Patent Publication Number: US-2023164855-A1

Title: Method and device for providing local data network information to terminal in wireless communication system

Description:
TECHNICAL FIELD 
     The disclosure relates to a wireless communication system and, more particularly, to a method and apparatus for providing local data network information according to movement of a terminal in a cellular wireless communication system, for example, a 5G system. 
     BACKGROUND ART 
     Since the commercialization of 4G communication systems, efforts have been made to develop improved 5G or pre-5G communication systems to meet the ever increasing demand for wireless data traffic. As such, 5G or pre-5G communication systems are also called “beyond 4G network”or “post LTE system”. 
     To achieve higher data rates, 5G communication systems are being considered for implementation in the extremely high frequency (mmWave) band (e.g., 60 GHz band). To decrease path loss and increase the transmission distance in the mmWave band, various technologies including beamforming, massive multiple-input multiple-output (massive MIMO), full dimensional MIMO (FD-MIMO), array antennas, analog beamforming, and large scale antennas are considered for 5G communication systems. Additionally, to improve system networks in 5G communication systems, technology development is under way regarding evolved small cells, advanced small cells, cloud radio access networks (cloud RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving networks, cooperative communication, coordinated multi-points (CoMP), interference cancellation, and the like. 
     In addition, advanced coding and modulation (ACM) schemes such as hybrid FSK and QAM modulation (FOAM) and sliding window superposition coding (SWSC), and advanced access technologies such as filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) are also under development for 5G communication systems.  
     Meanwhile, to evolve from the existing 4G LTE system to the 5G system, 3GPP in charge of cellular mobile communication standards has named a new core network architecture as 5G core (5GC) and is in the process of standardization. 
     Compared to the evolved packet core (EPC) being the core for the existing 4G network, the 5GC supports the following differentiated functions. 
     First, a network slice functionality is introduced in the 5GC. As 5G requirements, the 5GC should support various types of terminals and services such as enhanced mobile broadband (eMBB), ultra-reliable low-latency communications (URLLC), and massive machine type communications (mMTC). These terminals/services have different requirements for the core network. For example, an eMBB service requires a high data rate, and a URLLC service requires high stability and low latency. A technique proposed to meet such various service requirements is a network slice scheme. 
     The network slice is a way to create multiple logical networks through virtualization of a single physical network, and individual network slice instances (NSIs) may have different characteristics. Hence, various service requirements can be satisfied by having a network function (NF) suitable for the characteristic of each NSI Various 5G services can be efficiently supported by allocating an NSI suitable for the characteristic of a service requested by each terminal. 
     Second, the 5GC can facilitate the support of the network virtualization paradigm by separating the mobility management function and the session management function. In existing 4G LTE, all terminals are able to be provided with services from the network through signaling exchange with a single core equipment called mobility management entity (MME) that takes charge of registration, authentication, mobility management, and session management functions. However, in 5G, as the number of terminals increases explosively and the mobility and traffic/session characteristics to be supported are subdivided according to the types of terminals, if all functions are supported by a single equipment such as the MME, the scalability of adding an entity for each required function is inevitably reduced. Hence, to improve scalability in terms of function/implementation complexity and signaling load of the core  equipment in charge of the control plane, various functions are being developed based on the structure separating the mobility management function and the session management function. 
     Meanwhile, techniques for applying edge computing technology that transmits data using an edge server to a wireless communication system are being discussed in recent years. Edge computing technology may include, for example, multi-access edge computing (MEC) or fog computing. Edge computing technology may refer to a technique for providing data to an electronic device (terminal or user equipment) through a separate server (edge server or MEC server) installed at a location geographically close to the electronic device, for example, inside or near a base station. For example, an application that requires low latency among at least one application installed in the electronic device may transmit or receive data via an edge server installed at a geographically close location, without using a server located on an external data network (DN) (e.g., Internet). 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     In the 5G core network supporting edge computing, when a local PDU session anchor user plane function (local PSA-UPF) entity for a local data network (local DN) is added/changed/deleted, relocation of the application server may occur. As such, when a local PSA-UPF is added/changed/deleted, the session management function (SMF) entity of the 5G core network should notify the terminal of control information about the upper network layer. Then, when the terminal receives the control information for the upper network layer from the SMF entity, it performs an appropriate operation correspondingly. 
     However, the 5G core network does not provide an operation in which this procedure is performed. Also, the terminal cannot perform an operation for the case of receiving control information about the upper network layer from the SMF entity. 
     Accordingly, the disclosure provides a procedure that notifies control information about the upper network layer to the terminal from the 5G core network when a local PSA-UPF is added/changed/deleted.  
     In addition, the disclosure provides an apparatus and method that handle control information about the upper network layer received by the terminal from the 5G core network in response to addition/change/deletion of a local PSA-UPF. 
     Solution to Problem 
     A method according to an embodiment of the disclosure, as a method for a session management function (SMF) entity to provide local data network information to a terminal in a wireless communication system, may include: determining to add a protocol data unit (PDU) session anchor-user plane function (PSA-UPF) for a PDU session based on first information according to mobility of the terminal; establishing a PDU session with the PSA-UPF having been determined to be added; configuring PDU paths for downlink and uplink between the PSA-UPF and the terminal; and transmitting a PDU session modification command indicating new PSA-UPF addition to the terminal. 
     The first information may include at least one of policy and charging control (PCC) information or local data network (DN) configuration information received from a policy control function (PCF) entity. 
     A method according to another embodiment of the disclosure, as a method for a terminal to receive local data network information from a session management function (SMF) entity in a wireless communication system, may include: transmitting and receiving a protocol data unit (PDU) by using a PDU session configured with the terminal; receiving a PDU session modification command indicating addition of a new PDU session anchor-user plane function (PSA-UPF) from the SMF entity; receiving, through the new PSA-UPF, a router advertisement (RA) message transmitted by the SMF; reconfiguring the new PSA-UPF; and performing upper layer control based on reconfiguration of the new PSA-UPF. 
     Advantageous Effects of Invention 
     According to the disclosure, when a local PSA-UPF is added (or changed/deleted), the upper layer network context of the terminal needs to be released. In this case, the SMF provides information on the local DN to the terminal, so that the terminal can control the upper layer context. Further, by defining this procedure, the wireless  communication network can provide control information about the upper network layer to the terminal in response to addition/change/deletion of a local PDU session anchor user plane function (local PSA-UPF) entity. Also, the terminal may receive the control information about the upper network layer due to addition/change/deletion of the local PSA-UPF from the wireless communication network and may take an appropriate operation. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a diagram illustrating the 5G system architecture using a reference point representation in a wireless communication system. 
         FIG.  2    is a diagram illustrating the architecture of network entities in a wireless communication system according to various embodiments of the disclosure. 
         FIG.  3    is a diagram illustrating another architecture of the 5G core network supporting edge computing according to an embodiment of the disclosure. 
         FIG.  4    is an illustrative diagram for explaining a case in which the UE moves by using a network topology according to the disclosure. 
         FIGS.  5 A and  5 B  are illustrative diagrams for explaining the internal configuration of a UE and a case of establishing a PDU session with a wireless communication network and a data network according to an embodiment of the disclosure. 
         FIG.  5 C  is an illustrative diagram for describing a local DN binding context according to an embodiment of the disclosure. 
         FIG.  6    is a signal flow diagram for a case where the SMF provides control information on the upper layer network context together with information on the PDU session and local DN to the UE according to an embodiment of the disclosure. 
         FIGS.  7 A and  7 B  are signal flow diagrams for a case where the SMF provides local DN notification and upper layer network context control information to the UE according to an embodiment of the disclosure. 
         FIGS.  8 A and  8 B  are signal flow diagrams depicting operations of individual nodes to provide corresponding information to the UE when a local PSA is changed in response to an AF request in the network according to an embodiment of the disclosure. 
         FIGS.  9 A and  9 B  are illustrative diagrams for explaining a procedure for providing  local DN information and upper layer network context control information to the UE, and operations in the UE according to an embodiment of the disclosure. 
         FIG.  10    is a block diagram of an NF according to the disclosure. 
     
