Method and device for supporting emergency service

Abstract

The present disclosure relates to a 5G or 6G communication system for supporting higher data transmission rates. A method performed by a user equipment (UE) may comprise the steps of: transmitting, to an access and mobility management function (AMF) entity, a registration request message; receiving, from the AMF entity, a registration accept message including first information about a 5th generation (5G) public land mobile network (PLMN) of a roaming area and second information about an evolved packet core (EPC) PLMN of the roaming area; when the 5G PLMN is unavailable, identifying the EPC PLMN associated with a mobility management entity (MME) on the basis of the second information; and transmitting, to the MME, an attach request message including an indicator indicating temporary access to the EPC PLMN.

Description

Methods and devices for supporting emergency services

[0001] The present disclosure relates to a wireless communication system, and more particularly to a method and apparatus for supporting emergency services.

[0002] 5G mobile communication technology defines a wide frequency band to enable fast transmission speeds and new services, and can be implemented not only in the sub-6GHz frequency band such as 3.5 gigahertz (3.5GHz), but also in the ultra-high frequency band called millimeter wave (mmWave) such as 28GHz and 39GHz ('Above 6GHz'). In addition, for 6G mobile communication technology, which is called the system after 5G communication (Beyond 5G), implementation in the terahertz band (for example, the 3 terahertz (3THz) band at 95GHz) is being considered to achieve a transmission speed that is 50 times faster than 5G mobile communication technology and an ultra-low latency time that is reduced to one-tenth.

[0003] In the early stages of 5G mobile communication technology, the goal is to support services and satisfy performance requirements for enhanced Mobile Broadband (eMBB), Ultra-Reliable Low-Latency Communications (URLLC), and massive Machine-Type Communications (mMTC). These include beamforming and massive MIMO to mitigate path loss of radio waves in ultra-high frequency bands and increase the transmission distance of radio waves, support for various numerologies (such as operation of multiple subcarrier intervals) and dynamic operation of slot formats for efficient use of ultra-high frequency resources, initial access technology to support multi-beam transmission and wideband, definition and operation of BWP (Bidth Part), new channel coding methods such as LDPC (Low Density Parity Check) codes for large-capacity data transmission and Polar Code for reliable transmission of control information, and L2 pre-processing (L2). Standardization has been made for network slicing, which provides dedicated networks specialized for specific services, and pre-processing.

[0004] Currently, discussions are underway to improve and enhance the initial 5G mobile communication technology in consideration of the services that 5G mobile communication technology was intended to support, and physical layer standardization is in progress for technologies such as V2X (Vehicle-to-Everything) to help autonomous vehicles make driving decisions and increase user convenience based on their own location and status information transmitted by vehicles, NR-U (New Radio Unlicensed) for the purpose of system operation that complies with various regulatory requirements in unlicensed bands, NR terminal low power consumption technology (UE Power Saving), Non-Terrestrial Network (NTN), which is direct terminal-satellite communication to secure coverage in areas where communication with terrestrial networks is impossible, and Positioning.

[0005] In addition, standardization of wireless interface architecture / protocols is in progress for technologies such as intelligent factories (Industrial Internet of Things, IIoT) to support new services through linkage and convergence with other industries, Integrated Access and Backhaul (IAB) that provides nodes for expanding network service areas by integrating wireless backhaul links and access links, Mobility Enhancement technology including Conditional Handover and Dual Active Protocol Stack (DAPS) handover, and 2-step random access (2-step RACH for NR) that simplifies random access procedures. Standardization is also in progress for system architecture / services such as 5G baseline architecture (e.g., Service-based Architecture, Service-based Interface) for grafting Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technologies, and Mobile Edge Computing (MEC) that provides services based on the location of the terminal.

[0006] Once these 5G mobile communication systems are commercialized, an explosive increase in connected devices will be connected to the communication network, necessitating enhanced functionality and performance of 5G mobile communication systems and integrated operation of these connected devices. To this end, new research will be conducted on improving 5G performance and reducing complexity, supporting AI services, supporting metaverse services, and drone communications by utilizing eXtended Reality (XR), Artificial Intelligence (AI), and Machine Learning (ML) to efficiently support Augmented Reality (AR), Virtual Reality (VR), and Mixed Reality (MR).

[0007] In addition, the development of these 5G mobile communication systems includes new waveforms to ensure coverage in the terahertz band of 6G mobile communication technology, multi-antenna transmission technologies such as Full Dimensional MIMO (FD-MIMO), Array Antenna, and Large Scale Antenna, metamaterial-based lenses and antennas to improve the coverage of terahertz band signals, high-dimensional spatial multiplexing technology using Orbital Angular Momentum (OAM), Reconfigurable Intelligent Surface (RIS) technology, as well as full duplex technology to improve the frequency efficiency and system network of 6G mobile communication technology, satellite, AI (Artificial Intelligence) from the design stage and AI-based communication technology that realizes system optimization by internalizing end-to-end AI support functions, and ultra-high-performance communication and computing resources to provide services with complexity that exceeds the limits of terminal computing capabilities. It can serve as a basis for the development of next-generation distributed computing technologies that can be realized by utilizing them.

[0008] According to one embodiment of the present disclosure, a device and method for effectively providing a service in a mobile communication system are provided.

[0009] According to one embodiment of the present disclosure, a method performed by a user equipment (UE) may include the steps of: transmitting a registration request message to an access and mobility management function (AMF) entity; receiving, from the AMF entity, a registration acceptance message including first information about a fifth generation (5G) public land mobile network (PLMN) of a roaming area and second information about an evolved packet core (EPC) PLMN of the roaming area; identifying, if the 5G PLMN is unavailable, the EPC PLMN associated with a mobility management entity (MME) based on the second information; and transmitting, to the MME, an attach request message including an indicator indicating temporary access to the EPC PLMN.

