section 8 (i.e., a multiple of 8 bits) VarinterRAT-ShortMAC-Input;   4&gt; with the previously configured KRR Cint  key and the E-UTRA integrity protection algorithms corresponding to the previously configured integrity protection algorithm; and   4&gt; with all input bits for COUNT, BEARER and DIRECTION set to binary ones;   
               
           1&gt; for a NB-IoT UE for which AS security has not been activated, set the ue-Identity as follows:
           2&gt; request upper layers for calculated ul-NAS-MAC and ul-NAS-Count using the cellIdentity of the PCell in which the trigger for the re-establishment occurred;   2&gt; set the s-TMSI to the S-TMSI provided by upper layers;   2&gt; set the ul-NAS-MAC to the ul-NAS-MAC value provided by upper layers;   2&gt; set the ul-NAS-Count to the ul-NAS-Count value provided by upper layers;   
           1&gt; set the reestablishmentCause as follows:
           2&gt; if the re-establishment procedure was initiated due to reconfiguration failure as specified in 5.3.5.5 (the UE is unable to comply with the reconfiguration):
               3&gt; set the reestablishmentCause to the value reconfigurationFailure;   
               2&gt; else if the re-establishment procedure was initiated due to handover failure as specified in 5.3.5.6 (intra-LTE handover failure) or 5.4.3.5 (inter-RAT mobility from EUTRA failure):
               3&gt; set the reestablishmentCause to the value handoverFailure;   
               2&gt; else:
               3&gt; set the reestablishmentCause to the value otherFailure;   
               
           1&gt; if the UE is a NB-IoT UE:
           2&gt; if the UE supports DL channel quality reporting and cqi-Reporting is present in SystemInformationBlockType2-NB:
               3&gt; set the cqi-NPDCCH to include the latest results of the downlink channel quality measurements of the serving cell as specified in TS 36.133 [16];
 
NOTE: The downlink channel quality measurements may use measurement period T 1  or T 2 , as defined in TS 36.133 [16]. In case period T 2  is used the RRC-MAC interactions are left to UE implementation.
   
               
           2&gt; set earlyContentionResolution to TRUE;
 
The UE shall submit the RRCConnectionReestablishmentRequest message to lower layers for transmission.
 
 FIG. 15  schematically illustrates an example diagram of how the procedure may be done. In  FIG. 15  actions performed by the wireless device  120  being connected to a NR cell and when detecting failure are shown. In this example, the wireless device  120  initiates RRC Reestablishment towards LTE or NR. Further, the wireless device  120  calculates the inter-RAT integrity checksum using a new IE defined in LTE format and use LTE procedures.
       

     In Action  1501 , the wireless device  120  is connected to a first cell  11  being a NR cell, and in Action  1502 , the wireless device  120  detects an RLF. In Action  1503  the wireless device  120  initiates an RRC reestablishment procedure and selects a suitable target cell, e.g. the second cell  12 . In Action  1504 , the wireless device  120  checks whether or not the target cell, i.e. the second cell  12 , belongs to the same RAT as the source cell, i.e. the first cell  11 . In other words, and in case the source cell is a NR cell, the wireless device  120  checks whether or not the target cell is also a NR cell. 
     In an intra-RAT procedure, i.e. when then the target cell is also a NR cell, the wireless device  120  performs Actions  1505  and  1506 . In Actions  1505 , the wireless device  120  calculates the NR security token, e.g. the ShortMAC-I, using the source PhysCellID, the source C-RNTI and the target cell identity in the NR varShortMAC-Input. 
     In Action  1506 , the wireless device  120  transmits an RRCReestablishmentRequest to the network node, e.g. to the first radio network node  110  and/or to the second radio network node  112 . The RRCReestablishmentRequest comprises the calculated security token. 
     In an inter-RAT procedure, i.e. when then the target cell is not in the same RAT as the source cell, e.g. when the source cell is a NR cell and the target cell is an LTE cell, the wireless device  120  performs Actions  1507 ,  1508 , and  1509 . In Action  1507 , the wireless device  120  uses PhysCellID, uses source NR C-RNTI as C-RNTI, and uses target cell identity in LTE VarInter-RAT-ShortMAC-Input. In Action  1508 , the wireless device  120  calculates the security token in LTE, e.g. the LTE ShortMAC-I, using the LTE VarInter-RAT-ShortMAC-Input. Thus, the wireless device  120  calculates the security token using LTE format and LTE procedures. In Action  1509 , the wireless device  120  transmits an RRCConnectionReestablishmentRequest to the network node, e.g. to the second radio network node  112 . The RRCConnectionReestablishmentRequest comprises the calculated security token. 
     2.7.2 Solution 3.2: Define New IE (e.g. VarinterRAT-ShortMAC-Input) in Source RAT and Define Procedures to Calculate Security Token in Target RAT 
     2.7.2.1. Failure in LTE and Reestablishment in NR: 
     If the UE is connected to an LTE cell and detects failure and attempts to reestablish to an NR cell, the UE and network could calculate the Reestablishment ShortMAC-I using the source (LTE) C-RNTI and source (LTE) PCI along with the target (NR) Cell identity in a newly defined IE. The IE would be defined in LTE, but the procedures would be defined in NR. 
     Note: the parameter names are suffixed with an “-rxx” to indicate which release of the specification they are introduced. Whatever the suffix may be, this will not change the solutions described. 
     2.7.2.1.1. Updates of TS 36.331 
     TS 36.331 5.3.7.3 Actions following cell selection while T 311  is running 
     Upon selecting a suitable E-UTRA cell, the UE shall:
         1&gt; stop timer T 311 ;   1&gt; start timer T 301 ;   1&gt; apply the timeAlignmentTimerCommon included in SystemInformationBlockType2;   1&gt; if the UE is a NB-IoT UE supporting RRC connection re-establishment for the Control Plane CIoT EPS optimisation and AS security has not been activated; and   1&gt; if cp-reestablishment is not included in SystemInformationBlockType2-NB:
           2&gt; perform the actions upon leaving RRC_CONNECTED as specified in 5.3.12, with release cause ‘RRC connection failure’;   
           1&gt; else:
           2&gt; initiate transmission of the RRCConnectionReestablishmentRequest message in accordance with 5.3.7.4;   
               

     NOTE: This procedure applies also if the UE returns to the source PCell. 
     Upon selecting an inter-RAT cell, the UE shall:
         1&gt; if the target cell is an NR cell and the previously configured integrity protection algorithms are available to configure in the target system:
           2&gt; stop timer T 311 ;   2&gt; start timer T 301 ;   2&gt; apply the timeAlignmentTimerCommon included in SystemInformationBlockType2;   2&gt; initiate transmission of the RRCReestablishmentRequest message in accordance with TS 38.331 section 5.3.7.4;   
           1&gt; else:
           2&gt; if the selected cell is a UTRA cell, and if the UE supports Radio Link Failure Report for Inter-RAT MRO, include selectedUTRA-CellId in the VarRLF-Report and set it to the physical cell identity and carrier frequency of the selected UTRA cell;   2&gt; perform the actions upon leaving RRC_CONNECTED as specified in 5.3.12, with release cause ‘RRC connection failure’;   
           VarinterRAT-ShortMAC-Input       

     The UE variable VarinterRAT-ShortMAC-Input specifies the input used to generate the ShortMAC-I in NR during inter-RAT RRC Connection Reestablishment procedure when the UE experienced failure in E-UTRA and reestablishes in NR. 
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 -- ASN1START 
               
               
                   
                 -- TAG-VAR-INTER-RAT-SHORT-MAC-INPUT-START 
               
            
           
           
               
               
               
            
               
                   
                 VarInterRAT-ShortMAC-Input ::= 
                 SEQUENCE 1 
               
               
                   
                  eutra-phys-CellId-rxx 
                  PhysCellId, 
               
               
                   
                  nr-CellIdentity-rxx 
                  BIT STRING (SIZE (36)), 
               
               
                   
                  nr-C-RNTI-rxx 
                  C-RNTI 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 -- TAG-VAR-INTER-RAT-SHORT-MAC-INPUT-STOP 
               
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 VarInterRAT-ShortMAC-Input field descriptions 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 nr-CellIdentity 
               
               
                 This field contain the NR CellIdentity of the target NR cell i.e. the cell to 
               
               
                 which the UE is trying to reestablish the connection. 
               
