Patent Publication Number: US-2023164881-A1

Title: Method for user plane connection activation or deactivation per session

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/205,848 filed on Mar. 18, 2021, which is a continuation of U.S. patent application Ser. No. 16/321,304 filed on Jan. 28, 2019, which issued as U.S. Pat. No. 11,026,292, which is a National Stage Entry of International Application No. PCT/JP2017/029618 filed on Aug. 18, 2017, which claims priority to European Patent Application No. 16185042.5 filed on Aug. 19, 2016, the entire disclosures of which ae incorporated herein their entirety by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a communication system. The disclosure has particular but not exclusive relevance to wireless communication systems and devices thereof operating according to the 3rd Generation Partnership Project (3GPP) standards or equivalents or derivatives thereof. The disclosure has particular although not exclusive relevance to the so-called ‘Next Generation’ systems. 
     BACKGROUND ART 
     The disclosure includes a method for independent activation or deactivation of user plane connection per Protocol Data Unit (PDU) session or network slice, where the session contexts in a User Equipment (UE) and in a network (e.g. a Session Management Function (SMF), and a User Plane Function (UPF)) are already established. The solution proposes a (Session Management (SM)) state machine for each established PDU session, where the state machine is maintained either in the SMF or in a Mobility Management Function (MMF) network function. The SM state machines run independently of a Mobility Management (MM) state machine. 
     General 
     The following terminologies are used within this document and can be applied to any generation of mobile networks like 2G (Global System of Mobile communications (GSM)), 3G (Universal Mobile Telecommunication System (UMTS)), 4G (Long Term Evolution (LTE)/Evolved Packet Core (EPC)), 5G (New Radio (NR)/NextGen) or any other. For example, if the “UE” or a “serving node” is mentioned in the below description, it can be any generation of the UE or the serving node. 
     The terms ‘serving node’, ‘Mobility Management Entity (MME)/Serving General Packet Radio Service (GPRS) Support Node (SGSN)’, ‘Mobile Switching Centre (MSC)/SGSN/MME’, or Cellular Internet of Things (CIoT) Serving Gateway Node (C-SGN) is generally used through the various embodiments of this document to describe a functional entity like the MSC, the SGSN, the MME, the C-SGN, or other possible control plane functional entities in the mobile network which terminate a control plane signalling (known as a Non Access Stratum (NAS) signalling) between a core network and a terminal. The serving node (MME/SGSN) can be also a functional entity from future generation networks which is responsible for mobility and session management. 
     The term Home Subscriber Server (HSS)/Home Location Register (HLR) means a repository where the UE&#39;s subscription data is stored and can be either the HSS or the HLR or a combined entity. Instead of the HSS also the term Next Generation User Data Management (UDM), Subscriber Database Management (SDM) or Authentication Authorization Accounting (AAA) could be used synonymously. 
     Functional entities or a network function used in this document as separate entities could be also collocated together or even finer separated in particular deployments or as described in the architecture figures. 
     The terms ‘terminal’, ‘device’, ‘user terminal’, ‘User Equipment (UE)’, or ‘Mobile Terminal (MT)’ are used in an inter-exchangeable manner where all of the terms express similarly an equipment used to send/receive data and signalling from the network, a mobile network, or a radio access network. 
     The term “session” is used in the same meaning as a “PDU session”, a “Packet Data Network (PDN) connection”, an “Access Point Name (APN) connection”, or a “connection for a particular network slice”. The existing sessions are those sessions for which already UE context exists (is established) in the core network control plane and/or user plane and the UE itself. The “existing sessions” has the same meaning as an “established PDU session” or an “established PDN connection”. Each session can be identified with a “session ID”, which can be similar to an “Evolved Packet System (EPS) bearer ID”, the “APN”, a “slice ID”, a “slice instance ID”, a “service ID” or any other temporary or a permanent identifier of the PDN connection, the PDU session or a service used by the UE. 
     The term “connection” is mostly used for user plane connection where a kind of “path” is established to send uplink (UL) or downlink (DL) data between the UE and a user plane Gateway (GW) terminating the PDU session. Depending on the context, a connection can be either the whole user plane path for the PDU session; or only a connection over a given interface, e.g. connection over a radio interface, or connection over NG3 interface (between the UPF in a next generation core network (NG CN) and a (Radio) Access Network ((R)AN). 
     The following terminology for the procedures is used:
         Session establishment: e.g. PDU session establishment where SM context exists (is established) in the UE and in the NG CN control plane and/or user plane.   Session release: deletion of the PDU session, which means the SM context is deleted (released) in the UE and in the NG CN control plane and/or user plane.   Session/connection activation: activating an UP connection path for session, for which the SM context exist in the UE and in the NG CN.   Session/connection deactivation: deactivating the UP connection path without deleting the SM context in the UE and in the NG CN. With other words just releasing the UP connection.       

     The mobility states of the UE are called De-Registered, Registered-Standby (“Standby” for simplicity) and Registered-Ready (“Ready” for simplicity). These states are also called MM states. Please note that there is a difference between the mobility states (the MM states) and session states (SM states). 
     The telecommunication industry started to work on new generation of network referred as 5th generation (5G) networks. Activities in multiple research and standardization organizations were initiated to develop the 5G network which shall offer services to multiple vertical service providers and serving high variety of terminals. Especially 3GPP in activities were initiated in the RAN area under the term “New Radio” (NR) and in the core network (CN) under the term “NextGen” (NG). Please note that those terms will most probably change before the 5G system is introduced to the market. Therefore terms like NG CN (or NG AN) as used in this document have the meaning of any 5G CN or AN technology. 
     3GPP studies the NG system architecture and corresponding issues and solutions are captured in 3GPP TR 23.799 [see, NPL 1].  FIG.  1    describes the NG architecture for simultaneous access to multiple PDN connections (called PDU sessions in the NG study), as agreed in [see, NPL 1] by the time of writing. The upper part of  FIG.  1    shows an example for NG control plane (NG CP) including a subscriber database management (SDM)  22 , a Policy Control function (PCF)  24  and Core Control functions (CCFs)  26 . The NG CCF  26  includes among others mobility management function (MMF) and session management function (SMF). The user plane (UP) function(s) are shows as a Core User plane function (NG UPF)  28 , as there could be one or multiple UPFs per PDU session configured. Further information about the description of the interfaces and the network functions can be found in TR 23.799 clause 7.3 [see, NPL 1]. 
     One main feature of a 5G system is called network slicing. The 5G use cases demand very diverse and sometimes extreme requirements. The current architecture utilizes a relatively monolithic network and transport framework. Thus, it is anticipated that the current architecture is not flexible and scalable enough to efficiently support a wider range of business needs. To meet such needs, the 5G NG system can be “sliced” in multiple network instances which are referred as network slice instances (NSI). The network slices can be referred as logically separated networks where the resources (processing, storage and networking resources) for different network slices are isolated. A network operator uses a Network Slice Template/Blueprint to create a NSI. The NSI provides the network characteristics which are required by a Service Instance. One example of network architecture allowing a UE to connect to multiple NSIs simultaneously is shown in  FIG.  2   , as described in [see, NPL 1]. 
       FIG.  2    shows a first network slice type/category (e.g. for IoT services) and a second slice type (e.g. for broadband services). The second network slice type can have multiple NSIs for particular 3rd party customers. This figure shows that the (R)AN is shared and network slicing is applied in the NG CN. However, in future also network slicing the (R)AN is possible where the RAN resources are sliced/isolated, either in baseband processing or in frequency spectrum or both. 
     [NPL 1] also describes the Common Control Network Functions (CCNF)  32  and Slice-specific Control Plane Network Functions (SCNF), as shown in detail in  FIG.  3   . The CCNF  32  can include fundamental control plane network functions to support basic functions operation common among the NSIs, for example:
         1. Subscriber Authenticator,   2. Mobility Management,   3. Network Slice Instance Selector (NSI Selector),   4. NAS Routing Function, etc.       

     In general, the NG system design should enable the transmission of any kind of data. It is assumed that the NG system supports the following PDU session types:
         IP type (e.g. IPv4 or IPv6 or both), or   non-IP session (any unstructured data) or   Ethernet type.       