    
    
     MODE FOR THE INVENTION 
     Hereinafter, embodiments of the disclosure will be described in detail with reference to the accompanying drawings. In the description of the disclosure, descriptions of well-known functions and structures incorporated herein may be omitted to avoid obscuring the subject matter of the disclosure. Also, the terms described below are defined in consideration of their functions in the disclosure, and these may vary depending on the intention of the user, the operator, or the custom. Hence, their meanings should be determined based on the overall contents of this specification. In the following description, the term “base station” refers to a main agent allocating resources to terminals and may be at least one of eNode B, Node B, BS, radio access network (RAN), access network (AN), RAN node, radio access unit, base station controller, or network node. The term “terminal” may refer to at least one of user equipment (UE), mobile station (MS), cellular phone, smartphone, computer, or multimedia system with a communication function. In the disclosure, the term “downlink (DL)” refers to a wireless transmission path through which the base station sends a signal to the terminal, and the term “uplink (UL)” refers to a wireless transmission path through which the terminal sends a signal to the base station. Additionally, embodiments of the disclosure are described using LTE or LTE-A systems as illustration, but the embodiments of the disclosure may be applied to other communication systems having similar technical backgrounds or channel configurations. Further, it should be understood by those skilled in the art that the embodiments of the disclosure are applicable to other communication systems without significant modifications departing from the scope of the disclosure. 
     In the following description of the disclosure, a description will be given of the session management according to the movement of the UE in the wireless communication system. Further, in the disclosure, according to the movement of the UE, a procedure related to relocation of an application server accessed by the UE in  the edge computing system may also be applied. 
       FIG.  1    is a diagram illustrating the 5G system architecture using a reference point representation in a wireless communication system. 
     With reference to  FIG.  1   , the 5G system architecture may include various components (i.e., network functions (NFs)). Among them, authentication server function (AUSF) entity  160 , (core) access and mobility management function (AMF) entity  120 , session management function (SMF) entity  130 , policy control function (PCF) entity  140 , application function (AF) entity  150 , unified data management (UDM) entity  170 , data network (DN)  180 , user plane function (UPF) entity  110 , (radio) access network ((R)AN)  20 , and terminal (i.e., user equipment (UE))  10  are illustrated in  FIG.  1   . 
     Each of the devices illustrated in  FIG.  1    may be implemented as a server or equipment, or may be implemented as a network slice instance as described above. When implemented as a network slice instance, two or more identical or different network slice instances may be implemented on one server or equipment, and one network slice instance may be implemented on two or more servers or equipments. 
     The above NFs may support the following functions. 
     The AUSF  160  may process and store data for authentication of the UE. 
     The AMF  120  may provide a function for the connection and mobility management for each UE, and one UE may be basically connected to one AMF. Specifically, the AMF may support functions, such as signaling between CN nodes for mobility between 3GPP access networks, termination of the radio access network (RAN) CP interface (i.e., N 2  interface), termination N 1  of NAS signaling, NAS signaling security (NAS ciphering and integrity protection), AS security control, registration management (registration area management), connection management, idle mode UE reachability (including control and execution of paging retransmission), mobility management control (subscription and policy), support of intra-system mobility and inter-system mobility, support of network slicing, SMF selection, lawful intercept (for AMF event and L1 system interface), session management (SM) message delivery between the UE and the SMF, transparent proxy for routing SM messages, access authentication, access authorization including roaming authority check, delivery of  SMS messages between the UE and the short message service function (SMSF), security anchor function (SAF), and/or security context management (SCM). Some or all of these functions of the AMF  120  can be supported in a single AMF instance operating as one AMF. 
     The DN  180  may mean, for example, an operator service, Internet access, or a 3rd party service. The DN  180  may transmit a downlink protocol data unit (PDU) to the UPF  110  or may receive a PDU transmitted from the UE  10  through the UPF  110 . 
     The PCF  140  may provide a function of receiving information on the packet flow from the application server and determining policies for mobility management, session management, and the other. Specifically, the PCF  140  may support functions, such as supporting a unified policy framework for controlling the network behavior, providing policy rules so that the control plane function(s) (e.g., AMF, SMF) can enforce the policy rules, and implementing a front end to access relevant subscription information for policy making in a user data repository (UDR). 
     The SMF  130  provides a session management function, and when the UE has a plurality of sessions, the individual sessions may be managed by different SMFs. specifically, the SMF  130  may support functions, such as session management (e.g., session establishment, modification, and release, including tunnel maintenance between the UPF and the AN node), UE IP address allocation and management (including selective authentication), setting up traffic steering to route traffic to the appropriate destination in the UPF, termination of interfaces toward policy control functions, enforcing the control part of the policy and quality of service (QoS), lawful intercept (for SM event and L1 system interface), termination of the SM part of NAS messages, downlink data notification, initiation of AN specific SM information (transmitted to AN via the AMF over N 2 ), determining SSC mode of the session, and roaming functionality. As described above, some or all functions of the SMF  130  may be supported in a single SMF instance operating as one SMF. 
     The UDM  170  may store users subscription data, policy data, and the like. The UDM  170  may include two parts, that is, an application front end (FE) (not shown) and a user data repository (UDR) (not shown).  
     The FE may include a UDM-FE taking charge of location management, subscription management, and processing of credentials, and a PCF-FE taking charge of policy control. The UDR may store data required for functions provided by the UDM-FE and a policy profile required by the PCF. Data stored in the UDR may include user subscription data including subscription identifier, security credential, access and mobility related subscription data, and session related subscription data, and policy data. The UDM-FE may access subscription information stored in the UDR and may support functions such as authentication credential processing, user identification handling, access authentication, registration/mobility management, subscription management, and SMS management. 
     The UPF  110  may transmit a downlink PDU received from the DN  180  to the UE  10  via the (R)AN  20  and transmits an uplink PDU received via the (R)AN  20  from the UE  10  to the DN  180 . Specifically, the UPF  110  may support functions, such as anchor point for intra/inter radio access technology (RAT) mobility, external PDU session point of interconnect to data network, packet routing and forwarding, packet inspection and user plane part of policy rule enforcement, lawful intercept, traffic usage reporting, uplink classifier to support traffic flow routing toward data network, branching point to support multi-homed PDU session, QoS handling for user plane (e.g., packet filtering, gating, uplink/downlink rate enforcement), uplink traffic verification (service data flow (SDF) to QoS flow mapping), transport level packet marking in uplink and downlink, and downlink packet buffering and downlink data notification triggering. Some or all functions of the UPF  110  may be supported in a single UFP instance operating as one UPF. 
     The AF  150  may interact with the 3GPP core network to provide services (e.g., support functions including access to application influence on traffic routing and network capability exposure, and interaction with a policy framework for policy control). 
     The (R)AN  20  may collectively refer to new radio access networks supporting both evolved E-UTRA (e-UTRA) being an evolved version of 4G radio access technology and New Radio (NR) access technology (e.g., gNB).  
     The gNB may support functions, such as radio resource management function (i.e., radio bearer control, radio admission control, connection mobility control, dynamic allocation of resources to the UE in uplink/downlink (scheduling)), Internet Protocol (IP) header compression, encryption and integrity protection of user data streams, selection of AMF  120  upon attachment of the UE  10  if routing toward the AMF  120  is not determined based on information provided to the UE  10 , routing of user plane data toward UPF(s)  110 , routing of control plane information toward the AMF  120 , connection setup and release, scheduling and transmission of paging messages (generated from AMF), scheduling and transmission of system broadcast information (generated from AMF or operation and maintenance (O&amp;M)), configuration of measurement and measurement reporting for mobility and scheduling, transport level packet marking in uplink, session management, support of network slicing, QoS flow management and mapping to data radio bearer, support of UE in inactive mode, NAS message distribution function, NAS node selection function, radio access network sharing, dual connectivity, and tight interworking between NR and E-UTRA. 
     The UE  10  may mean a user equipment The user equipment may be referred to as a term such as a terminal, a mobile equipment (ME), and a mobile station (MS). Also, the user equipment may be a portable device such as a notebook computer, a cellular phone, a personal digital assistant (PDA), a smartphone, and a multimedia device, or a non-portable device such as a personal computer (PC) and a vehicle-mounted device. Hereinafter, it will be referred to as a user equipment (UE) or a terminal. 
     A network exposure function (NEF) entity and an NF repository function (NRF) entity are not shown in  FIG.  1    for clarity of description, but all NFs shown in  FIG.  5    to be described later may perform mutual operations with the NEF and the NRF as necessary. 
     A description is given of the NRF. The NRF (not shown in  FIG.  1   ) may support a service discovery function. When receiving a second NF discovery request from a first NF instance, the NRF may perform a discovery operation for the second NF and provide information on the discovered second NF instance to the first NF instance. It can also maintain available NF instances and the services they support.  
     Meanwhile,  FIG.  1    illustrates a reference model for a case in which the UE accesses one DN by using one PDU session for convenience of description, but the disclosure is not limited thereto. 
     The UE  10  may simultaneously access two (i.e., local and central) data networks by using multiple PDU sessions. Here, two SMFs may be selected for different PDU sessions. However, each SMF may have a capability of controlling both a local UPF and a central UPF within a PDU session. 
     Further, the UE  10  may simultaneously access two (i.e., local and central) data networks provided within a single PDU session. 
     In the 3GPP system, a conceptual link between the NFs in the 5G system is defined as a reference point. The following illustrates reference points included in the 5G system architecture represented in  FIG.  1   .
     N 1 : reference point between UE and AMF   N 2 : reference point between (R)AN and AMF   N 3 : reference point between (R)AN and UPF   N 4 : reference point between SMF and UPF   N 5 : reference point between PCF and AF   N 6 : reference point between UPF and data network   N 7 : reference point between SMF and PCF   N 8 : reference point between UDM and AMF   N 9 : reference point between two core UPFs   N 10 : reference point between UDM and SMF   N 11 : reference point between AMF and SMF   N 12 : reference point between AMF and AUSF   N 13 : reference point between UDM and authentication server function (AUSF)   N 14 : reference point between two AMFs   N 15 : reference point between PCF and AMF in case of a non-roaming scenario, reference point between PCF in visited network and AMF in case of a roaming scenario   

