Patent Publication Number: US-2023164537-A1

Title: Reliable data delivery over non-access stratum

Description:
This application is a continuation of U.S. patent application Ser. No. 17/100,002, filed Nov. 20, 2020, which is a continuation of U.S. patent application Ser. No. 16/338,818, filed Apr. 2, 2019, now U.S. Pat. No. 10,869,185, which is a 35 U.S.C. § 371 national phase filing of International Application No. PCT/EP2016/073914, filed Oct. 6, 2016, the disclosures of which are incorporated herein by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The invention relates to a method in a mobility management node and a mobility management node for delivering user data to wireless communication device where the user data is sent by a Network Entity (NE), e.g. a Service Capability Exposure Function (SCEF). 
     BACKGROUND 
     A Global System for Mobile communications (GSM) or a Universal Mobile Telecommunications System (UMTS) or a Long-Term Evolution (LTE) network or similar is, like most other cellular networks, basically a network of individual cells each covering a small geographical area. Each cell is associated with a radio access node (e.g. a base station or similar) for communicating wirelessly with a WCD located within the cell. By combining the coverage of all cells of a cellular network and their corresponding radio access nodes extends the coverage of the cellular network over a much wider area than a single cell. 
     In GSM EDGE Radio Access Network (GERAN)/UMTS Terrestrial Radio Access Network (UTRAN) a number of adjacent or neighbouring cells can be grouped into a so-called Routing Area (RA), and into a so-called Tracking Area (TA) in Evolved UTRAN (E-UTRAN). A mobility procedure in the form of a Tracking Area Update (TAU) or a Routing Area Update (RAU) is initiated when a UE enters a new TA or RA respectively. The mobility procedure may e.g. be initiated by moving UE. 
     Another mobility procedure in cellular networks is the so-called handover procedure, which is the process of transferring an ongoing session such as a call or data session or similar from one radio access node to another radio access node without loss or interruption of service. Typically, handover occurs when a UE moves away from the area covered by one cell and entering the area covered by another cell, whereupon the ongoing session is transferred to the second cell in order to avoid service termination handover may occur in other situations, e.g. handover from a first cell to second cell when the UE is located in an area overlapped by both cell and the capacity of the first cell is exhausted, or handover from a macro cell to a nearby micro cell to off load the macro cell etc. 
     The above mentioned and exemplifying mobility procedures TAU, RAU and handover are well known to those skilled in the art and they need no detailed description as such. 
       FIG.  1   a    shows a schematic block diagram illustrating a known communication network  10   a  wherein embodiments of the present solution may be implemented. The wireless communication network  10   a  comprises a Radio Access Network (RAN)  103  in turn comprising a RAN node  102  connected to a Mobility Management Entity (MME)  105  and to a Serving Gateway (SGW)  108 , in turn connected to the MME  105 , and a Packet Data Network Gateway (PGW)  110 , which in turn is connected to a Policy and Charging Rules Function (PCRF)  130 . The RAN node  102  is a radio access node that interfaces with a wireless communication device (WCD). 
     The WCD, as exemplified by an UE  101  in  FIG.  1   a   , is a device by which a subscriber accesses services offered by an operator&#39;s network and services outside operator&#39;s network to which the operators radio access network and core network provide access, e.g. access to the Internet (c.f. the Packet Data Network (PDN)  115  in  FIG.  1   a   ). The UE  101  in  FIG.  1   a    may be any device, mobile or stationary, enabled to communicate in the communications network, for instance but not limited to e.g. user equipment, mobile phone, smart phone, sensors, meters, vehicles, household appliances, medical appliances, media players, cameras, Machine to Machine (M2M) device, Device to Device (D2D) device, Internet of Things (IoT) device or any type of consumer electronic, for instance but not limited to television, radio, lighting arrangements, tablet computer, laptop or Personal Computer (PC). The UE  101  may be portable, pocket storable, hand held, computer comprised, or vehicle mounted devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another UE or a server. 
     The RAN  103  in  FIG.  1   a    is represented by an Evolved-Universal Terrestrial Radio Access Network (E-UTRAN) and the RAN node  102  in the E-UTRAN is represented by an evolved NodeB (eNode B, eNB). However, the RAN node may for example be a base station (in the GSM EDGE Radio Access Network (GERAN)  122 ), a NodeB (in the Universal Terrestrial Radio Access Network (UTRAN)  125 ), Radio Network Controller (RNC) (in the UTRAN  125 ) or any other element capable of wireless communication with the UE  101  or similar at one end and a Core Network (CN) serving the UE  101  at the other end. The reference point between the UE  101  and the E-UTRAN  103  may be referred to as Long Term Evolution-Uu (LTE-Uu). GSM is short for Global System for Mobile Communications and EDGE is short for Enhanced Data Rates for GSM Evolution. 
     The MME  105  is connected to the E-UTRAN  103  via the reference point S1-MME, also known as the S1-interface for the MME. The S1 Application Protocol (S1AP) supports the functions of S1 interface by signalling procedures, e.g. as defined in the specification 3GPP TS 36.413 V14.0.0 (2016-09) 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 Application Protocol (S1AP) (Release 14). The MME  105  is an element having functions such as e.g. Non-Access Stratum (NAS) signalling, Inter Core Network (CN) node signalling for mobility between 3rd Generation Partnership Project (3GPP) access networks, UE reachability, Tracking Area (TA) list management, PGW and SGW selection, MME selection for handover with MME change etc. S10 is the reference point between MMEs  105  for MME relocation and MME to MME information transfer. 
     The SGW  108  routes and forwards user data packets for the UE  101  over the S1-U interface, whilst also acting as the mobility anchor for the user plane of the UE  101  during inter-eNodeB handovers and as the anchor for mobility between LTE and other 3GPP technologies (terminating S4 interface and relaying the traffic between 2G/3G systems and the PGW  110   a ). For idle state UEs, the SGW terminates the downlink (DL) data path and triggers paging when DL data arrives for the UE  101  and further manages and stores UE contexts, e.g. parameters of the IP bearer service, network internal routing information. It also performs replication of the user traffic in case of lawful interception. The SGW communicates with the MME  105  via the S11 interface and with the PGW  110   a  via the S5 interface. Further, the SGW may communicate with the UTRAN  125  and with the GERAN  122  via the S12 interface. 
     The PGW  110   a  is the gateway which terminates the SGi interface towards the Packet Data Network (PDN)  115 . The PDN  115  is illustrated in  FIG.  1   a    by the Operator&#39;s IP Services (e.g. IMS, PSS etc.). IMS is short for IP Multimedia Subsystem or IM Multimedia core network Subsystem and PSS is short for Packet Switched Streaming. If the UE  101  is accessing multiple PDNs, there may be more than one PGW  110   a  for that UE  101 . Functions of the PGW  110   a  are e.g. providing connectivity from the UE  101  to external PDNs by being the point of exit and entry of traffic for the UE  101  with respect to the Core Network (CN) of the communications network  10   a , performing policy enforcement, packet filtering for each user, charging support, lawful interception and packet screening etc. S5 is the reference point which provides user plane tunnelling and tunnel management between the SGW  108  and the PGW  110   a.    
     The SGSN  118  is responsible for the delivery of data packets from and to the UE&#39;s  101  within its geographical service area. One of the SGSN&#39;s  118  functions is to provide signaling for mobility between 2G/3G and E-UTRAN  103  access networks. 2G/3G access network are exemplified with GERAN  122  and UTRAN  125  in  FIG.  1   a   . Some further functions of the SGSN  118  are to handle packet routing and transfer, mobility management (attach/detach and location management), logical link management, and authentication and charging functions etc. S3 is the interface between the SGSN  118  and the MME  105 . S4 is a reference point between the SGSN  118  and the SGW  108 . S12 is the reference point between the SGW  108  and the UTRAN  125 . In some embodiments, the SGSN  118  and the MME  105  are co-located in one node. In this text, the term MME/SGSN will refer to any one of a standalone MME  105  or a standalone SGSN  108  or a combined MME  105  and SGSN  118  node. The SGSN  118  may also be referred to as a S4-SGSN. In the following, when the term MME is used, it refers to any of the standalone MME, a combined MME/SGSN or a combined MME/S4-SGSN. The term MME is used for the sake of simplicity. 
     The Home Subscriber Server (HSS)  128  is a subscriber server node similar to the GSM Home Location Register (HLR) and Authentication Centre (AuC). The HSS  128  comprises subscriber-related information (subscriber profiles), performs authentication and authorization of the user, and may provide information about the subscriber&#39;s location and IP information. The reference point S6a enables transfer of subscription and authentication data for authenticating/authorizing user access to the evolved system between the MME  105  and the HSS  128 . 
     The PCRF  130  is a policy and charging control element. The PCRF  130  encompasses policy control decision and flow based charging control functionalities, it provides network control regarding the service data flow detection, gating, Quality of Service (QoS) and flow based charging etc. The PCRF  130  may be described as a functional entity which may be a standalone node or a function implemented in another node. The reference point Gx provides transfer of (QoS) policy and charging rules from the PCRF  130  to a Policy and Charging Enforcement Function (PCEF) in the PGW  110   a  or similar. Rx is the reference point which resides between the PCRF  130  and the Operator&#39;s IP Services represented by the PDN  115  in  FIG.  1   a   . The Rx reference point is used to exchange application level session information between the PCRF  130  and one or more Application Functions (AF) (not shown). 
     In some embodiments, a communications network may be divided into a RAN and a Core Network (CN). Thus, the UE  101  reaches the CN using a suitable RAN technology, for example the E-UTRAN  103  as exemplified in  FIG.  1   a   . Note that  FIG.  1   a    uses E-UTRAN  103  as an example, and that the UE  101  may reach the CN using any other suitable access technology, both 3GPP technologies and non-3GPP technologies. 
     As described above, the E-UTRAN  103  may comprise a RAN node such as e.g. an eNB  102 . Using  FIG.  1   a    as an example, the CN may comprise several or even all of the MME  105 , the SGWs  108 , the PGW  110   a , the SGSN  118 , the HSS  128  and the PCRF  130 . The RAN and the CN may each comprises additional entities not shown in  FIG.  1   a   . The CN may be a Packet Switched (PS) core network or a Circuit Switched (CS) core network. In other embodiments, the communications network  10   a  is not divided into a RAN and a CN. Instead, the communications network  10   a  may comprise a virtualized CN, and the control and user planes may be split. Terms such as Software Defined Network (SDN), Network Functions Virtualization (NFV) and Network Virtualization (NV) may be used in a scenario with a virtualized CN where the control and user planes are split. The user plane (sometimes known as the data plane, forwarding plane, carrier plane or bearer plane) carries the network user traffic and that the control plane carries signalling traffic. As the SDN may decouple the user and control planes, it removes the control plane from network hardware and implements it in software instead, which enables programmatic access and, as a result, makes network administration much more flexible. The control plane signalling may be routed to the virtualized CN and the user plane signalling is bypassed the virtualized CN. A virtualized CN may comprise virtual network services enabled by a virtualized MME (vMME), virtualized SGSN (vSGSN), virtualized PGW (vPGW), virtualized SGW (vSGW), virtualized Gateway GPRS Support Node (vGGSN), virtualized PCRF (vPCRF), virtualized Deep Packet Inspection (vDPI), vProbe, virtualized Evolved Packet Data Gateway (vePDG) and virtualized Trusted Wireless Local Area Network Access Gateway (vTWAG) etc. 
     It should be noted that the communication links in the communications systems seen in  FIG.  1   a    may be of any suitable kind including either a wired or wireless link. The link may use any suitable protocol depending on type and level of layer (e.g. as indicated by the Open Systems Interconnection (OSI) model) as understood by the person skilled in the art. 
       FIG.  1   b    shows a schematic block diagram illustrating a known communication network  10   b  wherein embodiments of the present solution may be implemented. In particular,  FIG.  1   b    shows an architecture for a User Equipment (UE) used for non-roaming Machine Type Communication (MTC) connecting to the 3GPP network (UTRAN, E-UTRAN, GERAN, etc.) via the Um/Uu/LTE-Uu interfaces.  FIG.  1   b    also shows the 3GPP network service capability exposure to Service Capability Server (SCS) and Application Server (AS). 
       FIG.  1   c    shows a schematic block diagram illustrating a known communication network  10   b  wherein embodiments of the present solution may be implemented. In particular,  FIG.  1   c    shows an architecture for a User Equipment (UE) used for roaming Machine Type Communication (MTC) connecting to the 3GPP network (UTRAN, E-UTRAN, GERAN, etc.) via the Um/Uu/LTE-Uu interfaces.  FIG.  1   c    also shows the 3GPP network service capability exposure to Service Capability Server (SCS) and Application Server (AS). 
       FIGS.  1   b  and  1   c    are copied from the above mentioned specification 3GPP TS 23.682 V14.1.0 (2016-09), which specifies architecture enhancements to facilitate communications with packet data networks and applications (e.g. Machine Type Communication (MTC) applications on the (external) network/MTC servers. Both roaming and non-roaming scenarios are covered. The specification TS 23.682 also specifies transmission of non-IP data via Service Capability Exposure Function (SCEF) and Interworking SCEF (IWK-SCEF) for the Cellular Internet of Things (CIoT) Evolved Packet Core (EPS) Optimization. 
     Reference points (interfaces) shown in  FIGS.  1   b - 1   c    are:
         Tsms: Reference point used by an entity outside the 3GPP network to communicate with UEs used for MTC via SMS.   Tsp: Reference point used by a SCS to communicate with the MTC-IWF related control plane signalling.   T4: Reference point used between MTC-IWF and the SMS-SC in the HPLMN.   T6a: Reference point used between SCEF and serving MME.   T6b: Reference point used between SCEF and serving SGSN.   T6ai: Reference point used between IWK-SCEF and serving MME.   T6bi: Reference point used between IWK-SCEF and serving SGSN.   T7: Reference point used between IWK-SCEF and SCEF.   S6m: Reference point used by MTC-IWF to interrogate HSS/HLR.   S6n: Reference point used by MTC-AAA to interrogate HSS/HLR.   S6t: Reference point used between SCEF and HSS.   Rx: Reference point used by SCEF and PCRF. Functionality for Rx reference point is specified in TS 23.203 [27].   Ns: Reference point used between SCEF and RCAF.   Nt: Reference point used by SCEF and PCRF. Functionality for Nt reference point is specified in TS 23.203 [27].   Nu: Reference point used by SCEF to interact with the PFDF.       