     One further solution described in 23.799 in clause 6.4.3 is shown in  FIG.  4   . The UE  34  may establish multiple PDU Sessions to the same data network in order to satisfy different connectivity requirements of different applications (e.g. session continuity) that require connectivity to the same data network. In this solution, the MM and SM functions are separated. With this, one main concept is that multiple SM contexts can be available per MM context. Also, different session continuity types per PDU session are possible. 
     CITATION LIST 
     Non Patent Literature 
     [NPL 1] 
     
         
         3GPP TR 23.799 v0.6.0, 2016-07, “Study on Architecture for Next Generation System” 
       
    
     [NPL 2] 
     
         
         3GPP TS 23.401, v14.0.0, 2016-06, “General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access” 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     The scenario considered in this document is that a UE is attached to the network and can be associated with multiple UP-GWs (UPFs). The different UPFs can be part of the (a) same PDU session, (b) part of different PDU sessions, or (3) part of different network slice instances (NSIs). With other words, multiple NG3 connections (e.g. tunnels over NG3 interface) between the (R)AN and the UP-GWs can be available. If the UE has established multiple PDU sessions, then multiple Session Management Function (SMF) instances may exist per UE. 
     One assumption in this document is that a UE&#39;s “session” (or also called “PDN connection” or “PDU session” to a particular data network) can be in Idle (inactive) state or Active (connected) state. In this sense the terms “Idle session” or “Active session” are used. If a session is in “IDLE” state, then there is no NG3 connection/tunnel established between the UPF and (R)AN. If a session is in “ACTIVE” state, then there is NG3 connection/tunnel established between the UPF and (R)AN. It is further assumed that for an established UE&#39;s session a Session Management Function (SMF) is instantiated/configured in the control plane and corresponding one or more UPFs are instantiated/configured in the user plane. Further details about the IDLE and ACTIVE session state of the Control Plane Function (CPF) and the UPF can be found below. 
     Assuming that between the AN and the multiple UPFs there will be NG3 tunnels setup for transmitting data packets, the problem occurs of establishment, modification and release of multiple NG3 tunnels each time when the UE transfers from Standby to Ready mobility state. 
     Compared with EPC where a single Serving GW is configured per UE, and thus a single S1-U tunnel is established and released during Standby-&gt;Ready transition, in NG having multiple UPFs, multiple tunnels over NG3 interface are established/released. Therefore the problem is that the signalling for tunnel establishment is increased when a single UPF (or PDU session) is in use, but multiple NG3 tunnels are established/released. 
     Further, if all existing sessions are in IDLE state and downlink data arrives for a particular session, there should be a way to synchronize SM state between the UE and the NG system. Thus, for a MT call, it is currently not possible for the UE to activate only a single Application which is associated to a session that triggers the MT call. 
     In addition, it is possible that a mobility management mechanism maintains MM state always in Ready state in the NG core network (CN) as long as the UE is attached/registered to the NG system. With this, the NG CN has only Registered and Deregistered mobility states of the UE. This MM mechanism is advantageous for paging of mainly stationary devices or low-mobility devices for which the paging area is relatively narrow. With this architecture, the NG CN knows the location of the UE and the NG3 tunnels are always active. This means that the Session state is always “Active”. This document also targets to solve a potential problem in case such devices have another application which is configured to access with a different session at the same time. In the case, the NG CN performs session management while the (R)AN performs mobility management. As a result, all NG3 connections/tunnels for all sessions are always established, i.e. all sessions are always in Active session state. When the UE moves and changes (R)AN node, all tunnels needs to be updated, meaning that the CCNF and the SMFs needs to update all UPFs with the new tunnel endpoint information. This would result in increased signalling. 
     This disclosure seeks to solve or at least alleviate the above problems by reducing the required signalling for NG3 tunnel establishment allowing the activation of a particular session out of multiple existing sessions. 
     Solution to Problem 
     An example aspect of the present disclosure is a User Equipment (UE), including: a transmitter configured to transmit at least one Protocol Data Unit (PDU) session identifier (ID), each of which indicates a PDU session that the UE needs to use in a Non Access Stratum (NAS) Service Request message to a Mobility Management Function (MMF) via an access network (AN) node when the UE has user data to send. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    describes the NG architecture for access to multiple PDN connections (called PDU sessions in the NG study); 
         FIG.  2    shows one example of network architecture allowing a UE to connect to multiple NSIs; 
         FIG.  3    describes the CCNF and SCNF; 
         FIG.  4    shows one further solution described in 23.799 in clause 6.4.3; 
         FIG.  5    shows an example architecture showing multiple network slices or PDU sessions with corresponding multiple CPFs and UPFs; 
         FIG.  6    shows multiple session state machines (one per established session) and a single mobility state machine; 
         FIG.  7    shows the existence of 2 sessions already established for a given UE; 
         FIG.  8    shows that a paging procedure where the session ID for activation of a single PDU/PDN session is indicated to the UE during the Radio Resource Control (RRC) connection establishment request; 
         FIG.  9    shows a possible solution 2.1 for the activation of additional session when another session is already in Active state; 
         FIG.  10    shows another alternative solution 2.2 where NAS SM signalling between the SMF2 and UE is used for the activation of the session 2 towards UPF2; 
         FIG.  11    shows that the UE has two session contexts for session #1 and session #2; 
         FIG.  12    describes a case where two sessions are Active and one of them becomes Idle due to no user plane activity within predefined UE inactivity period determined by the (R)AN node; 
         FIG.  13    describes an alternative solution where the session deactivation procedure is initiated by the UPF of the corresponding session; 
         FIG.  14    is a block diagram illustrating the main components of the UE shown in  FIG.  1   ; and 
         FIG.  15    is a block diagram illustrating the main components of the MMF/SMF node shown in  FIG.  1   . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In order to solve the above described problem, different solutions are described in various example embodiments herewith. 
     Please note that the terms “Idle” session or “Active” session are used for the SM states, whereas Standby and Ready states are used for the UE&#39;s mobility states. Also the transition from Idle session state to Active session state can be called “session activation” whereas the transition from Active session state to Idle session state can be called “session deactivation”. This is shown in  FIG.  6   . 
     The terms “session activation” procedure or “session deactivation” procedure relates to the establishment or release of NG3 connections/tunnels. These terms are different from “session establishment” or “session release” procedures which relates to the establishment of a new session including establishment of SM context in both UE and NG CN or correspondingly deletion of existing session, i.e. deletion of the SM context in the UE and the NG CN. 
     For the purposes of this document the reference architecture from  FIG.  1    for a single established session (network slice or PDU session) is assumed. For multiple established sessions  FIG.  5    is assumed as reference architecture where a UE has established 3 different sessions A, B and C. The different sessions can belong to different network slices or to the same network slice but having multiple PDU sessions. In the control plane there is a box denoting CCNF  32  which are shared among network slices or PDU sessions. These CCNFs can include mobility management Network Function (NF) (called MMF), Authentication/Authorization/Security NF, NAS signaling routing NF and others. As it is shown in  FIG.  5   , each PDU session or network slice can have independent dedicated CPFs. The Dedicated CPFs can include the following exemplary network functionality:
         SMF: it is assumed in this document that this function is responsible for the session management for a specific session (network slice, or PDU sessions).   CPF of a GW (aka GW-C of the UPF), as the Control Plane (CP) of the GW is known as S/PGW-CP function from the control/user plane separation in EPC, called Control and User Plane Separation (CUPS).   PCF: the complete or part of the PCF as described in  FIG.  1   . This means that some parts of the PCF can be a part of the CCNF  32  and other parts can be part of the Dedicated CPF.   Authentication, Authorization and Security functions related to the specific Network slice of PDU session.       

     Please note that the UE  34  is shown in  FIG.  5    by having 3 arrows towards the (R)AN node  30  which represents 3 radio connections corresponding to the 3 sessions/slices A, B and C. However, this is just an example. The UE  34  can have e.g. 3 user plane radio connections (each per session) and just a single control plane radio connection. Alternatively the UE  34  can have 3 user plane radio connections and 3 control plane radio connection (each per session). 
     For simplicity, within this document the term SMF is used to denote all Dedicated CPFs as listed above for a PDU session or network slice. Each SMF has a signaling association with the CCNF  32  per the UE  34 . For each established session, the CCNF (e.g. MMF)  32  and the SMF know each other and can send signaling at any time independent of the UE&#39;s mobility or session state. Further, the CCNF  32  and the SMF have exchanged a UE ID or a subscriber ID (temporary or permanent) and use this ID in each signaling message exchange in order to point to the corresponding UE&#39;s context in the CCNF  32  or in the SMF. 
     In addition, a UPF (3GPP specified GW functionality e.g. to enforce Quality of Service (QoS) or traffic policies) per network slice or PDU session is configured/instantiated. Each of the (NG3) connections A, B or C can be managed independent, i.e. can be established, modified or released independent from the other connections. Please note that there can be one or multiple UPFs. For example a UPF closer to the Edge can be used as mobility anchor and a UPF deeper in the CN can be used as IP anchor (hosting the UE&#39;s IP address). For simplicity, in this document a single UPF is used. However, the SMF is able to configure multiple UPFs if multiple UPFs are needed and instantiated/configured for a given session. 
     As exemplary shown in  FIG.  5   , it is assumed that there are 3 connections (e.g. tunnels over NG3) between (R)AN and UPFs: a single connection for slice/session A  36 , slice/session B  38  and slice/session C  40 . If tunneling over NG3 is used per UE  34  between (R)AN and UPFs A/B/C  36 / 38 / 40 , then there will be 3 tunnels activated/modified/released each time when the UE  34  transfers among Standby&lt;-&gt;Ready mobility state. Even worse, if the tunneling over NG3 is per IP flow or per bearer then even more tunnels need to be activated/modified/released for each Standby and Ready mobility state transition. 
       FIG.  5    shows for session C that the dedicated CPFs can include the SMF and the PCF. It is noted that the existence of PCF in the dedicated CPF may be based on the particular use case, e.g. for some network slices the PCF can be instantiated/configured per slice, whereas for other network slices the PCF can be instantiated/configured as common CPNF. 
     In this document it is proposed that in case of multiple existing/established PDU sessions (or connectivity to multiple network-slices simultaneously) the system architecture allows to activate/deactivate a single session, which means 1) activating the session state in the corresponding CPF, e.g. SMF; and 2) to activate a single UP session by establishing a corresponding connection/tunnel between the (R)AN node  30  and the UPF. Other UP sessions (for other PDU sessions or other network slices) are not activated (i.e. in Idle state) if there is no data sent in uplink or downlink (UL or DL). 
     As depicted in  FIG.  6   , there are independent session state machines per existing session (i.e. per network slice, or PDU session). This is shown as Session A state machine and Session B state machine. This session state machines are applicable both in the UE  34  and in the NG CN. During the establishment of a UE session, a SMF entity is selected and configured by the CCNF (MMF). The SMF entity starts maintaining UE&#39;s context related to this session. For example, the UE&#39;s session context in the SMF can contain among others the following parameters:
         UE temporary or permanent ID, corresponding session ID;   session type (e.g. IPv4/Ipv6, non-IP, Ethernet);   session continuity and/or service continuity mode(s) (e.g. Session and Service Continuity (SSC) mode 1/2/3);   QoS parameters (e.g. non-Guaranteed Bit Rate (non-GBR), GBR parameters, maximum session bit rate);   policy parameters;   needed session subscription parameters;   session state machine, etc.       

