Patent Publication Number: US-2021185570-A1

Title: Ue context forwarding

Description:
TECHNICAL FIELD 
     The invention relates to methods and devices for enabling a connection of a wireless communication device released by a source radio base station to be resumed by a target radio base station. 
     BACKGROUND 
     The third generation partnership project (3GPP) is currently working on standardization of the 5th generation of mobile radio access system, also called Next Generation Radio Access Network (NG-RAN). The NG-RAN may include nodes providing radio connections according to the standard for New Radio (NR), as well as nodes providing radio connections according to the Long-Term Evolution (LTE) standard. 
     The NG-RAN needs to be connected to a network that provides non-access stratum functions, i.e. functions for managing establishment of communication sessions and for maintaining continuous communications with a moving wireless communication device commonly referred to as User Equipment (UE), and further provides connection to communication networks outside NG-RAN, e.g. the Internet. 
     With reference to  FIG. 1 , such a network may be embodied by a fifth generation (5G) Core Network (CN), being referred to as 5GC.  FIG. 1  illustrates a simplified version of 5GC comprising core network nodes Access and Mobility Management Function (AMF) and User Plane Function (UPF). 
     The AMF  10 ,  12  is a core network control plane function configured to provide mobility management for providing UE-based authentication, authorization, mobility management, etc., while the UPF  11 ,  13  is a service function that processes user plane packets; processing may include altering the packet&#39;s payload and/or header, interconnection to data network(s), packet routing and forwarding, etc. 
     As further can be seen in  FIG. 1 , the NG-RAN comprises a plurality of radio base stations referred to as gNBs  14 ,  15 , and LTE radio base stations referred to as ng-eNBs  16 ,  17 . 
     The AMFs  10 ,  12  and UPFs  11 ,  13  connect to the radio base stations via a so-called NG interface, while the gNBs  14 ,  15  and ng-eNBs  16 ,  17  interconnect via an Xn interface. 
     A main task of a wireless communications network is to provide radio connections for UEs in order to enable services that users of the UEs wish to utilize. In this process, it is of utmost importance to find the most suitable cells or antenna beams of a radio base station for every UE as it moves. 
     Currently, this is achieved by requesting the UE to measure strength and quality of radio signals from the serving beams as well from neighbour beams. The results of the measurements are reported to one or more radio base stations in the RAN, which takes a decision on what cells/beams shall serve the UE in the following. 
       FIG. 2  illustrates a UE  18  being connected to a source radio base station  14  denoted gNB 1  and providing three cells. Now, as the UE  18  moves toward a target radio base station  15  denoted gNB 2  (also providing three cells), it will eventually be determined that the target radio base station  15  is better suited for serving the UE  18 , and a handover of the UE  18  from the source radio base station gNB 1  to the target radio base station gNB 2  will be performed. 
     Such handover procedure is described in detail for instance in 3GPP technical specification TS 23.502, V15.2.0, in particular with reference to section 4.9, “Handover procedures” and FIG. 4.9.1.2.2-1—Xn based inter NG-RAN handover without UPF re-allocation. 
     With reference to  FIG. 2 , when the UE  18  does not send or receive data from the currently serving source base station  14  for some time, the source base station  14  typically disconnects the UE  18  from the RAN, and the UE  18  will move around with no supervision from the RAN. In this state, the RAN can store information about the UE  18 , which enables a faster establishment of the connection once the UE  18  reconnects. This information, referred to as UE context, is in the current procedure stored in the source base station  14  and subsequently fetched by nodes requiring the information, for having the target base station  15  resume a connection having been released by the source base station  14 , which is an inefficient procedure. 
     SUMMARY 
     An object of the present invention is to solve, or at least mitigate, this problem in the art and thus to provide and improved method of enabling a connection of a wireless communication device released by a source radio base station to be resumed by a target radio base station. 