       FIG.  2    is a diagram illustrating the architecture of network entities in a wireless  communication system according to various embodiments of the disclosure. 
     The network entity of the disclosure is a concept including a network function according to system implementation. A term such as ‘part’ or ‘device’ used hereafter indicates a unit for processing at least one function or operation, which may be implemented using hardware, software, or a combination thereof. In addition, as described above, each function may be implemented in one device or server, or may be implemented by using two or more servers or devices. 
     In  FIG.  2   , the components are substantially the same as those of  FIG.  1   , but with the following differences. 
     Compared with  FIG.  1   , the NEF  190  added in  FIG.  2    provides a means to securely expose services and capabilities provided by 3GPP network functions for, e.g., 3rd party, internal exposure/re-exposure, application function, and edge computing. The NEF  190  may receive information from other network function(s) (based on exposed capabilities of other network function(s)). The NEF  190  may store the received information as structured data by using a standardized interface to a data storage network function. The stored information can be re-exposed by the NEF  190  to other network functions and other application functions, and can be used for other purposes such as analytics. 
     Also, 3 different UPFs  210 ,  220  and  230  and a new DN  240  are illustrated in  FIG.  2   . The first UPF  210  connected to the AN  20  as in  FIG.  1    may be connected over N 9  to the third UPF  230  for connecting to the new DN  240 . Further, the first UPF  210  may be connected to the existing DN  180  through the second UPF  220 . 
     The configuration illustrated in  FIG.  2    exemplifies one of the structures of the 5G core network supporting edge computing. The control plane functional entities of the 5G core network shown in  FIG.  2    are the same as those of  FIG.  1    described above, and the same reference symbols are given to the same parts. A 5G core network architecture in which the UE  10  communicates with an edge application server (EAS) via the first UPF  210  acting as an uplink classifier (ULCL)/branching point (BP) is shown. The UE  10  may be connected to the second UPF  220  through the first UPF  210  serving as ULCL/BP UPF for users protocol data units (PDUs), and may then be  connected to the data network (DN)  180 . Here, the second UPF  220  may be the first PDU session anchor user plane function (PSA-UPF) in  FIG.  2   . 
     Further, the first UPF  210  may be connected to the third UPF  230  while being connected to the second UPF  220 . Here, the third UPF  230  as the second PSA-UPF may connect to the DN  240  at a location geographically close to the UE. An edge application server (EAS)  241  providing edge computing services is located on the regionally close data network  240 , and the UE  10  may communicate with the EAS  241  to provide an edge computing service. The SMF  130  may establish N 4  sessions with the first UPF  210 , the second UPF  220 , and the third UPF  230 , and transmit a rule for forwarding traffic for each of the UPFs  210 ,  220  and  230  to control the individual UPFs  210 ,  220  and  230 . In addition, the SMF  130  may transmit 3-tuple information including destination IP address, destination port number, and protocol number to the ULCL/BP UPF  210 , the first UPF  210  operating as a ULCP so that the UE  10  connects to the third UPF  230  being locally close second PSA-UPF, and may determine whether to route the traffic of the UE  10  to the local data network or the first PSA-UPF  220 . In this structure, to enable the UE  10  to communicate with the EAS  241  through the nearby local PSA-UPF  230 , the 5G core network may perform a procedure for adding/changing/removing the ULCL/BP  210  and the local PSA-UPF  230 . 
     Meanwhile, in the legacy 3GPP 5G core network, relocation of a PDU session anchor-user plane function (PSA-UPF) does not take into account data path delay. That is, in the legacy 3GPP 5G core network, the session management function (SMF) internally determines the relocation of a PSA-UPF by using topology information. Various embodiments of the disclosure may provide a method for the 5G core network and an application program to determine whether to relocate a PSA-UPF in consideration of the delay time of the data path in response to a request from an application function requiring a low-latency service. 
     According to various embodiments of the disclosure, the 5G core network and the application program determine the relocation of a PSA-UPF in consideration of the delay of the data path. When a handover occurs due to a case where the UE receiving  services from one or more application programs exits the service area in which the currently connected application program is deployed, if PSA-UPF relocation is performed, the IP address of the UE may be changed and service interruption may occur. 
     According to various embodiments of the disclosure, considering the delay requested by the application, if the delay requested by the application is satisfied by the existing data path in the area to which the UE has moved, service interruption may be minimized by not performing PSA-UPF relocation. 
     According to various embodiments of the disclosure, when the UE moves and provides a service through a newly changed path, or when the delay requested by the application program is not satisfied, it is possible to provide a service that satisfies the delay time requested by the application program by reconfiguring the path with a new PSA-UPF. 
       FIG.  3    is a diagram illustrating another architecture of the 5G core network supporting edge computing according to an embodiment of the disclosure. 
     As described above, for the control plane functions of the 5G core network shown in  FIG.  3   , the same reference symbols are given to the same components as described in  FIGS.  1  and  2   . Hence, additional descriptions of the same components will be omitted.  FIG.  3    according to the disclosure illustrates a 5G core network architecture in which the UE  10  communicates with an EAS  321  included in the DN  320  without using ULCL/BP. In this network architecture, in order for the UE  10  to access the EAS  321  through the PSA-UPF  310  close to the UE  10  after UE movement, a procedure for PSA-UPF relocation may be performed using service and session continuity (SSC) mode 2 or SSC mode 3. 
       FIG.  4    is an illustrative diagram for explaining a case in which the UE moves by using a network topology according to the disclosure. 
     According to the diagram shown in  FIG.  4   , a network configuration diagram in which local data networks have separate IP ranges in an IPv4 ULCL environment is illustrated. 
     Referring to the configuration of  FIG.  4   , a specific application (app, not shown in FIG.   4 ) in the UE  10  may connect to a first data network  410 , for example, the data network whose IP address is set to “10.10.10.*”. When the UE  10  connects to the first data network  410  in this way, it can connect through PSA-UPF #1 ( 411 ) being a UPF for connecting to the first data network  410 , a ULCL/BP  401 , and the RAN  20  connected to the ULCL/BP  401 . Further, when the UE  10  connects to the Internet, it can connect through the ULCL/BP  401  being a UPF for connecting to the Internet and the corresponding RAN  20 . Here, when the UE  10  connects to the first data network  410 , the UE may have “10.10.10.xx”as a data network access identifier (DNAI) as described above. 
     When the UE moves to a second RAN  21  as illustrated in  FIG.  4   , it can connect to a data network whose IP address is set to “10.10.20.*” through a ULCL/BP  402  being a new UPF and new PSA-UPF #2 ( 421 ). As another example, although the UE  10  moves to the second RAN  21 , it may be connected to previous PSA-UPF #1 ( 411 ) through the ULCL/BP  402  being a new UPF. 
     A case may occur in which the UE  10  connects through the ULCL/BP  402  being a new UPF and new PSA-UPF #2 ( 421 ). In this case, before the DNAI change, the UE  10  is connected to the first local data network  410 , and the app of the UE  10  is connected to EAS #1 ( 413 ), so that the UE  10  can create a TCP context. Further, when the DNAI is changed due to the movement of the UE  10  as described above, the SMF (not shown in  FIG.  4   ) may perform a procedure for adding an additional PSA. After the DNAI change, the app of the UE  10  should be connected to the IP address (e.g., “10.10.20.1”) of EAS #1 ( 423 ) of the second local data network  420 . However, the TCP context of the UE  10  is maintained, and the app of the UE  10  cannot connect to EAS #1 ( 420 ) of the second local data network  420  because the app is not aware of the local network change and the existing TCP context is still maintained. 
     A more detailed explanation of this is as follows. 
     In the network configuration diagram of  FIG.  4   , the UE  10  may be moved from a place where the first local DN  410  is located to a place where it accesses the second local DN  420 . In such a case, as illustrated in  FIG.  4   , the first PSA-UPF  411  of the UE  10  may be not changed. That is, the UE  10  may maintain PSA-UPF #1 ( 411 ). In this  case, the IP address of the UE  10  is maintained, but in the application layer session to which the UE  10  is to be connected through first local PSA-UPF #1 ( 411 ), the context of the UE  10  should be removed when the PSA-UPF  411  for the first local DN  410  is released. However, in the current ULCL or local PDU-UPF deletion operation, there is no information notifying this to the UE  10 . In this case, when the UE  10  connects to the second local DN  420  and attempts to access the same EAS, the upper layer context for the first local DN  410  remains in the UE  10 . As a result, the UE  10  cannot access the EAS of the second local DN  420 . More specifically, this upper layer context may be DNS (domain name system or domain name server) information for a fully qualified domain name (FQDN) of the EAS. The DNS address of the EAS received from the first local DN may be, for example, “10.10.10.1”. This DNS procedure may be cached in the DNS client of the UE  10  by the lifetime of the DNS record. Even when the UE  10  connects to the second local DN due to movement or SMF (not shown in  FIG.  4   ) determination, when a DNS query for the same EAS #1 is issued, the connection is made to the address of “10.10.10.1”due to the information cached in the DNS client of the UE  10 . In such a case, it is not possible to transmit or receive data traffic to or from EAS #1 ( 423 ) in the second local DN. 
     As another example, this is a case in which a connection-oriented upper layer session is established between the first local DN  410  and EAS #1 ( 413 ). For example, a TCP connection of the UE  10  may be established between the first local DN  410  and EAS #1 ( 413 ). In this situation, due to movement of the UE  10  or local determination of the SMF, when the SMF removes the PSA-UPF  411  connected to the first local DN  410  and connects the session with PSA-UPF #2 ( 421 ) toward the second local DN  420 , the TCP connection, which is one of the upper layer network contexts of the UE  10 , is maintained without being disconnected from the previous session. Hence, the UE  10  cannot connect to the IP address (e.g., “10.10.20.1”) of EAS #1@LDN2 ( 423 ) located in the second local DN  420 . 
     To solve this problem, the disclosure assumes a structure inside the UE as shown in  FIGS.  5 A and  5 B . 
       FIGS.  5 A and  5 B  are illustrative diagrams for explaining the internal configuration of  a UE and a case of establishing a PDU session with a wireless communication network and a data network according to an embodiment of the disclosure. 
