2. The method according to claim 1, further comprising: receiving a Radio Resource Control (RRC) message including information for requesting by the network node for session management, for releasing the resource related to at least one PDU session; and releasing the resource related to the at least one PDU session based on the RRC message.

3. A method for controlling a session in a network node for session management, the method comprising: receiving, from User Equipment (UE), a first request including at least one session identifier (ID) for releasing a resource related to at least one Protocol Data Unit (PDU) session corresponding to the at least one session ID; and releasing information in the network node for session management, related to the at least on PDU session corresponding to the at least one session ID.

4. A method for controlling a session in an access network node, the method comprising: maintaining a parameter related to a period on communication of User Equipment (UE) per session; and maintaining activity for a session using the parameter related to the session. 5.A method for controlling a session in an access network node, the method comprising: sending, to a network node for session management, a request for releasing a Protocol Data Unit (PDU) session wherein the request includes a session identifier (ID) corresponding to the PDU session, based on inactivity of the PDU session.

6. The method according to claim 5, further comprising: receiving a message including information for requesting by the network node for session management, for releasing the resource related to at least one PDU session; and sending a request, to User Equipment (UE), for releasing the resource related to the at least one PDU session.

7. A method for controlling a session in a network node for session management, the method comprising: receiving, from an access network node, a request including at least one session identifier (ID) for releasing a resource related to at least one Protocol Data Unit (PDU) session corresponding to the at least one session ID, based on inactivity of the PDU session; and releasing information in the network node for session management, related to the at least on PDU session corresponding to the at least one session ID.

8. The method according to claim 7, further comprising: sending a message including information for requesting by the network node for session management, for releasing the resource related to at least one PDU session, wherein the message causes the access network node to send a request, to User Equipment (UE), for releasing the resource related to the at least one PDU session.

9. User Equipment (UE), comprising: a memory storing instructions; and at least one processor configured to process the instructions to: send, to a network node for session management, a first request including at least one session identifier (ID) for releasing a resource related to at least one Protocol Data Unit (PDU) session corresponding to the at least one session ID.10.The UE according to claim 9, wherein the at least one processor is configured to process the instructions to: receive a Radio Resource Control (RRC) message including information for requesting by the network node for session management, for releasing the resource related to at least one PDU session, and release the resource related to the atleast one PDU session based on the RRC message.

11. A network node for session management, comprising: a memory storing instructions; and at least one processor configured to process the instructions to: receive, from User Equipment (UE), a first request including at least one session identifier (ID) for releasing a resource related to at least one Protocol Data Unit (PDU) session corresponding to the at least one session ID, and release information in the network node for session management, related to the at least on PDU session corresponding to the at least one session ID.

12. An access network node, comprising: a memory storing instructions; and at least one processor configured to process the instructions to: maintain a parameter related to a period on communication of User Equipment (UE) per session, and maintain activity for a session using the parameter related to the session. 13.An access network node, comprising: a memory storing instructions; and at least one processor configured to process the instructions to: send, to a network node for session management, a request for releasing a Protocol Data Unit (PDU) session wherein the request includes a session identifier (ID) corresponding to the PDU session, based on inactivity of the PDU session.

14. The access network node according to claim 13, wherein the at least one processor is configured to process the instructions to: receive a message including information for requesting by the network node for session management, for releasing the resource related to at least one PDU session, and send a request, to User Equipment (UE), for releasing the resource related to the at least one PDU session.

15. Anetwork node for session management, comprising: a memory storing instructions; and at least one processor configured to process the instructions to: receive, from an access network node, a request including at least one session identifier (ID) for releasing a resource related to at least one Protocol Data Unit (PDU) session corresponding to the at least one session ID, based on inactivity of the PDU session, and release information in the network node for session management, related to the at least on PDU session corresponding to the at least one session ID.