     This object is attained in a first aspect of the invention by a method of a source radio base station of enabling a connection of a wireless communication device released by the source radio base station to be resumed by a target radio base station. The method comprises acquiring an indication that a connection established with the wireless communication device is to be released, identifying a target base station with which the connection to be released can be resumed for the wireless communication device, and transmitting, to the identified target base station, information required to resume the connection to be released by the source base station for the wireless communication device. 
     This object is attained in a second aspect of the invention by a method of a source radio base station configured to enable a connection of a wireless communication device released by the source radio base station to be resumed by a target radio base station. The source radio base station comprises a processing unit and a memory, said memory containing instructions executable by said processing unit, whereby the source radio base station is operative to acquire an indication that a connection established with the wireless communication device is to be released, identify a target base station with which the connection to be released can be resumed for the wireless communication device, and to transmit, to the identified target base station, information required to resume the connection to be released by the source base station for the wireless communication device. 
     This object is attained in a third aspect of the invention by a method of a target radio base station of enabling a connection of a wireless communication device released by a source radio base station to be resumed by the target base station. The method comprises receiving, from the source base station, information required to resume the connection to be released by the source base station for the wireless communication device after the source base station has determined that the connection to the wireless communication device is to be released and further has identified the target base station as a base station with which the connection can be resumed. 
     This object is attained in a fourth aspect of the invention by a target radio base station configured to enable a connection of a wireless communication device released by a source radio base station to be resumed by the target base station. The target radio base station comprising a processing unit and a memory, said memory containing instructions executable by said processing unit, whereby the target radio base station is operative to receive, from the source base station, information required to resume the connection to be released by the source base station for the wireless communication device after the source base station has determined that the connection to the wireless communication device is to be released and further has identified the target base station as a base station with which the connection can be resumed. 
     This object is attained in a fifth aspect of the invention by a method of a wireless communication device of enabling a connection released by a source radio base station for the wireless communication device to be resumed by a target base station. The method comprises receiving, from the source base station, a connection release message including an identifier associated with information required to resume the connection with the target base station. 
     This object is attained in a sixth aspect of the invention by a wireless communication device configured to enable a connection released by a source radio base station for the wireless communication device to be resumed by a target base station. The wireless communication device comprises a processing unit and a memory, said memory containing instructions executable by said processing unit, whereby the wireless communication device is operative to receive, from the source base station, a connection release message including an identifier associated with information required to resume the connection with the target base station. 
     Hence, the source base station acquires an indication that a connection established with the wireless communication device (referred to in the following as a UE) is to be released. Thereafter, the source base station identifies a target base station with which the connection to be released can be resumed for the UE. 
     For instance, in an embodiment, a current heading of the UE is estimated by observing movement of the UE. From this estimated heading, the source base station concludes that the UE is moving towards the target base station. 
     After the target base station has been identified, the source base station transmits, to the target base station, information required to resume the connection to be released by the source base station for the UE. In a 5G wireless communications network, this information is commonly referred to as “UE context”. 
     Hence, before releasing the radio connection to the UE, the source base station transmits the UE context required by the target base station for the target base station to subsequently resume the released connection. 
     Advantageously, as compared to the prior art procedure of having the target base station fetch the UE context from the source base station before resuming the connection with the UE that is released by the source base station, the setup time for the resumed connection is greatly shortened when the UE connects with the identified target base station, which improves time-to-service and mitigates any need for data buffering in the network. 
     In an embodiment, the source radio base station receives the indication from the wireless communication device that the connection is to be released. 
     In an embodiment, the source radio base station estimates a current heading of the wireless communication device, wherein a closest adjacent radio base station located in said heading is identified to be the target base station with which the released connection is to be resumed. 
     In a further embodiment, the target radio base station associates an identifier with the information required to resume the connection to be released by the source base station, and transmits, to the source base station, the identifier associated with the information required to resume the connection to be released by the source base station, for forwarding to the wireless communication device in a connection release message. 
     In an embodiment, the source radio base station receives, from the identified target base station, an instruction to release the UE context for the wireless communication device. 
     In yet an embodiment, the identifier associated with the information required to resume the connection to be released by the source base station is an Inactive Radio Network Temporary Identifier (I-RNTI). 