               
                 nr-C-RNTI 
               
               
                 Set to E-UTRA C-RNTI that the UE had in the PCell it was connected to 
               
               
                 prior to the failure. 
               
               
                 eutra-PhysCellId 
               
               
                 Set to the E-UTRA physical cell identity of the PCell the UE was 
               
               
                 connected to prior to the failure. 
               
               
                   
               
            
           
         
       
     
     2.7.2.1.2. Updates of TS 38.331 
     TS 38.331 5.3.7.4 Actions related to transmission of RRCReestablishmentRequest message 
     The UE shall set the contents of RRCReestablishmentRequest message as follows:
         1&gt; set the ue-Identity as follows:
           2&gt; set the c-RNTI to the C-RNTI used in the source PCell (reconfiguration with sync or mobility from NR failure) or used in the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; set the physCellId to the physical cell identity of the source PCell (reconfiguration with sync or mobility from NR failure) or of the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; if the source cell is an NR cell:
               2&gt; set the shortMAC-I to the 16 least significant bits of the MAC-I calculated:   4&gt; over the ASN.1 encoded as per section 8 (i.e., a multiple of 8 bits) VarShortMAC-Input;   4&gt; with the KRR Cint  key and integrity protection algorithm that was used in the source PCell (reconfiguration with sync or mobility from NR failure) or of the PCell in which the trigger for the re-establishment occurred (other cases); and   4&gt; with all input bits for COUNT, BEARER and DIRECTION set to binary ones;   
               
           1&gt; else (source cell is an E-UTRA cell):
           2&gt; set the shortMAC-I to the 16 least significant bits of the MAC-I calculated:
               3&gt; over the ASN.1 encoded as per section 8 (i.e., a multiple of 8 bits) VarinterRAT-ShortMAC-Input as defined in TS 36.331;   3&gt; with the previously configured E-UTRA KRR Cint  key and the NR integrity protection algorithms corresponding to the previously configured integrity protection algorithm; and   3&gt; with all input bits for COUNT, BEARER and DIRECTION set to binary ones;   
               
           1&gt; set the reestablishmentCause as follows:
           2&gt; if the re-establishment procedure was initiated due to reconfiguration failure as specified in 5.3.5.8.2:
               3&gt; set the reestablishmentCause to the value reconfigurationFailure;   
               2&gt; else if the re-establishment procedure was initiated due to reconfiguration with sync failure as specified in 5.3.5.8.3 (intra-NR handover failure) or 5.4.3.5 (inter-RAT mobility from NR failure):
               3&gt; set the reestablishmentCause to the value handoverFailure;   
               2&gt; else:
               3&gt; set the reestablishmentCause to the value otherFailure;   
               
           1&gt; restore the RRC configuration and security context from the stored UE AS context;   1&gt; restore the PDCP state and re-establish PDCP for SRB1;   1&gt; re-establish RLC for SRB1;   1&gt; resume SRB1;   1&gt; The UE shall submit the RRCReestablishmentRequest message to lower layers for transmission.
 
 FIG. 16  schematically illustrates an example diagram of how the procedure may be done. In  FIG. 16  actions performed by the wireless device  120  being connected to an LTE cell and when detecting a failure are shown. In this example, the wireless device  120  initiates RRC Reestablishment towards LTE or NR. Further, the wireless device  120  calculates the inter-RAT integrity checksum using a new IE defined in LTE format and use NR procedures.
       

     In Action  1601 , the wireless device  120  is connected to a first cell  11  being an LTE cell, and in Action  1602 , the wireless device  120  detects an RLF. In Action  1603  the wireless device  120  initiates an RRC reestablishment procedure and selects a suitable target cell, e.g. the second cell  12 . In Action  1604 , the wireless device  120  checks whether or not the target cell, i.e. the second cell  12 , belongs to the same RAT as the source cell, i.e. the first cell  11 . In other words, and in case the source cell is an LTE cell, the wireless device  120  checks whether or not the target cell is also an LTE cell. 
     In an intra-RAT procedure, i.e. when then the target cell is also an LTE cell, the wireless device  120  performs Actions  1605  and  1606 . In Actions  1605 , the wireless device  120  calculates the LTE security token, e.g. the ShortMAC-I, using the source PhysCellID, the source C-RNTI and the target cell identity in the LTE varShortMAC-Input. In Action  1606 , the wireless device  120  transmits an RRCConnectionReestablishmentRequest to the network node, e.g. to the first radio network node  110  and/or to the second radio network node  112 . The RRCConnectionReestablishmentRequest comprises the calculated security token. 
     In an inter-RAT procedure, i.e. when then the target cell is not in the same RAT as the source cell, e.g. when the source cell is an LTE cell and the target cell is a NR cell, the wireless device  120  performs Actions  1607 ,  1608 , and  1609 . In Action  1607 , the wireless device  120  uses source PhysCellID, uses source E-UTRA C-RNTI as C-RNTI, and uses target cell identity as cellIdentity in LTE VarInter-RAT-ShortMAC-Input. In Action  1608 , the wireless device  120  calculates the security token in NR, e.g. the NR ShortMAC-I, using the LTE VarInter-RAT-ShortMAC-Input. Thus, the wireless device  120  calculates the security token using LTE format and NR procedures. In Action  1609 , the wireless device  120  transmits an RRCReestablishmentRequest to the network node, e.g. to the second radio network node  112 . The RRCReestablishmentRequest comprises the calculated security token. 
     2.7.2.2. Failure in NR and Reestablishment in LTE 
     If the UE is connected to a cell in the first RAT being NR and detects failure and attempts to reestablish the connection in the second RAT being LTE, the UE and network could calculate the Reestablishment ShortMAC-I using the source (NR) C-RNTI and source (NR) PCI along with the target (LTE) Cell identity. in a newly defined IE. The IE would be defined in NR, but the procedures would be defined in LTE. 
     2.7.2.2.1. Updates of TS 38.331 
     TS 38.331 5.3.7.3 Actions following cell selection while T 311  is running 
     Upon selecting a suitable NR cell, the UE shall:
         1&gt; stop timer T 311 ;   1&gt; start timer T 301 ;   1&gt; apply the timeAlignmentTimerCommon included in SIB1;   1&gt; initiate transmission of the RRCReestablishmentRequest message in accordance with 5.3.7.4;       

     NOTE: This procedure applies also if the UE returns to the source PCell. 
     Upon selecting an inter-RAT cell, the UE shall:
         1&gt; if the target cell is an E-UTRA cell and the previously configured integrity protection algorithms are available to configure in the target system:
           2&gt; stop timer T 311 ;   2&gt; start timer T 301 ;   2&gt; apply the timeAlignmentTimerCommon included in SIB1;   2&gt; initiate transmission of the RRCConnectionReestablishmentRequest message in accordance with TS 36.331 section 5.3.7.4;   
           1&gt; else:
           2&gt; perform the actions upon going to RRC_IDLE as specified in 5.3.11, with release cause   
               

     ‘RRC connection failure’;
         VarInterRAT-ShortMAC-Input
 
The UE variable VarinterRAT-ShortMAC-Input specifies the input used to generate the ShortMAC-I during inter-RAT RRC Connection Reestablishment procedure when the UE detected failure in NR and reestablishes the connection in E-UTRA.
       

     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 -- ASN1START 
               
               
                   
                 -- TAG-VAR-INTER-SHORT-RAT-MAC-INPUT-START 
               
            
           
           
               
               
               
            
               
                   
                 VarInterRAT-ShortMAC-Input ::= 
                 SEQUENCE { 
               
               
                   
                  nr-Source-PhysCellId-rxx 
                  PhysCellId, 
               
               
                   
                  eutra-TargetCellIdentity-rxx 
                  BIT STRING (SIZE (28)), 
               
               
                   
                  nr-Source-C-RNTI-rxx 
                  RNTI-Value 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 -- TAG-VAR-INTER-RAT-SHORT-MAC-INPUT-STOP 
               
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 VarInterRAT-ShortMAC-Input field descriptors 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 eutra-TargetCellIdentity 
               
               
                 This field contain the E-UTRA CellIdentity of the target E-UTRA cell i.e. 
               