       FIGS.  5 A and  5 B  are shown separately because it is difficult to represent both the configuration of the UE and the configuration of the network in one drawing. In addition, it can be seen from  FIGS.  5 A and  5 B  that components included in one specific component, for example, the communication processor or modem  1010  of the UE may include the NAS control plane  1011 . 
     First, with reference to  FIG.  5 A , the UE  10  may include a communication processor or modem  1010  and an application processor (AP)  1030 . Hereinafter, the communication processor or modem  1010  may be referred to as “communication processor” or “modem” and all of them may correspond to reference numeral  1010  in  FIGS.  5 A and  5 B . In addition, it should be noted that all elements unnecessary in describing the disclosure have been omitted in  FIGS.  5 A and  5 B . For example, elements essential for wireless communication such as memory, power, and antenna may be further included. In addition, the UE  10  may include various circuits or logics for user convenience. For example, various circuits, logics and/or modules such as RF transceiver circuit, display module, touch screen, speaker, and microphone may be further included. 
     The application processor  1030  may basically run at least one application.  FIG.  5 A  illustrates a case in which two different applications  1031  and  1032  are running. In the application processor  1030 , a TCP/IP stack  1020  may be included in the operating system (OS) kernel. For convenience of description, it will be referred to as “TCP/IP stack”. Layer 4 contexts  1021  and  1022  may be included in the TCP/IP stack  1020 . The layer 4 contexts  1021  and  1022  may be, for example, a socket. The sockets  1021  and  1022  may be connected to the corresponding applications  1031  and  1032  through a socket application interface (API). 
     Also, the communication processor  1010  and the application processor  1030  may be connected through network interfaces  1031 ,  1032  and  1033 . In  FIG.  5 A , three different network interfaces  1031 ,  1032  and  1033  are illustrated, and among them, the first network interface  1031  is illustrated as being connected to the sockets  1021  and   1022 . 
     The UE  10  may connect to the 5G core network  500  through an access network  20  such as a base station. As such, when the UE  10  is connected to the 5G core network  500 , a PDU session may be established between the UE  10  and the PSA-UPF of the 5G core network  500 .  FIG.  5 A  illustrates a case in which N PDU sessions  521 ,  522  and  523  can be configured in one UE. 
     In addition, the UE  10  may ultimately receive a service from the 5G core network  500 , or may receive a data service from at least one data network  510  among the data networks  510 ,  514  and  515  through the 5G core network  500 .  FIG.  5 A  illustrates a case in which the first data network  510  is an edge computing data network. However, the data network  510  may be a local data network (local DN). 
     Next, with reference to  FIG.  5 B , in the TCP/IP stack  1020  of the UE  10 , a modem control interface  1021  for connecting to the modem, a URSP manager  1022 , a DNS client  1023 , a context manager  1024 , and an interface manager  1025  may be included. Also, in the TCP/IP stack  1020  of the UE  10 , additional components may be further included as necessary in addition to the components described in  FIG.  5 B . 
     The communication processor  1010  may include a NAS control plane  1011 . 
     In addition, as described above, the 5G core network  500  may include the AMF  120 , the SMF  130 , the PCF  140 , the UDM  170 , and the NEF  190 . Additionally, the UDR  504  that has been described above in  FIG.  1    is further illustrated. The 5G core network  500  may be connected to an AF  150  located outside through the NEF  190 . 
     Although the configuration of the UE  10  has been separately illustrated in  FIG.  5 A  and  FIG.  5 B , those skilled in the art can identify the overall configuration of the UE from the drawings of  FIGS.  5 A and  5 B , and it should be noted that the diagrams of  FIGS.  5 A and  5 B  are configurations for the network interface and the upper layer context. Also, in the following description,  FIG.  5 A  and  FIG.  5 B  will be collectively referred to as  FIG.  5   . 
     In  FIG.  5   , the user equipment (UE)  10  is depicted as being composed of an application processor (AP) and a communication processor (CP) as described above. However, in the UE  10 , the application processor and the communication processor may be  implemented as a single chip. In this case, both the application processor and the communication processor may be included in one processor. For example, even when one process physically exists, the logical function performed by the AP and the logical function performed by the CP may be the same. Applications of the UE  10  may reside in the AP, and such an application may send/receive a request/response to/from the mobile operating system (e.g., Android, Linux, Tizen, BSD Unix, iOS) by invoking a network-related system call and a system library call through the socket interface  1041 . In addition, as described above, the TCP/IP stack  1020  resides in the mobile operating system running on the AP, and the TCP context may be managed by a kernel socket for TCP context management. Also, the mobile operating system may communicate with the CP  1010  through at least one of the network interfaces  1031 ,  1032  and  1033 . Further, in the AP  1030 , a URSP manager  1022  for URSP processing, a DNS client  1023 , a context manager  1024  for upper network layer context management, and an interface manager  1025  for network interface management may be included. In addition, these managers  1022 ,  1023 ,  1024  and  1025  may be connected to the CP  1010  through the modem control interface (modem control I/F)  1021  and used for control purposes. The CP  1010  may interwork with a base station by implementing functions provided by the 3GPP air interface. Further, a module for controlling the NAS control plane  1011  may exist in the CP  1010 , and the NAS control plane  1011  may interwork with the AMF  120  of the 5G core network  500 . A session-related NAS control message may be delivered through the AMF  120  to the SMF  130 . 
     The protocol data unit (PDU) transmitted through the network interface of the UE  10  is an IP datagram when the PDU session type is IP. This IP datagram may reach the PSA-UPF  501  of the 5G core network  500  through the PDU session ( 521  in  FIG.  5   ). The PSA-UPF  501  may transmit the received IP datagram to the data network  510  being an IP network. 
     In the disclosure, it is assumed that the data network is an edge computing data network. Edge application servers (ESAs)  511  and  512  and a domain name server (DNS)  513  may reside in the data network  501 . The ESAs  511  and  512  and the DNS  513  may communicate with the UE  10 . The UDM, UDR, NEF, AF, AMF, SMF, and  PCF residing in the 5G core network  500  perform the same function as the network functions described in  FIG.  1   , and thus a repeated description will be omitted herein. 
     In  FIG.  5   , the relationship between the network interface of the UE  10  and the PDU session is illustrated on the assumption of one-to-one connection. When the application program of the UE  10  requests a TCP connection, a TCP session is established. In this process, establishment of a TCP session may be requested through a method such as “connect” system call. When a TCP session is successfully established in the operating system, the TCP context can be bound to an interface having the source IP address of the UE. 
     If the network interface goes down, all contexts corresponding to the TCP session bound to the interface are removed. Due to this behavior, if a SSC mode 2 operation is performed, the SMF  130  may release a first PDU session and establish a second PDU session for PSA-UPF relocation. In this process, all TCP contexts bound to the first PDU session of the UE  10  are removed, so that the continuity of the session cannot be guaranteed. 
     In addition, for SSC mode 3 operation, the SME  130  may instruct to establish a second session for PSA-UPF relocation, and the UE  10  may establish the second PDU session and temporarily exchange data traffic through both the first PDU session and the second PDU session. In this situation, while the first network interface corresponding to the first PDU session is maintained in the UE  10 , a second network interface is generated in correspondence to establishment of the second PDU session. Later, when the first PDU session is released, the network interface for the first PDU session goes down, and all TCP contexts bound to this network interface are removed. Hence, the upper layer context of the first PDU session cannot maintain continuity. 
     In an operation proposed in the disclosure, when a first local DN is generated or released, the SMF  130  transmits information about the local DN to the UE  130  through NAS signaling, for example, a PDU session change message. Upon receiving this, the UE  10 , according to the policy determined by the SMF  130 , based on the information received from the local DN, may forward the relevant information to the upper network context manager, DNS client, URSP manager  1022  residing in the AP   1030  of the UE  10 . Also, if there is a command to be performed in the upper network layer in relation to the local DN, the UE  10  may forward such information together. When the modem (CP)  1010  of the UE receives information corresponding to the upper layer, it forwards the information and instruction to the AP  1030 , and the corresponding manager in the AP  1030  may carry out this. For example, when the SMF  130  generates a new local DN and sets a DNS server address for the corresponding local DN, the AP  1030  receives this information and may forward the information to the DNS client  1023 . Alternatively, when the SMF  130  creates a new local DN and informs the CP  1010  of the UE  10  of the corresponding IP address range, the CP  1010  of the UE may transfer the corresponding IP address range to the AP  1030  so that the upper layer context manager  1024  may record it. Thereafter, when the local PSA-UPF for the corresponding local DN is removed, the SMF  130  may notify the CP  1010  of the UE  10  of local PSA-UPF removal information. Then, the SMF  130  may additionally transmit request information for releasing the upper layer context  1024  bound to the corresponding local DN to the CP  10  of the UE  10 . Upon receiving this, the CP  1010  of the UE informs the information received from the SMF  130  to the upper layer context manager  1024  of the AP  1030 , and the upper layer context manager  1024  of the AP  1030  may release the upper layer context (e.g., TCP context information) managed in the mobile operating system. This process can be expressed as “re-evaluate URSP”. 
       FIG.  5 C  is an illustrative diagram for describing a local DN binding context according to an embodiment of the disclosure. 
       FIG.  5 C  is another representation of the configuration diagram of the UE  10  described in  FIGS.  5 A and  5 B , and additionally explains the local DN binding context described in the disclosure. Descriptions of components not separately described are the same as in  FIGS.  5 A and  5 B . Parts with different reference numerals in  FIG.  5 C  are newly numbered ones for the description of the disclosure, and may be understood from the same viewpoint as in  FIGS.  5 A and  5 B . 