     In another embodiment, the source radio base station transmits a message to the wireless communication device that the connection with the source base station is released, the message including the identifier associated with the information required to resume the connection received from the target base station. 
     In an embodiment, the target radio base station transmits, to a network node configured to provide mobility management, a request to switch connection of the wireless communication device from the source base station to the target base station. 
     In another embodiment, the target radio base station receives, from the network node configured to provide mobility management, a confirmation that the connection of the wireless communication device is switched from the source base station to the target base station. 
     In another embodiment, the target radio base station receives, from the wireless communication device, a request to resume the connection released by the source base station, the request comprising said identifier, and resumes the connection with the wireless communication device. 
     Further embodiments will be discussed in the following. 
     Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to “a/an/the element, apparatus, component, means, step, etc.” are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is now described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  illustrates a prior art 5G wireless communications network in which the invention may be applied; 
         FIG. 2  illustrates a handover of a UE in a prior art 5G wireless communications network; 
         FIG. 3  illustrates the prior art procedure where a target base station initiates a context fetch procedure by sending a Retrieve UE Context Request message to a source base station; 
         FIG. 4  shows a signalling diagram illustrating a method of enabling a connection of a wireless communication device released by a source radio base station to be resumed by a target base station according to an embodiment; 
         FIG. 5 a    shows a signalling diagram illustrating a method of enabling a connection of a wireless communication device released by a source radio base station to be resumed by a target base station according to a further embodiment; 
         FIG. 5 b    shows a signalling diagram illustrating a method of enabling a connection of a wireless communication device released by a source radio base station to be resumed by a target base station according to another embodiment; 
         FIG. 6  shows a source radio base station according to an embodiment; 
         FIG. 7  shows a target radio base station according to an embodiment; and 
         FIG. 8  shows a wireless communication device according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout the description. 
       FIG. 1  illustrates a prior art 5G wireless communications network in which the invention may be applied.  FIG. 1  has previously been discussed and will not be discussed in further detail 
       FIG. 2  illustrates a handover of a UE in a prior art 5G wireless communications network. 
     With reference to  FIG. 2 , as previously has been discussed, when the UE  18  does not send or receive data from the currently serving source base station  14  for some time, the source base station  14  typically disconnects the UE  18  from the RAN, and the UE  18  will move around with very little supervision from the RAN, entering a Radio Resource Control (RRC) state referred to as RRC_INACTIVE. 
     In this state, the RAN can store information about the UE  18 , which enables a faster establishment of the connection once the UE  18  reconnects. This information, referred to as UE context, is in the art stored in the source base station  14  and subsequently fetched by nodes requiring the information to resume the connection between the RAN and the UE, which is an inefficient procedure. 
       FIG. 3  illustrates the prior art procedure where the target base station  15  (gNB 2 ) initiates the procedure by sending a Retrieve UE Context Request message to the source base station  14  (gNB 1 ). The Retrieve UE Context Request message contains a Resume ID to identify the UE Context of the particular UE  18  for which the request is made. If the source base station  14  is able to identify and verify the UE context, it shall respond to the target base station  15  with the Retrieve UE Context Response message which contains the UE Context. 
     If the source base station  14  is not able to identify the UE context, it shall respond with the Retrieve UE Context Failure message to inform the target base station  15  that the Retrieve UE Context procedure has failed. 
     When a UE  18  reconnects with a target base station  15  being different from the source base station  14  with which it previously disconnected, in which the UE context is stored, the retrieval of the UE context by the target base station  15  from the source base station  14  will delay the setup of the connection between the UE  18  and the target base station  15   
     Additionally, if the UE  18  has moved further away from the source base station  14 , the target base station  15  may not have a connection to the source base station  14  allowing retrieval of the UE context. If so, the UE  18  has to perform a new connection setup towards the core network, which will even further delay the connection of the UE  18  to the target base station  15 . 