     The Service Capability Exposure Function (SCEF)  210  shown in  FIGS.  1   b - 1   c    is the key entity within the 3GPP architecture for service capability exposure that provides a means to securely expose the services and capabilities provided by 3GPP network interfaces. MTC-IWF may be co-located with SCEF in which case Tsp functionality would be exposed via API, functions provided by the MME/SGSN (e.g. NIDD and Event Monitoring) would be exposed to the MTC-IWF by the SCEF and functions provided by the MTC-IWF (e.g. T4 Triggering) would be available to the SCEF. When they are not co-located, the SCEF may access MTC-IWF functionality via the Tsp interface. Defining interfaces that permit the SCEF to access services or capabilities at either a new or an existing 3GPP Network Element lies within 3GPP scope. The choice of which protocols to specify for such new 3GPP interfaces (e.g. DIAMETER, RESTful APIs, XML over HTTP, etc.) will depend on multiple factors including but not limited to the needs of that specific interface or ease of exposure of requested information. A capability of the SCEF is to monitor and provide notifications of desired events to the AS (Application Server) regarding a UE. For example, the SCEF can be the interface for small data transfers and control messaging between Enterprises and the Operators Core Network (CN). The Interworking SCEF (IWK-SCEF)  240  shown in  FIGS.  1   b - 1   c    is optional. When deployed, the IWK-SCEF is located in the Visited PLMN (VPLMN) as shown in  FIG.  1     c.    
     Service Capability Server (SCS)  220  shown in  FIGS.  1   b - 1   c    enables applications to access and use functionality provided by service components over standardized interfaces (APIs). An SCS hosts one or several service components. For example, in the 3GPP IP Multimedia Subsystem (IMS) architecture, the SCS may be a gateway device which translates Session Initiation Protocol (SIP) signalling into an Open Service Access (OSA) Application Programming Interface (API) and vice versa. As such, the SCS may be positioned between the Serving Call Session Control Function (S-CSCF) and the OSA service environment. 
     Application Server (AS)  230  shown in  FIGS.  1   b - 1   c    may be seen as a type of server designed to install, operate and host applications and associated services for end users, IT services and organizations. It facilitates the hosting and delivery of high-end consumer or business applications, which are used by multiple and simultaneously connected local or remote users. An AS may consists of a server operating system (OS) and server hardware that work together to provide computing-intensive operations and services to the residing application. An AS may execute and provide user and/or other application access when utilizing the installed application&#39;s business/functional logic. Key required features of an AS may include data redundancy, high availability, load balancing, user management, data/application security and a centralized management interface. An AS may be connected by enterprise systems, networks or intranet and remotely accessed via the Internet. Depending on the installed application, an AS may be classified in a variety of ways, e.g. as a Web server, database application server, general purpose application server or enterprise application (EA) server. 
     The Third Generation Partnership Project (3GPP) specifications have recently provided support for Non-Internet Protocol (IP) (Non-IP) Data Delivery (NIDD) as part of the Cellular Internet of Things (CIoT) Evolved Packet System (EPS) optimizations, see e.g. the specification 3GPP TS 23.682 V14.1.0 (2016-09) 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; Architecture enhancements to facilitate communications with packet data networks and applications (Release 14). For example, the Non-Access Stratum (NAS) protocol has been extended to allow small amounts of data to be transferred over the control plane using NIDD. 
     For the data delivery over NAS (e.g. DoNAS or “Control Plane CIoT Optimization”) which was introduced in 3GPP Release-13, there is a problem with reliable delivery that has been studied in a Release-14 study, see key issue #2 (clause 5.2) and solution #5 (clause 6.5) in the technical report 3GPP TR 23.730 V1.1.0 (2016-09) Technical Report 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; Study on extended architecture support for Cellular Internet of Things (Release 14). 
     The technical report 3GPP TR 23.730 discusses alternative delivery of data over NAS in alternative 5c “Based on hop by hop acknowledgment” in clause 6.5.1.4 and in alternative 5d in clause 6.5.1.5. Alternative 5c builds on 5d, such that 5d provides a Negative acknowledgement (unsuccessful delivery) and 5c provides both a Positive acknowledgement (successful delivery) and a Negative acknowledgement (based on 5d). 
     However, the eNB or similar in the serving Public Land Mobile Network (PLMN), e.g. in a Visited PLMN, may or may not be upgraded to support the Rel-14 reliability hop-by-hop feature (alternative 5c in TR 23.730 above). It is important that the SCEF knows if a reliable delivery was used or not. For example, the SCEF or the AS may decide to switch to application level acknowledgements i.e. UE-AS, if the reliability hop-by-hop feature is not supported by the 3GPP access in the cell where the device is camping. 
     Another problem is that the 3GPP standard does not specify any remedying action that the Mobility Management Entity (MME) may take in case the MME receives a Negative acknowledgement (S1-AP Non Delivery Indication). 
     SUMMARY 
     An object of the present invention is to solve, or at least mitigate, the problem(s) mentioned or indicated above. 
     This object is attained in a first aspect of the present solution directed to a method in a mobility management node for delivering data to a wireless communication device, WCD, served by the mobility management node, operating in a communication network comprising a network entity, NE, and a radio access network, RAN, node serving the WCD, the method comprises: obtaining capability information indicating whether the RAN node supports acknowledgement of a successful delivery of data to the WCD; receiving a data message sent by the NE comprising user data intended for the WCD; sending a control plane message comprising the user data to the RAN node for further delivery to the WCD; sending a response to the NE indicating an unsuccessful delivery of the user data to the WCD when a report is received from the RAN node indicating that the user data was not successfully delivered to the WCD; and otherwise indicating an acknowledged delivery of the user data to the WCD when the RAN node supports said acknowledgement and an acknowledgement is received from the RAN node indicating that the user data was successfully delivered to the WCD and indicating an unacknowledged delivery of user data to the WCD when the RAN node does not support said acknowledgement. 
     This object is attained in a second aspect of the present solution directed to a mobility management node for delivering data to a wireless communication device, WCD, where the mobility management node is configured to operatively serve the WCD in a communication network comprising a network entity, NE, and a radio access network, RAN, node serving the WCD, the mobility management node comprises: a network interface; one or more processors; and memory storing instructions executable by the one or more processors whereby the mobility management node is operable to: obtain capability information indicating whether the RAN node supports acknowledgement of a successful delivery of data to the WCD; receive a data message sent by the NE comprising user data intended for the WCD; send a control plane message comprising the user data to the RAN node for further delivery to the WCD; send a response to the NE indicating an unsuccessful delivery of the user data to the WCD when a report is received from the RAN node indicating that the user data was not successfully delivered to the WCD, and otherwise indicating an acknowledged delivery of the user data to the WCD when the RAN node supports said acknowledgement and an acknowledgement is received from the RAN node indicating that the user data was successfully delivered to the WCD and indicating an unacknowledged delivery of user data to the WCD when the RAN node does not support said acknowledgement. 
     The above indicated embodiments provides an acknowledgment scheme which discovers if reliable hop-by-hop delivery of Data over NAS can be provided in the current cell of the WCD. For mobile WCDs and WCDs in roaming situation this is especially advantageous, since e.g. home operator network may not be fully upgraded or the home operator has no control of support in visited operator&#39;s network. 
     For example, the SCEF will know if reliable delivery of DoNAS data was used or not. If not used, the SCEF or the AS can for example switch to using acknowledged mode on application level instead. However it is preferred not to use application layer acknowledgements since these consumes more battery in the device and more resources in the network, but is an alternative method for guarantee reliable delivery. 
     The above indicated embodiments and further embodiments of the invention will be discussed in more detail in the detailed description hereinbelow with reference made to the accompanying drawings. 
     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   a    shows a schematic block diagram of a known communication network ( 10   a ) wherein embodiments of the present solution may be performed; 
         FIG.  1   b    shows a schematic block diagram of a known communication network ( 10   b ) wherein embodiments of the present solution may be performed; 
         FIG.  1   c    shows a schematic block diagram of a known communication network ( 10   a ) wherein embodiments of the present solution may be performed; 
         FIG.  2    shows a signalling diagram illustrating the delivering of data to a WCD sent by a SCEF according to an embodiment of the present solution; 
         FIG.  3    shows a signalling diagram illustrating some details of a delivery of data to a WCD sent by a SCEF according to an embodiment of the present solution; 
         FIG.  4    shows a signalling diagram illustrating some details of the delivery of data to a WCD sent by a SCEF according to an embodiment of the present solution; 
         FIG.  5    shows a schematic signalling diagram illustrating the delivering of data to a WCD sent by a NE according to an embodiment of the present solution; 
         FIG.  6    shows a flowchart illustrating a method according to an embodiment of the present solution; 
         FIG.  7   a    illustrates a mobility management node according to an embodiment of the present solution; 
         FIG.  7   b    illustrates a mobility management node according to some other embodiments of the present solution. 
     