[0010] According to one embodiment of the present disclosure, a device and method for effectively providing a service in a wireless communication system can be provided.

[0011] The effects that can be obtained from the present disclosure are not limited to the effects mentioned above, and other effects that are not mentioned can be clearly understood by a person having ordinary skill in the art to which the present disclosure belongs from the description below.

[0012] FIG. 1 illustrates an example of a terminal and network environment for smoothly providing communication services in a 5G (generation) network environment and / or a 4G network environment according to one embodiment of the present disclosure.

[0013] FIG. 2 is a flowchart illustrating a procedure for smoothly providing a communication service in a 5G network environment and / or a 4G network environment according to one embodiment of the present disclosure.

[0014] FIG. 3 is a flowchart illustrating a procedure for smoothly providing a communication service in a 5G network environment and / or a 4G network environment according to one embodiment of the present disclosure.

[0015] FIG. 4 is a flowchart illustrating a procedure for smoothly providing a communication service in a 5G network environment and / or a 4G network environment according to one embodiment of the present disclosure.

[0016] FIG. 5 is a diagram showing the configuration of a terminal according to an embodiment of the present disclosure.

[0017] FIG. 6 is a diagram illustrating a configuration of a network entity according to an embodiment of the present disclosure.

[0018] FIG. 7 illustrates a base station according to one embodiment of the present disclosure.

[0019] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the attached drawings. In describing the embodiments, descriptions of technical details that are well-known in the technical field to which the present disclosure pertains and are not directly related to the present disclosure will be omitted. This is to avoid obscuring the gist of the present disclosure by omitting unnecessary explanations and to convey the gist more clearly.

[0020] For the same reason, some components in the attached drawings are exaggerated, omitted, or schematically depicted. Furthermore, the dimensions of each component do not entirely reflect its actual size. Identical or corresponding components in each drawing are assigned the same reference numbers.

[0021] The advantages and features of the present disclosure, and methods for achieving them, will become clearer with reference to the embodiments described in detail below together with the accompanying drawings. However, the present disclosure is not limited to the embodiments disclosed below and may be implemented in various different forms. These embodiments are provided solely to ensure that the disclosure of the present disclosure is complete and to fully inform those skilled in the art of the scope of the invention, and the present disclosure is defined only by the scope of the claims. Like reference numerals designate like elements throughout the specification.

[0022] At this time, it will be understood that each block of the processing flow diagrams and combinations of the flow diagrams can be performed by computer program instructions.

[0023] Additionally, each block may represent a module, segment, or portion of code that contains one or more executable instructions for performing a specific logical function(s). It should also be noted that in some alternative implementation examples, the functions described in the blocks may occur out of order. For example, two blocks depicted in succession may actually be executed substantially concurrently, or the blocks may sometimes be executed in reverse order, depending on their respective functions.

[0024] Here, the term '~ unit' used in this embodiment means software or hardware components such as FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Circuit), and the '~ unit' performs certain roles. However, the '~ unit' is not limited to software or hardware. The '~ unit' may be configured to be on an addressable storage medium or may be configured to play one or more processors. Accordingly, as an example, the '~ unit' may include components such as software components, object-oriented software components, class components, and task components, processes, functions, properties, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and / or variables. The functions provided within the components and '~ units' may be combined into a smaller number of components and '~ units' or further separated into additional components and '~ units'. Additionally, the components and '~parts' may be implemented to play one or more central processing units (CPUs) within the device or secure multimedia card. In addition, in an embodiment, the '~parts' may include one or more processors.

[0025] The terms used in the following description to identify connection nodes, terms referring to network entities, terms referring to messages, terms referring to interfaces between network entities, and terms referring to various identification information are provided as examples for convenience of explanation. Therefore, the present disclosure is not limited to the terms described below, and other terms referring to objects with equivalent technical meanings may be used.

[0026] For the convenience of explanation below, this disclosure uses terms and names defined in the 3GPP LTE (3rd Generation Partnership Project Long Term Evolution) standard, or terms and names modified based thereon. However, this disclosure is not limited to the above-described terms and names, and can be equally applied to systems conforming to other standards. In this disclosure, eNB (E-UTRAN (evolved Universal Terrestrial Radio Access network) Node B) may be used interchangeably with gNB (next generation Node B) for the convenience of explanation. That is, a base station described as an eNB may represent a gNB. In this disclosure, the term “terminal” may refer to various wireless communication devices as well as mobile phones, NB-IoT devices, and sensors.

[0027] That is, in specifically explaining the embodiments of the present disclosure, the communication standards specified by 3GPP will be the main target, but the main gist of the present disclosure can be applied to other communication systems with similar technical backgrounds with slight modifications within a range that does not significantly deviate from the scope of the present disclosure, and this can be done at the discretion of a person skilled in the technical field of the present disclosure.

[0028] In 5G or NR systems, the Access and Mobility Management Function (AMF), which manages the mobility of terminals, and the Session Management Function (SMF), which manages sessions, are separated. Accordingly, unlike in 4G LTE (long term evolution) communication systems, where the Mobility Management Entity (MME) performed both mobility management and session management, in 5G or NR systems, the entities performing mobility management and session management are separate, which has changed the communication method and communication management method between terminals and network entities.

[0029] In 5G or NR systems, mobility management for non-3GPP access is performed through the AMF entity via the N3IWF (Non-3GPP Inter-Working Function), and session management is performed through the SMF entity. Furthermore, security-related information, a critical element in mobility management, is also processed through the AMF.

[0030] As described above, in 4G LTE systems, the MME is responsible for both mobility management and session management. 5G or NR systems can support a non-standalone architecture that utilizes these network entities from the 4G LTE system to perform communications.