     With other words, independent of the state (Active or Idle) of the session state machine in the SMF, the SMF maintains UE&#39;s session context like the parameters listed above. 
     In addition, in case that the UE  34  is a permanent Ready mobility state from NG CN perspective, this may result in permanently activated connections/tunnels over NG3 interface and correspondingly resulting in sessions which are in permanent Active session state in the NG CN. Then the session (SM) state machines can be managed either in the (R)AN or in the NG CN. The transition from Idle to Active session state happens for example 1) if data for transmission in the UL or the DL is available or 2) if a scheduled session activation is configured in the SMF. In Active session state the SMF knows the current location of the UE in terms of (R)AN node UP details for data forwarding. Correspondingly the UPF has established connection with the (R)AN node  30  over NG3 interface and policy and QoS parameters has been enforced in the UPF for the given session. If there is no data in the UL or the DL or there is no need to keep the user plane connection for a particular session, the (R)AN node  30  or the UPF can trigger transition to Idle session state. Please note that the UP connection deactivation is different from session release, as in connection deactivation the UE&#39;s context is still kept in the NG CN (e.g. SMF). In Idle session state the UPF does not have an established connection over NG3 interface and the SMF does not know (R)AN node UP details and exact MM mobility state (i.e. Registered Standby or Ready). 
     When the SMF for a given session (e.g. SMF-A) is in Idle state, in CP the SMF doesn&#39;t know the (R)AN node UP details, e.g. IP address, tunnel identifier, transport port ID, or other parameters. The SMF does have UE&#39;s context about this session, for example including QoS parameter, policy parameters (e.g. Charging policies or Application Detection policies), or needed session subscription parameters, etc. In the UP, the UPF does not have connection (e.g. no tunnel established) towards the (R)AN node  30 . 
     On the other hand, if an SM instance in Active state, in CP the SMF (e.g. SMF-A) knows the (R)AN node details like IP address, tunnel identifier, transport port ID, or other parameters. In the UP, the UPF has a connection/tunnel established to the (R)AN node  30 . 
     This document focuses on the procedures for activation and deactivation of sessions (i.e. activation/deactivation of UP connections), which is different from the procedures for establishment of a new session or release of an existing session. For example the establishment of a new session means the establishment of UE&#39;s SM session context in the SMF, the session context in the UE  34  itself and the corresponding NAS SM message exchange between the UE  34  and the SMF. It is assumed that for each established session, the SMF and the MMF  32  maintain a signalling association for exchanging session-related signalling. 
     In another example, the release of an existing session means the deletion of the SM context in the SMF, in the UPF and in the UE. For example if the UE  34  is detached from the network, i.e. the MM state is Deregistered, then the MMF  32  triggers a session release procedure, which is also not in the scope of this this document. 
     This document proposes that the CCNF (e.g. MMF)  32  maintains UE&#39;s context having knowledge about the session (SM) state in the SMF(s). With other words, the MMF  32  knows the session state (Idle or Active) of all configured SMF(s) for the established sessions. In addition to the mobility (MM) context, the MMF  32  maintains also information for all established sessions. For example the MMF  32  needs to know if a session A is activated, i.e. the SMF-A is in Active state, so that the MMF  32  is able to update the SMF with the new (R)AN node details (e.g. IP address, tunnel identifier, transport port ID, or other parameters) each time when (R)AN node changes. On the other hand, if a session A is deactivated, i.e. the SMF-A is in Idle state, then the MMF  32  does not need to update the SMF when (R)AN node changes. In one alternative, the session states as shown in  FIG.  6    can be also maintained in the MMF  32  only, or in both the MMF  32  and the SMF. 
     For this purpose, the signalling exchange between the SMF and the MMF  32  may be based on various alternatives:
         Direct/explicit signalling between the SMF and the MMF  32  (in both directions) is used to exchange information about the current session state. The SMF can inform the MMF  32  about the session&#39;s state each time when the session state changes. If the MMF  32  knows that a particular session is in Active state, the MMF  32  informs the SMF corresponding to this session about (R)AN node changes, other Radio Access Technology (RAT) events (e.g. RAT changes) and other possible mobility events. Further, during Active session state the SMF may inform the MMF  32  about UPF changes, e.g. due to load balancing or other events the UPF for this session can change.   Alternatively, there may be no explicit signalling between the SMF and the MMF  32  needed to inform the session state change, as the MMF  32  may derive the session state based on the NAS signalling between the UE  34  and the SMF.       