       FIG. 4  shows a signalling diagram illustrating a method of enabling a connection of a wireless communication device  18  released by a source radio base station  14  (gNB 1 ) to be resumed by a target base station  15  (gNB 2 ) according to an embodiment. The wireless communication device  18  will be referred to in the following as a UE. 
     In a first step S 101 , the source base station  14  acquires an indication that a connection established with the UE  18  is to be released. The source base station  14  may for instance detect that the UE  18  does not send any data (and may not have done so for some time). 
     Thereafter, in step S 102 , the source base station  14  identifies a target base station  15  with which the connection to be released can be resumed for the UE  18 . 
     For instance, in an embodiment, a current heading of the UE  18  is estimated by observing movement of the UE  18 . From this estimated heading, the source base station  14  concludes that the UE  18  is moving towards the target base station  15 . It is noted that various measurements may be performed to determine the heading of the UE  18 , such as signal strength, and further the UE  18  itself may report measurement data based on which the source base station  18  may estimate the UE heading. 
     After the target base station  15  has been identified, the source base station  14  transmits in step S 103 , to the target base station  15 , information required to resume the connection to be released by the source base station  14  for the UE in a Context Forward Request message. In a 5G wireless communications network, this information is commonly referred to as “UE context”, and comprises i.a. UE RRC state information, security information, UE capability information, etc. 
     Hence, in this embodiment, before releasing the radio connection to the UE  18 , the source base station  14  transmits the UE context required by the target base station  15  for the target base station to subsequently resume the released connection. 
     It should be noted that the UE  18  is in the RRC_INACTIVE state after release where the UE  18  may stay for several seconds or even minutes and once the UE  18  resumes its connection, the UE context has already been moved and its connection with the source base station  14  has been switched to the target base station  15 . 
     Advantageously, as compared to the prior art procedure of having the target base station  15  fetch the UE context from the source base station  14  before resuming the connection with the UE  18  that is released by the source base station  14 , the setup time for the resumed connection is greatly shortened when the UE  18  connects with the identified target base station  15 , which improves time-to-service and mitigates any need for data buffering in the network. 
       FIG. 5 a    shows a signalling diagram illustrating a method of enabling a connection of the UE  18  released by the source radio base station  14  (gNB 1 ) to be resumed by the target base station  15  (gNB 2 ) according to a further embodiment. 
     The steps S 101 -S 103  are identical to those already described with reference to  FIG. 4 . Steps and actions indicated with dotted lines are also performed in the prior art. However, it should be noted that in the art steps S 104 -S 106  are performed at a later stage in connection to performing steps S 110  and S 111 . 
       FIG. 5 a    further illustrates with step S 100  that the UE  18  itself may signal to the source base station  14  that the connection is to be released. 
     Upon the target base station  15  receiving the information required to resume the connection with the UE  18 —i.e. the UE context—from the source base station  14  in step S 103 , the target base station  15  transmits a request to switch connection of the UE  18  between the 5GC and the NG-RAN from the source base station  14  to the target base station  15 , to a network node  10  configured to provide mobility management in step S 104 , in this exemplifying embodiment in the form of an AMF. 
     Hence, the target base station  15  transmits a Path Switch Request message requesting the AMF  10  to move the connection of the UE  18  from the source base station  14  to the target base station  15 . 
     The AMF  10  will co-operate in step S 105  with the UPF  11  to trigger 5GC to switch a downlink data path towards the target base station  15  and to establish an NG-C interface (i.e. a control plane interface between NG-RAN and 5GC) instance towards the target base station  15 , and the 5GC will switch the downlink data path towards the target base station  15 . 
     The AMF  10  may further transmit a Path Switch Request Ack message in step S 106  indicating to the target base station  15  that the path switch is acknowledged. 
     Thereafter, the target base station  15  associates, in step S 107 , an identifier with the UE context that was received from the source base station  14  in step S 103 . In an embodiment, the identifier is a so called Inactive Radio Network Temporary Identifier (I-RNTI). 
     The I-RNTI is transmitted in step S 108  to the source base station  14  in a Context Forward Response message for subsequent forwarding to the UE  18  in a connection release message. 