[0031] The present disclosure relates to a roaming user (or a UE receiving a roaming service), and provides a method and device for providing communication services to an international roamer when a 5G of a visited network becomes unavailable to a roaming terminal capable of only 5G roaming access. For example, when a roaming user has only 5G roaming access but a 5G VPLMN (visited public land mobile network) service becomes unavailable (e.g., when a 5G network with a roaming agreement in the area to which the user is roaming becomes unavailable to provide communication services due to a fire, etc.), a method and device for providing services to the terminal may be provided.

[0032] To meet the growing demand for wireless data traffic following the commercialization of 4G communication systems, efforts are being made to develop improved 5G or pre-5G communication systems. For this reason, 5G or pre-5G communication systems are also referred to as "Beyond 4G Network" or "Post-LTE" systems. The 5G communication system specified by 3GPP is called the New Radio (NR) system. To achieve high data rates, 5G communication systems are being considered for implementation in ultra-high frequency (mmWave) bands (e.g., the 60 GHz band). To mitigate the path loss of radio waves in ultra-high frequency bands and increase the transmission distance of radio waves, beamforming, massive MIMO, full-dimensional MIMO (FD-MIMO (multiple input multiple output)), array antenna, analog beam-forming, and large scale antenna technologies have been discussed and applied to NR systems in 5G communication systems.In addition, to improve the network of the system, the fifth-generation (5G) communication system is developing technologies such as evolved small cells, advanced small cells, cloud radio access network (cloud RAN), ultra-dense network, device to device communication (D2D), wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), and interference cancellation. In addition, in the 5G system, advanced coding modulation (ACM) methods such as FQAM (Hybrid FSK and QAM Modulation) and SWSC (Sliding Window Superposition Coding), and advanced access technologies such as FBMC (Filter Bank Multi Carrier), NOMA (non-orthogonal multiple access), and SCMA (sparse code multiple access) are being developed.

[0033] According to one embodiment of the present disclosure, when a roaming user has only 5G roaming access but the 5G VPLMN is in a state where the service is unavailable (e.g., when a 5G network with a roaming agreement in the roaming area cannot provide communication service due to a fire, etc.), the terminal can receive the service.

[0034] FIG. 1 illustrates an example of a terminal and network environment for smoothly providing communication services in a 5G network environment and / or a 4G network environment according to one embodiment of the present disclosure.

[0035] Referring to FIG. 1, a 5G or NR core network may include network functions (NFs) such as a User Plane Function (UPF) (131), a Session Management Function (SMF) (121), an Access and Mobility Management Function (AMF) (111), a 5G Radio Access Network (RAN) (103), a User Data Management (UDM) (151), a Policy Control Function (PCF) (161), an Application Function (AF) (181), a Unified Data Management (UDM) (151), and / or an Operations, Administration and Maintenance (OAM) (191).

[0036] For example, a 5G or NR core network may include entities such as an Authentication Server Function (AUSF) (141) and / or authentication, authorization and accounting (AAA) (171) for authentication of the entities described above.

[0037] According to one embodiment, a UE (User Equipment) (or Terminal) (101) may access a 5G core network through a base station (e.g., a 5G RAN, BS (base station)) (103). For example, the base station may be a gNB (next generation node B) and / or an eNB.

[0038] According to one embodiment, UE (101) may be referred to as a user device. The user device may be referred to as a terminal, mobile equipment (ME), or mobile station (MS). In addition, the user device may be a portable device such as a laptop, a mobile phone, a personal digital assistant (PDA), a smartphone, or a multimedia device. The user device may also be a non-portable device such as a personal computer (PC) or a vehicle-mounted device.

[0039] According to one embodiment, a UE (101) can access two (e.g., local and central) data networks simultaneously using multiple protocol data unit (PDU) sessions. In this case, two SMFs can be selected for different PDU sessions. However, each SMF can have the ability to control both the local UPF and the central UPF within the PDU session.

[0040] According to one embodiment, the UE (101) may simultaneously access two (e.g., a local data network and a centralized data network) data networks provided within a single PDU session.

[0041] According to one embodiment, the core network may have an N3 interworking function (N3IWF) (e.g., a non-3GPP entity (104)) for cases where a UE communicates via non-3GPP access. When a UE communicates via non-3GPP access, session management may be controlled by the UE, non-3GPP access, N3IWF, and / or SMF (121), and mobility management may be controlled by the UE, non-3GPP access, N3IWF, and / or AMF.

[0042] According to one embodiment, UE (101) may include various types of UEs. For example, UE (101) may include a RedCap (reduced capability) UE, a general UE, and / or a sidelink relay.

[0043] According to one embodiment, in a 5G or NR system, entities performing mobility management and session management may be separated into AMF (111) and SMF (121).

[0044] According to one embodiment, each network function (NF) of a 5G system can support the following functions.

[0045] According to one embodiment, AUSF (141) can process and store data for authentication of UE (101).

[0046] According to one embodiment, AMF (111) provides a function for access and mobility management per UE, and one UE can be connected to one AMF by default. Specifically, the AMF (111) provides signaling between core network (CN) nodes for mobility between 3GPP access networks, termination of a radio access network (RAN) control plane (CP) interface (i.e., N2 interface), termination (N1) of non-access stratum (NAS) signaling, NAS signaling security (non-access stratum (NAS) ciphering and integrity protection), access stratum (AS) security control, registration management (registration area management), connection management, idle mode UE reachability (including control and performance of paging retransmission), mobility management control (subscription and policy), intra-system mobility and inter-system mobility support, support for network slicing, SMF selection, lawful intercept (for AMF events and interfaces to the LI system), provision of forwarding of session management (SM) messages between UE and SMF, and SM message routing. It may support functions such as transparent proxy, access authentication, access authorization including roaming authorization check, provision of SMS message delivery between UE and SMSF, security anchor function (SAF) and / or security context management (SCM). Some or all of the functions of AMF (111) may be supported within a single instance of AMF.