     In  FIG.  5 C , application program 1 ( 1034 ) of the UE has a TCP connection with EAS #1 ( 552 ) of the local DN  551 , and layer 4 context #1 ( 1021 ) is created in the high  layer OS. Also, application program 2 ( 1035 ) of the UE has a connection with AC #1 ( 553 ) located in the central DN  542 . The layer 4 context  1021  of the UE having a connection with EAS #1 ( 552 ) of the local DN  541  may be an example of the local DN binding context. In the operation described in this disclosure, upper layer network context information may be a local DN binding context. In particular, it can be said that the operation of controlling the upper layer network context due to a notification of the local DN  541  corresponds to the operation of controlling the local DN binding context, and the operation for the local DN binding context may include, for example, removing or maintaining layer 4 context #1 shown in  FIG.  5 C , or refreshing the DNS cache information received from the DNS server  551  configured for the local DN  541 . 
     First Embodiment 
     The first embodiment of the disclosure proposes a scheme by which, when the SMF  130  determines to add a BP/ULCL and a local PSA-UPF, the SMF  130  informs the UE  10  of information about the local DN to be added through a PM session change message. The SMF  130  may deliver control information for the upper layer network context together with information on the PDU session and local DN. 
       FIG.  6    is a signal flow diagram for a case where the SMF provides control information on the upper layer network context together with information on the PDU session and local DN to the UE according to an embodiment of the disclosure. 
     Before referring to  FIG.  6   , the configuration information for the local DN may include at least one of the following information. 
     (1) DNS server address, domain name on which DNS server operates 
     (2) Identifier for local DN 
     (3) Indication for addition/relocation/deletion of local DN: this indication indicates addition of a local DN when the SMF  130  determines to add a local PSA-UPF, and indicates deletion of a local DN when the SMF  130  deletes a local PSA-UPF. 
     (4) Information on IP address range of local DN to be added 
     (5) Server IP address for traffic to be routed to local DN, or destination IP address, destination port number, and upper layer protocol number of IP, for example, protocol number indicating TCP or UDP  
     Next, the upper layer network context control information related to the local DN may include at least one of the following information. 
     (1) Whether to delete previous DNS cache information for local DN 
     (2) Context control information for upper layer protocols. For example, preservation indication for upper layer protocol (e.g., TCP context, HTTP context) 
     (3) Re-evaluation indication for URSP: instructs to release binding of URSP to application traffic and evaluate URSP rules. 
     (4) Refresh indication for PDU session binding to application traffic: instructs to release binding of PDU session to specific application traffic and delete corresponding context. 
     In addition, the SMF  130  may receive AF traffic control information including a DNAI (AF influenced traffic steering enforcement control information) from the PCF  140 . When the SMF  130  detects a change in DNAI due to the movement of the UE  10 , additional PSA addition and LDN addition information may be determined. 
     When the SMF  130  determines to add an additional PSA, the SMF  130  may perform a procedure for ULCL and local PSA addition. 
     At operation  610  (procedure 0), the UE  10  may have a previously established PDU session and may be connected to the UPF  602  being PSA1 through the RAN  20  and a tunnel. 
     At operation  612  (procedure 1), the SMF  130  may determine the UPF  603  corresponding to PSA2 being new PSA based on a UE mobility event, and generate N 4  with new PSA2. Also, upon receiving (or detecting) a UE mobility event, the SMF  130  may determine, based on the PCC rule and/or local DN configuration received from the PCF  140 , “local DN notification control information”, “UE upper layer context control information (i.e., local DN binding context information)”, and the steering for local processing traffic. The SMF  130  may transmit an early notification requested by the AF. Then, the SMF  130  may wait for a response to the notification. 
     At operation  614  (procedure 2), the SMF  130  may select a new local PSA-UPF  603  and establish an N 4  session with the local PSA-UPF  603 . 
     At operation  610  (procedure 3), the SMF  130  may select the ULCL/BP UPF   601 , and generate uplink forwarding rules for the ULCL/BP UPF  601 , PSA1  602  and PSA2  603 . The SMF  130  may forward the traffic rules directed to PSA1  602  and PSA2  603  to the ULCL UPF  601 . That is, the SMF  130  may transmit an AF traffic influence late notification to the AF. Then, the SMF  130  may wait for a response. 
     At operation  618  (procedure 4), the SMF  130  may update the N 4  session with PSA1  602 . Also, for DL traffic, the SMF  130  may provide tunnel information about the ULCL-BP  601  to PSA1  602 . 
     Thereafter, at operation  620 , PSA1  602  may transmit a downlink PDU to the first UPF  601 . Then, the first UPF  601  may forward the received downlink PDU to the UE  10 . Also, at operation  622 , the UE  10  may transmit an uplink PDU to be delivered to PSA1  602  by using a corresponding tunnel. The order of operation  620  and operation  622  may be changed when tunnel information is known in advance to the UE and PSA1  602 . That is, if the tunnel information is mutually known, operation  620  may be performed after operation  622 . 
     At operation  624  (procedure 5), the SMF  130  may update the N 4  session with PSA2  603 . Thereby, for DL traffic, the SMF  130  may provide tunnel information about the ULCL-BP  601  to PSA2  603 . 
     At operation  626  (procedure 6A), when the SMF  130  needs to notify the UE  10  of L-PSA configuration information, the SMF  130  may transmit a PDU session modification command to the UE  10 . 
     Local DN configuration information may be configured directly in the SMF  130  or configured in the PCF  140 . When the SMF  130  receives policy and charging control (PCC) information for the UE  10  from the PCF  140  through the SMPolicyAssociation creation or change procedure, it may also receive the local DN configuration information, where the local DN configuration information may include 3-tuple information, DNS address, and local DN subnet address. 
     If the SMF  130  determines to add/change/delete a local PSA-UPF, the SMF  130  may record this as local DN event information and deliver it to the UE  10 . 
     The SMF  130  may receive the local DN binding control information from the AF request or the PCF  140 . Based on this information, the SMF  130  may deliver at least  one of the following information to the UE  10 . 
     (1) L-PSA addition, 
     (2) Added 3-tuple 
     (3) Added subnet address, 
     (4) DNS address, 
     (5) Existing DNS refresh indication, 
     (6) Upper network context preservation indication, 
     (7) URSP traffic re-evaluation indication information 
     Upon receiving this information, the UE  10  may perform an operation specified in the LDN information. That is, the upper layer context may be maintained, and URSP traffic may be re-evaluated. Thereafter, at operation  628  (procedure 6B), the SMF  130  may transmit N 2  SM information to the RAN  20  through N 11  and the AMF  120 . That is, the SMF  130  may deliver new CN tunnel information (ULCL/BP tunnel information) to the RAN  20 . 
     Meanwhile, at operation  630 , the UE  10  may still transmit an uplink PDU to PSA1  602  through the first UPF  601  by using the previous tunnel. 
     At operation  632  (procedure 7), in case of IPv6 multi-homing (MH), the SMF  130  may transmit a router advertisement (RA) (new IP prefix, routing rule) message to the UE  10  through PSA2  603 . The SMF  130  may also transmit a late notification to the AF. 
     At operation  634  (procedure 8), in case of IPv6 MH, the SMF  130  may transmit an RA (original IP prefix, routing rule) through PSA1  602  for reconfiguring the previous IP prefix. 
     Thereby, at operation  636 , the UE  10  may transmit an uplink PDU to be delivered to PSA1  602  to the first UPF  601 . Then, the first UPF  601  may forward it to PSA2  603 . 
     Thereafter, at operation  640 , the UE  10  may perform upper layer control, such as URSP re-evaluation, or upper layer context retrain or refresh. 
     Second Embodiment 
     The second embodiment of the disclosure defines UE and system operations when the SMF  130  performs a procedure of detecting a DNAI change due to the movement of  the UE  10  and removing a local PSA. In this procedure, the SMF  130  may determine to notify the local DN configuration information and deliver upper layer network context control information to the UE  10  together with the local DN configuration change notification. 
     The procedure according to the second embodiment may be performed as follows. The following description will be given using the components of  FIG.  6    described above. 
     At step 1, the UE  10  has a PDU session with an added local PSA (procedure for deleting PSA1 and maintaining PSA2). 
     At step 2, in case of IPv6 MH, the SMF  130  may reconfigure the UE IPv6 prefix for PSA1  602  and PSA2  603 . 
     At step 3, the SMF  130  may determine to remove the local PSA based on various reasons. When the SMF  130  requires notification of the L-PSA configuration information to the UE  10 , the SMF  130  may transmit a PDU session modification command to the UE  10 . The LDN configuration information for transmission may include information regarding LDN removal, LDN identifier, removed 3-tuple list, removed subnet address, removed DNS address, existing DNS refresh indication, upper network context preservation indication, and URSP traffic re-evaluation indication. 
     At step 4, the SMF  130  may update PSA2 CN tunnel information to the RAN  20 . If there is an additional UPF between the RAN  20  and the ULCL  601  (corresponding to a case of cascaded UPFs), CN tunnel information for this UPF may be updated. 
     At step 5, the SMF  130  may update AN tunnel information in the N 4  session for PSA2  603 . If there is an additional UPF between the RAN  20  and the ULCL  601  (corresponding to a case of cascaded UPFs), CN tunnel information for this UPF may be updated. 
     At step 6, the SMF  130  may release N 4  of PSA1  602 . In case of IPv6 MH, the SMF  130  may release the IPv6 prefix. 
     At step 7, if step 4/5 described above is performed, the SMF  130  may release the N 4  session corresponding to the ULCP/BP  601 .  
     Third Embodiment 
     The third embodiment of the disclosure is a procedure for the SMF  130  to deliver local DN notification and upper layer network context control information to the UE based on the operator policy for the local DN. 
       FIGS.  7 A and  7 B  are signal flow diagrams for a case where the SMF provides local DN notification and upper layer network context control information to the UE according to an embodiment of the disclosure. 
     The mobile communication operator may set in advance configuration information for a local DN in operator policy information of the PCF  140 . The operator policy, information set in the PCF  140  may include information on the local DN for each DNAI (operator configured local DN information). 
     The operator policy information may include, for example, at least one of the following information.
     Local DIN identifier: DNAI   Service area for local DN: tracking area or cell list   IP address range, e.g., 10.10.10.*   Whether local DNS is operated   Local DNS address and domain name for local DNS   Service provider identifier or sponsor identifier   Whether to provide service continuity when moving local DN   Whether to notify local DN information to UE   