16. The network node for session management according to claim 15, wherein the at least one processor is configured to process the instructions to: send a message including information for requesting by the network node for session management, for releasing the resource related to at least one PDU session, wherein the message causes the access network node to send a request, to User Equipment (UE), for releasing the resource related to the at least one PDU session

Title of Invention : METHOD FOR USER PLANE CONNECTION ACTIVATION OR DEACTIVATION PER SESSION
Technical Field
[0001]
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
[0002]
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.
[0003]
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.
[0004]
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.
[0005]
The term Home Subscriber Server (HSS)/Home Location Register (HLR) means a repository where the UE’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.
[0006]
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.
[0007]
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.
[0008]
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.
[0009]
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).
[0010]
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.
[0011]
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).
[0012]
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.
[0013]
3GPP studies the NG system architecture and corresponding issues and solutions are captured in 3GPP TR 23.799 [see, NPL 1]. Figure 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 Figure 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].
[0014]
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 Figure 2, as described in [see, NPL 1].
[0015]
Figure 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.
[0016]
[NPL 1] also describes the Common Control Network Functions (CCNF) 32 and Slice-specific Control Plane Network Functions (SCNF), as shown in detail in Figure 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.
[0017]
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.
[0018]
One further solution described in 23.799 in clause 6.4.3 is shown in Figure 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
[0019]
nplcit 1 : 3GPP TR 23.799 v0.6.0, 2016-07, “Study on Architecture for Next Generation System”
nplcit 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
[0020]
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.
[0021]
One assumption in this document is that a UE’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’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.
[0022]
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.
[0023]
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->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.
[0024]
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.
[0025]
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.
[0026]
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
[0027]
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
[0028]
[fig. 1] Figure 1 describes the NG architecture for access to multiple PDN connections (called PDU sessions in the NG study);
[fig. 2] Figure 2 shows one example of network architecture allowing a UE to connect to multiple NSIs;
[fig. 3] Figure 3 describes the CCNF and SCNF;
[fig. 4] Figure 4 shows one further solution described in 23.799 in clause 6.4.3;
[fig. 5] Figure 5 shows an example architecture showing multiple network slices or PDU sessions with corresponding multiple CPFs and UPFs;
[fig. 6] Figure 6 shows multiple session state machines (one per established session) and a single mobility state machine;
[fig. 7] Figure 7 shows the existence of 2 sessions already established for a given UE;
[fig. 8] Figure 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] Figure 9 shows a possible solution 2.1 for the activation of additional session when another session is already in Active state;
[fig. 10] Figure 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] Figure 11 shows that the UE has two session contexts for session#1 and session#2;
[fig. 12] Figure 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] Figure 13 describes an alternative solution where the session deactivation procedure is initiated by the UPF of the corresponding session;
[fig. 14] Figure 14 is a block diagram illustrating the main components of the UE shown in Figure 1; and
[fig. 15] Figure 15 is a block diagram illustrating the main components of the MMF / SMF node shown in Figure 1.
Description of Embodiments
[0029]
In order to solve the above described problem, different solutions are described in various example embodiments herewith.
[0030]
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’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 Figure 6.
[0031]
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.
[0032]
For the purposes of this document the reference architecture from Figure 1 for a single established session (network slice or PDU session) is assumed. For multiple established sessions Figure 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 Figure 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 Figure 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.
[0033]
Please note that the UE 34 is shown in Figure 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).
[0034]
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’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’s context in the CCNF 32 or in the SMF.
[0035]
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’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.
[0036]
As exemplary shown in Figure 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 <-> 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.
[0037]
Figure 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.
[0038]
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).
[0039]
As depicted in Figure 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’s context related to this session. For example, the UE’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.
[0040]
With other words, independent of the state (Active or Idle) of the session state machine in the SMF, the SMF maintains UE’s session context like the parameters listed above.
[0041]
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.
[0042]
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’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).
[0043]
When the SMF for a given session (e.g. SMF-A) is in Idle state, in CP the SMF doesn’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’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.
[0044]
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.
[0045]
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’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.
[0046]
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.
[0047]
This document proposes that the CCNF (e.g. MMF) 32 maintains UE’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 Figure 6 can be also maintained in the MMF 32 only, or in both the MMF 32 and the SMF.
[0048]
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’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.
[0049]
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.
[0050]
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.