[0047] According to one embodiment, PCF (161) may provide a function to determine policies such as mobility management, session management, etc. by receiving information about packet flow from an application server. For example, PCF (161) may support functions such as supporting a unified policy framework for controlling network operations, providing policy rules so that control plane functions (e.g., AMF, SMF, etc.) can enforce the policy rules, and implementing a front end for accessing related subscription information for policy determination within a user data repository (UDR).

[0048] According to one embodiment, the SMF (121) may provide a session management function. When a UE has multiple sessions, the SMF (121) may be managed by different SMFs for each session. For example, the SMF (121) may support functions such as session management (e.g., session establishment, modification, and termination, including tunnel maintenance between the UPF (131) and (R)AN (103) nodes), UE IP (internet protocol) address allocation and management (optionally including authentication), selection and control of UP functions, traffic steering setup to route traffic from the UPF (131) to the appropriate destination, termination of the interface to policy control functions, enforcement of the control portion of policies and quality of service (QoS), lawful intercept (for SM events and interfaces to the LI system), termination of the SM portion of NAS messages, downlink data notification, initiation of AN-specific SM information (e.g., forwarding it to the (R)AN (103) via N2 via the AMF (111)), determination of the SSC (Session and Service Continuity) mode of the session, roaming functions, etc. Some or all of the functions of SMF (121) may be supported within a single instance of an SMF.

[0049] According to one embodiment, UDM (151) may store user subscription data, policy data, etc. UDM (151) may include two parts (e.g., an application front end (FE) (not shown) and a user data repository (UDR) (not shown)).

[0050] According to one embodiment, UPF (131) can forward a downlink PDU (protocol data unit) received from DN (data network) to UE (101) via (R)AN (103). UPF (131) forwards an uplink PDU received from UE (101) to DN (data network) via (R)AN (110). For example, the UPF (131) may support functions such as an anchor point for intra / inter RAT (radio access technology) mobility, an external PDU session point for interconnection to a Data Network, a user plane portion of packet routing and forwarding, packet inspection and policy rule enforcement, an uplink classifier to support lawful intercept, traffic usage reporting, and routing of traffic flows to the Data Network, a branching point to support multi-homed PDU sessions, QoS handling for the user plane (e.g., packet filtering, gating, uplink / downlink rate enforcement), uplink traffic validation (service data flow (SDF) to QoS flow mapping), transport level packet marking in uplink and downlink, downlink packet buffering and / or downlink data notification triggering. Some or all of the functions of UPF (131) may be supported within a single instance of a UPF.

[0051] In one embodiment, AF (181) interacts with a 3GPP core network to provide services. For example, AF (181) may interact with a 3GPP core network to support functions such as application impact on traffic routing, access to network capability exposure, and / or interaction with a policy framework for policy control.

[0052] According to one embodiment, a base station (103) (e.g., RAN) refers to a new radio access network that supports both evolved E-UTRA (evolved UTRA), which is an evolved version of 4G (fourth-generation) radio access technology, and new radio (NR) technology (e.g., gNB).

[0053] According to one embodiment, the gNB may support functions for radio resource management. For example, the gNB may support functions of radio bearer control, radio admission control, connection mobility control, dynamic allocation of resources to UEs in uplink / downlink (i.e., scheduling), IP (internet protocol) header compression, and encryption and / or integrity protection of user data streams. For example, the gNB may support functions such as selection of an AMF upon UE attachment, routing of user plane data to UPF(s), routing of control plane information to AMF, connection setup and teardown, scheduling and transmission of paging messages (originating from AMF), scheduling and transmission of system broadcast information (originating from AMF or operating and maintenance (O&M)), measurement and measurement reporting setup for mobility and scheduling, transport level packet marking in uplink, session management, support for network slicing, QoS flow management and mapping to data radio bearers, support for UEs in inactive mode, distribution of NAS messages, NAS node selection, sharing of radio access networks, dual connectivity, and tight interworking between NR and E-UTRA.

[0054] According to one embodiment, a 5G or NR system may include a stand-alone deployment architecture that performs communication only with 5G or NR entities and a non-stand alone deployment architecture that uses 4G entities and 5G or NR entities together.

[0055] As illustrated in Fig. 1, when a UE communicates with a network, control is performed by an eNB (E-UTRAN (Evolved Universal Terrestrial Radio Access Network) Node B), and deployment in a form in which a 5G entity of a core network is used may be possible. For example, mobility management between a UE (101) and an AMF (111) and session management between a UE (101) and an SMF (121) may be performed in a NAS (Non Access Stratum) layer, which is layer-3.

[0056] The communication network upon which this disclosure is based assumes a 5G and / or 4G (or LTE) network. However, the same concepts can be applied to other communication systems within a scope understandable to those of ordinary skill in the art. For example, this disclosure can also be applied to 2G and / or 3G networks.

[0057] The present disclosure proposes a method for providing service to a terminal when a roaming user has only 5G roaming access and the accessible 5G VPLMN is unavailable for service (e.g., when a 5G network with a roaming agreement in the roaming area is unable to provide communication service due to a fire, etc.).

[0058] Referring to Figure 1, each of the second area (B) and the third area (C) may be a VPLMN (visited PLMN) area. For example, the second area (B) and the third area (C), which are separately indicated by circles, may be VPLMN areas. For example, the first area (A) may be a home network.