     The PCF  140  may generate a PCC rule by including local DN control information in the AF traffic steering enforcement control information based on the configuration information about the local DN, and may transmit local DN notification control information to the SMF  130 . The local DN notification control information may include at least one of the following information.
     Local DN identifier (e.g., data network access identifier (DNAI))   Whether to notify local DN information to UE   Local DN binding control information: local DN binding control information may include layer 4 (TCP) context preservation/refresh information and DNS cache refresh  information.   UE upper network context refresh indication when leaving local DN   Local DN configuration information   

     The SMF  130  may receive the PCC rule, and may perform local PSA and ULCL addition operations when the UE  10  enters the DNAI area. Hence, the UE  10  may operate according to the local DN control information. 
     The SMF  130  may deliver a local DN addition notification to the UE  10 , and may deliver upper network layer control information. 
     Then, signal flows and associated operations according to the disclosure will be described with reference to the accompanying  FIGS.  7 A and  7 B .  FIG.  7 A  and  FIG.  7 B  may be sequentially performed. For example, after the flow of  FIG.  7 A  is completed, the signal flow of  FIG.  7 B  may be continued. As another example,  FIG.  7 B  may be performed independently of  FIG.  7 A . The following description will be given based on a case where  FIGS.  7 A and  7 B  are sequentially performed. 
     In procedures  701  and  702 , the UE  10  may transmit a PDU session establishment request (PDUSession_CreateSMcontext request) message to the SMF  130  via the AMF  120 . For establishment of the first PDU session, the UE  10  may transmit information such as whether the local DN control function is supported and whether the upper layer network context control function is supported to the SMF  130 . 
     Upon receiving the PDU session request from the UE  10 , in procedure  703 , the SMF  130  may receive subscription information from the UDM  170  to identify the subscription information of the UE  10 . 
     Upon obtaining the subscription information of the UE  10 , in procedure  704 , the SMF  130  may transmit a PDU session establishment context response (PDUSession_CreateSMcontext response) message to the AMF  120 . 
     In procedure  705 , the SMF  130  may create a connection with the PCF  140  for receiving the SM policy and may receive a PCC rule for the PDU session of the UE  10  from the PCF  140 . The PCC rule may include the AF influenced traffic steering enforcement control information. The AF influenced traffic steering enforcement control rule may include at least one of the following information.  
     (1) DNAI (data network access identifier) 
     (2) Whether local routing is supported: it may indicate more specifically whether IPv6 multihoming or ULCL is supported. 
     (3) IP address preservation indication (or, network interface preservation indication) 
     (4) Upper layer context preservation indication, or upper layer network refresh indication 
     (5) Whether application layer relocation is possible 
     (6) N 6  routing information 
     ( 7 ) Local DN control information 
     When the SMF  130  adds a local PSA-UPF for connecting to the local DN the local DN control information may include whether to notify the local DN information to the UE  10  and information to be notified to the UE  10 . 
     In procedure  706 , the SMF  130  may select a first PSA-UPF  701  capable of supporting the SSC support provided by the UE and the AF influenced traffic steering enforcement control information received from the PCF  130 . 
     In procedures  707  and  708 , the SMF  130  may determine to establish a PDU session, and transmit a PDU session establishment response message to the UE  10  through the AMF  120 . 
     In procedures  709  and  710 , the SMF  130  may receive RAN tunnel information provided by the RAN  20  from the AMF  120 , and may configure tunnel information for downlink traffic of PSA-UPF1  791 . 
     Hereinabove, the PDU session establishment procedure has been described. Next, a case in which a local PSA is newly added (triggering of local PSA insertion) will be described. 
     In procedure  711 , when the UE  10  detects an exit from the current registration area, it may transmit a registration request message to the AMF  120  through the RAN. Or, when the UE  10  performs handover to another base station according to a command of the base station  20 , the AMF  120  may detect an occurrence of handover from the base station  20  during the handover process. Or, when the UE  10  transmits a service request in an idle state (connection management idle (CM-IDLE) state), the AMF  120   may detect that the UE  10  has been moved. To update the PDU session, the AMF  120  may transmit a PDUSesssion_Update_SMContext request including location information of the UE  10  to the SMF  120 . 
     In procedure  712 , when the PCF  140  receives a request for AF traffic steering from the AF or the AF traffic steering rule inside the operator is changed, the PCF  140  may transmit a policy and charging control (PCC) rule including the AF influenced traffic steering enforcement control information to the SMF  130 . The AF influenced traffic steering enforcement control information may include the information in procedure  705  described above, such as local DN control information and upper layer network context control information. 
     In procedure  713 , when the location movement of the UE  10  is detected due to the movement of the UE  10  (procedure  711 ), the SMF  130  may determine whether it has moved to a DNAI set in advance in the SMF  130  or registered through a PCC rule. Or, when AF influenced traffic control enforcement information is received from the PCC, the SMF  130  may determine whether the location of the corresponding UE is included in the location mapped to the DNAI. When the SMF  130  determines to perform ULCL/BP and local PSA-UPF addition, the SMF  130  may perform a procedure corresponding to phase C of  FIG.  7   . 
     Next, phase C will be described. Phase C may be a procedure for ULCL/BP and local PSA-UPF addition (insertion). 
     In procedure  714 , the SMF  130  may establish an N 4  session with PSA2  792 . 
     In procedure  715 , the SMF  130  may establish an N 4  session with the ULCL/BP UPF  793 . 
     In procedure  716 , the SMF  130  may change the N 4  session of PSA1 for downlink traffic. That is, the tunnel information directed to the RAN  20  may be updated with the tunnel information of the ULCL/BP UPF  793  generated in procedure  15 . Thereafter, the downlink traffic from PSA1  791  is directed to the ULCL/BP  793 . 
     In procedure  717 , the SMF  130  may update the N 4  session with PSA2  792 . 
     In procedure  718 , the SMF  130  may detect a change in the location of the UE  10  through the trigger condition in procedure  713 , that is, the location information of the  UE  10  from the AMF  120 , and determine whether the corresponding DNAI change is made. Or, the SMF  130  may receive the PCC rule including AF influenced traffic steering enforcement control information from the PCF  140 . The PCC rule may include local DN control information including local DN configuration information, and upper layer network context control information of the UE. When a new local UPF connected to the local DN is added, the local DN control information may include local DN control information instructing delivery of upper layer network context control information of the UE together with local DN configuration information to the UE. When the SMF  130  receives this local DN control information and determines to add a local PSA-UPF, it may determine to transmit a PDU session modification command message to the UE  10  through the AMF  120  for delivering local DN configuration information and upper layer network context control information to the UE  10 . 
     In procedure  719 , the SMF  130  may transmit an N 1 N 2 MessageTransfer message including the PDU session modification command message to the AMF  120 . This message may include a PDU session identifier, local DN configuration information, and upper layer network context control information, which may be information for modifying the PDU session. 
     The local DN configuration information may be the same as the local DN information described in the first embodiment described above. Also, the upper layer network context control information may be the same as the upper layer network context control information described in the first embodiment described above. 
     When the SMF  130  determines to add a ULCL/BP, to transmit CN tunnel information to the RAN  20  for tunnel establishment between ULCL/BP and PSA1 and between ULCL/BP and PSA2, the CN tunnel information may be further included in the N 1 N 2 MessageTransfer message transmitted to the AMF  120 . 
     In procedure  720 , the AMF  120  may transmit, to the RAN  20 , all or at least some of the information received from the SMF  130  as an N 2  message, that is, the contents included in N 1 N 2 MessageTransfer. 
     In procedure  721 , among the contents included in the RAN N 2  message, tunnel  information may be configured for uplink traffic received from the RAN for the local ULCL/BP. The RAN  20  may perform an AN-specific resource modification procedure on the UE  10  and transmit the PDU session modification command message included in the N 2  message to the UE. Then, the RAN  20  may receive a response to this from the UE  10 . 
     In procedure  722 , the RAN  20  may transmit, to the AMF  120 , tunnel information newly created for PSA2  792  and a response message received from the UE  10  in correspondence to the PDU session modification command. 
     In procedure  723 , the AMF  120  may transfer the information received from the RAN  10  to the SMF  130  and receive a response thereto. 
     In procedure  724 , in case of IPv6 multihoming, the SMF  130  may allocate a new IP prefix for PSA2  792  to the UE  10 , and deliver it to the UE  10 . 
     In procedure  725 , in case of IPv6 multihoming, the SMF  130  may reconfigure the existing IP prefix information for PSA1  791  in the UE  10 . 
     Fourth Embodiment 
     The fourth embodiment provides a procedure and corresponding node operations for transferring local DN information and upper layer network context information to the UE during a procedure for changing a local PSA due to an AF request. 
       FIGS.  8 A and  8 B  are signal flow diagrams depicting operations of individual nodes to provide corresponding information to the UE when a local PSA is changed in response to an AF request in the network according to an embodiment of the disclosure. In the following description,  FIG.  8 A  and  FIG.  8 B  will be collectively referred to as  FIG.  8   , unless it is necessary to distinguish between  FIG.  8 A  and  FIG.  8 B . Also, the operation of  FIG.  8 B  may be performed after the operation of  FIG.  8 A . As another example, the operation of  FIG.  8 B  may be performed after another operation without the operation of  FIG.  8 A . 
     In procedure  801 , the UE  10  may establish a PDU session with the SMF  120 . The SMF  120  may select PSA-UPF0  802  in this process (procedure  801 - 1 ). A more detailed procedure for this is described in procedures  701  to  710  of the third embodiment, and thus a repeated description thereof will be omitted. In addition, the  SMF  120  may determine to add a ULCP/BP and local PSA-UPF1 (procedure  801 - 2 ). This is described in procedures  711  to  725  of the third embodiment, and thus a repeated description will be omitted. 
     In procedure  802 , the source EES  807  may act as a source AF and transmit an AF request to the PCF  805 . In  FIG.  8   , the PCF  140  and the NEF  190  described in  FIGS.  1  to  3    are shown as one node. This is for convenience of drawing configuration although they perform different operations. Hence, in the following description, the node indicated by indicia  895  will be described as PCF  895  when it operates as PCF, and will be described as NEF  895  when it operates as NEF. As a method of transferring the AF request to the PCF  895 , the AF request may be stored in the UDR (not shown in  FIG.  8   ) through the NEF  895 , and the PCF  895  having received a UDR information change notification may receive it. Upon receiving the AF request, in consideration of the operator policy for the local DN described above in the third embodiment, the PCF  895  may transmit the AF influenced traffic steering enforcement control information including local DN control information and UE upper layer network context control information to the SMF  130 . Both the local DN control information and UE upper layer network context control information may be delivered to the SMF  130 . 
     In procedure  803 , the SMF  130  may receive the PCC rule for the PDU session of the UE  10  from the PCF  895 . The PCC rule may include AF influenced traffic steering enforcement control information. The AF influenced traffic steering enforcement control rule may include at least one of the following information. 
     (1) DNAI (data network access identifier) 
     (2) Information on service area mapped to DNAI 
     (3) Whether local routing is supported: it may indicate more specifically whether IP-v6 multihoming or ULCL is supported. 
     (4) IP address preservation indication (or, network interface preservation indication) 
     (5) Upper layer context preservation indication, or upper layer network refresh indication 
     (6) Whether application layer relocation is possible, 
     (7) N 6  routing information 
     (8) Local DN control information  
     When the SMF  130  adds a local PSA-UPF for connecting to the local DN, the local DN control information may include whether to notify the local DN information to the UE  10  and information to be notified to the UE  10 . 
     In procedure  804 , when the UE  10  detects an exit from the current registration area, the UE  10  may transmit a registration request message to the AMF  120  through the RAN  20 . Or, when the UE  10  performs handover to another base station according to a command of the base station, the AMF  120  may detect an occurrence of handover from the base station during the handover process. Or, when the UE  10  transmits a service request in an idle state (connection management idle (CM-IDLE) state, the AME  120  may detect that the UE  10  has been moved. The AMF  120  may transmit a PDUSessssion_Update_SMContext request including location information of the UE  10  to the SMF  120  for updating the PDU session. 
     In procedure  805 , the SMF  120  may determine whether to relocate the local PSA based on the PCC rule received in procedure  803  or the location information of the UE  10  received in procedure  804 . For example, it is assumed that the information about local DN is set as follows. 
     1) Information about local DN 1
     Local DN identifier: DNAI-A   Service area: TA1, TA2   Associated local PSA-UPF: PSA-UPF #1   IP subnet address: 10.10.10.*   Local DNS address: 10.10.10.200   Local DNS domain name: local1.example.com   