    
    
     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. 
     Embodiments described herein may comprise one or more of the following properties: 
     1) A new cause code may be sent from the MME to the SCEF, which can cause code distinguish two successful deliveries, i.e. acknowledged delivery from unacknowledged delivery, in addition to delivery failure (undelivered).
         Acknowledged delivery means that RLC Acknowledged mode is known to have been used and successful delivery was indicated.   Unacknowledged delivery means that either a) RLC unacknowledged delivery was used, or b) RLC acknowledged delivery was used but the successful result has not been propagated to the MME (is unknown in MME). For both a) and b) cases delivery is considered successful.   Delivery failure (undelivered) is when the MME knows that delivery was not possible to the device. This may e.g. be done by legacy indication S1-AP NAS NON DELIVERY INDICATION as described in solution 5d in TR 23.730.       

     2) A new capability indication may be added in the S1-AP INITIAL UE MESSAGE that DL NAS Data acknowledgements from the eNB to the MME are supported. This indication may be added in the S1-AP INITIAL UE MESSAGE, e.g. when used for NAS Service Request, for Attach request, or for Tracking Area Update request. 
     3) A new indication may be added in the S1-AP DOWNLINK NAS TRANSPORT message indicating that MME requests acknowledgement from the eNB (positive and negative depending on result) of the DL NAS Data delivery result. This indication may be added in the S1-AP DOWNLINK NAS TRANSPORT to request the eNB to use the Acknowledged mode of the RLC protocol and to return the result back to the MME. A positive result may be indicated back to MME in an existing message or a new message e.g. “S1-AP: NAS DELIVERY INDICATION”. A negative result may be indicated back to MME in the existing message “S1-AP: NAS NON DELIVERY INDICATION” or a new message e.g. with a specific parameter in the new message above “S1-AP: NAS DELIVERY INDICATION”. 
     4) Retransmission of UL NAS data in the UE based on the transmission result indicated from the RLC layer when RLC acknowledged mode is used. The RLC Acknowledged mode has not been used to secure delivery of NAS PDUs or at least not been used for retransmission, since NAS is typically acknowledged on NAS level and therefore has its own retransmission mechanisms (using NAS time out and retransmission count). Thus, the MME shall resend DL data in case the MME receives a Negative acknowledgement (S1-AP Non Delivery Indication). This is advantageous since 3GPP devices using DoNAS (“Control Plane CIoT Optimization” in the 3GPP specs) may suddenly change to another cell or eNB during a transmission of UL and DL packets. The MME shall retransmit any failed DL DoNAS packets as soon as the 3GPP device has connected to the new cell or eNB. 
     5) Retransmission of DL NAS data in the MME based on the transmission result indicated over S1-AP (see TR 23.730 solution 5c/5d) originating from the RLC layer when RLC acknowledged mode was used in the eNB. 
       FIG.  2    shows a signalling diagram illustrating a delivery of user data to a UE (WCD  101 ) sent by a SCEF  210  according to an embodiment of the present solution.  FIG.  2    illustrates a procedure in which the SCS  220 /AS  230  sends non-IP data to a given UE as identified via External Identifier or a Mobile Station International Subscriber Directory Number (MSISDN) or similar. 
     Action  201 . If the SCS  220 /AS  230  has already activated the NIDD service for a given UE (WCD  101 ), and has downlink non-IP data to send to the UE, the SCS/AS sends a NIDD Submit Request (External Identifier or MSISDN, SCS/AS Reference ID, non-IP data) message to the SCEF. 
     Action  202 . If an SCEF EPS bearer context corresponding to the External Identifier or MSISDN included in step  201  is found, then the SCEF  210  checks whether the SCS  220 /AS  230  is authorised to send NIDD requests and that the SCS  230  has not exceeded its quota (e.g. 200 bytes in 24 hrs) or rate (e.g. 10 bytes/hour) of data submission. If this check fails, the SCEF  210  sends a NIDD Submit Response (action  205 ) with a cause value indicating the reason for the failure condition and the flow stops at this step. Otherwise, the flow continues with action  203 . 
     If no SCEF EPS bearer context is found, then the SCEF  210 , depending on configuration, may either:
         send a NIDD Submit Response with appropriate error cause value. The flow stops at this step; or   perform device triggering towards the UE (using T4 SMS trigger) to establish a Non-IP PDN connection towards the SCEF  210 . In this case, action  205  with an appropriate cause value is executed; or   accept the NIDD Submit Request, and execute action  205  with an appropriate cause value, and wait for the UE to perform a procedure causing the establishment of a PDN connection to the SCEF. The duration for which the SCEF may wait for establishment of a PDN connection to the SCEF for the given UE is implementation dependent.       