     In general, the SMF does not need to maintain current MM state information. For example, if a particular session is in Idle state, the SMF does not need to know whether the UE  34  changes from Ready to Standby mobility state due to transmission of UL or DL data for other sessions. In contrast, if a session is in Active state, the corresponding SMF needs to know about (R)AN node details (UP details like IP address and/or tunnel endpoint IDs), other RAT events (RAT changes) and change from Ready to Standby MM state. The latter event of change from Ready to Standby MM state would result in the SMF to trigger the UPF to deactivate the NG3 connection/tunnel. 
     Assuming that the session states (Idle, Active) are maintained in the UE  34  and the SMF, then direct signalling exchange between the UE  34  and the SMF is advantageous. Such signalling exchange is based on NAS SM signalling enhanced with additional parameters like session ID or indication for UP connection activation or deactivation. 
     Several procedures are described below to cover the activation and deactivation of a session considering the various trigger sources. 
     Solution 1: Session Activation when No Another Active Session Exists (e.g. UE is in Standby MM State) 
     The solution described herewith is related to the scenario where multiple sessions have been established (e.g. towards different network slices or different PDU sessions) and the UE  34  is in Standby mobility state. This means that all session are in Idle session state. If a downlink data arrives for a given session, then the solution proposed herewith allows activating only this particular session or in addition another session(s) whereas other existing sessions continue to be Idle state. 
     Solution 1.1: Indication of Session ID to UE During the Paging Procedure 
     In particular,  FIG.  7    shows the existence of 2 sessions already established for a given UE  34 . This means that the UE  34  has IP configuration for each session and can send and receive data over each session. As the UE  34  is in Standby mobility state (shown as the CCNF  32  in Standby state), the corresponding session #1 state (represented by the SMF1  42  in the CP) and session #2 state (represented by the SMF2 44 in the CP) are in Idle too. In the UP, the UPF1  46  and the UPF2  48  have a UE-related context (e.g. to enforce policies for the configured UE&#39;s IP addresses and association with the corresponding CPF like the SMF), but there is no connection/tunnel to any (R)AN node  30  to transmit packets. 
     The steps from  FIG.  7    are described in detail as follows:
         Step (1) Downlink data arrives at the UPF2  48 . As the session #2 is in Idle state, the UPF2  48  does not have an established connection/tunnel towards any (R)AN node  30 . It is assumed that there is a NG4 session established for the given the UE  34  between the CPF and the UPF. Thus, the UPF2  48  requests the CPF corresponding to this session (e.g. the SMF2  44 ) to initiate session activation.   Step (2) The UPF2  48  initiates a procedure for activating the user plane connection (e.g. NG3 tunnel) towards the (R)AN. The UPF2  48  sends an Activate session request to the SMF2  44 . This message can be also called a Create session request, a NG3/UP session request, or any other similar to corresponding Sx interface related message specified in TS 23.214. The Activate session request can include one or several of the following informational elements: a UE temporary or a permanent identifier, a session identifier, a DL packet buffering indication, and other parameters.   Step (3) The SMF2  44  receives the request from the UPF2  48  and validates the message and determines the corresponding UE&#39;s context and session(s) which needs to be activated. The SMF2  44  sends an Activate session request towards the CCNF (e.g. MMF)  32 . Similar to step (2), this message can be called differently e.g. the Create session request (or the NG3/UP session request) as long as the message serves the purpose of activating/establishing a UP connection between the (R)AN node  30  and the UPF. This message can also be called a Session activation request or any other expressing the activation of an existing PDN (PDU/bearer) context. The request from the SMF2  44  can contain UE ID(s), a session ID, a UPF ID (needed for NG3 tunnel establishment, e.g. an IP address, a tunnelling endpoint ID and/or a transport layer port ID), required QoS indication, optionally security keys and other parameters. Depending on the power saving mode, if the Activate session request may contain a user packet to be buffered. The SMF2  44  determines whether another UPF served by the same SMF2  44  has already an active session. If this is not the case, the SMF2  44  requests the associated CCNF (e.g. MMF)  32  to perform the session activation procedure toward the (R)AN, if needed.   The security keys can be used in case that there is different security required for the particular UP session and the keys are stored in the SMF.   Step (4) The CCNF (e.g. MMF)  32  determines whether the UE  34  is in Standby or Ready mobility state. In this example, because the UE  34  is Standby state, e.g. not know (R)AN location, the CCNF  32  initiates a paging procedure.   Step (5) The CCNF  32  sends a paging request towards the possible (R)AN nodes  30  where the UE  34  camps. In this paging message, the CCNF  32  includes single or multiple session ID(s). The session ID(s) can be any of an APN, a slice ID, a slice instance ID or a service ID. The CCNF  32  includes multiple session ID(s) based on subscriber data in the CCNF  32  that has been obtained from the HSS. Additional session ID(s) may be related to the original session ID that corresponds to the SMF2  44  in this flow or totally independent from the original session ID.   Step (6) The (R)AN node  30  performs the paging procedure over the radio interface including the received session ID(s) in step (5).   Step (7) After the UE  34  receives a paging message, the UE  34  performs radio connection establishment with the (R)AN node  30  and sends a NAS Service Request message to the CCNF  32  over NG1. Both the radio connection establishment message and the NAS Service Request message may include single or multiple session ID(s). The UE radio layer(s) indicates via internal Application Programing Interfaces (APIs) to the service, application or existing PDN/APN/PDU/bearer context that corresponds to this explicit session to be activated. Such internal cross-layer exchange in the UE  34  can be performed either at step (7) or after step (9).   The UE  34  can include the session ID(s) in the NAS Service request message in order to indicate to the MMF (as part of the CCNF  32 ) that the session ID(s) has been successfully processed in the UE  34 . Please note that the CCNF  32  may have a front-end functionality for NAS signalling, so that the NAS Service Request message after reaching the front-end can be internally forwarded to the correct MMF for further processing. If the session ID(s) is/are missing in the Service request message, this may be an implicit indication that the UE  34  couldn&#39;t process the session ID(s) from the paging message.   Step (8) The CCNF (e.g. MMF)  32  determines (correlates) that the NAS Service Request message is as result to the Paging procedure. The CCNF  32  determines that only a session requested by the SMF2  44  needs to be activated. The CCNF  32  generates the corresponding UE context setup request message and sends it to the (R)AN node  30 . The UE context setup request message contains, in addition to other UE parameters like required QoS indication and security parameters, also a session ID parameter. When multiple sessions need to be activated, this step (8) can be either executed session by session or one procedure activates all requested sessions at once.   Step (9) The (R)AN node  30  performs radio connection reconfiguration shown as Radio Resource Control (RRC) connection reconfiguration in the figure. During this procedure, the (R)AN node  30  indicates the session ID parameter to the UE  34 .   Based on the received session ID, the UE  34  can activate the corresponding service, application or existing PDN/APN/PDU/bearer context. The UE  34  does not activate all existing PDN/APN/PDU/bearer contexts. The UE  34  updates SM state in the UE  34  that corresponds to the session ID(s) received by step (6).   Step (10) The (R)AN node  30  responds to the request in step (8) about the establishment of the radio connection. The (R)AN node  30  for example sends a UE context setup response message. The response can be positive or negative. The UE context setup response message includes the UP identifier of the (R)AN node  30  (IP address and tunnelling endpoint ID and/or transport layer port ID) shown as (R)AN UPF ID in the figure. In case the CCNF  32  decided to add additional session ID(s) in step (5), then the CCNF  32  initiates to activate session(s) towards associated UPF to each additional sessions. The CCNF  32  informs all associated UPF(s) via associated SMF(s) of the UP identifier of the (R)AN node  30  (an IP address, a tunnelling endpoint ID and/or a transport layer port ID) shown as (R)AN UPF ID in the figure.   Step (11) The CCNF  32  responds to the SMF2  44  corresponding to the request in step (3). For example the CCNF  32  sends an Activate session response message which can contain an indication about the successful or unsuccessful activation of the session corresponding to the session ID. This message includes in addition to other UE parameters like required a QoS indication (or modified QoS parameters) and security parameters, also a session ID parameter.   The SMF2  44  derives the policy and QoS parameters to be enforced in the UPF2  48 .   The SMF2  44  transfers from Idle session state to Active session state.   Step (12) The SMF2  44  responds to the step (2) procedure. The SMF2  44  establishes or modifies the needed UE context in the UPF2  48  by sending an Activate session response message. This message can include parameters for policy enforcement (like a traffic QoS indication, a traffic gating behaviour, a session maximum bitrate), the (R)AN UPF ID (including the (R)AN node IP address, the tunnelling endpoint ID and/or the transport layer port ID), charging related configuration (e.g. for Charging Data Record (CDR) generation and/or online/offline charging session establishment), optionally security parameters, among others.   Please note that the security parameters are needed in case of security termination at the CN UPF node like the UPF2  48 . In case where the security is terminated at the (R)AN node  30 , security parameters are not needed at this step.   Step (13) to step (15): If the UPF information for NG3 connection/tunnel establishment hasn&#39;t been exchanged during step (3), then the UPF2  48  may optionally perform the Update session procedure towards the SMF2  44  in order to update the UP connection information called a UPF ID (e.g. an IP address, a tunnelling endpoint ID and/or a transport layer port ID). Alternatively the SMF2  44  may have such a NG3-related UP information itself, so that SMF2  44  can initiate the Update session procedure (by sending a session update request message including the UPF ID) towards the CCNF (e.g. MMF)  32 . Finally the CCNF (e.g. MMF)  32  updates the (R)AN node  30  with the UPF ID.       

     Solution 1.2: Indication of Session ID to UE During the Service Request or Corresponding RRC Establishment Procedure 
       FIG.  8    shows an alternative solution where the paging procedure is enhanced to include the session ID parameter in the paging request message. 
       FIG.  8    shows that a paging procedure where the Paging message does not include a session ID, but instead the session ID for activation of a single PDU/PDN session is indicated to the UE  34  during the RRC connection establishment procedure. Only steps (5)-(9) are described in details below, as the rest of the steps are similar to  FIG.  7   .
         Step (5) The CCNF  32  sends a paging request towards the possible (R)AN nodes  30  where the UE  34  camps. The paging request message does not include a session ID parameter to indicate to the UE  34  which session should be activated.   Step (6) The (R)AN node  30  performs paging over the radio interface. This message does not include the session ID as per step (5).   Step (7) After the UE  34  receives a paging message, the UE  34  performs radio connection establishment with the (R)AN node  30  and sends a NAS Service Request message to the CCNF  32  over NG1.   Step (8) The CCNF  32  determines (correlates) that the NAS Service Request message is as result to the Paging procedure. The CCNF  32  determines that only a session requested by the SMF2  44  in step (3) needs to be activated. The CCNF (e.g. MMF)  32  changes the UE mobility state from Standby state to Ready state.   The CCNF  32  generates the corresponding UE context setup request message and sends it to the (R)AN node  30 . The UE context setup request message contains, in addition to other UE parameters like QoS and security parameters, also a session ID parameter. When multiple sessions need to be activated, this step (8) can be either executed session by session or one procedure activates all requested sessions at once (e.g. by including a list of all session IDs and corresponding parameters).   Step (9) The (R)AN node  30  performs radio connection reconfiguration shown as RRC connection reconfiguration in the figure. During this procedure, the (R)AN node  30  indicates to the UE the session ID parameter for the session to be activated.   Based on the received session ID, the UE  34  can activate the corresponding service, application or existing PDN/APN/PDU/bearer context. The UE  34  does not activate all existing PDN/APN/PDU/bearer contexts, but only the indicated ones. The UE  34  updates its session/SM state(s) that corresponds to the session ID(s) received by step (9).       