[0059] In FIG. 1, the first area (A), the second area (B), and the third area (C) are depicted as circular or oval-shaped, but this is merely an example, and the scope and shape of the first area (A), the second area (B), and the third area (C) may vary. In addition, the expression “area” may be replaced with the terms “region,” “zone,” “section,” or “district.”

[0060] Accordingly, the present disclosure explains that when a UE (101) connected to a first area (A) (e.g., a home network) moves to a VPLMN of a second area (B) and / or a third area (C), the UE (101) originally had a roaming agreement to connect to the B network (i.e., a PLMN belonging to 5G) (e.g., the second area (B)), but the 5G network of the B network becomes unusable due to some problem, a 4G LTE network such as C (e.g., the third area (C)) can be temporarily used.

[0061] For example, AMF (111) may be an AMF entity associated with a home network (e.g., a 5G network). The second AMF (511) may be an AMF entity associated with a first visited network (e.g., a 5G network).

[0062] According to one embodiment, the description of AMF (111) described in FIG. 1 may also be applied to the second AMF (511) as long as it is not contradictory. For example, the second AMF (511) provides functions for UE-level access and mobility management, and one UE can be connected to one AMF by default. Specifically, the second AMF (511) provides signaling between CN nodes for mobility between 3GPP access networks, termination of a radio access network (RAN) CP interface (i.e., N2 interface), termination of non-access stratum (NAS) signaling (N1), 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 performance of paging retransmission), mobility management control (subscription and policy), intra-system mobility and inter-system mobility support, support for network slicing, SMF selection, lawful intercept (for AMF events and interfaces to the LI system), provision of forwarding of session management (SM) messages between UE and SMF, transparent proxy for SM message routing, access authentication, and roaming authorization check. It may support functions such as access authorization, provision of SMS message transmission between UE and SMSF, security anchor function (SAF) and / or security context management (SCM).Some or all of the functions of the second AMF (511) may be supported within a single instance of one AMF.

[0063] For example, the second base station (503) may be a base station associated with the first visited network (e.g., a 5G network). For example, an MME (e.g., an MME (271) of FIG. 2) may be a network entity associated with the second visited network (e.g., a 4G network), and an eNodeB (e.g., an eNodeB (273) of FIG. 2) may be a base station associated with the second visited network (e.g., a 4G network).

[0064] The description of the base station (103) may also be applied to the second base station (503) unless it is contradictory.

[0065] FIG. 2 is a flowchart illustrating a procedure for smoothly providing a communication service in a 5G network environment and / or a 4G network environment according to one embodiment of the present disclosure.

[0066] Referring to FIG. 2, the UE (101) is in a home network (e.g., the first area (A)) as described in steps 201, 205, 211, 231, and / or 233, and then the UE (101) can move to a VPLMN, i.e., a visited network, and perform steps 251, 261, and / or 263.

[0067] In the case of FIG. 2, when a UE (101) moves from a Home PLMN (HPLMN) to a VPLMN, if only the use of the 5G network is agreed upon with the VPLMN through a 5G roaming agreement with respect to the UE (101), the 5G network may be (temporarily) unavailable for service. In this case, during the PLMN selection process, the terminal (101) can temporarily select a 4G LTE EPC network and use the network.

[0068] To summarize the scenario, in the case of FIG. 2, 1) the UE (101) registers in the Home PLMN, receives information necessary for roaming (e.g., step 205), and communicates, and 2) the UE (101) moves to a VPLMN, and only the use of the 5G network may be agreed upon by the VPLMN and a 5G roaming agreement. 3) However, if the 5G network in the roaming area is (temporarily) unavailable or there is no available 5G network, 4) based on information previously received or stored after reception, the UE (10) may (temporarily) select a 4G LTE EPC network during the PLMN selection process and use the network.

[0069] Referring to FIG. 2, in step 201, the UE (101) may transmit a registration request message to the AMF (111). For example, the UE (101) may transmit the registration request message to the AMF (111) through the base station (103). For example, the base station (103) may receive the registration request message from the UE (101), and the base station (103) may transmit the registration request message to the AMF (111).

[0070] According to one embodiment, in step 205, AMF (111) sends a registration accept message to UE (101). For example, AMF (111) may send a registration accept message to UE (101) in response to a registration request message.

[0071] The registration approval message may contain at least some of the following information:

[0072] - PLMN information may be transmitted. For example, PLMN information may be 5G PLMN information that allows access to networks (e.g., 5G networks) with which the operator has a roaming agreement. For example, PLMN information may be 5G PLMN information that allows access to 5G networks.

[0073] - D-EPC (evolved packet core)-PLMN-in roaming information may be transmitted. The information may refer to an EPC (e.g., an eUTRAN network) that can be connected as an alternative to a network with roaming agreement (e.g., a 5G network) when there is no 5G network with a roaming agreement in the roaming area or when the 5G network with a roaming agreement in the roaming area becomes unavailable for service. For example, the D-ECP-PLMN-in roaming information may refer to information about a network (e.g., an alternative network) that the UE (101) can connect as an alternative to the network with roaming agreement to receive service when there is no network with roaming agreement or the network becomes (temporarily) unavailable.

[0074] - d-EPC indicator information may be transmitted. The d-EPC information may be indicator information to indicate that an EPC (e.g., an eUTRAN network) that can be connected as an alternative to a 5G network with a roaming agreement can be connected when there is no network (e.g., a 5G network) with a roaming agreement in the roaming area. For example, the d-EPC indicator information may be referenced as information indicating whether the UE (101) can connect to an alternative network. For example, the d-EPC indicator information may include a field value, a bit map, and / or a bit value.

[0075] According to one embodiment, the UE (101) may store at least some of the following information in step 211.