               
                 the cell to which the UE is trying to reestablish the connection. 
               
               
                 nr-Source-C-RNTI 
               
               
                 Set to NR C-RNTI that the UE had in the PCell it was connected to 
               
               
                 prior to the failure. 
               
               
                 nr-Source-PhysCellId 
               
               
                 Set to the NR physical cell identity of the PCell the UE was 
               
               
                 connected to prior the failure. 
               
               
                   
               
            
           
         
       
     
     2.7.2.2.1. Updates of TS 36.331 
     The procedures of section 5.3.7.4 in TS 36.331 may be extended to e.g.: 
     TS 36.331 5.3.7.4 Actions related to transmission of RRCConnectionReestablishmentRequest message 
     Except for NB-IoT, if the procedure was initiated due to radio link failure or handover failure, the UE shall:
         1&gt; set the reestablishmentCellId in the VarRLF-Report to the global cell identity of the selected cell;
 
The UE shall set the contents of RRCConnectionReestablishmentRequest message as follows:
   1&gt; except for a NB-IoT UE for which AS security has not been activated, set the ue-Identity as follows:
           2&gt; set the c-RNTI to the C-RNTI used in the source PCell (handover and mobility from E-UTRA failure) or used in the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; set the physCellId to the physical cell identity of the source PCell (handover and mobility from E-UTRA failure) or of the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; if source cell is an E-UTRA cell:
               3&gt; set the shortMAC-I to the 16 least significant bits of the MAC-I calculated:   4&gt; over the ASN.1 encoded as per section 8 (i.e., a multiple of 8 bits) VarShortMAC-Input (or VarShortMAC-Input-NB in NB-IoT);   4&gt; with the KRR Cint  key and integrity protection algorithm that was used in the source PCell (handover and mobility from E-UTRA failure) or of the PCell in which the trigger for the re-establishment occurred (other cases); and   4&gt; with all input bits for COUNT, BEARER and DIRECTION set to binary ones;   
               2&gt; else:
               3&gt; set the shortMAC-I to the 16 least significant bits of the MAC-I calculated:   4&gt; over the ASN.1 encoded as per section 8 (i.e., a multiple of 8 bits) VarInterRAT-ShortMAC-Input as defined in TS 38.331;   4&gt; with the previously configured K RRCint  key and the E-UTRA integrity protection algorithms corresponding to the previously configured integrity protection algorithm; and   4&gt; with all input bits for COUNT, BEARER and DIRECTION set to binary ones;   
               
           1&gt; for a NB-IoT UE for which AS security has not been activated, set the ue-Identity as follows:
           2&gt; request upper layers for calculated ul-NAS-MAC and ul-NAS-Count using the cellIdentity of the PCell in which the trigger for the re-establishment occurred;   2&gt; set the s-TMSI to the S-TMSI provided by upper layers;   2&gt; set the ul-NAS-MAC to the ul-NAS-MAC value provided by upper layers;   2&gt; set the ul-NAS-Count to the ul-NAS-Count value provided by upper layers;   
           1&gt; set the reestablishmentCause as follows:
           2&gt; if the re-establishment procedure was initiated due to reconfiguration failure as specified in 5.3.5.5 (the UE is unable to comply with the reconfiguration):
               3&gt; set the reestablishmentCause to the value reconfigurationFailure;   
               2&gt; else if the re-establishment procedure was initiated due to handover failure as specified in 5.3.5.6 (intra-LTE handover failure) or 5.4.3.5 (inter-RAT mobility from EUTRA failure):
               3&gt; set the reestablishmentCause to the value handoverFailure;   
               2&gt; else:
               3&gt; set the reestablishmentCause to the value otherFailure;   
               
           1&gt; if the UE is a NB-IoT UE:
           2&gt; if the UE supports DL channel quality reporting and cqi-Reporting is present in SystemInformationBlockType2-NB:
               3&gt; set the cqi-NPDCCH to include the latest results of the downlink channel quality measurements of the serving cell as specified in TS 36.133 [16];   
               
           NOTE: The downlink channel quality measurements may use measurement period T 1  or T 2 , as defined in TS 36.133 [16]. In case period T 2  is used the RRC-MAC interactions are left to UE implementation.
           2&gt; set earlyContentionResolution to TRUE;   
               

     The UE shall submit the RRCConnectionReestablishmentRequest message to lower layers for transmission. 
       FIG. 17  schematically illustrates an example diagram of how the procedure may be done. In  FIG. 17  actions performed by the wireless device  120  being connected to a NR cell and when detecting failure are shown. In this example, the wireless device  120  initiates RRC Reestablishment towards LTE or NR. Further, the wireless device  120  calculates the inter-RAT integrity checksum using a new IE defined in NR format and use LTE procedures. 
     In Action  1601 , the wireless device  120  is connected to a first cell  11  being a NR cell, and in Action  1602 , the wireless device  120  detects an RLF. In Action  1603  the wireless device  120  initiates an RRC reestablishment procedure and selects a suitable target cell, e.g. the second cell  12 . In Action  1604 , the wireless device  120  checks whether or not the target cell, i.e. the second cell  12 , belongs to the same RAT as the source cell, i.e. the first cell  11 . In other words, and in case the source cell is a NR cell, the wireless device  120  checks whether or not the target cell is also a NR cell. 
     In an intra-RAT procedure, i.e. when then the target cell is also a NR cell, the wireless device  120  performs Actions  1605  and  1606 . In Actions  1605 , the wireless device  120  calculates the NR security token, e.g. the NR ShortMAC-I, using the source PhysCellID, the source C-RNTI and the target cell identity in the NR varShortMAC-Input. 
     In Action  1606 , the wireless device  120  transmits an RRCReestablishmentRequest to the network node, e.g. to the first radio network node  110  and/or to the second radio network node  112 . The RRCReestablishmentRequest comprises the calculated security token. 
     In an inter-RAT procedure, i.e. when then the target cell is not in the same RAT as the source cell, e.g. when the source cell is a NR cell and the target cell is an LTE cell, the wireless device  120  performs Actions  1607 ,  1608 , and  1609 . In Action  1607 , the wireless device  120  uses PhysCellID, uses source NR C-RNTI as C-RNTI, and uses target cell identity in NR VarInterRAT-ShortMAC-Input. In Action  1608 , the wireless device  120  calculates the security token in LTE, e.g. the LTE ShortMAC-I, using the NR VarInterRAT-ShortMAC-Input. Thus, the wireless device  120  calculates the security token using NR format and LTE procedures. In Action  1609 , the wireless device  120  transmits an RRCConnectionReestablishmentRequest to the network node, e.g. to the second radio network node  112 . The RRCConnectionReestablishmentRequest comprises the calculated security token. 
     2.8. Some Fourth Exemplifying Embodiments. Update Current Definition of Variables to Include Both Intra-RAT and Inter-RAT Parameters and Define Procedures in Target RAT 
     2.8.1. Solution 4.1: Update Definition of VarShortMAC-Input in LTE and NR to Also Include Inter-RAT Parameters and Define Procedures in the Target RAT, 
     Another solution to the problem is to introduce a new parameters (or extend the VarShortMAC-Input in LTE and NR) to include both LTE and NR variables, and used in both intra-RAT and inter-RAT failure/reestablishment. This variable could for instance be defined using a choice structure, where depending on the type of source and target 
     RAT, the appropriate choice were made. 
     2.8.1.1. Failure in NR and Reestablishment in LTE 
     If the UE is connected to an NR cell and detects failure and reestablishes the connection in LTE, the UE and network would use the variables and procedures in the target RAT (i.e. LTE). 
     2.8.1.1.1. Updates of TS 38.331 
     TS 38.331 5.3.7.3 Actions following cell selection while T 311  is running 
     Upon selecting a suitable NR cell, the UE shall:
         1&gt; stop timer T 311 ;   1&gt; start timer T 301 ;   1&gt; apply the timeAlignmentTimerCommon included in SIB1;   1&gt; initiate transmission of the RRCReestablishmentRequest message in accordance with 5.3.7.4;       