     Please note that steps (13) to (15) in  FIG.  7    can be performed in solution 1.2 as well (although not shown in  FIG.  8   ). 
     The choice between the solution alternatives shown in  FIG.  7    or in  FIG.  8    can be done in the CCNF (e.g. MMF)  32  based on the capabilities of the (R)AN nodes  30  or based on the capabilities of the UE  34 . The UE capabilities regarding supported paging feature(s) can be exchanged during the Attach procedure or other mobility procedure via NAS MM signaling. The (R)AN node capabilities can be exchanged during the interface setup between the (R)AN node  30  and the CCNF  32  (e.g. NG2 interface or S1-MME setup exchange). 
     Solution 2: Activation of Session when Other Active Session(s) Exist (e.g. UE is in MM Ready State) 
     While the scenario solved in solution 1 has the assumption that there are no other session in Active state (e.g. the UE  34  is in Standby mobility state), the assumption for solution 2 is that the UE  34  is in Ready mobility state during DL data is arriving for a session which is in Idle state. In particular, considering  FIG.  9   , it is assumed that the UE  34  has an Active session context for Session #1 terminated at the UPF1  46 . 
     The unique problem is that the UE  34  already has existing PDU session (e.g. SM) contexts in Idle session state and the radio connection to be established shall be linked to this single PDU context out of multiple existing PDU session contexts. It is proposed that such a linkage between a new data radio connection/bearer and existing session context in the UE  34  is performed by using the session ID. 
       FIG.  9    shows a possible solution 2.1 for the activation of an additional session when another session is already in Active state. This solution 2.1 alternative is based on a new UE context modification request procedure. 
     The steps in  FIG.  9    are described as follows:
         Step (1) Similar to step (1) in  FIG.  7   .   Step (2) Similar to step (2) in  FIG.  7   .   Step (3) Similar to step (3) in  FIG.  7   .   Step (4) The CCNF (e.g. MMF)  32  determines that the UE  34  is in Ready mobility state. The CCNF  32  initiates a UE context modification procedure used to update the UE&#39;s context in the (R)AN node  30  with the new session parameters.   Step (5) The CCNF  32  sends for example a UE context modification request message. This message includes, in addition to other UE parameters like QoS and security parameters, also a session ID parameter received during step (3).   Step (6) The (R)AN node  30  performs a radio connection reconfiguration procedure shown as RRC connection reconfiguration in the figure. During this procedure, the (R)AN node  30  indicates the session ID parameter to the UE  34 . The (R)AN node  30  can setup a new data radio bearer or can re-use an existing data radio bearer. The (R)AN node  30  takes this decision based on the QoS parameters related to the new session and the already established data radio bearer.   Based on the received session ID, the UE  34  activates the corresponding service, application or existing PDN/APN/PDU/bearer context. The UE  34  does not activate any additional existing PDN/APN/PDU/bearer contexts. With other words the UE  34  makes a linkage between the new established data radio bearer and the existing PDN/APN/PDU/bearer context based on the session ID parameter.   Step (7) The (R)AN node  30  responds to the CCNF  32 . For example the (R)AN node  30  can send a UE context modification response message referring to the request in step (5).   Step (8) Similar to step (11) in  FIG.  7   . The SMF2  44  transfers from Idle session state to Active session state.   Step (9) Similar to step (12) in  FIG.  7   .       

     Please note that steps (13) to (15) in  FIG.  7    can be performed in solution 2.1 as well (although not shown in  FIG.  9   ). 
       FIG.  10    shows another alternative solution 2.2 where NAS SM signalling between the SMF2  44  and the UE  34  is used for the activation of the session 2 towards the UPF2  48 . 
     The steps in  FIG.  10    are described as follows:
         Step (1) Similar to step (1) in  FIG.  7   .   Step (2) Similar to step (2) in  FIG.  7   .   Step (3) The SMF2  44  generates a NAS SM message (exemplary called a NAS SM Activation request) and sends it toward the UE  34 . This NAS message includes a UE ID, a session ID, cause values (e.g. activation, modify, deleted) and other parameters. For the transmission of the NAS SM Activation request message to the UE  34 , there can be multiple options:
           (A) sent via the MMF  32  by encapsulating the NAS SM Activation request message into an Activate session request message from the SMF2  44  to the MMF  32 ; or   (B) sent in a separate transmission/transport message between the SMF2  44  and the MMF  32 ; or   (C) sent to a NAS front-end functionality within the CCNF  32 , which forwards the message to the UE  34 , i.e. the NAS SM message does not traverse through the MMF  32 . In this latter case (C), the SMF2  44  needs to send another message to the MMF  32 , e.g. an Activate session request message, in order to inform the MMF  32  about the need to activate the session #2 (UP connection).   
           Step (4) The CCNF (e.g. MMF)  32  determines that the UE  34  is in Ready mobility state and the session corresponding to “session ID” parameter needs to be activated. In addition the CCNF  32  needs to route and encapsulate the NAS SM Activation request towards the (R)AN node  30 . The CCNF  32  can initiate a UE context modification procedure used to update the UE&#39;s context in the (R)AN node  30  with the new session parameters.   Step (5) The CCNF  32  sends for example a UE context modification request message. This message includes, in addition to other UE parameters like QoS parameters and security parameters, also a session ID parameter received during step (3). The CCNF  32  transmits the NAS SM Activation request towards the (R)AN node  30  either within the UE context modification request message or in another NG2 message used for transport of NAS signalling, e.g. a NG DL transport message (not shown in  FIG.  10   ).   Step (6) This step may contain 2 independent message transmissions: step (6.a) represents an example of a Radio Resource Control (RRC) DL Direct transfer message to carry the NAS SM Activation request towards the UE  34 . In step (6.b) the (R)AN node  30  performs a radio connection reconfiguration procedure shown as RRC connection reconfiguration similar to step (6) in  FIG.  9   .   Based on the received NAS SM Activation request, the UE  34  activates the corresponding service, application or existing PDN/APN/PDU/bearer context. The UE  34  does not activate any additional existing PDN/APN/PDU/bearer contexts. With other words the UE  34  makes a linkage between the new established data radio bearer and the existing PDN/APN/PDU/bearer context based on the session ID parameter.   Step (7) The (R)AN node  30  responds to the CCNF  32 . For example the (R)AN node  30  can send a UE context modification response message referring to the request in step (5).   Step (8) The UE  34  generates a NAS SM Activation response message and sends it towards the SMF2  44 . This NAS SM message can be transmitted over a RRC UL Direct transfer message.   Step (9) The (R)AN node  30  receives the RRC UL Direct transfer message, extracts the NAS SM Activation response message and forwards it to the CCNF  32 .   Step (10) Similar to step (11) in  FIG.  7   . In addition the CCNF (MMF)  32  transfers the NAS SM Activation response message to the SMF2  44  either as part of the Activate session response message or as part of a new transfer message between the MMF  32  and the SMF2  44 .       

     The SMF2  44  transfers from Idle session state to Active session state.
         Step (11) Similar to step (12) in  FIG.  7   .       

     Please note that steps (13) to (15) in  FIG.  7    can be performed in solution 2.2 as well (although not shown in  FIG.  10   ). 
     Alternatively, in solution 2.2 the SMF2  44  may trigger the session activation by itself, i.e. without trigger from the UPF2  48 . This is possible in case there is a scheduled session activation in the SMF2  44 . Such scheduling can be based on a timer or clock running in the SMF2  44  as part of the processing of the UE&#39;s SM context in the SMF2  44 . The SMF2  44 , based on such a clock for scheduling, can trigger the establishment of UP connection by performing step (3) towards the MMF  32 , and perform a new step to insert UP-related information towards the UPF2  48  (basically step (11) above). 
     In summary, solution 2.1 or solution 2.2 allows to activate an individual session (UP connection) while other UP connection exists. 
     Solution 3: Activation of Session Triggered by UL Data (in the UE) 
     While solution 1 and solution 2 (with their variants) explain the activation of the UP connection triggered by DL data (in the UPF), this solution describes the activation of a single UP connection triggered by UL data (in the UE). 
       FIG.  11    shows that the UE  34  has two session contexts for session #1 and session #2. There are two different cases described. In case (A) the UE  34  is in Standby mobility (MM) state, and thus, all session states are in Idle state. In case (B) the UE  34  is in Ready mobility (MM) state and session #1 is in use, i.e. there are the radio connection and the NG3 connection established. 
     The steps in  FIG.  11    are described in details as follows:
         Step (1) UL data from particular App/service has to be sent by the UE  34 , e.g. over session #2. As session #2 is in Idle state, the UE  34  needs to activate the UP connection in order to transmit the data.   Step (2) If the UE  34  is in MM Standby state, the UE  34  first needs to activate the radio CP connection (RRC) and the NAS connection by initiating a service request procedure. For this purpose the UE  34  first establishes RRC connection.   Step (3) If the UE  34  is in MM Standby state, the UE  34  transmits a NAS Service Request message to activate the NAS signalling connection. The NAS Service Request message can contain among others also a “session ID” parameter. If the NAS signalling connection is terminated at a NAS front-end functionality, the NAS front-end functionality forwards the NAS Service Request message to the MMF  32 .   Step (4) The CCNF (e.g. MMF)  32  verifies and processes the NAS Service Request message. Based on the “session ID” parameter, the MMF  32  determines which session needs to be activated. In this particular example the MMF  32  determines that session #2 needs to be activated. The MMF  32  initiates towards the SMF2  44  a procedure for activation of the UP connection. The MMF  32  sends an Activate session request message (or a similar message as already described in step (3) in  FIG.  7   ). This message contains among other parameters, a UE ID, a session ID, a cause value (e.g. activation, modification, delete), etc.   Step (5) If the UE  34  is in MM Ready state, the UE  34  already has a signalling connection towards the NG CN. The UE  34  can initiate a NAS connection activation procedure. For this purpose, the UE  34  sends a NAS SM session activation request message towards the corresponding SMF, in this particular example SMF2  44 . The NAS SM session activation request message can be either forwarded via a common NAS front-end functionality towards the SMF2  44 , or forwarded via the MMF  32  towards the SMF2  44 . The NAS SM session activation request message contains among others also the parameters of the UE ID, the session ID, and/or the cause value (e.g. activation, modification, delete), etc.   Step (6) The SMF2  44  receives the messages either in step (4) or in step (5) and processes it. The SMF2  44  determines the QoS parameters and other policy parameters to be enforced in the UPF2  48 . The SMF2  44  initiates a session activation procedure towards the UPF2  48 . The SMF2  44  sends an Activate session request message to the UPF2  48  including among others QoS and policy parameters and optionally NG3-specific parameters (e.g. tunnelling information like an IP address to be used by the UPF2  48  and/or a General packet radio service Tunneling Protocol (GTP) Tunnel Endpoint Identifier (TEID)).   Step (7) The UPF2  48  receives the Activate session request message and processes it. The UPF2  48  sends an Activate session response message to the SMF2  44  and if needed, indicates an activation result cause value and NG3-specific parameters (e.g. tunnelling information like the IP address to be used by the UPF2  48  and/or the GTP TEID).   Step (8) If needed, the SMF2  44  may send a NAS SM message, e.g. a NAS SM session activation response message, to the UE  34 . Such a NAS SM message can include various session management parameters, e.g. for session QoS or policy modification.   Step (9) Depending on the previous options (A) or (B), the SMF2  44  can have different behaviour. In one option, the SMF2  44  replies to step (4). In another option, the SMF2  44  may initiate a session activation procedure towards the CCNF (e.g. MMF)  32  and the (R)AN node  30 . For example the SMF2  44  can send an Activate session request/response message towards the CCNF (e.g. MMF)  32  including the session ID, and UPF NG3-related information (e.g. tunnelling information like the IP address of the UPF2  48  and/or the GTP TEID)   Step (10) Depending on the MM state in which the UE  34  was in the beginning, i.e. depending on options (A) and (B), the CCNF (e.g. MMF)  32  initiates different procedures:
           in case of option (A), i.e. the UE  34  was in MM Standby state, the CCNF  32  initiates a UE context setup procedure towards the (R)AN node  30  by sending a UE context setup request message. This message may include among others, the session ID, QoS, security and other parameters needed for the establishment of the radio connection, e.g. UPF NG3-related information (e.g. tunnelling information like the IP address of the UPF2  48  and/or the GTP TEID).   in case of option (B), i.e. the UE  34  was in MM Ready state, the CCNF (MMF)  32  initiates a UE context modification procedure towards the (R)AN node  30 . The CCNF (MMF)  32  sends a UE context modification request message to the (R)AN node  30  to modify the radio connection and to assist the establishment of NG3 connection towards the UPF2  48 . The UE context modification request message can contain among others, the session ID, the QoS, security and other parameters needed for the establishment of the radio connection, e.g. UPF NG3-related information (e.g. tunnelling information like the IP address of the UPF2  48  and/or the GTP TEID).   
           Step (11) The (R)AN node  30  performs RRC connection reconfiguration to establish the data radio connection for session #2. For this purpose the (R)AN node  30  performs a RRC connection reconfiguration procedure.   Step (12) The (R)AN node  30  replies to step (10). The (R)AN node  30  sends a UE context setup response message including the (R)AN node UP NG3-related information (e.g. tunnelling information like IP address of the UPF2  48  and/or GTP TEID), to the CCNF  32 .       