     Action  203 . If an SCEF EPS bearer context corresponding to the External Identifier or MSISDN included in step  201  is found, then the SCEF  210  sends a NIDD Submit Request (User Identity, EPS Bearer ID, SCEF ID, non-IP data, SCEF Wait Time, Maximum Re-transmission time) message toward the MME  105 . The SCEF Wait Time indicates how long the SCEF  210  is prepared to wait for MME  105  response. Maximum Re-transmission indicates how long the SCEF  210  is prepared to re-transmit the message. If the IWK-SCEF  240  receives a NIDD Submit Request message from the SCEF  210 , it relays the message to the MME  105 . 
     Action  204 . If the MME  105  can immediately deliver the non-IP data to the UE e.g. when UE is already in ECM_CONNECTED mode, or UE is in ECM_IDLE and the MME  105  can initiate paging procedure, the procedure proceeds at action  8 . 
     If the MME  105  is aware of the UE being temporarily unreachable, or if the MME  105  that the UE is not scheduled to be reachable within the SCEF Wait Time, while using power saving functions e.g. UE Power Saving Mode or extended idle mode DRX, then the MME  105  may send a NIDD Submit Response (Cause, Requested Re-Transmission Time) message towards the SCEF  210 . The Cause parameter indicates that Non-IP data was not delivered to the UE, as the UE is temporarily not reachable due to power saving but the MME  105  will notify the SCEF  210  when the MME  105  determines that the UE is reachable. The MME  105  sets the Not Reachable for NIDD flag in the EMM context for this UE and stores the corresponding SCEF address. If the Maximum Re-transmission Time was included in the Request, the MME  105  may indicate in Requested Re-Transmission time IE the time when the SCEF  210  is expected to re-transmit the DL data to the currently unreachable UE. 
     Action  205 . The SCEF  210  may send a NIDD Submit Response to the SCS  220 /AS  230  informing of the received results from the MME  105 . If the SCEF  210  receives from the MME  105  a Cause value indicating that UE is temporarily not reachable due to power saving, the SCEF  210  can buffer the non-IP data requested at action  203  based on the configuration. 
     Action  206 . When the MME  105  detects that the UE is reachable (e.g. when coming out of PSM mode by performing TAU/RAU, when initiating MO communication etc), or when the UE is about to become reachable (e.g. extended idle mode DRX cycle expiring, MME  105  anticipating MO communication pattern for the UE etc), and the MME  105  has the Not Reachable for NIDD flag set, then the MME  105  sends a NIDD Submit Indication (User Identity) message towards the SCEF  210 . The MME 105  clears the Not Reachable for NIDD flag from its EMM context. 
     If the MME  105  included the Requested Re-transmission-Time in the NIDD Submit Response, the MME  105  sends a NIDD Submit Indication (User Identity) message towards the SCEF  210  only if the UE becomes reachable before the Requested Re-transmission Time. The MME  105  shall clear the Not Reachable for NIDD flag when the Requested Re-transmission Time expires and the UE has not become reachable yet. 
     Action  207 . The SCEF  210  sends a NIDD Submit Request (User Identity, EPS Bearer ID, SCEF ID, non-IP data, SCEF Wait Time, Maximum Re-transmission time) message toward the MME  105 . 
     Action  208 . If required, the MME  105  pages the UE and delivers the non-IP data to the UE using data transfer via the MME procedure, e.g. as described below with reference to  FIG.  3  or  4   , see e.g. Actions  313 - 314  and Actions  411 - 412 . Depending on operator configuration, the MME  105  may generate the necessary accounting information required for charging. 
     Action  209 . If the MME  105  was able to initiate action  208 , then the MME  105  sends a NIDD Submit Response (cause) message towards the SCEF  210  acknowledging the NIDD Submit Request from SCEF  210  received in action  203  or  207  above. If the eNodeB supported reliably hop-by-hop delivery, the cause is ‘Success Acknowledged Delivery’ otherwise ‘Success Unacknowledged Delivery’. If the delivery failed, the cause is ‘Unsuccessful delivery’. The SCEF  210  confirms the non-IP data transfer towards the SCS  220 /AS  230  and may include the success reliability level. 
     The ‘Success Acknowledged Delivery’ implies reliable delivery to the UE, e.g. using RLC acknowledged mode. The ‘Success Unacknowledged Delivery’ successful result does not imply the data is successfully received at the UE, but just the MME  105  has sent the non-IP data in NAS signalling to the UE. 
       FIG.  3    shows a signalling diagram illustrating some details of the delivery of data to a UE (WCD  101 ) sent by the SCEF  210  according to an embodiment of the present solution. 
     Action  300 . The UE is EPS attached and in ECM-Idle mode. 
     Action  301 . When the S-GW  108  receives a downlink data packet/control signalling for a UE, if the S-GW context data indicates no downlink user plane TEID towards the MME  105 , it buffers the downlink data packet and identifies which MME  105  is serving that UE. 
     If that MME  105  has requested the S-GW to throttle downlink low priority traffic and if the downlink data packet is received on a low priority bearer to be throttled, the S-GW drops the downlink data. The actions below are not executed. 
     If that MME  105  has requested the S-GW to delay sending the Downlink Data Notification, the S-GW buffers the downlink data and waits until the timer expires before continuing with action  302 . If the DL-TEID and MME address for that UE is received before the expiry of the timer, the timer shall be cancelled and the Mobile Terminated Data transport procedure is progressed from step  11  as Downlink data are sent to the UE. 
     If the S-GW receives additional downlink data packets/control signalling for this UE before the expiry of the timer, the S-GW does not restart this timer. 
     Action  302 . If the S-GW  108  is buffering data in action  301 , the S-GW sends a Downlink Data Notification message (ARP, EPS Bearer ID) to the MME  105  for which it has control plane connectivity for the given UE. The ARP and EPS Bearer ID are always set in Downlink Data Notification. The MME  105  responds to the S-GW  108  with a Downlink Data Notification Ack message. 
     An MME  105  detecting that the UE is in a power saving state (e.g. Power Saving Mode) and cannot be reached by paging at the time of receiving Downlink data notification, shall invoke extended buffering depending on operator configuration, except for cases described in next paragraphs. The MME  105  derives the expected time before radio bearers can be established to the UE. The MME  105  then indicates Downlink Buffering Requested to the S-GW in the Downlink Data Notification Ack message and includes a Downlink Buffering Duration time and optionally a Downlink Buffering Suggested Packet Count. The MME  105  stores a new value for the Downlink Data Buffer Expiration Time in the MM context for the UE based on the Downlink Buffering Duration time and skips the remaining steps of this procedure. The Downlink Data Buffer Expiration Time is used for UEs using power saving state and indicates that there are buffered data in the S-GW  108  and that the user plane setup procedure is needed when the UE makes signalling with the network. When the Downlink Data Buffer Expiration Time has expired, the MME  105  considers no Downlink data to be buffered and no indications of Buffered Downlink Data Waiting are sent during context transfers at TAU procedures. 
     If there is an “Availability after DDN Failure” monitoring event configured for the UE in the MME  105 , the MME does not invoke extended buffering. Instead, the MME  105  sets the Notify-on-available-after-DDN-failure flag to remember to send an “Availability after DDN Failure” notification when the UE becomes available. If there is a “UE Reachability” monitoring event configured for the UE in the MME  105 , the MME does not invoke extended buffering. 
     When “Availability after DDN failure” and “UE reachability” monitoring events are used for a UE, the application server is assumed to send data only when the UE is reachable, hence no extended buffering is needed. If there are multiple application servers, the event notifications and extended buffering may be needed simultaneously. It is assumed this is handled through additional information based on SLA as described in the next paragraph. 
     The MME  105  may use additional information based on a SLA with the MTC user for when to invoke extended buffering, e.g. only invoke it for a certain APN, do not invoke it for certain subscribers, invoke extended buffering in conjunction with “Availability after DDN failure” and “UE reachability” monitoring events, etc. 
     A S-GW  108  that receives a Downlink Buffering Requested indication in a Downlink Data Notification Ack message stores a new value for the Downlink Data Buffer Expiration Time based on the Downlink Buffering Duration time and does not send any additional Downlink Data Notification if subsequent downlink data packets are received in the Serving GW before the buffer time Downlink Data Buffer Expiration Time has expired for the UE. 
     If the S-GW  108 , while waiting for the user plane to be established, is triggered to send a second Downlink Data Notification for a bearer with higher priority (i.e. ARP priority level) than that of the bearer for which the first Downlink Data Notification was sent, the S-GW sends a new Downlink Data Notification message indicating the higher priority to the MME  105 . If the S-GW receives additional downlink data packets for a bearer with same or lower priority than the first Downlink Data Notification was sent for or if the S-GW has sent the second Downlink Data Notification message indicating the higher priority and receives additional downlink data packets for this UE, the S-GW buffers these downlink data packets and does not send a new Downlink Data Notification. 
     If the S-GW  108 , while waiting for the user plane to be established, receives a Modify Bearer Request message from an MME other than the one it sent a Downlink Data Notification message to, the S-GW re-sends the Downlink Data Notification message but only to the new MME from which it received the Modify Bearer Request message. 
     Upon reception of a Downlink Data Notification Ack message with an indication that the Downlink Data Notification message has been temporarily rejected and if the Downlink Data Notification is triggered by the arrival of downlink data packets at the S-GW  108 , the S-GW may start a locally configured guard timer and buffers all downlink user packets received to the given UE and waits for a Modify Bearer Request message to come. Upon reception of a Modify Bearer Request message, the S-GW re-sends the Downlink Data Notification message but only to the new MME from which it received the Modify Bearer Request message. Otherwise the S-GW releases buffered downlink user packets upon expiry of the guard timer or upon receiving the Delete Session Request message from MME  105 . 
     If the S11-U is already established (buffering is in the MME  105 ), action  302  is not executed and actin  311  is immediately executed. Actions  307 ,  308 ,  309 ,  310  are executed only if conditions are met when the NAS service request is received at action  306 , as outlined below in the respective clauses. 
     An MME  105  detecting that the UE is in a power saving state (e.g. Power Saving Mode) and cannot be reached by paging at the time of receiving Downlink data, shall start extended buffering depending on operator configuration, except for cases described in next paragraphs. The MME derives the expected time before radio bearers can be established to the UE, stores a new value for the Downlink Data Buffer Expiration Time in the MM context for the UE and skips the remaining steps of this procedure. When the Downlink Data Buffer Expiration Time has expired, the MME considers no Downlink data to be buffered. 
     Also for the case of buffering in the MME  105  the “Availability after DDN Failure” monitoring event can be configured for the UE, even though the actual DDN is not received and the Downlink data is received. The “UE Reachability” monitoring event can be configured also. The extended buffering can also be configured as per what is described above in this step of the procedure for the case of buffering in S-GW  108 . 
     Action  303 . If the UE is registered in the MME  105  and considered reachable, the MME  1105  sends a Paging message (NAS ID for paging, TAI(s), UE identity based DRX index, Paging DRX length, list of CSG IDs for paging, Paging Priority indication) to each eNodeB  102  belonging to the tracking area(s) in which the UE is registered. 
     Paging priority indication is included only:
         if the MME  105  receives a Downlink Data Notification (or a Downlink packet for a EPS bearer, for the case of buffering in MME  105 ) with an ARP priority level associated with priority services, as configured by the operator.   One Paging Priority level can be used for multiple ARP priority level values. The mapping of ARP priority level values to Paging Priority level (or levels) is configured by operator policy.       