     Further in an embodiment, the message in step S 108  comprises a notification to the source base station  14  that the UE context can be released, in response to which the source base station  14  can release radio and control plane related resources associated with the UE context. Advantageously, since no service is ongoing between the UE  18  and the source base station  15 , only the UE context is forwarded to the identified target base station  15 , and the UE  18  is sent an identifier which uniquely identifies the UE context before the radio connection to the UE  18  is released. With the unique identifier—exemplified in the form of the I-RNTI—the UE  18  is informed of where its UE context is located and the target base station  15  is able to identify the UE context for this particular UE  18 . It should be noted that no radio resources need to be allocated; only the Resume ID (i.e. the I-RNTI) for the UE context is transmitted. 
     Hence, the source base station  14  transmits a message to the UE  18  in step S 109  thereby releasing the connection with the UE  18 , which message includes the I-RNTI and possibly the cause for the release. This message may e.g. be embodied in the form of an RRC Release message or an RRC Connection Reconfiguration message. The UE  18  will thus transit from RRC_ACTIVE state to RRC_INACTIVE state upon receiving the message comprising the I-RNTI in step S 109 . 
     The UE  18  which now is in the RRC_INACTIVE state will in step S 110  transmit a request to resume the connection previously established with the source base station  14  in the form of an RRC Connection Resume Request message, which includes the I-RNTI. 
     In response thereto, the target base station  15  will internally fetch the UE context associated with the received I-RNTI and resume the connection with the UE  18  by transmitting an RRC Connection Resume message in step S 111 . 
     As previously mentioned, in the art, the step S 104 -S 106  are in contrast performed just prior to step S 110 . 
     Upon receiving the message in step S 111  the UE  18  will enter RRC_CONNECTED state. 
     Advantageously, since the target base station  15  already received the UE context in step S 103  and performed the path switch in steps S 104 -S 106 , there is no need to fetch the context with a Retrieve UE Context procedure as was described with reference to  FIG. 3  upon receiving the request in step S 110 , nor is it needed to perform a path switch; instead the connection can be resumed immediately. 
       FIG. 5 b    shows a signalling diagram illustrating a method of enabling a connection of the UE  18  released by the source radio base station  14  (gNB 1 ) to be resumed by the target base station  15  (gNB 2 ) according to a further embodiment. 
     In this particular embodiment, after having detected that no more data is to be transferred by the UE  18  in step S 101 , the source base station  14  allocates in step S 101   a  an identifier (e.g. the I-RNTI) with the UE context to be transmitted to the target base station  15  in step S 103 . 
     By having the source base station  14  assign the I-RNTI, the UE context can advantageously be sent to several potential target base stations as identified by the source base station  15  in step S 102  (even though only one single target base station subsequently will effect a path switch, in this example gNB 2 ). 
     Along with the information required to resume the connection with the UE  18 —i.e. the UE context—sent from the source base station  14  in step S 103  to one or more potential target base stations a UE context release timer is included, which has the advantage that the I-RNTI which is allocated by the source base station  14  subsequently can be re-used for another UE upon expiration of the UE context release timer. 
     In this example, the target base station  15  (gNB 2 ) is the base station performing the path switch. As previously mentioned, only one potential target base station  15  can perform the path switch. Optionally, this may be indicated by the source base station  14  to the target base station  15  upon transmitting the UE context in step S 103 . 
     Similarly to  FIG. 5 a   , in step S 104 , the target base station  15  transmits a request to switch connection of the UE  18  between the 5GC and the NG-RAN from the source base station  14  to the target base station  15 , to a network node  10  configured to provide mobility management, in this exemplifying embodiment in the form of an AMF. 
     Hence, the target base station  15  transmits a Path Switch Request message requesting the AMF  10  to move the connection of the UE  18  from the source base station  14  to the target base station  15 . 