     2) Information about local DN 2
     Local DN identifier: DNAI-B   Service area: TA3, TA4   Associated local PSA-UPF: PSA-UPF #2   IP subnet address: 10.10.20.*   Local DNS address: 10.10.20.200   Local DNS domain name: local2.example.com    

     The SMF  130  may also receive local DN control information from the PCF  895 . The local DN configuration information described above may be configured directly in the SMF or may be configured in the PCF  140  and then received by the SMF  130  from the PCF  140 . This information may include the following operator policy. Such operator information may be configured in advance locally in the SMF  130 .
     Whether to notify UE of local DN configuration information when DNAI is generated   Whether to notify UE of local DN change information when DNAI is changed   Whether to notify UE of local DN removal information when DNAI is removed   

     The SMF  130  may identify the related DNAI based on the location information of the UE  10  received from the AMF  120 , and may determine local PSA-UPF relocation to PSA-UPF #2  804  supporting the DNAI. This determination means a change of the local DN, and the SMF  130  may determine to notify the UE of local DN configuration information, local DN change information, or previous local DN control information according to the local DN control information policy received from the PCF  895 . When the local DN is changed, the SMF  130  may perform a PDU session modification procedure for delivering local DN configuration information to the UE  10 . 
     Further, along with the local DN control information, the PCF  805  may include upper layer network context information of the UE  10  in the PCC rule and deliver it to the SMF  120 . The configuration information for this may include the following information.
     UE upper layer network context preservation or refresh indication when DNAI is changed   UE upper layer network context preservation or refresh indication when DNAI is removed   

     For instance, if local DN1 and local DN2 are in different IP address ranges as in the example described above, the PCF  895  may transmit a policy indicating a refresh of the upper layer network context to the SMF  130  when the DNAI is changed. Upon receiving such a policy, the SMF  130  may select an indication corresponding to the  policy and transmit it to the UE  10  through a PDU session modification command message. For example, the SMF  130  may deliver an upper layer network context refresh indication to the UE  10 . Alternatively, when the DNAI is changed, the SMF  130  may determine to refresh the context by checking the range of the IP address in the local DN information, and transmit an upper layer context refresh indication to the UE  10 . 
     The SMF  130  may determine to release the previously generated local PSA-UPF in response to a DNAI change. In this case, the SMF  130  may deliver an upper layer network context refresh indication together with the local DN deletion information to the UE  10 . The local DN deletion information may include a local DN identifier and an indication indicating that it has been deleted. 
     If a condition for user event notification is satisfied, the SMF  130  may determine whether PSA-UPF relocation that can satisfy the AF request can be performed at the current location of the UE  10  and transmit a corresponding notification to the AF (source EES)  897 . An early notification of the AF may include at least one of the following contents.
     Whether the IP address can be maintained   Whether to perform PSA relocation   Information on expected PDB when relocating PSA   Destination DNAI information in case of DNAI change   

     The source EES  897  may receive an early notification for a user plane event from the SMF  130 . The source EES  897  may determine whether to relocate the application context based on the received information. The source EES  897  may determine to relocate the application context when the following condition is satisfied. The source EES  897  may determine not to relocate the application context when the condition is not satisfied. 
     When the source EES  897  determines to relocate the application context, procedures  816  and  817  may be performed. 
     When the source EES  897  determines to perform PSA relocation, the source EES  897  may deliver a positive response through an AppRelocationInfo message. When the  source EES  897  determines that PSA-UPF relocation is not necessary, the source EES  897  may deliver a negative response to the SMF  130 . 
     When the source EES  897  determines to positively respond to PSA relocation, the EES  897  may make a response by including at least one of the following information in an AppRelocationInfo message.
     Positive response to PSA relocation   Indication that the AF will be changed   Notification address of target AF to be notified.   UE upper layer network context preservation indication   

     The SMF  130  may receive a response message to the early notification from the source EES (AF)  897 . Upon receiving a positive result via the response message, the SMF  130  may select a new PSA-UPF1 and establish an N 4  session. 
     The SMF  130  may deliver a late notification to the source EES (AF)  897 . 
     The late notification message sent by the source EES  897  to the AF may include at least one of the following information.
     Target DNAI   UE IP address   Whether to provide upper layer context preservation information   Whether to notify local DN information to UE   Local DN binding information control information (e.g., whether to delete or maintain L4 context bound to local DN, or whether to delete DNS cache information)   

     After receiving the late notification, the source EES  897  may perform application context transfer as in procedures  823  and  824 . The source EES  897  may deliver context relocation response information to the edge enabler client (EEC) of the UE  10  in procedure  814 - 2 . 
     Thereafter, the source EES  897  makes a response to the SMF  130  by including at least one of the following information in AppRelocation Info in procedure  815 - 1 .
     Whether AppRelocation is successfully performed   Target DNAI   Subscription information of UE (GPSI, etc.)    