     Please note that several options are possible:
         option 1: The (R)AN node  30  sends the UE context setup response message to the MMF  32 .   option 2: The (R)AN node  30  sends the UE context setup response message to a NG2 front-end functionality within the CCNF  32 . The front-end functionality can forward the content of the UE context setup response message to the MMF  32  and/or the SMF2  44 .   option 3: The (R)AN node  30  sends the UE context setup response message to the SMF2  44 .   option 4: The (R)AN node  30  sends 2 different messages to the MMF  32  and the SMF2  44 . The message to the MMF  32  confirms the successful establishment of the new data radio connection, whereas the message to the SMF2  44  carries in addition (R)AN node UP NG3-related information (e.g. tunnelling information like the IP address of the UPF2  48  and/or the GTP TEID)   Step (13) In case of option 1 from step (12) above, the MMF  32  initiates a session update procedure towards the SMF2  44  in order to update the (R)AN node UP NG3-related information (e.g. tunnelling information like the IP address of the UPF2  48  and/or the GTP TEID).   Step (14) The SMF2  44  initiates a session update procedure towards the UPF2  48 . The SMF2  44  sends a Update session request message to the UPF2  48  including the (R)AN node UP NG3-related information (e.g. tunnelling information like the IP address of the UPF2  48  and/or the GTP TEID).       

     Solution 4: Deactivation of Single Session while Other Session(s) Continue to be in Active State Solution 4.1: Session Deactivation Initiated by the RAN Node 
     In order to manage sessions independently (i.e. per session basis), it shall be possible to release the UP connection of a single session (called “session deactivation” in this document). With other words a single radio connection and a NG3 connection can be released, while keeping the remaining existing session&#39;s connection active. 
     In one alternative solution it is assumed that (R)AN node  30  triggers the deactivation of a session. Usually the (R)AN node  30  manages radio related parameters, such as a UE inactivity timer, an active discontinuous reception (DRX) cycle, an idle DRX cycle, etc. This solution proposes that such radio parameters are maintained per session. With this, if multiple radio connections for multiple sessions are activated, the (R)AN node  30  maintains a so called “session inactivity timer” per activated session. This “session inactivity timer” is different from the UE inactivity timer, as the “session inactivity timer” applies to a single session (a radio connection like a data radio bearer (DRB) in LTE). 
       FIG.  12    describes a case where two sessions are Active and one of them becomes Idle due to no user plane activity within a predefined UE inactivity period determined by the (R)AN node  30 . As starting point, the thick arrows show the data flow in UL and DL between the UE  34  and, the UPF1  46  and the UPF2  48  correspondingly. 
     The steps in  FIG.  12    are described as follows:
         Step (1) The UE Inactivity timer in the (R)AN node  30  expires for the session #1. It means that the (R)AN node  30  has determined that no data has been transmitted in the UL or the DL for a given period of time denoted as the “inactivity timer” for session #1.   Step (2) The (R)AN node  30  has 2 options depending on the number of remaining active sessions (or radio connections).   Option (2.a) If this is not the last active session, (R)AN node  30  initiates a UE connection release procedure towards the CCNF  32 . The (R)AN node  30  sends a UE connection release request message to the CCNF  32 . This message includes a UE temporary/permanent ID, an indication which session has to be deactivated (e.g. session #1), a cause value and other parameters.   Option (2.b) If this is the last active session (e.g. existing radio connection), the (R)AN node  30  initiates a UE context release procedure. This would enforce change of the mobility (MM) state from Ready to Standby. This message includes a UE temporary/permanent ID, an indication about a cause value and other parameters.   Step (3) The CCNF  32  processes the UE connection release request message and determines which SMF needs to be contacted. The CCNF  32  sends a NG3 release request to the SMF1  42 . Please note that this message can be also called a Deactivate session request. The meaning is that the NG3 connection/tunnel should be released, but the UE&#39;s context in the SMF1  42  should be kept and transferred from Active to Idle. This message includes the UE temporary/permanent ID, the indication for the specific session ID (e.g. session #1) and other parameters.   Step (4) The SMF1  42  sends a NG3 release request message to the UPF1  46 . This message includes the UE temporary/permanent ID, an indication for the specific session ID (e.g. session #1) and other parameters. The UPF1  46  releases all associated resources to session #1 with regard to the NG3 reference point.   Step (5) The UPF1  46  sends a NG3 release response message to the SMF1  42  including the UE ID, the session ID and other parameters. At this point, the SMF1  42  change session status from Active to Idle.   Step (6) The SMF1  42  sends a NG3 release response message to the CCNF  32  including the UE ID, the session ID and other parameters.   Step (7) The CCNF  32  has two alternatives depending on the number of remaining active sessions.   Option (7.a) If this is not the last active session, the CCNF  32  sends a UE connection release command message to the (R)AN node  30  including the UE ID, the session ID and other parameters. This message has information that indicates that only session #1 is to be deactivated.   Option (7.b) If this is the last active session, the CCNF  32  sends a UE context release command message to the (R)AN node  30  including the UE ID, the session ID and other parameters. This message has information that indicates that only session #1 is to be released.   Step (8) There are 2 alternatives possible depending on the number of remaining active sessions and instruction from the CCNF  32 :   Option (8.a) The (R)AN node  30  performs a RRC connection modification procedure. For this purpose the (R)AN node  30  sends a RRC connection reconfiguration message to the UE  34  in order to release an associated data radio connection to the session #1. Other active radio connection(s) are not released.   Option (8.b) The (R)AN node  30  performs a RRC connection release procedure if this is the last existing radio connection for the UE  34 . For this purpose the (R)AN node  30  sends a RRC connection reconfiguration message to the UE  34  in order to release an associated radio connection to the session #1.   If Option (8.a) has been performed, the UE  34  transfers the state of the corresponding session (e.g. session #1) from Active to Idle state.   It is important to mention that in the UE  34 , the session #1 context is not deleted, but kept in Idle state, while other session states may be in Active states.   Step (9) The (R)AN node  30  sends either (9.a) a UE connection release complete message to the CCNF  32  or (9.b) a UE context release complete message to the CCNF  32 .   Assuming that the deactivated session #1 is not the last active sessions,  FIG.  12    shows at the bottom that the radio connection and the NG3 connection/tunnel for session #2 are kept after performing the deactivation procedure for session #1.       