     During a congestion situation the eNodeB  102  may prioritise the paging of UEs according to the Paging Priority indications. 
     If the MME  105 , while waiting for a UE response to the Paging Request message sent without Paging Priority indication, receives a Downlink Data Notification (or a Downlink packet for a EPS bearer, for the case of buffering in MME  105 ) which indicates an ARP priority level associated with priority services, as configured by the operator, the MME  105  shall send another paging message with the suitable Paging Priority. 
     When the MME  105  is configured to support CSG paging optimisation in the CN, the MME should avoid sending Paging messages to those eNodeB(s) with CSG cells for which the UE does not have a CSG subscription. When the MME is configured to support CSG paging optimisation in the HeNB Subsystem, the list of CSG IDs for paging is included in the Paging message. For CSG paging optimisation, the CSG IDs of expired CSG subscriptions and valid CSG subscriptions are both included in the list. If the UE has emergency bearer service the MME shall not perform the CSG paging optimisation. 
     The MME  105  and the E-UTRAN  103  may support further paging optimisations in order to reduce the signalling load and the network resources used to successfully page a UE by one or several following means:
         by the MME  105  implementing specific paging strategies (e.g. the S1 Paging message is sent to the eNB  102  that served the UE last);   by the MME  105  considering Information On Recommended Cells and eNodeBs provided by the E-UTRAN at transition to ECM IDLE. The MME takes the eNB related part of this information into account to determine the eNBs  102  to be paged, and provides the information on recommended cells within the S1 Paging message to each of these eNBs;   by the E-UTRAN  103  considering the Paging Attempt Count Information provided by the MME  105  at paging.       

     When implementing such optimisations/strategies, the MME  105  shall take into account any PSM active timer and the DRX interval for the UE. 
     If the UE Radio Capability for Paging Information is available in the MME  105 , the MME adds the UE Radio Capability for Paging Information in the S1 Paging message to the eNB  102 . 
     If the Information on Recommended Cells and ENBs for Paging is available in the MME  105 , the MME shall take that information into account to determine the eNBs for paging and, when paging an eNB  102 , the MME may transparently convey the information on recommended cells to the eNB. 
     The MME  105  may include in the S1AP Paging message(s) the paging attempt count information. The paging attempt count information shall be the same for all eNBs selected by the MME for paging. 
     If the MME  105  has Information for Enhanced Coverage stored, the MME shall include it in the Paging message for all eNBs selected by the MME for paging. 
     Action  304 . If eNodeBs receive paging messages from the MME  105 , the UE is paged by the eNodeBs. 
     Action  305 - 306 . As the UE is in the ECM-IDLE state, upon reception of paging indication, the UE sends a UE triggered Service Request NAS message over RRC Connection request and an S1-AP initial message or similar. The eNodeB  102  indicates in the S1-AP Initial UE message or similar if the eNodeB  102  supports acknowledgments for downlink NAS data Packet Data Units (PDUs) (including e.g. non-IP data units), e.g. based on RLC acknowledged mode. The Service Request NAS message, when C-IoT Control Plane optimisation applies, does not trigger Data radio bearer establishment by the MME  105  and the MME can immediately send Downlink Data it receives using a NAS PDU to the eNodeB  102 . The MME  105  supervises the paging procedure with a timer. If the MME  105  receives no response from the UE to the Paging Request message, it may repeat the paging according to any applicable paging strategy described in action  303 . 
     If the MME  105  receives no response from the UE after this paging repetition procedure, it shall use the Downlink Data Notification Reject message to notify the S-GW  108  about the paging failure (or, equivalently, if the buffering is in the MME, the MME simply discards data for the UE locally), unless the MME is aware of an ongoing MM procedure that prevents the UE from responding, i.e. the MME received a Context Request message indicating that the UE performs TAU with another MME. When a Downlink Data Notification Reject message is received, the S-GW  108  deletes the buffered packet(s). The S-GW  108  may invoke the procedure P-GW Pause of Charging if UE is in ECM IDLE and the PDN GW has enabled “PDN charging pause” feature. If buffering is in the MME, Pause Charging is triggered by the MME  105  via a Release Access Bearer Request to the S-GW (not shown in  FIG.  3   ) including a “Abnormal Release of Radio Link” cause, which releases the S11-U. 
     To assist the MME  105  in any NAS PDU retransmission strategies, the eNB  102  indicates the UE&#39;s Coverage Level to the MME  105 . 
     The MME  105  performs (and the UE responds to) any EMM or ESM procedures if necessary, e.g. the security related procedures. Actions  307  to  311  can continue in parallel to this, however, steps  312  and  313  shall await completion of all the EMM and ESM procedures. 
     Action  307 . If the S11-U is not established, the MME  105  sends a Modify Bearer Request message (MME address, MME TEID DL, Delay Downlink Packet Notification Request, RAT Type) for each PDN connection to the S-GW  108 . The S-GW  108  is now able to transmit downlink data towards the UE. The usage of the Delay Downlink Packet Notification Request Information Element is specified with reference to the UE initiated service request procedure, but it equally applies in this case. The MME  105  shall indicate S11-U tunnelling of NAS user data and send its own S11-U IP address and MME DL TEID for DL data forwarding by the S-GW  108 . Also, regardless of whether the S11-U was already established:
         If the P-GW  110  requested UE&#39;s location and/or User CSG information and the UE&#39;s location and/or User CSG information has changed, the MME  105  shall send the Modify Bearer Request message and also includes the User Location Information IE and/or User CSG Information IE in this message.   If the Serving Network IE has changed compared to the last reported Serving Network IE then the MME  105  shall send the Modify Bearer Request message and also includes the Serving Network IE in this message.   If the UE Time Zone has changed compared to the last reported UE Time Zone then the MME  105  shall send the Modify Bearer Request message and include the UE Time Zone IE in this message.       