     NOTE: This procedure applies also if the UE returns to the source PCell. 
     Upon selecting an inter-RAT cell, the UE shall:
         1&gt; if the target cell is an E-UTRA cell and the previously configured integrity protection algorithms are available to configure in the target system:
           2&gt; stop timer T 311 ;   2&gt; start timer T 301 ;   2&gt; apply the timeAlignmentTimerCommon included in SIB1;   2&gt; initiate transmission of the RRCConnectionReestablishmentRequest message in accordance with TS 36.331 section 5.3.7.4;   
           1&gt; else:
           2&gt; perform the actions upon going to RRC_IDLE as specified in 5.3.11, with release cause ‘RRC connection failure’;   
               

     2.8.1.1.2. Updates of TS 36.331 
     The updated IE may be defined in LTE only as e.g.: 
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 -- ASN1START 
               
               
                   
                 -- TAG-VAR-SHORT-MAC-INPUT-START 
               
            
           
           
               
               
               
            
               
                   
                 VarShortMAC-Input-rxx ::= 
                 SEQUENCE { 
               
               
                   
                  sourcePhysCellId 
                  CHOICE { 
               
               
                   
                   eutra-PhysCellId 
                   PhysCellId, 
               
               
                   
                   nr-PhysCellId 
                   PhysCellIdNR 
               
               
                   
                  } 
                   
               
               
                   
                  targetCellIdentity 
                  CHOICE { 
               
               
                   
                   eutra-CellIdentity 
                   CellIdentity, 
               
               
                   
                   nr-CellIdentity 
                   BIT STRING (SIZE (28)) 
               
               
                   
                  } 
                    
               
               
                   
                  source-C-RNTI 
                   BIT STRING (SIZE (16)) 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 -- TAG-VAR-SHORT-MAC-INPUT-STOP 
               
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 VarShort-Input field descriptions 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 targetCellIdentity 
               
               
                 Set to CellIdentity of the target cell i.e. the cell the UE is trying 
               
               
                 to reestablish. In case of inter-RAT reestablishment from E-UTRA to NR, 
               
               
                 this field contain the NR target cell identity. 
               
               
                 source-C-RNTI 
               
               
                 Set to C-RNTI that the UE had in the PCell it was connected to prior 
               
               
                 to the failure. In case of inter-RAT reestablishment from NR to E-UTRA, 
               
               
                 this field contain the NR source C-RNTI of the PCell the UE was 
               
               
                 connected to in NR prior to the failure. 
               
               
                 sourcePhysCellId 
               
               
                 Set to the physical cell identity of the PCell the UE was connected to prior 
               
               
                 to the failure. In case of inter-RAT reestablishment from NR to E-UTRA, 
               
               
                 this field contain the NR source physical cell identity of the PCell the 
               
               
                 UE was connected to in NR prior to the failure. 
               
               
                   
               
            
           
         
       
     
     And the procedures may be updated as: 
     TS 36.331 5.3.7.4 Actions related to transmission of RRCConnectionReestablishmentRequest message
 
Except for NB-IoT, if the procedure was initiated due to radio link failure or handover failure, the UE shall:
         1&gt; set the reestablishmentCellId in the VarRLF-Report to the global cell identity of the selected cell;
 
The UE shall set the contents of RRCConnectionReestablishmentRequest message as follows:
   1&gt; except for a NB-IoT UE for which AS security has not been activated, set the ue-Identity as follows:
           2&gt; set the c-RNTI to the C-RNTI used in the source PCell (handover and mobility from E-UTRA failure) or used in the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; set the physCellId to the physical cell identity of the source PCell (handover and mobility from E-UTRA failure) or of the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; set the shortMAC-I to the 16 least significant bits of the MAC-I calculated:
               3&gt; over the ASN.1 encoded as per section 8 (i.e., a multiple of 8 bits) VarShortMAC-Input (or VarShortMAC-Input-NB in NB-IoT);   3&gt; with the KRR Cint  key and integrity protection algorithm that was used in the source PCell (handover and mobility from E-UTRA failure) or of the PCell in which the trigger for the re-establishment occurred (other cases); and   3&gt; with all input bits for COUNT, BEARER and DIRECTION set to binary ones;   
               NOTE: If the Source RAT was NR, use the previous NR K RRCint  key as E-UTRA KRR Cint  key and use integrity protection algorithm matching the previously configured NR integrity protection algorithm.   
               

     2.8.1.2. Failure in LTE and Reestablishment in NR 
     If the UE is connected to a cell in LTE and detects failure and attempts to reestablish in NR, the UE would use the variables and procedures of the target RAT (i.e. NR). This could either be an extension of the existing VarShortMAC-Input, or a new parameter 
     2.8.1.2. Updates of TS 36.331 
     TS 36.331 5.3.7.3 Actions following cell selection while T 311  is running 
     Upon selecting a suitable E-UTRA cell, the UE shall:
         1&gt; stop timer T 311 ;   1&gt; start timer T 301 ;   1&gt; apply the timeAlignmentTimerCommon included in SystemInformationBlockType2;   1&gt; if the UE is a NB-IoT UE supporting RRC connection re-establishment for the Control Plane CIoT EPS optimisation and AS security has not been activated; and   1&gt; if cp-reestablishment is not included in SystemInformationBlockType2-NB:
           2&gt; perform the actions upon leaving RRC_CONNECTED as specified in 5.3.12, with release cause ‘RRC connection failure’;   
           1&gt; else:
           2&gt; initiate transmission of the RRCConnectionReestablishmentRequest message in accordance with 5.3.7.4;   
               

     NOTE: This procedure applies also if the UE returns to the source PCell. 
     Upon selecting an inter-RAT cell, the UE shall:
         1&gt; if the target cell is an NR cell and the previously configured integrity protection algorithms are available to configure in the target system:
           2&gt; stop timer T 311 ;   2&gt; start timer T 301 ;   2&gt; apply the timeAlignmentTimerCommon included in SystemInformationBlockType2;   2&gt; initiate transmission of the RRCReestablishmentRequest message in accordance with TS 38.331 section 5.3.7.4;   
           1&gt; else:
           2&gt; if the selected cell is a UTRA cell, and if the UE supports Radio Link Failure Report for Inter-RAT MRO, include selectedUTRA-CellId in the VarRLF-Report and set it to the physical cell identity and carrier frequency of the selected UTRA cell;   2&gt; perform the actions upon leaving RRC_CONNECTED as specified in 5.3.12, with release cause ‘RRC connection failure’;   
               

     2.8.1.2.1. Updates of TS 38.331 
     The updates to 38.331 may be: 
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 -- ASN1START 
               
               
                   
                 -- TAG-VAR-SHORT-MAC-INPUT-START 
               
            
           
           
               
               
               
            
               
                   
                 VarShortMAC-Input-rxx ::= 
                 SEQUENCE { 
               
               
                   
                  sourcePhysCellId 
                  CHOICE { 
               
               
                   
                   eutra-PhysCellId 
                   EUTRA-PhysCellId, 
               
               
                   
                   nr-PhysCellId 
                   PhysCellId 
               
               
                   
                  } 
                   
               
               
                   
                  targetCellIdentity 
                  CHOICE { 
               
               
                   
                   eutra-CellIdentity 
                   BIT STRING (SIZE (28)) 
               
               
                   
                   nr-CellIdentity 
                   CellIdentity, 
               
               
                   
                  source-C-RNTI 
                   BIT STRING (SIZE (16)) 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 -- TAG-VAR-SHORT-MAC-INPUT-STOP 
               
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 VarShort-MAC-Input field descriptions 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 targetCellIdentity 
               
               
                 Set to CellIdentity of the target cell i.e. the cell the UE is trying to 
               
               
                 reestablish. In case of inter-RAT reestablishment from NR to E-UTRA, 
               
               
                 this field contain the E-UTRA target cell identity. 
               