     Solution 4.2: Session Deactivation Initiated by the UPF 
       FIG.  13    describes an alternative solution where the session deactivation procedure is initiated by the UPF of the corresponding session. This solution proposes that each UPF manages an inactivity timer, which can be called a “session inactivity timer”. This timer can be configured by the SMF when a session is activated, e.g. step (12) in  FIG.  7    or in  FIG.  8    can contain a “session inactivity timer” parameter. The UPF measures the time for which there are no DL or UL data exchanged. When the measured time for data inactivity reaches the value of the parameter “session inactivity timer”, the UPF triggers a UP connection release procedure. 
     As a starting point, the UE  34  is in MM Ready state and session #1 and session #2 are activated. This is shown by the thick arrows corresponding to 2 radio connections and 2 NG3 connections between the (R)AN node  30  and, the UPF1  46  and the UPF2  48  correspondingly. 
     The steps in  FIG.  13    are described as follows:
         Step (1) The UPF1  46  detects that the session inactivity timer expires. It means that the UPF1  46  has determined that no data has been transmitted in the UL or DL for a given period of time denoted as the “inactivity timer” for session #1.   Step (2) The UPF1  46  initiates a release request procedure for the UP connection towards the (R)AN. The UPF1  46  sends a NG3 release request message (or similar message e.g. a Deactivate session request or a Release connection request) to the SMF1  42 . This message can contain a UE ID, a session ID, a cause value and other parameters.   Step (3) The SMF1  42  initiates a UP connection release procedure. The SMF1  42  sends a NG3 release request message (or a similar message e.g. a Deactivate session request or a Release connection request) to the CCNF  32 . This message can contain the UE ID, the session ID, the cause value and other parameters.   Step (4) The CCNF (e.g. MMF)  32  has 2 options depending on the number of remaining active sessions (or radio connections)   Option (4.a) If this is not the last active session, the CCNF  32  initiates a UE connection release procedure towards the (R)AN node  30 . The CCNF  32  sends a UE connection release request message to the (R)AN node  30 . This message includes a UE temporary/permanent ID, indication which session has to be deactivated (e.g. session #1) and other parameters.   Option (4.b) If this is the last active session (e.g. there are no more active sessions and corresponding radio or NG3 connections), the CCNF  32  initiates a UE context release procedure. This would enforce change of the mobility (MM) state from Ready to Standby.   Step (5) There are 2 alternatives possible depending on the number of remaining active sessions and instruction from the CCNF  32 :   Option (5.a) The (R)AN node  30  performs a RRC connection modification procedure. For this purpose the (R)AN node  30  sends a RRC connection reconfiguration message to the UE  34  in order to release an associated radio connection to the session #1. It is assumed that the radio data bearer/connection to be released have 1-to-1 association with the NAS SM context corresponding with the session to be deactivated. Also, the radio signalling over RRC contains an indication about the session to be deactivated (session ID). Other active radio connection(s) are not released.   Option (5.b) The (R)AN node  30  performs a RRC connection release procedure if this is the last existing radio connection for the UE  34 . For this purpose the (R)AN node  30  sends a RRC connection reconfiguration message to the UE  34  in order to release an associated radio connection to the session #1.   If Option (5.a) has been performed, the UE  34  transfers the state of the corresponding session (e.g. session #1) from Active to Idle state.   Step (6) The (R)AN node  30  sends either (6.a) a UE connection release complete message to the CCNF  32  or (6.b) a UE context release complete message to the CCNF  32 .   Step (7) The CCNF  32  replies to the UP connection release procedure in step (3). The CCNF  32  sends a NG3 release response message (or a similar message e.g. a Deactivate session response or a Release connection response) to the SMF1  42 . This message can contain the UE ID, the session ID, the cause value and other parameters.   Step (8) The SMF1  42  replies to the UP connection release procedure in step (2). The SMF1  42  sends a NG3 release response message (or a similar message e.g. a Deactivate session response or a Release connection response) to the UPF1  46 . This message can contain the UE ID, the session ID, the cause value and other parameters.   At this point, the SMF1  42  change session status from Active to Idle.       

     Another alternative to solution 4.2 would be to use a NAS SM Session deactivation procedure between the SMF1  42  and the UE  34 . This procedure can be used by the SMF1  42  to inform the UE  34  about the SM context deactivation, which results in changing the session SM state in the UE  34  from Active to Idle. Such a NAS SM procedure can be initiated by the SMF1  42  in parallel to steps (3), (4) and (5) in  FIG.  13   . 
     Solution 4.3: Session Deactivation Initiated by the UE 
     This is another alternative way of session deactivation (i.e. release of UP connection) where the procedure is initiated by the UE  34 . Since the UE  34  can be aware about the Applications running on higher layers, the UE  34  may know whether an application has finished with the data transfer. If such an indication is available from the higher layers to the NAS layer, then the NAS layer in the UE  34 , specifically the NAS SM part, can initiate a session deactivation procedure towards the NG CN. 
     In a particular example, if an Application associated with session A indicates to the NAS SM instance in the UE  34  that such an application does not need any more UP connections, or the NAS SM instance is aware by any means that the active UP connection is not used, the UE&#39;s NAS SM instance for session A can initiate session deactivation procedure towards the NG CN. The following steps can be performed:
         Step (1) The UE  34  initiates a NAS SM Session deactivation procedure towards the SMF1  42  in order to inform the SMF1  42  that the UP connection can be released. The UE  34  generates a NAS SM Deactivation session request message and sends it over NAS signaling towards the NG CN. This message includes besides the usual NAS SM parameters an indication about the UP connection deactivation and session ID. The NG CN processes the message and forwards it to the corresponding SMF1  42 .   Step (2) The SMF1  42  initiates a NG3 release procedure towards the UPF1  46 .   Step (3) The SMF1  42  initiates a NG3 release request (or a Deactivate session request) procedure towards the CCNF (e.g. MMF)  32 .   Step (4) The MMF  32  processes the NG3 release request message from the SMF1  42 . The MMF  32  initiates the NG3 release procedure (or the Deactivate session procedure) towards the (R)AN node  30 .   Step (5) The (R)AN node  30  performs the NG3 release procedure (or the Deactivate session procedure) towards the UE  34 , e.g. via a RRC connection modification procedure. The (R)AN node  30  also modifies the context of the UE  34  by deleting the NG3 parameters of the corresponding UPF node. The (R)AN node  30  replies to the MMF  32  with the result of the NG3 release procedure.   Step (6) The MMF  32  changes the status of the corresponding session to Idle. The MMF  32  replies to the SMF1  42  with the result of the NG3 release procedure.   Step (7) The SMF1  42  acknowledges the NAS SM Session deactivation request message in step (1).       

     Please note that the steps (2)-(6) above are similar to steps (3)-(7) in solution 4.2 shown in  FIG.  13   . The major difference from solution 4.3 compared to 4.2 is the NAS SM Session deactivation procedure performed between the UE  34  and the SMF1  42 . 
     The descriptions below apply to all solutions described in this document. 
     The examples above describe solutions for the activation or deactivation of a single session. However, it is also possible to activate/deactivate several sessions simultaneously by including several Session IDs in the corresponding messages. The activation of several sessions simultaneously can be beneficial in case of multiple PDU sessions per data network, where it is assumed that the same SMF controls the multiple PDU sessions. In one alternative, the SMF decides whether to activate a single PDU session (e.g. to which DL data arrives) or to activate some or even all PDU session controlled by this SMF (which probably means some or all PDU sessions toward a particular network slice or data network). 
     Please note that the signalling to/from the (R)AN node  30  over NG2 interface can be terminated at a common front-end NG2 termination functionality in the CCNF  32 . The common front-end NG2 functionality can route/forward the content of the NG2 message to the MMF  32  and/or the SMF2  44 . Further, it is possible that the (R)AN node  30  sends 2 different NG2 messages, a separate message to the MMF  32  and a separate message to the SMF2  44 . The message to the MMF  32  may request an MM-specific action or can confirm the successful establishment/release of a data radio connection. The message to the SMF2  44  can mainly contain (R)AN node UP NG3-related information (e.g. tunnelling information like the IP address of UPF2  48  and/or the GTP TEID). 
     Please note that all figures above show scenarios of a single UPF per session. However, this document is applicable to scenarios with multiple different UPFs served by a single SMF. In such case it can be assumed that there are multiple PDU sessions for the same data network. The sessions can be activated independently for each UPF. In such case, an activated session exists to another UPF served by the same SMF2  44  (i.e. the UE  34  is in Ready mobility state and the SMF2  44  is in Active session state). Then the SMF2  44  doesn&#39;t need to initiate paging procedure, but instead the SMF2  44  can either modify existing session or initiate the activation on new UP session. For this purpose the SM requests the CCNF (MMF)  32  to add a new UP session including the UPF2  48  information. 
     Co-location of control plane functions like the MMF and the SMF in a common control plane functional entity is possible. 
     The proposed solution is based on the following principles:
         The session management function (SMF) and mobility management function (MMF) are split in different network functions. In the particular case of UE registered with multiple network slice instances, the UE would be served by multiple SMFs, i.e. multiple PDU session are established.   Multiple PDU sessions (to the same or to different network slices) are established for a given UE. A PDU session can be in Idle state or Active state.   A UP connection (including data radio connection and NG3 tunnel establishing) can be activated for a single PDU session. UP connections for other PDU sessions (to the same or to other network slices) can be activated/deactivated independently.   The procedures for PDU session activation and deactivation are proposed, meaning:   PDU session activation is the transition to “Active” session state in the SMF and the UP connection is established;   PDU session deactivation is the transition to “Idle” session state in the SMF and the UP connection is released.       