     If the Radio Access Technology (RAT) currently used is NB-IoT this shall be reported as different from other—E-UTRA flavors. 
     Action  308 . If the RAT Type has changed compared to the last reported RAT Type or if the UE&#39;s Location and/or Info IEs and/or UE Time Zone and Serving Network id are present in action  307 , the S-GW shall send the Modify Bearer Request message (RAT Type) to the P-GW  110 . User Location Information IE and/or User CSG Information IE and/or Serving Network IE and/or UE Time Zone are also included if they are present in action  307 . 
     If the Modify Bearer Request message is not sent because of above reasons and the P-GW charging is paused, then the S-GW  108  shall send a Modify Bearer Request message with PDN Charging Pause Stop Indication to inform the P-GW  110  that the charging is no longer paused. Other IEs are not included in this message. 
     Action  309 . The P-GW  110  sends the Modify Bearer Response to the S-GW  108 . 
     Action  310 . If a Modify Bearer Request message was sent at action  307 , the S-GW  108  shall return a Modify Bearer Response (Serving GW address and TEID for uplink traffic) to the MME  105  as a response to a Modify Bearer Request message. The S-GW address for S11-U User Plane and S-GW TEID are used by the MME  105  to forward UL data to the S-GW  108 . 
     Action  311 . Buffered (if S11-U was not established) Downlink data (e.g. such as non-IP data) is sent by the S-GW  108  to the MME  105 . 
     Actions  312 - 313 . The MME  105  encrypts and integrity protects the Downlink data received in action  311  above and sends it to the eNodeB  102 , preferably using a NAS PDU preferably carried by a Downlink S1-AP message or similar. If the eNodeB  102  supports acknowledgements of downlink NAS data PDUs, the MME  105  indicates in the Downlink S1-AP message or similar that an acknowledgment of the data delivery is requested (positive and negative depending on result) from the eNodeB  102 . This parameter makes possible to avoid unnecessary acknowledgement signaling from eNB  102  to MME  105  when not required. For IP PDN type PDN connections configured to support Header Compression, the MME  105  shall apply header compression before encapsulating data into the NAS message. 
     If the eNodeB  102  reports an unsuccessful delivery of the data, e.g. using a S1-AP NAS Non Delivery Indication, (the MME  105  may e.g. decide that it may have been because of a cell change) the MME should wait for some time, e.g. until the UE has changed cell and re-established contact with the MME  105 , and then resend the Downlink S1-AP message to the eNodeB  102 . If the eNodeB  102  still reports an unsuccessful delivery of the MME  105  should report an unsuccessful delivery to the SCEF. This should also preferably be don in case of a T6a procedure. If the eNodeB  102  reports a successful delivery, e.g. with a S1-AP NAS Delivery Indication and if the Downlink data was received over the T6a interface, the MME  105  should respond to the SCEF  210 , see e.g. action  209  described above referring to  FIG.  2   . If the eNodeB  102  doesn&#39;t support acknowledgement of a successful delivery of the data to the UE, e.g. supports a S1-AP NAS Delivery Indications, the MME  105  indicates a cause code ‘Success Unacknowledged Delivery’ to the SCEF  210 . If the eNodeB  102  supports acknowledgement of a successful delivery of the data to the UE then the MME  105  indicates a cause code ‘Success acknowledged Delivery’ to the SCEF  210 . 
     Action  314 . The NAS PDU with data is delivered to the UE via a Downlink RRC message. This is taken by the UE as implicit acknowledgment of the Service Request message sent in action  305 . If header compression was applied, to the PDN, the UE shall perform header decompression to rebuild the IP header. 
     Action  315 . While the RRC connection is still up, further Uplink and Downlink data can be transferred using NAS PDUs. In action  316  an Uplink data transfer is shown using an Uplink RRC message encapsulating a NAS PDU with data. At any time the UE has no user plane bearers established, the UE may provide a Release Assistance Information with Uplink data in the NAS PDU. 
     For IP PDN type PDN connections configured to support Header Compression, the UE shall apply header compression before encapsulating it into the NAS message. 
     Action  316 . The NAS PDU with data is send to the MME  105  in an Uplink S1-AP message. 
     Action  317 . The data is checked for integrity and decrypted. If header compression was applied to the PDN, the MME  105  shall perform header decompression to rebuild the IP header. 
     Action  318 . The MME  105  sends Uplink data to the PGW  110  via the S-GW  108  and preferably executes any action related to the presence of Release Assistance Information as follows:
         for the case where the release assistance information indicates there is no downlink data to follow the uplink data then unless the MME  105  is aware of pending MT traffic, and unless S1-U bearers exist, the MME  105  immediately releases the connection and therefore step  20  is executed.   for the case where the release assistance information indicates that downlink data will follow the uplink transmission then unless the MME  105  is aware of additional pending MT traffic and unless S1-U bearers exist, the MME  105  sends a S1 UE Context Release Command to the eNodeB  102  immediately after the S1-AP message including the Downlink data encapsulated in NAS PDU.       

     Action  319 . If no NAS activity exists for a while the eNB  102  detects inactivity and executes action  320 . 
     Action  320 . The eNB  102  starts an eNodeB initiated S1 release procedure or a Connection Suspend Procedure. 
       FIG.  4    shows a signalling diagram illustrating some details of the delivery of data to a UE (WCD  101 ) sent by the SCEF  210  according to an embodiment of the present solution. 
     Action  400 . The UE is in ECM-Idle mode. 
     Action  401 . The UE establishes a RRC connection and sends as part of it an integrity protected NASPDU. The NAS PDU carries the EPS Bearer ID and encrypted Uplink Data. The UE may also indicate in a Release Assistance Information in the NAS PDU whether no further Uplink or Downlink Data transmissions are expected, or only a single Downlink data transmission (e.g. Acknowledgement or response to Uplink data) subsequent to this Uplink Data transmission is expected. If a cell change happens before the UE has received acknowledgement of successful uplink transmission, the UE shall retransmit the NAS PDU when connectivity has been established in the new cell. 
     Action  402 . The NAS PDU sent in action  401  is relayed to the MME  105  by the eNodeB  102 , preferably using a S1-AP Initial UE message or similar. The eNodeB  102  indicates in the S1-AP Initial UE message or similar if the eNodeB  102  supports acknowledgments for downlink NAS data Packet Data Units (PDUs) (including e.g. non-IP data units), e.g. based on RLC acknowledged mode. 
     To assist the MME  105  in any NAS PDU retransmission strategies, the eNB  102  may indicate the UE&#39;s Coverage Level to the MME  105 . 
     Action  403 . The MME  105  checks the integrity of the incoming NAS PDU and decrypts the data it contains. The MME  105  shall decompress the IP header if header compression applies to the PDN connection. 
     The MME  105  performs (and the UE responds to) any EMM or ESM procedures if necessary, e.g. the security related procedures. Action  404  to  409  can continue in parallel to this, however, actions  410  and  411  shall await completion of all the EMM and ESM procedures. 
     Action  404 . 
       404   a . If the S11-U connection is not established, the MME  105  sends a Modify Bearer Request message (MME address, MME TEID DL, Delay Downlink Packet Notification Request, RAT Type, MO Exception data counter) for each PDN connection to the S-GW  108 . The S-GW  108  is now able to transmit downlink data towards the UE. The usage of the Delay Downlink Packet Notification Request Information Element is specified with reference to the UE initiated service request procedure, but it equally applies in this case. The MME  105  shall indicate S11-U tunnelling of NAS user data and send its own S11-U IP address and MME DL TEID for DL data forwarding by the S-GW  108 . Also, regardless of whether the S11-U was already established:
         If the P-GW  110  requested UE&#39;s location and/or User CSG information and the UE&#39;s location and/or User CSG information has changed, the MME  105  shall send the Modify Bearer Request message and also includes the User Location Information IE and/or User CSG Information IE in this message.   If the Serving Network IE has changed compared to the last reported Serving Network IE then the MME  105  shall send the Modify Bearer Request message and also includes the Serving Network IE in this message.   If the UE Time Zone has changed compared to the last reported UE Time Zone then the MME  105  shall send the Modify Bearer Request message and include the UE Time Zone IE in this message.       