     The AMF  10  will co-operate in step S 105  with the UPF  11  to trigger 5GC to switch a downlink data path towards the target base station  15  and to establish an NG-C interface (i.e. a control plane interface between NG-RAN and 5GC) instance towards the target base station  15 , and the 5GC will switch the downlink data path towards the target base station  15 . 
     The AMF  10  may further transmit a Path Switch Request Ack message in step S 106  indicating to the target base station  15  that the path switch is acknowledged. 
     Optionally, should the Context Forward Request of step S 103  not contain an identifier in the form of an I-RNTI but only a UE context release timer (as well as the UE context), the target base station  15  associates the received UE context with an I-RNTI in step  107  and transmits the I-RNTI in step S 108  as previously described with reference to  FIG. 5   a.    
     However, in this exemplifying embodiment, since the source base station  14  indeed did assign the I-RNTI to the UE context in step S 101   a , the target base station  15  will not perform step S 107 , and the Context Forward Response message of step S 108  will basically be an acknowledgement that the path switch is performed. 
     The source base station  14  transmits a message to the UE  18  in step S 109  thereby releasing the connection with the UE  18 , which message includes the I-RNTI and possibly the cause for the release. The UE  18  will thus transit from RRC_ACTIVE state to RRC_INACTIVE state upon receiving the message comprising the I-RNTI in step S 109 . 
     Advantageously, the UE  18  is sent an identifier which uniquely identifies the UE context before the radio connection to the UE  18  is released. With the unique identifier—exemplified in the form of the I-RNTI—the UE  18  is informed of where its UE context was allocated and the target base station  15  that has already received the UE context is able to identify the UE context for this particular UE  18 . It should be noted that no radio resources need to be allocated; only the Resume ID (i.e. the I-RNTI) for the UE context is transmitted. 
     The UE  18  which now is in the RRC_INACTIVE state will in step S 110  transmit a request to resume the connection previously established with the source base station  14  in the form of an RRC Connection Resume Request message, which includes the I-RNTI. 
     In response thereto, the target base station  15  will internally fetch the UE context associated with the received I-RNTI and resume the connection with the UE  18  by transmitting an RRC Connection Resume message in step S 111 . 
     As previously mentioned, in the art, the step S 104 -S 106  are in contrast performed just prior to step S 110 . 
     Upon receiving the message in step S 111  the UE  18  will enter RRC_CONNECTED state. 
     Advantageously, since the target base station  15  already received the UE context in step S 103  and performed the path switch in steps S 104 -S 106 , there is no need to fetch the context with a Retrieve UE Context procedure as was described with reference to  FIG. 3  upon receiving the request in step S 110 , nor is it needed to perform a path switch; instead the connection can be resumed immediately. In case the path switch has not been performed to the target base station, the path switch is performed when the UE resumes the connection with steps S 110 -S 111 . 
     Further advantageous is that when the connection has been resumed or the context release timer has expired, the I-RNTI can be re-used for another UE. 
       FIG. 6  illustrates a source radio base station  14  according to an embodiment. The steps of the method performed by the source radio base station  14  of enabling a connection of a wireless communication device released by the source radio base station  14  to be resumed by a target radio base station according to embodiments are in practice performed by a processing unit  115  embodied in the form of one or more microprocessors arranged to execute a computer program  116  downloaded to a suitable storage volatile medium  117  associated with the microprocessor, such as a Random Access Memory (RAM), or a non-volatile storage medium such as a Flash memory or a hard disk drive. The processing unit  115  is arranged to cause the source radio base station  14  to carry out the method according to embodiments when the appropriate computer program  116  comprising computer-executable instructions is downloaded to the storage medium  117  and executed by the processing unit  115 . The storage medium  117  may also be a computer program product comprising the computer program  116 . Alternatively, the computer program  116  may be transferred to the storage medium  117  by means of a suitable computer program product, such as a Digital Versatile Disc (DVD) or a memory stick. As a further alternative, the computer program  116  may be downloaded to the storage medium  117  over a network. The processing unit  115  may alternatively be embodied in the form of a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a complex programmable logic device (CPLD), etc. 