     The SMF  130  may receive a response to the late notification. 
     In procedure  816 , the SMF  130  performs an update procedure for the N 4  session. 
     In procedure  817 , the SMF  130  may deliver a PDU session modification message to the UE  10  through the AMF  120  as determined in procedure  805 . As described in the first embodiment, the PDU session modification message may include local DN information and upper layer network context control information and may be delivered to the UE  10 . 
     In procedure  818 , for IPv6 multihoming, the SMF  130  may allocate a new IPv6 prefix to be used in PSA2  894  and transmit it to the UE  10 . 
     In procedure  819 , for IPv6 multihoming, the SMF  130  may reconfigure the settings of UE IPv6 for PSA0  892 . 
     In procedure  820 , the SMF  130  may release the N 4  session for local PSA-UPF1  803  previously connected to the UE  10 . 
     Fifth Embodiment 
     The fifth embodiment defines how the local DN information and upper layer network context control information transmitted from the SMF  130  to the UE  10  through the AMF  120  are used in the UE. 
       FIGS.  9 A and  9 B  are illustrative diagrams for explaining a procedure for providing local DN information and upper layer network context control information to the UE, and operations in the UE according to an embodiment of the disclosure. 
     In the description of  FIGS.  9 A and  9 B , the same reference symbols used in  FIG.  8    will be used for the same elements as those of  FIG.  8   . 
     In procedure  901 , the UE  10  may request the SMF  130  to establish a new PDU session. The SMF  130  may select PSA-UPF0  892 , create a tunnel between PSA-UPF0  892  and the RAN  20 , and transmit an acknowledgement message for the PDU session establishment request to the UE  10 . As described in  FIG.  5   , since the UE  10  has established a new PDU session, a network interface corresponding to the new PDU session may be created, and a mapping may be made therebetween. That is, a network interface corresponding to the new PDU session may be generated between the CP  1010  and the AP  1030  in the UE  10 , and a mapping may be made between the new  network interface and the established PDU session. In addition, applications corresponding to the mapping therebetween may be mapped together. 
     In procedure  902 , the UE  10  may create a TCP connection with the server residing in the central DN connected to PSA-UPF0  802 . A TCP context may be created in an upper layer of the UE  10 . In  FIG.  9   , this is denoted by indicia (A). 
     In procedure  903 , according to various embodiments described above, the SMF  130  may determine to perform local PSA-UPF and ULCL/BP addition, select local PSA-UPF1  893 , and deliver information including 3-tuple (destination IP address, destination port number, and protocol number) to the ULCL/BP  891  for the traffic toward the local PSA-UPF. The SMF  130  may transmit information on the local DN to the UE  10 . Upon receiving this, the UE  10  may store the information on the local DN. Since the local DN information has been described in detail in the first embodiment, a description thereof is omitted herein. The information included in this may include local DN identifier, subnet address, local DNS address. EAS address in local DNS, 3-tuple address transmitted by the SMF to the ULCL, and the like. 
     In procedure  904 , the UE  10  may invoke a DNS query procedure for EAS #1 FQDN at the request of the application layer. The DNS query procedure can be processed by the local DNS server located in local DN1 or by the DNS server located in the central DN. Accordingly, the UE  10  obtains the IP address for EAS #1, where local DN #1 is located. 
     In procedure  905 , the UE  10  may establish a TCP connection by making a TCP connection request to the destination IP address for EAS #1 found through the DNS query procedure. The TCP connection thus created is denoted by indicia (B) in  FIG.  9   . In procedure  906 , when the SMF  130  detects a DNAI change due to movement of the UE  10  or receives a PCC rule including AF influenced traffic steering enforcement control information, the SMF  130  may determine to perform local-PSA relocation and perform a procedure of changing the local PSA-UPF. In this process, the SMF  130  may deliver a local DN addition notification to the UE  10  indicating that a second local DN has been newly added. Additionally, the SMF  130  may notify the UE  10  that previously connected local DN1 has been deleted. Here, upper layer context control  information for local DN1 may be delivered together with the information that local DN1 has been removed. The upper layer context control information may include an upper layer context refresh indication for local DN2. When the upper layer network context control information includes context information refresh information corresponding to local DN2, the UE  10  may remove the upper layer context information corresponding to local DN2. For example, the TCP context associated with EAS1 of local DN1 created in procedure  904  described above may be released. Further, DNS cache refresh information is included in the upper layer control information. The DNS cache refresh indication may include a domain name FQDN provided by the local DN or the IP subnet address of local DN1. When the upper layer, that is, the AP  1030  in the UE receives the included information, the DNS cache information corresponding to the included subnet address may be deleted. Or, the DNS cache information corresponding to the target FQDN or domain name information may be deleted. 
     In procedure  907 , the application program becomes aware that the TCP connection with EAS #1. has been lost, and may attempt to reestablish a connection with EAS #1. Here, as the corresponding DNS cache information has been deleted, it is possible to newly request and receive address information for the EAS #1 FQDN from the DNS server. 
     In procedure  908 , at the request of the application program, if EAS #1 resides in local DN2, a TCP session may be established with local DN2 via local PSA-UPF2  894 . 
     In procedure  909 , when the UE  10  leaves the DNAI-B area or an AF request is received, the SMF  130  may remove local PSA-UPF2  894 . The SMF  130  may deliver local DIN information for DNAI-B to the UE  10  according to the determination of a policy that local DN information in the UE  10  should be changed from the PCC rule or self-determination of the SMF  130 . The information sent to the UE  10  is information on the removal of the local DN, and upper layer network context control information may also be transmitted for a case where the local DN is to be removed. The higher layer network context control information may include a request for upper layer network context refresh and DNS cache deletion for local DN2. Upon receiving  this request, the AP of the UE removes the TCP context and erases the DNS cache. 
     Meanwhile, each of the first to fifth embodiments described above may be independently carried out, but two or more embodiments may be operated together. For example, the first embodiment describes a procedure of adding a BP/ULCL and local PSA-UPF, the second embodiment describes a procedure of detecting a DNAI change and removing a local PSA, the third embodiment describes a method of delivering local DN notification and upper layer network context control information to the UE based on the operator policy, the fourth embodiment describes a procedure for delivering local DN information and upper layer network context information to the UE during the procedure of changing a local PSA based on an AF request, and the fifth embodiment describes a method in which the local DN information and upper layer network context control information delivered to the UE are used in the UE. 
     Hence, the first embodiment and the fifth embodiment may be used together, and the second embodiment and the fifth embodiment may be used together. Also, since one local PSA-UPF is added according to the first embodiment, when another local PSA is removed, the second embodiment may be used together. In addition, the first embodiment, the second embodiment, and the fifth embodiment may be used together. Further, the first embodiment and the third embodiment may be carried out in sequence, such as when the first embodiment is applied after the third embodiment is applied, or when the third embodiment is applied after the first embodiment is applied. As another example, when the first embodiment is carried out based on the fourth embodiment, the second embodiment may be carried out together, so that the fifth embodiment may be carried out. 
     In this way, when different embodiments are used together, some overlapping operations may be omitted in a specific embodiment or all may be performed. 
       FIG.  10    is a block diagram of an NF entity according to the disclosure. 
     With reference to  FIG.  10   , the NF entity may include a transceiver  1101 , a controller  1102 , and a memory  1103 . The NF entity may be a specific AF among the RAN, the AMF, the UPF, the SMF, the UDM, the PCF, the AUSF, the AF, and the DN described above.  
     The transceiver  1101  may provide an interface for communicating with other network entities. For example, when the NF is the AMF  120 , the transceiver  1101  may transmit and receive signals/messages/information to and from the RAN  20 , the AUSF  160 , the SMF  130 , the PCF  140 , and another AMF. In addition, when the NF is the SMF  130 , the transceiver  1101  may transmit and receive signals/messages/information to and from the AMF  120 , the UDM  170 , the UPF  110 , and the PCF  140 . 
     The controller  1102  may control the operation of the corresponding NF described above. For example, it is possible to control the operation of each NF described with reference to  FIGS.  6  to  9   . The controller  1102  may be implemented with one or more processors. 
     The memory  1103  may store data required by the corresponding NF, and may store information included in various messages/signals described in the disclosure. 
     In the disclosure described above, specific examples have been presented to help the understanding of the disclosure. However, the disclosure is not limited thereto, and may be modified in various ways based on the contents disclosed herein. 
     INDUSTRIAL APPLICABILITY 
     The disclosure can be applied when the UE performs addition/change/deletion of a PDU session in a wireless communication system.