     If the RAT currently used is NB-IoT this shall be reported as different from other E-UTRA flavors. 
     The MME  105  only includes MO Exception data counter if the RRC establishment cause is set to “MO exception data” and the UE is accessing via the NB-IoT RAT. The S-GW  108  indicates each use of this RRC establishment cause by the related counter on its CDR. The MME maintains the MO Exception Data Counter and sends it to the S-GW  108 . 
       404   b . If the S11-U connection is established and the UE is accessing via the NB-IoT RAT with the RRC establishment cause set to “MO exception data”, the MME  105  should notify the S-GW  108 . The MME  105  maintains the MO Exception Data Counter and sends it to the S-GW  108 . 
     Action  405 . If the RAT Type has changed compared to the last reported RAT Type or if the UE&#39;s Location and/or Info IEs and/or UE Time Zone and Serving Network id are present in action  404 , the S-GW  108  shall send the Modify Bearer Request message (RAT Type, RRC establishment cause) to the P-GW  110 . User Location Information IE and/or User CSG Information IE and/or Serving Network IE and/or UE Time Zone are also included if they are present in action  404 . 
     If the Modify Bearer Request message is not sent because of above reasons and the P-GW charging is paused, then the SGWS-GW shall send a Modify Bearer Request message with PDN Charging Pause Stop Indication to inform the P-GW  110  that the charging is no longer paused. Other IEs are not included in this message. 
     If the Modify Bearer Request message is not sent because of above reasons but the MME  105  indicated MO Exception data counter, then the S-GW  108  should notify the P-GW  110  that this RRC establishment cause has been used by the indication of the MO Exception Data Counter. The S-GW  108  indicates each use of this RRC establishment cause by the related counter on its CDR. 
     Action  406 . The P-GW  110  sends the Modify Bearer Response to the S-GW  108 . 
     The P-GW  110  indicates each use of the RRC establishment cause “MO Exception Data” by the related counter on its CDR. 
     Action  407 . If a Modify Bearer Request message was sent at actin  404  the S-GW  108  shall return a Modify Bearer Response (Serving GW address and TEID for uplink traffic) to the MME  105  as a response to a Modify Bearer Request message. The Serving GW address for S11-U User Plane and Serving GW TEID are used by the MME to forward UL data to the S-GW. 
     Action  408 . The MME  105  sends Uplink data to the P-GW  110  via the S-GW  108 . 
     Action  409 . If no Downlink Data are expected based on the Release Assistance Information from the UE in action  401 , this means that all application layer data exchanges have completed with the UL data transfer, and therefore, unless the MME  105  is aware of pending MT traffic and unless S1-U bearers are established, the MME immediately releases the connection and therefore actin  414  is executed. 
     Otherwise, Downlink data may arrive at the P-GW  110  and the P-GW sends them to the MME  105  via the S-GW  108 . If no data is received actions  410 - 412  are skipped and the eNB  102  may trigger actin  414  after action  413  detects no activity. While the RRC connection is active, the UE may still send Uplink data and may receive Downlink data in NAS PDUs that are carried in a S1AP Uplink or (respectively) Downlink messages (not shown in the figure). At any time the UE has no user plane bearers established it may provide Release Assistance Information with the Uplink data. 
     Action  410 . If Downlink data are received in action  409 , the MME  105  encrypts and integrity protects the Downlink data. 
     Action  411 . If action  410  is executed then Downlink data are encapsulated in a NAS PDU and sent to the eNB  102 , preferably in a Downlink S1-AP Message or similar. If the eNodeB  102  supports acknowledgements of downlink NAS data PDUs, the MME  105  indicates in the Downlink S1-AP message or similar that an acknowledgment of the data delivery is requested (positive or negative depending on result) from the eNodeB  102 . This parameter makes possible to avoid unnecessary acknowledgement signaling from eNB  102  to MME  105  when not required. For IP PDN type PDN connections configured to support Header Compression, the MME shall apply header compression before encapsulating data into the NAS message. If action  410  is not executed, the MME  105  sends Connection Establishment Indication message to the eNB  102 . The UE Radio Capability may be provided from the MME to the eNB in the Connection Establishment Indication message, and the eNB shall store the received UE Radio Capability information. If the Release Assistance Information was received with Uplink data and it indicated that Downlink data was expected, it means that the next downlink packet following the sending of the Release Assistance Information is the last packet of the application layer data exchange, then for this case, unless the MME is aware of additional pending MT traffic and unless S1-U bearers are established, the MME sends a S1 UE Context Release Command immediately after the S1-AP message including the Downlink data encapsulated in NAS PDU so that the an indication that the eNodeB  102  shall release the RRC connection after successfully sending data to the UE. 
     If the eNodeB  102  reports an unsuccessful delivery of the data, e.g. using a S1-AP NAS Non Delivery Indication, (the MME  105  may e.g. decide that it may have been because of a cell change) the MME should wait for some time, e.g. until the UE has changed cell and re-established contact with the MME  105 , and then resend the Downlink S1-AP message to the eNodeB  102 . If the eNodeB  102  still reports an unsuccessful delivery of the MME  105  should report an unsuccessful delivery to the SCEF. This should also preferably be don in case of a T6a procedure. If the eNodeB  102  reports a successful delivery, e.g. with a S1-AP NAS Delivery Indication and if the Downlink data was received over the T6a interface, the MME  105  should respond to the SCEF  210 , see e.g. action  209  described above referring to  FIG.  2   . If the eNodeB  102  doesn&#39;t support acknowledgement of a successful delivery of the data to the UE, e.g. supports a S1-AP NAS Delivery Indications, the MME  105  indicates a cause code ‘Success Unacknowledged Delivery’ to the SCEF  210 . If the eNodeB  102  supports acknowledgement of a successful delivery of the data to the UE then the MME  105  indicates a cause code ‘Success acknowledged Delivery’ to the SCEF  210 . 
     Action  412 . The eNB  102  sends a RRC Downlink data message including the Downlink data encapsulated in NAS PDU. If in action  411  the S1-AP message with the NAS DATA PDU was followed by a S1 UE Context Release Command action  414  is completed promptly after the Downlink Data transmission of the NAS PDU to the UE is complete at the eNB  102  and the eNB does not need to enter action  413 . If header compression was applied to the PDN, the UE would perform header decompression to rebuild the IP header. 
     Action  413 . If no NAS PDU activity exists for a while, the eNB  102  starts an S1 release in action  414 . 
     Action  414 . An S1 release procedure is triggered by the eNodeB  102  or the MME  105 . Alternatively, if the MME  105  in action  411  sent S1 UE Context Release Command then the procedure starts with a Connection Suspend Procedure or similar. 
       FIG.  5    shows a schematic signalling diagram illustrating the delivering of data to a WCD sent by a NE according to an embodiment of the present solution. 
     The delivery method shown in figure is preferably performed in a MME  105  for delivering data to a WCD  101  that is served by the MME  105 . While performing the method it is preferred that the operates in a communication network  10   b ,  10   c  comprising a Network Entity (NE), e.g. a SGW  108 , a PGW  110 , a SCEF  210  or an IWK-SCEF  240 , and a RAN node  102  serving the WCD  101 . 
     The delivery method comprises the following actions, which may be performed in any suitable order: 
     Action  610 . Obtaining capability information indicating whether the RAN node  102  supports acknowledgement of a successful delivery of data to the WCD  101 . This action corresponds to actions or steps  306 ,  402  discussed above. 
     Action  620 . Receiving a data message sent by the NE, which data message comprises user data intended for the WCD. This action corresponds to actions or steps  207 ,  311 ,  409  discussed above. 
     Action  630 . Sending a control plane message comprising the user data to the RAN node  102  for further delivery to the WCD  101 . This action corresponds to actions or steps  313 ,  411  above. 
     Action  640 . Here a report may be received from the RAN node  102  indicating that the user data was not successfully delivered to the WCD  101 . This action corresponds to actions or steps  313 ,  411  discussed above. 
     Alternatively, when the RAN node  102  supports acknowledgement of data delivery to the WCD  101 , then an acknowledgement may be received from the RAN node  102  indicating that the user data sent in action  630  was successfully delivered to the WCD  101 . This action corresponds to actions or steps  313 ,  411  discussed above. 
     Alternatively, when the RAN node  102  does not support said acknowledgement of data delivery to the WCD  101 , then no acknowledgement will be received from the RAN node  102  indicating that the user data sent in action  630  was successfully delivered to the WCD  101 . This has been illustrated by a dashed line in  FIG.  5   . This action corresponds to actions or steps  313 ,  411  discussed above. 
     Action  650 . Sending a response to the NE. This action corresponds to actions or steps  209  discussed above. 
     The response either:
         a) indicates an unsuccessful delivery of the user data to the WCD  101  when a report is received from the RAN node indicating that the user data was not successfully delivered to the WCD  101 ; and otherwise   b) indicating an acknowledged delivery of the user data to the WCD  101  when the RAN node  102  supports said acknowledgement and an acknowledgement is received from the RAN node  102  indicating that the user data was successfully delivered to the WCD  101 ; and   c) indicating an unacknowledged delivery of user data to the WCD  101  when the RAN node  102  does not support said acknowledgement.       