[0076] - PLMN information. For example, PLMN (Public Land Mobile Network) information may be information about a 5G PLMN that can access a 5G network with a roaming agreement with the operator associated with the UE (101).

[0077] - D-EPC-PLMN-in roaming information. For example, D-EPC-PLMN-in roaming information can be used to refer to an EPC (e.g., an eUTRAN network) that can be accessed as an alternative 5G network when there is no 5G network with a roaming agreement in the roaming area.

[0078] - d-EPC indicator information. For example, d-EPC information may be indicator information indicating that an EPC (e.g., an eUTRAN network) that can be accessed as an alternative to a 5G network with a roaming agreement can be accessed when there is no 5G network with a roaming agreement in the roaming area.

[0079] According to one embodiment, in step 231, the UE (101) may transmit a PDU session establishment request message to the SMF (121). For example, the UE (101) may request the SMF (121) to establish a PDU session after registration in the home network. For example, the UE (111) may transmit a PDU session establishment request message to the AMF through the base station (103), and the AMF may transmit a PDU session establishment request message to the SMF.

[0080] According to one embodiment, in step 233, the SMF (121) sends a PDU session establishment response message to the UE (101). For example, the SMF may send a PDU session establishment response message to the AMF (111), and the AMF (111) may send a PDU session establishment response message to the UE (101) via the base station (103).

[0081] For example, the SMF may send a PDU session establishment response message to the UE (101) in response to a PDU session establishment request message.

[0082] According to one embodiment, in step 251, the UE (101) may select (or identify) a PLMN. The PLMN selection performed by the UE (101) in step 251 may be different from a conventional PLMN selection.

[0083] That is, unlike the conventional PLMN selection, the PLMN selection of step 251 may be performed based on provided information (e.g., information that a 4G network that replaces a 5G network exists, information that the terminal (101) can use a 4G network, or information from a network that the terminal (101) can use a 4G network). For example, when a 5G network is not available, the UE (101) may receive information or notification from the network that there is an alternative 4G network (e.g., EPC (e.g., EUTRAN)) that is capable of using the 4G network or that the corresponding function is available, and the UE (101) may select a PLMN based on the received information.

[0084] For example, the UE (101) may receive first information about the existence of an alternative network (e.g., a 4G network) of the network, and / or second information about whether the terminal can use and / or access the alternative network (e.g., a 4G network). The UE (101) may select (or identify) a PLMN based on the first information and / or the second information (e.g., capability information).

[0085] Information used when selecting a PLMN may include at least some of the following:

[0086] - Temp information may be available. Temp information may be transmitted. This is to notify that the EPC or eUTRAN is being used temporarily.

[0087] - Limited information may be available. Limited information may be used to inform the UE (101) that limited services are provided, as the UE (101) is temporarily permitted to use EPC (e.g., alternative network) or E-UTRAN.

[0088] According to one embodiment, the UE (101) sends an attach request message to the MME (271) at step 261. For example, the MME (271) may be an MME (271) associated with a network (e.g., a 4G network) that replaces the network with which the roaming agreement exists. For example, the UE (101) may send the attach request message to the MME (271) via the eNB (273). For example, the eNB (273) may receive the attach request message from the UE (101), and the eNB (273) may send the attach request to the MME (271).

[0089] According to one embodiment, the UE (101) may transmit information to the MME (271) indicating that it is temporarily connected due to the absence of a 5G network in the roaming area. For example, when transmitting an attach request message to the MME (271), the UE (101) may transmit information (or an indicator) indicating that the UE (101) is temporarily connected.

[0090] According to one embodiment, the information included in the attach request message may include at least some of the following information:

[0091] - Temp information may be transmitted. Temp is intended to indicate that the corresponding EPC or eUTRAN is being used temporarily. For example, Temp information may be information indicating that the UE (101) is temporarily connected.

[0092] - Limited information may be transmitted. Limited information allows the UE (101) to temporarily use EPC or eUTRAN, and thus can be used to inform the UE (101) that limited services are provided. For example, limited information may be information indicating that the UE (101) is temporarily connected.

[0093] According to one embodiment, the MME (271) can identify the attach request (or connection request) of the UE (101) as temporary if either Temp information or Limited information is included in the attached request message.

[0094] However, the method of indicating that the connection of the UE (101) to the network is temporary may be explicit or implicit. For example, the UE (101) may transmit an attach request message to the MME (271) that includes information about the cause of the UE (101) temporarily connecting to the MME (271) (e.g., a cause value (e.g., connection to the 5G network is not possible)). In this case, the MME (271) may identify that the UE (101) is temporarily connected based on the information about the cause. That is, the UE (101) may directly transmit information indicating that the connection of the UE (101) is temporary to the MME (271), or may indirectly indicate that the connection of the UE (101) is temporary by transmitting information about the cause.

[0095] According to one embodiment, in step 263, the MME (271) may transmit an attach accept message to the UE (101). For example, the MME (271) may transmit a message indicating that the attach request has been accepted to the UE (101). For example, the MME (271) may transmit a message indicating that the UE (101) is allowed to access a network (e.g., a 4G network, an alternative network). For example, the MME (271) may transmit an attach accept message to the eNB (273), and the eNB (273) may transmit the attach accept message to the UE (101).

[0096] The attach accept message may contain at least one of the following information:

[0097] - Limited information may be transmitted. Limited information may be intended to inform the UE (101) that limited services are provided, as it allows the UE (101) to temporarily use EPC or eUTRAN.

[0098] Although FIG. 2 of the present disclosure illustrates that the network with roaming consent is a 5G network and the network replacing the network with roaming consent (e.g., the replacement network) is a 4G network, this is merely an example. For example, the network with roaming consent may be a 4G network and the replacement network may be a 5G network. For example, the network with roaming consent may be a first network that supports 5G, and the replacement network may be a second network that supports 5G. For example, the network with roaming consent may be one of 2G, 3G, 4G, and 5G, and the replacement network may be one of 2G, 3G, 4G, or 5G.