     The source base station  14  comprises acquiring means  140  adapted to acquire an indication that a connection established with the wireless communication device is to be released, identifying means  141  adapted to identify a target base station with which the connection to be released can be resumed for the wireless communication device, and transmitting means adapted to transmit, to the identified target base station, information required to resume the connection to be released by the source base station  14  for the wireless communication device. 
     The means  140 - 142  may comprise communication interface(s) for receiving and providing information, and further a local storage for storing data, and may (in analogy with that previously discussed) be implemented by a processor embodied in the form of one or more microprocessors arranged to execute a computer program downloaded to a suitable storage medium associated with the microprocessor, such as a RAM, a Flash memory or a hard disk drive. 
       FIG. 7  illustrates a target radio base station  15  according to an embodiment. The steps of the method performed by the target radio base station  15  of enabling a connection of a wireless communication device released by a source radio base station to be resumed by the target radio base station  15  according to embodiments are in practice performed by a processing unit  125  embodied in the form of one or more microprocessors arranged to execute a computer program  126  downloaded to a suitable storage volatile medium  127  associated with the microprocessor, such as a RAM, or a non-volatile storage medium such as a Flash memory or a hard disk drive. The processing unit  125  is arranged to cause the target radio base station  15  to carry out the method according to embodiments when the appropriate computer program  126  comprising computer-executable instructions is downloaded to the storage medium  127  and executed by the processing unit  125 . The storage medium  127  may also be a computer program product comprising the computer program  126 . Alternatively, the computer program  126  may be transferred to the storage medium  127  by means of a suitable computer program product, such as a DVD or a memory stick. As a further alternative, the computer program  126  may be downloaded to the storage medium  127  over a network. The processing unit  125  may alternatively be embodied in the form of a DSP, an ASIC, an FPGA, a CPLD, etc. 
     The target base station  15  comprises receiving means  140  adapted to receive, from the source base station, information required to resume the connection to be released by the source base station for the wireless communication device after the source base station has determined that the connection to the wireless communication device is to be released and further identified the target base station  15  as a base station with which the connection can be resumed. 
     The means  150  may comprise communication interface(s) for receiving and providing information, and further a local storage for storing data, and may (in analogy with that previously discussed) be implemented by a processor embodied in the form of one or more microprocessors arranged to execute a computer program downloaded to a suitable storage medium associated with the microprocessor, such as a RAM, a Flash memory or a hard disk drive. 
       FIG. 8  illustrates a wireless communication device  18  according to an embodiment. The steps of the method performed by the wireless communication device  18  of enabling a connection of the wireless communication device  18  released by a source radio base station to be resumed by a target radio base station according to embodiments are in practice performed by a processing unit  135  embodied in the form of one or more microprocessors arranged to execute a computer program  136  downloaded to a suitable storage volatile medium  137  associated with the microprocessor, such as a RAM, or a non-volatile storage medium such as a Flash memory or a hard disk drive. The processing unit  135  is arranged to cause the wireless communication device  18  to carry out the method according to embodiments when the appropriate computer program  136  comprising computer-executable instructions is downloaded to the storage medium  137  and executed by the processing unit  135 . The storage medium  137  may also be a computer program product comprising the computer program  136 . Alternatively, the computer program  136  may be transferred to the storage medium  137  by means of a suitable computer program product, such as a DVD or a memory stick. As a further alternative, the computer program  136  may be downloaded to the storage medium  137  over a network. The processing unit  135  may alternatively be embodied in the form of a DSP, an ASIC, an FPGA, a CPLD, etc. 
     The wireless communication device  18  comprises receiving means  160  adapted to receive, from the source base station, a connection release message including an identifier associated with information required to resume the connection with the target base station. 
     The means  160  may comprise communication interface(s) for receiving and providing information, and further a local storage for storing data, and may (in analogy with that previously discussed) be implemented by a processor embodied in the form of one or more microprocessors arranged to execute a computer program downloaded to a suitable storage medium associated with the microprocessor, such as a RAM, a Flash memory or a hard disk drive. 
     The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.