     Action  660 . Sending, the RAN node  102  supports acknowledgement of data delivery to the WCD  101 , a reliability message intended for the WCD  101  indicating that control plane communication of user data between the RAN node  102  and the mobility management node  105  is reliable. This actions is optional, which has been indicated by a dashed line in  FIG.  5     
       FIG.  6    shows a flowchart illustrating a method according to an embodiment of the present solution. 
     The method is preferably performed in a MME  105  for delivering data to a WCD  101  that is served by the MME  105 . While performing the method it is preferred that the operates in a communication network  10   b ,  10   c  comprising a Network Entity (NE), e.g. a SGW  108 , a PGW  110 , a SCEF  210  or an IWK-SCEF  240 , and a RAN node  102  serving the WCD  101 . 
     The method comprises the following steps, which may be performed in any suitable order: 
     Step  710 . Obtaining capability information indicating whether the RAN node  102  supports acknowledgement of a successful delivery of data to the WCD  101 . This action corresponds to actions or steps  306 ,  402 ,  610  discussed above. 
     Step  720 . Receiving a data message sent by the NE, which data message comprises user data intended for the WCD. This action corresponds to actions or steps  207 ,  311 ,  409 ,  620  discussed above. 
     Step  730 . Sending a control plane message comprising the user data to the RAN node  102  for further delivery to the WCD  101 . This action corresponds to actions or steps  313 ,  411 ,  630  discussed above. 
     Step  740 . Sending a response to the NE. This action corresponds to actions or steps  209 ,  650  discussed above. 
     The response either:
         d) indicates an unsuccessful delivery of the user data to the WCD  101  when a report is received from the RAN node indicating that the user data was not successfully delivered to the WCD  101 ; and otherwise   e) indicating an acknowledged delivery of the user data to the WCD  101  when the RAN node  102  supports said acknowledgement and an acknowledgement is received from the RAN node  102  indicating that the user data was successfully delivered to the WCD  101 ; and   f) indicating an unacknowledged delivery of user data to the WCD  101  when the RAN node  102  does not support said acknowledgement.       

       FIG.  7   a    is a schematic block diagram of a mobility management node according to some embodiments of the present disclosure. Here, the mobility management node may be a core network node such as, for example, the MME  105  or an SGSN  118 . As illustrated, the n mobility management node includes one or more processors  38  (e.g., Central Processing Units (CPUs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), and/or the like), memory  40 , and a network interface  42 . In some embodiments, the functionality of the mobility management node (e.g., the functionality of the MME  105 ) described above may be fully or partially implemented in software that is, e.g., stored in the memory  40  and executed by the processor(s)  38 . 
     In some embodiments, a computer program including instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of a network node according to any of the embodiments described herein is provided. In some embodiments, a carrier containing the aforementioned computer program product is provided. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium such as memory). 
       FIG.  7   b    is a schematic block diagram of the mobility management node  105  according to some other embodiments of the present disclosure. The mobility management node includes one or more modules  44 , each of which is implemented in software. The module(s)  44  provide the functionality of the mobility management node described herein. As an example, if the mobility management node  105  is the MME  105 , then the module(s)  44  may include: an obtaining module operable to obtain capability information indicating whether the RAN node  102  supports acknowledgement of a successful delivery of data to the WCD  101 ; a receiving module operable to receive a data message sent by the NE ( 108 ,  110 ,  210 ,  240 ) comprising user data intended for the WCD  101 ; and a sending module operable to send a control plane message comprising the user data to the RAN node  102  for further delivery to the WCD  101 , and operable to send a response to the NE ( 108 ,  110 ,  210 ,  240 ) indicating the status of the user data delivery to the WCD  101 , as described above. 
     Some embodiments described above may be summarised in the following manner: 
     A first embodiment is directed to a method in a mobility management node for delivering data to a WCD served by the mobility management node, operating in a communication network comprising a NE and a RAN node serving the WCD. 
     The method comprises:
         obtaining capability information indicating whether the RAN node supports acknowledgement of a successful delivery of data to the WCD,   receiving a data message sent by the NE comprising user data intended for the WCD,   sending a control plane message comprising the user data to the RAN node for further delivery to the WCD,   sending a response to the NE:
           a) indicating an unsuccessful delivery of the user data to the WCD when a report is received from the RAN node indicating that the user data was not successfully delivered to the WCD; and otherwise;   b) indicating an acknowledged delivery of the user data to the WCD when the RAN node supports said acknowledgement and an acknowledgement is received from the RAN node indicating that the user data was successfully delivered to the WCD;   c) indicating an unacknowledged delivery of user data to the WCD when the RAN node does not support said acknowledgement.   
               

     The method may comprise:
         receiving a report from the RAN node indicating that the user data was not successfully delivered to the WCD; and   before sending the response to the NE, resending the control plane message comprising the user data to the RAN node for further delivery to the WCD.       

     The method wherein the obtaining may comprise: receiving an initial message from the RAN node indicating whether the RAN node supports acknowledgement of a successful delivery of data to the WCD. 
     The initial message may correspond to an attach message or Tracking Area Update, TAU, message. 
     The control plane message may comprise information requesting an acknowledgment from the RAN node when the RAN node supports said acknowledgement. 
     The control plane message may be a Non-Access Stratum, NAS, message. 
     The control plane message may be a S1 Application Protocol, S1AP message. For more information about S1AP messages, see e.g. the specification 3GPP TS 36.413. 
     The control plane message may be a NIDD, Submit Request message. 
     The user data may be non-IP data. 
     The method may comprise: sending, when the RAN node supports said acknowledgement, a reliability message intended for the WCD indicating that control plane communication of user data between the RAN node and the mobility management node is reliable. 
     The reliability message may correspond to an attach message or a TAU message. 
     The reliability message may be a Non-Access Stratum, NAS, message. 
     The NE may be a S-GW or a P-GW or a SCEF or an IWK-SCEF. 
     Some other embodiments described above may be summarised in the following manner: 
     A second embodiment is directed to a mobility management node for delivering data to a WCD, where the mobility management node is configured to operatively serve the WCD in a communication network comprising a NE and a RAN node serving the WCD. 
     The mobility management node comprises: a network interface; one or more processors; and memory storing instructions executable by the one or more processors whereby the mobility management node is operable to:
         obtain capability information indicating whether the RAN node supports acknowledgement of a successful delivery of data to the WCD,   receive a data message sent by the NE comprising user data intended for the WCD,   send a control plane message comprising the user data to the RAN node for further delivery to the WCD,   send a response to the NE:
           a) indicating an unsuccessful delivery of the user data to the WCD when a report is received from the RAN node indicating that the user data was not successfully delivered to the WCD; and otherwise;   b) indicating an acknowledged delivery of the user data to the WCD when the RAN node supports said acknowledgement and an acknowledgement is received from the RAN node indicating that the user data was successfully delivered to the WCD;   c) indicating an unacknowledged delivery of user data to the WCD when the RAN node does not support said acknowledgement.   
               

     The mobility management node may be operable to:
         receive a report from the RAN node indicating that the user data was not successfully delivered to the WCD; and   before sending the response to the NE, resend the control plane message comprising the user data to the RAN node for further delivery to the WCD.       

     The mobility management node may be operable obtain capability information by: receive an initial message from the RAN node indicating whether the RAN node supports acknowledgement of a successful delivery of data to the WCD. 
     The initial message may correspond to an attach message or Tracking Area Update, TAU, message. 
     The control plane message may comprise information requesting an acknowledgment from the RAN node when the RAN node supports said acknowledgement. 
     The control plane message may be a NAS message. 
     The control plane message may be a S1AP message. 
     The control plane message may be a NIDD Submit Request message. 
     The user data may be non-IP data. 
     The mobility management node may be operable to send, when the RAN node supports said acknowledgement, a reliability message intended for the WCD indicating that control plane communication of user data between the RAN node and the mobility management node is reliable. 
     The reliability message may correspond to an attach message or a TAU message. 
     The reliability message may be a NAS message. 
     The NE may be a S-GW or P-GW or a SCEF or an IWK-SCEF. 
     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.