WE CLAIM:
1.A method for controlling a session in User Equipment (UE), the method comprising:
sending, to a network node for session management, a first request including at least one session identifier
(ID) for releasing a resource related to at least one Protocol Data Unit (PDU) session corresponding to the at least one
session ID.
2. The method according to claim 1, further comprising:
receiving a Radio Resource Control (RRC) message including information for requesting by the network node
for session management, for releasing the resource related to at least one PDU session; and
releasing the resource related to the at least one PDU session based on the RRC message.
3. A method for controlling a session in a network node for session management, the method comprising:
receiving, from User Equipment (UE), a first request including at least one session identifier (ID) for releasing
a resource related to at least one Protocol Data Unit (PDU) session corresponding to the at least one session ID; and
releasing information in the network node for session management, related to the at least on PDU session
corresponding to the at least one session ID.
4. A method for controlling a session in an access network node, the method comprising:
maintaining a parameter related to a period on communication of User Equipment (UE) per session; and
maintaining activity for a session using the parameter related to the session.
5.A method for controlling a session in an access network node, the method comprising:
sending, to a network node for session management, a request for releasing a Protocol Data Unit (PDU)
session wherein the request includes a session identifier (ID) corresponding to the PDU session, based on inactivity of
the PDU session.
6. The method according to claim 5, further comprising:
receiving a message including information for requesting by the network node for session management, for
releasing the resource related to at least one PDU session; and
sending a request, to User Equipment (UE), for releasing the resource related to the at least one PDU session.
7. A method for controlling a session in a network node for session management, the method comprising:
receiving, from an access network node, a request including at least one session identifier (ID) for releasing a
resource related to at least one Protocol Data Unit (PDU) session corresponding to the at least one session ID, based on
inactivity of the PDU session; and
releasing information in the network node for session management, related to the at least on PDU session
corresponding to the at least one session ID.
8. The method according to claim 7, further comprising:
sending a message including information for requesting by the network node for session management, for
releasing the resource related to at least one PDU session, wherein the message causes the access network node to send
a request, to User Equipment (UE), for releasing the resource related to the at least one PDU session.
9. User Equipment (UE), comprising:
a memory storing instructions; and
at least one processor configured to process the instructions to:
send, to a network node for session management, a first request including at least one session
identifier (ID) for releasing a resource related to at least one Protocol Data Unit (PDU) session corresponding to the at
least one session ID.10.The UE according to claim 9, wherein the at least one processor is configured to process the instructions to:
receive a Radio Resource Control (RRC) message including information for requesting by the
network node for session management, for releasing the resource related to at least one PDU session, and
release the resource related to the atleast one PDU session based on the RRC message.
11. A network node for session management, comprising:
a memory storing instructions; and
at least one processor configured to process the instructions to:
receive, from User Equipment (UE), a first request including at least one session identifier (ID) for
releasing a resource related to at least one Protocol Data Unit (PDU) session corresponding to the at least one session
ID, and
release information in the network node for session management, related to the at least on PDU
session corresponding to the at least one session ID.
12. An access network node, comprising:
a memory storing instructions; and
at least one processor configured to process the instructions to:
maintain a parameter related to a period on communication of User Equipment (UE) per session,
and
maintain activity for a session using the parameter related to the session.
13.An access network node, comprising:
a memory storing instructions; and
at least one processor configured to process the instructions to:
send, to a network node for session management, a request for releasing a Protocol Data Unit
(PDU) session wherein the request includes a session identifier (ID) corresponding to the PDU session, based on
inactivity of the PDU session.
14. The access network node according to claim 13, wherein the at least one processor is configured to process
the instructions to:
receive a message including information for requesting by the network node for session management,
for releasing the resource related to at least one PDU session, and
send a request, to User Equipment (UE), for releasing the resource related to the at least one PDU
session.
15. Anetwork node for session management, comprising:
a memory storing instructions; and
at least one processor configured to process the instructions to:
receive, from an access network node, a request including at least one session identifier (ID) for
releasing a resource related to at least one Protocol Data Unit (PDU) session corresponding to the at least one session
ID, based on inactivity of the PDU session, and
release information in the network node for session management, related to the at least on PDU
session corresponding to the at least one session ID.
16. The network node for session management according to claim 15, wherein the at least one processor is
configured to process the instructions to:
send a message including information for requesting by the network node for session management,
for releasing the resource related to at least one PDU session, wherein the message causes the access network node to
send a request, to User Equipment (UE), for releasing the resource related to the at least one PDU session