               
                 source-C-RNTI 
               
               
                 Set to C-RNTI that the UE had in the PCell it was connected to prior to 
               
               
                 the failure. In case of inter-RAT reestablishment from E-UTRA to NR, 
               
               
                 this field contain the E-UTRA source C-RNTI. 
               
               
                 sourcePhysCellId 
               
               
                 Set to the physical cell identity of the PCell the UE was connected to prior 
               
               
                 to the failure. In case of inter-RAT handover from E-UTRA to NR, this 
               
               
                 field contain the E-UTRA source physical cell identity of the PCell the 
               
               
                 UE was connected to in E-UTRA prior to the failure. 
               
               
                   
               
            
           
         
       
     
     As the procedures already calculate the ShortMAC-I based on the VarShortMAC-Input for both intra-RAT and inter-RAT reestablishment, the required updates to the procedures would be small: 
     TS 38.331 5.3.7.4 Actions related to transmission of RRCReestablishmentRequest message 
     The UE shall set the contents of RRCReestablishmentRequest message as follows:
         1&gt; set the ue-Identity as follows:
           2&gt; set the c-RNTI to the C-RNTI used in the source PCell (reconfiguration with sync or mobility from NR failure) or used in the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; set the physCellId to the physical cell identity of the source PCell (reconfiguration with sync or mobility from NR failure) or of the PCell in which the trigger for the re-establishment occurred (other cases);   2&gt; set the shortMAC-I to the 16 least significant bits of the MAC-I calculated:
               3&gt; over the ASN.1 encoded as per section 8 (i.e., a multiple of 8 bits) VarShortMAC-Input;   3&gt; with the KRR Cint  key and integrity protection algorithm that was used in the source PCell (reconfiguration with sync or mobility from NR failure) or of the PCell in which the trigger for the re-establishment occurred (other cases); and   3&gt; with all input bits for COUNT, BEARER and DIRECTION set to binary ones;
 
NOTE: If the Source RAT was E-UTRA, use the previous E-UTRA KRR Cint  key as NR K RRCint  key and use integrity protection algorithm matching the previously configured E-UTRA integrity protection algorithm.
   
               
               

     2.8.2 Solution 4.2: Update Only Definition of VarShort-MAC-Input in LTE to Also Include Inter-RAT Parameters and Define Procedures in the Target RAT, 
     Another solution to the problem is to introduce a new IE (or extend the VarShortMAC-I) in only LTE specification (as described in solution 4.1) which to be used for calculating the security token for reestablishment in either direction of inter-RAT RRC reestablishment. 
     If the UE is connected to an LTE cell and experiences a failure and attempts to reestablish to an NR cell, the UE and network could calculate the Short MAC-I using the source C-RNTI and source PCI along with the target Cell identity. However, if the IE VarShortMAC-Input is extended to also include inter-RAT handover, the same IE would be used both in intra-LTE and inter-RAT handover. 
     If the UE is connected to an NR cell experiences a failure and attempts to reestablish in a cell in LTE, the UE and network could calculate the shortMAC-I using the source C-RNTI and source PCI along with the target Cell Identity in the VarShort-MAC-Input (or similar) in LTE. 
     The changes to the message would be similar to that in solution 4.1 but in the procedures the changes would be that in NR it would refer to the VarShortMAC-Input in TS 36.331. 
     2.8.3 Solution 4.3: Update Definition of VarShortMAC-Input in NR to Also Include Inter-RAT Parameters and Define Procedures in the Target RAT, 
     Another solution to the problem is to introduce a new IE (or extend the VarShortMAC-I) in only NR specification which to be used for calculating the security token for reestablishment in either direction of inter-RAT RRC reestablishment. This message could for instance be defined using a choice structure, where depending on the type of source and target RAT, the appropriate choice were made. 
     If the UE is connected to a cell in NR and detects a failure and attempts to reestablish in a cell in LTE, the UE and network could calculate the Short MAC-I using the source C-RNTI and source PCI along with the target Cell identity. However, if the IE VarShortMAC-Input is extended to also include inter-RAT handover, the same IE would be used both in intra-LTE and inter-RAT handover. 
     If the UE is connected to a cell in LTE and experiences a failure and attempts to reestablish in NR, the UE and network could calculate the ShortMAC-I using the source C-RNTI and source PCI along with the target Cell Identity in the VarShortMAC-Input (or similar) in NR. 
     The changes to the message would be similar to that in solution 4.1, but only in NR, but in the procedures the changes would be that in LTE it would refer to the VarShortMAC-Input in TS 38.331. 
     2.9 Some Fifth Exemplifying Embodiments: Use Input Parameter Format of the Target System and Use Dummy Values in Place of Source System Parameters 
     In some embodiments, the definitions of the LTE VarShortMAC-Input, or similar parameter is used when target is LTE and the NR VarShortMAC-Input or similar parameter used when the target is NR. For the variables requiring parameters from the source RAT, e.g. the source C-RNTI and source PCI. The UE and network uses a constant dummy value in the format of the target RAT, e.g. a bit string of 0&#39;s. 
     This solution may be combined with e.g. solution 1, where e.g. the source C-RNTI is used in the target RAT, and only the source PCI is replaced with dummy values, or the other way around, where the source PCI is adopted to the target RAT format using e.g. padding or truncation, while the source C-RNTI is replaced with dummy values. 
     2.9.1 Failure in LTE and Reestablishment NR: Calculate and Use NR ShortMAC-I Using Dummy Values for Source PCI and C-RNTI and NR Cell Identity as Input 
     If the UE is connected to a cell in LTE and experiences failure and attempts to reestablish in a cell in NR, the UE and network would need to calculate the NR ShortMAC-I using the NR VarShortMAC-Input. The VarShortMAC-Input contain source PCI, source RNTI and target Cell identity. The target Cell identity is obtained from the SystemInformationBlockType1 (SIB1) which is broadcast by the target cell. 
     However, the source PCI and source RNTI were obtained in another RAT (i.e. LTE) and have different characteristics compared to corresponding parameters in NR. 
     For the parameter C-RNTI, the VarShortMAC-Input uses a constant bit string (e.g. 16 bits set to ‘0’) as input. 
     Similarly for the PCI, the VarShortMAC-Input uses a constant bit string (e.g. 10 bits set to ‘0’) as input 
     2.9.1.1. Updates of TS 38.331 
     UE variable
         VarShortMAC-Input       

     The UE variable VarShortMAC-Input specifies the input used to generate the shortMAC-I during RRC Connection Reestablishment procedure. 
     
       
         
           
               
             
               
                   
               
               
                 VarShortMAC-Input variable 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 -- ASN1START 
               
               
                   
                 -- TAG-VAR-SHORTMACINPUT-START 
               
            
           
           
               
               
               
            
               
                   
                 VarShortMAC-Input :: = 
                 SEQUENCE { 
               
               
                   
                  sourcePhysCellId 
                  PhysCellId, 
               
               
                   
                  targetCellIdentity 
                  CellIdentity, 
               
               
                   
                  source-c-RNTI 
                  RNTI-Value 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 -- TAG-VAR- SHORTMACINPUT-STOP 
               
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 VarShortMAC-Input field descriptions 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 targetCellIdentity 
               
               
                 Set to CellIdentity of the target cell i.e. the cell the UE is trying to 
               
               
                 reestablish the connection. 
               
               
                 source-c-RNTI 
               
               
                 Set to C-RNTI that the UE had in the PCell it was connected to prior to 
               
               
                 the reestablishment. If the source RAT was E-UTRA, the content of this 
               
               
                 field is set to 16 binary 0&#39;s. 
               
               
                 sourcePhysCellId 
               
               
                 Set to the physical cell identity of the PCell the UE was connected to prior 
               
               
                 to the reestablishment. If the source RAT was E-UTRA, the content of this 
               
               
                 field is set to 10 binary 0&#39;s. 
               