[0099] FIG. 3 is a flowchart illustrating a procedure for smoothly providing a communication service in a 5G network environment and / or a 4G network environment according to one embodiment of the present disclosure.

[0100] Referring to FIG. 3, the UE (101) may be in a situation where the UE (101) is in a home network as described in step 301, step 305, step 311, step 331, and / or step 333.

[0101] Referring to FIG. 3 and FIG. 1, the UE (101) may then move to a VPLMN, i.e., a visited network, and perform steps 351, 361, and / or 363 to attempt registration in a B network that supports 5G among the VPLMN networks.

[0102] And, however, if registration is not possible, the UE (101) may perform step 371 of selecting a C network that replaces 5G support in the VPLMN, and the UE (101) may perform steps 371, 381, and / or 383 of attempting an attach request in the LTE network.

[0103] To summarize the scenario, in the case of FIG. 3, 1) the UE (101) registers in the Home PLMN, receives information necessary for roaming, and communicates, 2) the UE (101) moves to the VPLMN, and when only the use of the 5G network is agreed upon by the VPLMN and the 5G roaming agreement, registration is attempted on the 5G network, but 3) the 5G network is (temporarily) unavailable for service, 4) the 4G LTE EPC network is temporarily selected during the PLMN selection process, and 5) the network (e.g., the 4G LTE EPC network) is used.

[0104] Referring to FIG. 3, in step 301 according to one embodiment, the UE (101) may transmit a registration request message to the AMF (111). For example, the UE (101) may transmit a registration request message to the AMF (111) through the base station (103). For example, the base station (103) may receive the registration request message from the UE (101), and the base station (103) may transmit the registration request message to the AMF (111).

[0105] According to one embodiment, in step 305, the AMF (111) may transmit a registration accept message to the UE (101). For example, the base station (103) may receive a registration accept message from the AMF (111), and the base station (103) may transmit a registration accept message to the UE (101).

[0106] The registration approval message may contain at least some of the following information:

[0107] - PLMN information may be transmitted. For example, the PLMN information may be 5G PLMN information that allows access to a network (e.g., a 5G network) with which the operator has a roaming agreement.

[0108] - D-EPC-PLMN-in roaming information may be transmitted. For example, D-EPC-PLMN-in roaming information may refer to an EPC (e.g., an eUTRAN network) (e.g., an alternative network) that can be accessed as an alternative to a 5G network when there is no network (e.g., a 5G network) with a roaming agreement in the roaming area.

[0109] - d-EPC indicator information may be transmitted. The d-EPC information is indicator information to indicate that an EPC (e.g., an eUTRAN network) that can be connected as an alternative to a 5G network can be connected when there is no network (e.g., a 5G network) with a roaming agreement in the roaming area. For example, the d-EPC indicator information may be information indicating whether the UE (101) can connect or attach to an alternative network (e.g., an EPC (e.g., an eUTRAN network)).

[0110] According to one embodiment, at step 311, the UE (101) may store at least some of the following information:

[0111] - PLMN information. For example, PLMN information may be 5G PLMN information that allows access to a 5G network with a roaming agreement with the carrier.

[0112] - D-EPC-PLMN-in roaming information. D-EPC-PLMN-in roaming information can be referenced as an EPC (e.g., an eUTRAN network) (e.g., an alternative network) that can be accessed as an alternative to a 5G network when there is no 5G network with a roaming agreement in the roaming area.

[0113] - d-EPC indicator information. For example, d-EPC information may be indicator information indicating that an EPC (e.g., an eUTRAN network) that can be accessed as an alternative to a 5G network can be accessed when there is no 5G network with a roaming agreement in the roaming area.

[0114] According to one embodiment, in step 331, the UE (101) may transmit a PDU session establishment request message to the SMF (121). For example, step 331 may correspond to step 231 of FIG. 2. For example, the UE (111) may transmit a PDU session establishment request message to the AMF (111) via the base station (103), and the AMF (111) may transmit a PDU session establishment request message to the SMF (121).

[0115] According to one embodiment, in step 333, the SMF (121) may transmit a PDU session establishment response message to the UE (101). For example, step 333 may correspond to step 233 of FIG. 2. For example, the SMF (121) may transmit a PDU session establishment response message to the AMF (111), and the AMF (111) may transmit the PDU session establishment response message to the UE (101) via the base station (103).

[0116] According to one embodiment, at step 351, the UE (101) may perform PLMN selection.

[0117] The PLMN selection performed in step 351 is a PLMN selection according to the prior art. For example, according to the automatic PLMN selection method,

[0118] This is a method to determine and select a PLMN that can be used preferentially among the RPLMN (Registered PLMN), VPLMN, and EPLMN (Equivalent PLMN).

[0119] This is a method of judging and selecting whether there is a PLMN that can be used preferentially among operator controlled PLMNs and access technologies.

[0120] According to one embodiment, in step 361, the UE (101) may transmit a registration request message to the second AMF (511). For example, the UE (101) may transmit the registration request message to the second AMF (511) through the second base station (503).

[0121] [Example 1]

[0122] According to one embodiment, in process 363, the second AMF (511) transmits a registration reject message to the UE (101). For example, the second base station (503) may receive a registration reject message from the second AMF (511) and transmit the registration reject message to the UE (101).

[0123] The registration rejection message may contain at least some of the following information:

[0124] - Redirect information may be sent to notify the EPC of a redirect.

[0125] - Temp information may be transmitted. This is to notify that the network is being used temporarily.