     General Nodes Description 
     The description below applies to all solutions described in this document. 
     UE Impact 
     Please note that the solutions in this document are mostly described including the UE as NG UE, but it is also possible to apply the solution to 2G, 3G and 4G access system, i.e. when the UE is 2G/3G/4G UE. 
     According to the above described example embodiments, the UE  34  is modified to be able to handle the signaling to/from the (R)AN and CN functional entities (e.g. (R)AN node, MMF, SMF). In addition, the UE  34  is able to receive, process and transmit the corresponding information to the (R)AN and CN functional entities. The UE  34  can be described schematically via the block diagram as in  FIG.  14   . 
       FIG.  14    is a block diagram illustrating the main components of the user equipment (UE)  34  shown in e.g.  FIG.  1    (where it is denoted ‘NG UE’). As shown, the UE  34  has a transceiver circuit  50  that is operable to transmit signals to and to receive signals from a radio access network node  30  via one or more antenna  52 . Such radio access network node  30  (denoted ‘NG (R)AN’ in  FIG.  1   , ‘RAN’ in  FIG.  2   , and ‘AN’ in  FIG.  4   ) may comprise a base station and/or any other suitable access point/transmission point. The UE  34  has a controller  54  to control the operation of the UE  34 . The controller  54  is associated with a memory  56  and is coupled to the transceiver circuit  50 . The UE  34  may have all the usual functionality of a conventional mobile device/mobile telephone (such as a user interface) and this may be provided by any one or any combination of hardware, software and firmware, as appropriate. Software may be pre-installed in the memory  56  and/or may be downloaded via the telecommunication network or from a removable data storage device (RMD), for example. 
     The controller  54  controls overall operation of the UE  34  by, in this example, program instructions or software instructions stored within the memory  56 . As shown, these software instructions include, among other things, an operating system  58 , a communication control module  60 , and a transceiver control module  62  (shown as forming part of the communication control module  60 ). 
     The communication control module  60  controls the communication between the UE  34  and the base station/access node of the (R)AN. The communications control module  60  also controls the separate flows of control data (Control Plane) and user data (User Plane, both uplink and downlink) that are to be transmitted to the base station/access node and other nodes (via the base station/access node) such as the Mobility Management Function (MMF) and the Session Management Function (SMF). 
     MMF/SMF Impact 
     According to the above described example embodiments, the Mobility Management Function (MMF) or Session Management Function (SMF) is modified/extended to be able to behave according to the proposed solution(s). The MMF or the SMF can be described schematically via the block diagram as in  FIG.  15   . 
       FIG.  15    is a block diagram illustrating the main components of the Mobility Management Function (MMF)/Session Management Function (SMF) node shown in e.g.  FIG.  1   . Although the MMF and the SMF are shown as part of a combined control function entity, their functionalities may be implemented in separate nodes. 
     As shown, the MMF/SMF has a transceiver circuit  64  and a network interface  66  for transmitting signals to and for receiving signals from other network nodes (including the UE  34 ). The MMF/SMF has a controller  68  to control the operation of the MMF/SMF node. The controller  68  is associated with a memory  70 . Software may be pre-installed in the memory  70  and/or may be downloaded via the communication network or from a removable data storage device (RMD), for example. The controller  68  is configured to control the overall operation of the MMF/SMF by, in this example, program instructions or software instructions stored within the memory  70 . As shown, these software instructions include, among other things, an operating system  72 , a communication control module  74 , and a transceiver control module  76  (shown as forming part of the communication control module  74 ). 
     The communication control module  74  controls the communication between the MMF/SMF and other network entities that are connected to the MMF/SMF (e.g. the base station/access node, and the UE  34  when connected to a base station/access node). 
     SUMMARY 
     Beneficially, the above described example embodiments include, although they are not limited to, one or more of the following functionalities. 
     1) The UE is able to link a data radio connection activation or deactivation procedures with an existing PDU session management context in the UE.
         a. Such a linkage in the UE is based on a session ID indication carried in the related signalling from the SMF to the UE.       

     2) The user plane connection deactivation is performed by the session management function in the NG CN triggered:
         a. either by the user plane function in the core network; or   b. by the UE via NAS SM signaling.       

     It can be seen that the above example embodiments describe a method for independent activation or deactivation of a user plane connection per PDU session or network slice, the method comprising: 
     1) The activation or deactivation of a user plane connection is initiated from the SMF based on:
         a. Trigger from the UPF (due to arriving of DL data for session activation or due to timer expiration for session deactivation);   b. Trigger from the UE (due to UL data transmission for session activation, or due to no need of UP connection for session deactivation).       

     2) The control plane session management function, mobility management function, access network and terminal use a session ID as a reference ID to refer to the same session. 
     Benefits 
     It can be seen that the above embodiments provide a number of benefits, including, but not limited to: 
     (1) The number of active NG3 connections is limited even if there are multiple user plane functions instantiated/configured for a UE, which also limits the signaling over radio and NG2 and NG3 interface in case of UE mobility. 
     (2) If the UE receives or transmits data over single particular session, the user plane connection only to this particular session is activated, which reduces the signaling for connection establishment for other sessions if frequent mobility state changes between Standby and Ready states happen. 
     MODIFICATIONS AND ALTERNATIVES 
     Detailed example embodiments have been described above. As those skilled in the art will appreciate, a number of modifications and alternatives can be made to the above example embodiments whilst still benefiting from the inventions embodied therein. By way of illustration only a number of these alternatives and modifications will now be described. 
     In the above description, the UE and the MMF/SMF node are described for ease of understanding as having a number of discrete modules (such as the communication control modules). Whilst these modules may be provided in this way for certain applications, for example where an existing system has been modified to implement the invention, in other applications, for example in systems designed with the inventive features in mind from the outset, these modules may be built into the overall operating system or code and so these modules may not be discernible as discrete entities. These modules may also be implemented in software, hardware, firmware or a mix of these. 
     Each controller may comprise any suitable form of processing circuitry including (but not limited to), for example: one or more hardware implemented computer processors; microprocessors; central processing units (CPUs); arithmetic logic units (ALUs); input/output (IO) circuits; internal memories/caches (program and/or data); processing registers; communication buses (e.g. control, data and/or address buses); direct memory access (DMA) functions; hardware or software implemented counters, pointers and/or timers; and/or the like. 
     In the above example embodiments, a number of software modules are described. As those skilled in the art will appreciate, the software modules may be provided in compiled or un-compiled form and may be supplied to the UE and the MMF/SMF node as a signal over a computer network, or on a recording medium. Further, the functionality performed by part or all of this software may be performed using one or more dedicated hardware circuits. However, the use of software modules is preferred as it facilitates the updating of the UE and the MMF/SMF node in order to update their functionalities. 
     Various other modifications will be apparent to those skilled in the art and will not be described in further detail here. 
     List of Abbreviations 
     3GPP: 3rd Generation Partnership Project 
     AS: Access Stratum (use similar to RRC signaling in this document) 
     CCF: Core Control Functions 
     CCNF: Common Control Network Functions 
     CPF: Control Plane Function 
     NB, eNB: Node B, evolved Node B (but can also be any ‘RAN node’ implementing 2G, 3G, 4G or future 5G technology)
 
E-UTRAN: Evolved Universal Terrestrial Radio Access Network (also used as EUTRAN)
 
     GGSN: Gateway GPRS Support Node 
     GPRS: General Packet Radio Service 
     HPLMN: Home Public Land Mobile Network 
     HSS: Home Subscriber Server 
     IE: Informational Element (used as part of a signalling message) 
     MME: Mobility Management Entity 
     MMF: Mobility Management Function 
     MNO: Mobile Network Operator 
     NAS: Non Access Stratum 
     NFV: Network Function Virtualization 
     NNSF: NAS/Network Node Selection Function 
     NSI: Network Slice Instances 
     PCF: Policy Control Function 
     PCRF: Policy and Charging Rules Function 
     PGW: Packet Data Network Gateway 
     PSM: Power Saving Mode 
     RAU: Routing Area Update 
     RNC: Radio Network Controller 
     RRC: Radio Resource Control 
     PLMN: Public Land Mobile Network 
     SCNF: Slice-specific Control Plane Network Functions 
     SMF: Session Management Function 
     SGSN: Serving GPRS Support Node 
     SGW: Serving Gateway 
     TAU: Tracking Area Update 
     UE: User Equipment 
     UPF: User Plane Function (any UP function used for policy/QoS enforcement, mobility, UE&#39;s IP anchor, similar to SGW/PGW in EPC) 
     UTRAN: UMTS Terrestrial Radio Access Network 
     VPLMN: Visited Public Land Mobile Network 
     This application is based upon and claims the benefit of priority from European Patent application No. EP 16185042.5, filed on Aug. 19, 2016, the disclosure of which is incorporated herein in its entirety by reference.