               
                   
               
            
           
         
       
     
     2.9.2. Failure in from NR and Reestablishment in LTE: Calculate and Use ShortMAC-I in LTE Using Dummy Values for Source PCI and C-RNTI and LTE Cell Identity as Input 
     If the UE is connected to a cell in NR and experiences failure and attempts to reestablish in a cell in LTE, the UE and network would need to calculate the LTE ShortMAC-I using the LTE VarShortMAC-Input (or similar variable). The VarShortMAC-Input contain the source PCI, source C-RNTI and target Cell identity. The target Cell identity is obtained from the SystemInformationBlockType1 (SIB1) which is broadcast by the target cell. 
     However, the source PCI and source RNTI were obtained in another RAT (i.e. NR) and have different characteristics compared to corresponding parameters in LTE. 
     For the parameter C-RNTI, the VarShortMAC-Input uses a constant bit string (e.g. 16 bits set to ‘0’) as input. 
     Similarly for the PCI, the VarShortMAC-Input uses a constant bit string (e.g. 9 bits set to ‘0’) as input. 
     If the UE was configured with an integrity protection algorithm in NR which is not supported in LTE (e.g. a hypothetical future NIA 4 , different from any algorithm in LTE), the UE could either:
         Abort the reestablishment procedure and fallback to RRC Setup   Use a predefined fallback algorithm which is supported in both LTE and NR (e.g. any of the algorithms EIA 0 -EIA 3 )       

     2.9.2.1. Updates of TS 36.331 
     UE Variables
         VarShortMAC-Input
 
The UE variable VarShortMAC-Input specifies the input used to generate the shortMAC-I.
       

     
       
         
           
               
             
               
                   
               
               
                 VarShortMAC-Input UE variable 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 -- ASN1START 
               
            
           
           
               
               
               
            
               
                   
                 VarShortMAC-Input ::= 
                 SEQUENCE { 
               
               
                   
                  cellIdentity 
                  CellIdentity, 
               
               
                   
                  physCellId 
                  PhysCellId, 
               
               
                   
                  c-RNTI 
                  C-RNTI 
               
               
                   
                 } 
                   
               
               
                   
                 -- ASN1STOP 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 VarShortMAC-Input field descriptions 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 cellIdentity 
               
               
                 Set to CellIdentity included in CellIdentity (without suffix) in 
               
               
                 SIB1 of the current cell. 
               
               
                 c-RNTI 
               
               
                 Set to C-RNTI that the UE had in the PCell it was connected to prior to 
               
               
                 the failure. If the source cell was an NR cell, the content of this field 
               
               
                 is set to 16 binary 0&#39;s. 
               
               
                 physCellId 
               
               
                 Set to the physical cell identity of the PCell the UE was connected 
               
               
                 to prior to the failure. If the source cell was an NR cell, the content 
               
               
                 of this field is set to 9 binary ‘0’s. 
               
               
                   
               
            
           
         
       
     
     2.10 Calculating Inter-RAT ShortMAC-I for Handover Preparation 
     When the network decides that a UE should perform a handover from one node to another, the source node may provide the target node with handover preparation information. 
     In LTE, this message contain (among other things) the AS Context: 
                             HandoverPreparationin formation message                                        -- ASN1START           HandoverPreparationInformation ::=   SEQUENCE {        criticalExtensions    CHOICE {         cl     CHOICE {          handoverPreparationInformation-r8      HandoverPreparationInformation-r8-IEs,          spare7 NULL,                        spare6 NULL, spare5 NULL, spare4 NULL,          spare3 NULL, spare2 NULL, spare1 NULL                       },             criticalExtensionsFuture     SEQUENCE {}        }           }                             HandoverPreparationInformation-r8-IEs    ::=   SEQUENCE 1                      ue-RadioAccessCapabilityInfo    UE-CapabilityRAT-ContainerList,                              as-Config    AS-Config    OPTIONAL,    -- Cond       HO                    rrm-Contig    RRM-Contig    OPTIONAL,            as-Context    AS-Context   OPTIONAL,   -- Cond HO                      nonCriticalExtension    HandoverPreparationInformation-v920-IEs        OPTIONAL           }                    
Where the AS-context contain the reestablishment info.
 
     
       
         
           
               
             
               
                   
               
             
            
               
                 -- ASN1START 
               
            
           
           
               
               
               
            
               
                 AS-Context ::= 
                 SEQUENCE { 
                   
               
            
           
           
               
               
               
               
            
               
                  reestablishmentInfo 
                  ReestablishmentInfo 
                 OPTIONAL 
                 -- Cond 
               
               
                 HO 
                   
                   
                   
               
               
                 } 
               
               
                   
               
            
           
         
       
     
     The reestablishmentInfo contain information required to perform reestablishment in both the target cell, but also any other cell the source node considers should be possible to reestablish to. 
                             ReestablishmentInfo information element                                    -- ASN1START                     ReestablishmentInfo ::=    SEQUENCE {        sourcePhysCellId     PhysCellId,        targetCellShortMAC-I     ShortMAC-I,                          additionalReestabInfoList     AdditionalReestabInfoList   OPTIONAL,                      ...           }           AdditionalReestabInfoList ::=    SEQUENCE ( SIZE (1..maxReestabInfo) ) OF                 AdditionalReestabInfo                     AdditionalReestabInfo ::=   SEQUENCE{        cellIdentity     CellIdentity,        key-eNodeB-Star     Key-eNodeB-Star,        shortMAC-I     ShortMAC-I       }           Key-eNodeB-Star ::=    BIT STRING (SIZE (256))       -- ASN1STOP                    
In NR, a similar message is introduced, although structured a little bit different:
 
     
       
         
           
               
             
               
                   
               
               
                 HandoverPreparationInformation message 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 -- ASN1START 
               
               
                 -- TAG-HANDOVER-PREPARATION-INFORMATION-START 
               
            
           
           
               
               
            
               
                 HandoverPreparationInformation ::= 
                  SEQUENCE { 
               
               
                  criticalExtensions 
                   CHOICE { 
               
               
                   cl 
                    CHOICE{ 
               
               
                    handoverPreparationInformation 
                     HandoverPreparationInformation-IEs, 
               
            
           
           
               
            
               
                    spare3 NULL, spare2 NULL, spare1 NULL   
               
            
           
           
               
               
            
               
                   }, 
                    
               
               
                   criticalExtensionsFuture 
                    SEQUENCE {} 
               
               
                  } 
                    
               
               
                 } 
                    
               
               
                 HandoverPreparationInformation-IEs 
                   ::=SEQUENCE { 
               
               
                  ue-CapabilityRAT-List 
                   UE-CapabilityRAT-ContainerList, 
               
            
           
           
               
               
               
               
            
               
                  sourceConfig 
                   AS-Config 
                 OPTIONAL, 
                 -- Cond HO 
               
               
                  rrm-Config 
                   RPM-Contig 
                 OPTIONAL, 
                   
               
               
                  as-Context 
                   AS-Context 
                 OPTIONAL, 
                   
               
               
                  nonCriticalExtension 
                   SEQUENCE {} 
                 OPTIONAL 
                   
               
               
                 } 
                   
                   
                   
               
            
           
           
               
               
               
               
            
               
                 AS-Config ::= 
                 SEQUENCE { 
                   
                   
               
            
           
           
               
               
            
               
                  rrcReconfiguration 
                   OCTET STRING (CONTAINING RRCReconfiguration), 
               
            
           
           
               
               
               
            
               
                  ... 
                   
                   
               
               
                 } 
                   
                   
               
            
           
           
               
               
               
               
            
               
                 AS-Context ::= 
                    SEQUENCE { 
                   
                   
               
               
                  reestablishmentInfo 
                   ReestablishmentInfo 
                   
                 OPTIONAL, 
               
               
                  configRestrictInfo 
                    ConfigRestrictInfoSCG 
                   
                 OPTIONAL, 
               
               
                  [[ ran-NotificationAreaInfo 
                     RAN-NotificationAreaInfo 
                  OPTIONAL 
                   
               
               
                  ]] 
                   
                   
                   
               
               
                 } 
                   
                   
                   
               
               
                 ReestablishmentInfo ::= 
                   SEQUENCE { 
                   
                   
               
               
                  sourcePhysCellId 
                     PhysCellId, 
                   
                   
               
               
                  targetCellShortMAC-I 
                     ShortMAC-I, 
                   
                   
               
               
                  additionalReestabInfoList 
                     ReestabNCellInfoList 
                   
                   
               
               
                  OPTIONAL 
                   
                   
                   
               
               
                 } 
                   
                   
                   
               
            
           
           
               
               
            
               
                 ReestabNCellInfoList ::= 
                  SEQUENCE ( SIZE (1..maxCellPrep) ) OF ReestabNCellInfo 
               
               
                 ReestabNCellInfo::= SEQUENCE{ 
                   
               
               
                  cellIdentity 
                     CellIdentity, 
               
               
                  key-gNodeB-Star 
                     BIT STRING (SIZE (256)), 
               
               
                  shortMAC-I 
                     ShortMAC-I 
               
               
                 } 
                   
               
               
                 RRM-Contig ::= 
                 SEQUENCE { 
               
               
                  ue-InactiveTime 
                  ENUMERATED { 
               
               
                   
                   s1, s2, s3, s5, s7, s10, s15, s20, 
               
               
                   
                   s25, s30, s40, s50, min1, min1s20, min1s40, 
               
               
                   
                   min2, min2s30, min3, min3s30, min4, min5, min6, 
               
               
                   
                   min7, min8, min9, min10, min12, min14, min17, min20, 
               
               
                   
                   min24, min28, min33, min38, min44, min50, hr1, 
               
               
                   
                   hr1min30, hr2, hr2min30, hr3, hr3min30, hr4, hr5, hr6, 
               
               
                   
                   hr8, hr10, hr13, hr16, hr20, day1, day1hr12, day2, 
               
               
                   
                   day2hr12, day3, day4, day5, day7, day10, day14, day19, 
               
            
           
           
               
               
               
            
               
                   
                   day24, day30, dayMoreThan30} 
                 OPTIONAL, 
               
            
           
           
               
               
               
               
            
               
                  candidateCellInfoList 
                  MeasResultList2NR 
                  OPTIONAL, 
                   
               
            
           
           
               
            
               
                  ... 
               
               
                 } 
               
               
                 -- TAG-HANDOVER-PREPARATION-INFORMATION-STOP 
               
               
                 -- ASN1STOP 
               
               
                   
               
            
           
         
       
     
     As may be noted, both the LTE and NR HandoverPreparationInfo message contain the ShortMAC-I of the target cell and possibly of any other cells. If the handover is inter-RAT (i.e. from NR to LTE or vice versa), the targetCellShortMAC-I would need to be calculated using any parameters from two different RATs. Likewise, if the source node decides that the UE should be prepared to perform reestablishment to another RAT, the ShortMAC-I in the AdditionalReestabInfo (in LTE) or the ReestabNCellInfo (in NR) would need to be calculated using parameters from two different RATs. 
     The method to calculate this inter-RAT ShortMAC-I would be the same as the solutions presented for the other embodiments. 
     Further Extensions and Variations 
     With reference to  FIG. 18 , in accordance with an embodiment, a communication system includes a telecommunication network  3210  such as the wireless communications network  100 , e.g. a WLAN, such as a 3GPP-type cellular network, which comprises an access network  3211 , such as a radio access network, and a core network  3214 . The access network  3211  comprises a plurality of base stations  3212   a ,  3212   b ,  3212   c , such as the network node  110 ,  112 ,  130 , access nodes, AP STAs NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area  3213   a ,  3213   b ,  3213   c . Each base station  3212   a ,  3212   b ,  3212   c  is connectable to the core network  3214  over a wired or wireless connection  3215 . A first user equipment (UE) e.g. the wireless device  120  such as a Non-AP STA  3291  located in coverage area  3213   c  is configured to wirelessly connect to, or be paged by, the corresponding base station  3212   c . A second UE  3292  e.g. the wireless device  122  such as a Non-AP STA in coverage area  3213   a  is wirelessly connectable to the corresponding base station  3212   a . While a plurality of UEs  3291 ,  3292  are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole UE is in the coverage area or where a sole UE is connecting to the corresponding base station  3212 . 
     The telecommunication network  3210  is itself connected to a host computer  3230 , which may be embodied in the hardware and/or software of a standalone server, a cloud-implemented server, a distributed server or as processing resources in a server farm. The host computer  3230  may be under the ownership or control of a service provider, or may be operated by the service provider or on behalf of the service provider. The connections  3221 ,  3222  between the telecommunication network  3210  and the host computer  3230  may extend directly from the core network  3214  to the host computer  3230  or may go via an optional intermediate network  3220 . The intermediate network  3220  may be one of, or a combination of more than one of, a public, private or hosted network; the intermediate network  3220 , if any, may be a backbone network or the Internet; in particular, the intermediate network  3220  may comprise two or more sub-networks (not shown). 
     The communication system of  FIG. 20  as a whole enables connectivity between one of the connected UEs  3291 ,  3292  and the host computer  3230 . The connectivity may be described as an over-the-top (OTT) connection  3250 . The host computer  3230  and the connected UEs  3291 ,  3292  are configured to communicate data and/or signaling via the OTT connection  3250 , using the access network  3211 , the core network  3214 , any intermediate network  3220  and possible further infrastructure (not shown) as intermediaries. The OTT connection  3250  may be transparent in the sense that the participating communication devices through which the OTT connection  3250  passes are unaware of routing of uplink and downlink communications. For example, a base station  3212  may not or need not be informed about the past routing of an incoming downlink communication with data originating from a host computer  3230  to be forwarded (e.g., handed over) to a connected UE  3291 . Similarly, the base station  3212  need not be aware of the future routing of an outgoing uplink communication originating from the UE  3291  towards the host computer  3230 . 
     Example implementations, in accordance with an embodiment, of the UE, base station and host computer discussed in the preceding paragraphs will now be described with reference to  FIG. 19 . In a communication system  3300 , a host computer  3310  comprises hardware  3315  including a communication interface  3316  configured to set up and maintain a wired or wireless connection with an interface of a different communication device of the communication system  3300 . The host computer  3310  further comprises processing circuitry  3318 , which may have storage and/or processing capabilities. In particular, the processing circuitry  3318  may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. The host computer  3310  further comprises software  3311 , which is stored in or accessible by the host computer  3310  and executable by the processing circuitry  3318 . The software  3311  includes a host application  3312 . The host application  3312  may be operable to provide a service to a remote user, such as a UE  3330  connecting via an OTT connection  3350  terminating at the UE  3330  and the host computer  3310 . In providing the service to the remote user, the host application  3312  may provide user data which is transmitted using the OTT connection  3350 . 
     The communication system  3300  further includes a base station  3320  provided in a telecommunication system and comprising hardware  3325  enabling it to communicate with the host computer  3310  and with the UE  3330 . The hardware  3325  may include a communication interface  3326  for setting up and maintaining a wired or wireless connection with an interface of a different communication device of the communication system  3300 , as well as a radio interface  3327  for setting up and maintaining at least a wireless connection  3370  with a UE  3330  located in a coverage area (not shown in  FIG. 21 ) served by the base station  3320 . The communication interface  3326  may be configured to facilitate a connection  3360  to the host computer  3310 . The connection  3360  may be direct or it may pass through a core network (not shown in  FIG. 21 ) of the telecommunication system and/or through one or more intermediate networks outside the telecommunication system. In the embodiment shown, the hardware  3325  of the base station  3320  further includes processing circuitry  3328 , which may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. The base station  3320  further has software  3321  stored internally or accessible via an external connection. 
     The communication system  3300  further includes the UE  3330  already referred to. Its hardware  3335  may include a radio interface  3337  configured to set up and maintain a wireless connection  3370  with a base station serving a coverage area in which the UE  3330  is currently located. The hardware  3335  of the UE  3330  further includes processing circuitry  3338 , which may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. The UE  3330  further comprises software  3331 , which is stored in or accessible by the UE  3330  and executable by the processing circuitry  3338 . The software  3331  includes a client application  3332 . The client application  3332  may be operable to provide a service to a human or non-human user via the UE  3330 , with the support of the host computer  3310 . In the host computer  3310 , an executing host application  3312  may communicate with the executing client application  3332  via the OTT connection  3350  terminating at the UE  3330  and the host computer  3310 . In providing the service to the user, the client application  3332  may receive request data from the host application  3312  and provide user data in response to the request data. The OTT connection  3350  may transfer both the request data and the user data. The client application  3332  may interact with the user to generate the user data that it provides. It is noted that the host computer  3310 , base station  3320  and UE  3330  illustrated in  FIG. 19  may be identical to the host computer  3230 , one of the base stations  3212   a ,  3212   b ,  3212   c  and one of the UEs  3291 ,  3292  of  FIG. 18 , respectively. This is to say, the inner workings of these entities may be as shown in  FIG. 19  and independently, the surrounding network topology may be that of  FIG. 18 . 
     In  FIG. 19 , the OTT connection  3350  has been drawn abstractly to illustrate the communication between the host computer  3310  and the use equipment  3330  via the base station  3320 , without explicit reference to any intermediary devices and the precise routing of messages via these devices. Network infrastructure may determine the routing, which it may be configured to hide from the UE  3330  or from the service provider operating the host computer  3310 , or both. While the OTT connection  3350  is active, the network infrastructure may further take decisions by which it dynamically changes the routing (e.g., on the basis of load balancing consideration or reconfiguration of the network). 
     The wireless connection  3370  between the UE  3330  and the base station  3320  is in accordance with the teachings of the embodiments described throughout this disclosure. 
     One or more of the various embodiments improve the performance of OTT services provided to the UE  3330  using the OTT connection  3350 , in which the wireless connection  3370  forms the last segment. More precisely, the teachings of these embodiments may improve the pSIM scheduling allowing more positioning assistance data to be broadcasted. 
     A measurement procedure may be provided for the purpose of monitoring data rate, latency and other factors on which the one or more embodiments improve. There may further be an optional network functionality for reconfiguring the OTT connection  3350  between the host computer  3310  and UE  3330 , in response to variations in the measurement results. The measurement procedure and/or the network functionality for reconfiguring the OTT connection  3350  may be implemented in the software  3311  of the host computer  3310  or in the software  3331  of the UE  3330 , or both. In embodiments, sensors (not shown) may be deployed in or in association with communication devices through which the OTT connection  3350  passes; the sensors may participate in the measurement procedure by supplying values of the monitored quantities exemplified above, or supplying values of other physical quantities from which software  3311 ,  3331  may compute or estimate the monitored quantities. The reconfiguring of the OTT connection  3350  may include message format, retransmission settings, preferred routing etc.; the reconfiguring need not affect the base station  3320 , and it may be unknown or imperceptible to the base station  3320 . Such procedures and functionalities may be known and practiced in the art. In certain embodiments, measurements may involve proprietary UE signaling facilitating the host computer&#39;s  3310  measurements of throughput, propagation times, latency and the like. The measurements may be implemented in that the software  3311 ,  3331  causes messages to be transmitted, in particular empty or ‘dummy’ messages, using the OTT connection  3350  while it monitors propagation times, errors etc. 
       FIGS. 18 and 19  and the corresponding text are about a downstream aspect of the radio-related invention, while  FIGS. 20 and 21  and the corresponding text discuss an upstream aspect. 
       FIG. 20  is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station such as a AP STA, and a UE such as a Non-AP STA which may be those described with reference to  FIGS. 18 and 19 . For simplicity of the present disclosure, only drawing references to  FIG. 18  will be included in this section. In a first action  3410  of the method, the host computer provides user data. In an optional subaction  3411  of the first action  3410 , the host computer provides the user data by executing a host application. In a second action  3420 , the host computer initiates a transmission carrying the user data to the UE. In an optional third action  3430 , the base station transmits to the UE the user data which was carried in the transmission that the host computer initiated, in accordance with the teachings of the embodiments described throughout this disclosure. In an optional fourth action  3440 , the UE executes a client application associated with the host application executed by the host computer. 
       FIG. 21  is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station such as a AP STA, and a UE such as a Non-AP STA which may be those described with reference to  FIGS. 18 and 19 . For simplicity of the present disclosure, only drawing references to  FIG. 21  will be included in this section. In a first action  3510  of the method, the host computer provides user data. In an optional subaction (not shown) the host computer provides the user data by executing a host application. In a second action  3520 , the host computer initiates a transmission carrying the user data to the UE. The transmission may pass via the base station, in accordance with the teachings of the embodiments described throughout this disclosure. In an optional third action  3530 , the UE receives the user data carried in the transmission. 
       FIG. 22  is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station such as a AP STA, and a UE such as a Non-AP STA which may be those described with reference to  FIGS. 18 and 19 . For simplicity of the present disclosure, only drawing references to  FIG. 22  will be included in this section. In an optional first action  3610  of the method, the UE receives input data provided by the host computer. Additionally or alternatively, in an optional second action  3620 , the UE provides user data. In an optional subaction  3621  of the second action  3620 , the UE provides the user data by executing a client application. In a further optional subaction  3611  of the first action  3610 , the UE executes a client application which provides the user data in reaction to the received input data provided by the host computer. In providing the user data, the executed client application may further consider user input received from the user. 
     Regardless of the specific manner in which the user data was provided, the UE initiates, in an optional third subaction  3630 , transmission of the user data to the host computer. In a fourth action  3640  of the method, the host computer receives the user data transmitted from the UE, in accordance with the teachings of the embodiments described throughout this disclosure. 
       FIG. 23  is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station such as a AP STA, and a UE such as a Non-AP STA which may be those described with reference to  FIGS. 18 and 19 . For simplicity of the present disclosure, only drawing references to  FIG. 23  will be included in this section. In an optional first action  3710  of the method, in accordance with the teachings of the embodiments described throughout this disclosure, the base station receives user data from the UE. In an optional second action  3720 , the base station initiates transmission of the received user data to the host computer. In a third action  3730 , the host computer receives the user data carried in the transmission initiated by the base station. 
     When using the word “comprise” or “comprising” it shall be interpreted as non-limiting, i.e. meaning “consist at least of”. 
     The embodiments herein are not limited to the above described preferred embodiments. Various alternatives, modifications and equivalents may be used. 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Abbreviation 
                 Explanation 
               
               
                   
                   
               
             
            
               
                   
                 MAC-I 
                 Message Authentication Code - Integrity 
               
               
                   
                 RRC 
                 Radio Resource Control 
               
               
                   
                 NG-RAN 
                 Next Generation Radio Access Network 
               
               
                   
                 RNTI 
                 Radio Network Temporary Identifier 
               
               
                   
                 C-RNTI 
                 Cell RNTI 
               
               
                   
                 I-RNTI 
                 Inactive RNTI 
               
               
                   
                 NR 
                 New Radio (5G) 
               
               
                   
                 LTE 
                 Long Term Evolution (4G) 
               
               
                   
                 MAC-I 
                 Message Authentication Code - Integrity 
               
               
                   
                 RRC 
                 Radio Resource Control 
               
               
                   
                 NG-RAN 
                 Next Generation Radio Access Network 
               
               
                   
                 RNTI 
                 Radio Network Temporary Identifier 
               
               
                   
                 C-RNTI 
                 Cell RNTI 
               
               
                   
                 I-RNTI 
                 Inactive RNTI 
               
               
                   
                 NR 
                 New Radio (5G) 
               
               
                   
                 LTE 
                 Long Term Evolution (4G) 
               
               
                   
                 EPC 
                 Evolved Packet Core 
               
               
                   
                 EPS 
                 Evolved Packet System 
               
               
                   
                 5GC 
                 5G Core 
               
               
                   
                 5GS 
                 5G System 
               
               
                   
                 PDCP 
                 Packet Data Convergence Protocol 
               
               
                   
                 PCI 
                 Physical Cell Identity 
               
               
                   
                 NAS 
                 Non Access Stratum 
               
               
                   
                 NIA 
                 NR Integrity Protection Algorithm 
               
               
                   
                 EIA 
                 E-UTRA Integrity Protection Algorithm 
               
               
                   
                 E-UTRA 
                 Evolved Universal Terrestrial Radio Access 
               
               
                   
                 RAT 
                 Radio Access Technology