[0126] [Example 2]

[0127] According to one embodiment, in step 363, the AMF (111) sends a registration reject message to the UE (101). For example, the AMF (111) may send a registration reject message to the UUE (101) in response to a registration request message. For example, the AMF (111) may allow the UE 5G service according to the roaming agreement, but may send a registration reject message to the UE (101) when the 5G network service is (temporarily) unavailable.

[0128] The registration rejection message may contain at least some of the following information:

[0129] - PLMN information may be transmitted. For example, PLMN information may be 5G PLMN information that allows access to networks (e.g., 5G networks) with which the operator has a roaming agreement. For example, PLMN information may be 5G PLMN information that allows access to 5G networks.

[0130] - D-EPC (evolved packet core)-PLMN-in roaming information may be transmitted. The information may refer to an EPC (e.g., an eUTRAN network) that can be connected as an alternative to a network with roaming agreement (e.g., a 5G network) when there is no 5G network with a roaming agreement in the roaming area or when the 5G network with a roaming agreement in the roaming area becomes unavailable for service. For example, the D-ECP-PLMN-in roaming information may refer to information about a network (e.g., an alternative network) that the UE (101) can connect as an alternative to the network with roaming agreement to receive service when there is no network with roaming agreement or the network becomes (temporarily) unavailable.

[0131] - d-EPC indicator information may be transmitted. The d-EPC information is indicator information to indicate that an EPC (e.g., an eUTRAN network) that can be connected as an alternative to a 5G network with a roaming agreement can be connected when there is no network (e.g., a 5G network) with a roaming agreement in the roaming area. For example, the d-EPC indicator information may be referenced as information indicating whether the UE (101) can connect to an alternative network. For example, the d-EPC indicator information may include a field value, a bit map, and / or a bit value.

[0132] According to one embodiment, the UE (101) may store at least some of the following information at step 365.

[0133] - PLMN information. For example, the PLMN information may be information about a 5G PLMN that can access a 5G network with a roaming agreement with the operator associated with the UE (101).

[0134] - D-EPC-PLMN-in roaming information. For example, D-EPC-PLMN-in roaming information can be used to refer to an EPC (e.g., an eUTRAN network) that can be accessed as an alternative 5G network when there is no 5G network with a roaming agreement in the roaming area.

[0135] - d-EPC indicator information. For example, d-EPC information may be indicator information indicating that an EPC (e.g., an eUTRAN network) that can be accessed as an alternative to a 5G network with a roaming agreement can be accessed when there is no 5G network with a roaming agreement in the roaming area.

[0136] [Example 3]

[0137] According to one embodiment, in step 363, the AMF (111) sends a registration reject message to the UE (101). For example, the AMF (111) may send a registration reject message to the UUE (101) in response to a registration request message. For example, the AMF (111) may allow the UE 5G service according to the roaming agreement, but may send a registration reject message to the UE (101) when the 5G network service is (temporarily) unavailable.

[0138] The registration rejection message may contain at least some of the following information:

[0139] For example, the AMF may send the UE registration reject information that includes information about the cause of the temporary connection to another network / another PLMN (e.g., a cause value (e.g., 5G network inaccessibility)). In this case, the UE may subsequently attempt registration to another network / PLMN based on the cause information.

[0140] - PLMN information may be transmitted. For example, PLMN information may be 5G PLMN information that allows access to networks (e.g., 5G networks) with which the operator has a roaming agreement. For example, PLMN information may be 5G PLMN information that allows access to 5G networks.

[0141] - D-EPC (evolved packet core)-PLMN-in roaming information may be transmitted. The information may refer to an EPC (e.g., an eUTRAN network) that can be connected as an alternative to a network with roaming agreement (e.g., a 5G network) when there is no 5G network with a roaming agreement in the roaming area or when the 5G network with a roaming agreement in the roaming area becomes unavailable for service. For example, the D-ECP-PLMN-in roaming information may refer to information about a network (e.g., an alternative network) that the UE (101) can connect as an alternative to the network with roaming agreement to receive service when there is no network with roaming agreement or the network becomes (temporarily) unavailable.

[0142] - d-EPC indicator information may be transmitted. The d-EPC information is indicator information to indicate that an EPC (e.g., an eUTRAN network) that can be connected as an alternative to a 5G network with a roaming agreement can be connected when there is no network (e.g., a 5G network) with a roaming agreement in the roaming area. For example, the d-EPC indicator information may be referenced as information indicating whether the UE (101) can connect to an alternative network. For example, the d-EPC indicator information may include a field value, a bit map, and / or a bit value.

[0143] According to one embodiment, the UE (101) may store at least some of the following information at step 365.

[0144] - PLMN information. For example, the PLMN information may be information about a 5G PLMN that can access a 5G network with a roaming agreement with the operator associated with the UE (101).

[0145] - D-EPC-PLMN-in roaming information. For example, D-EPC-PLMN-in roaming information can be used to refer to an EPC (e.g., an eUTRAN network) that can be accessed as an alternative to a 5G network with a roaming agreement in the roaming area.

[0146] - d-EPC indicator information. For example, d-EPC information may be indicator information indicating that an EPC (e.g., an eUTRAN network) that can be accessed as an alternative to a 5G network with a roaming agreement can be accessed when there is no 5G network with a roaming agreement in the roaming area.

[0147] - Cause information. For example, the AMF may send the UE registration reject information containing information about the cause of the temporary connection to a different network / PLMN (e.g., a cause value (e.g., 5G network inaccessibility)). In this case, the UE can store the cause information and subsequently attempt registration to a different network / PLMN based on the cause information.

[0148] According to one embodiment, in step 371, the UE (101) may select a PLMN. The PLMN selection in step 371 may be different from the existing PLMN selection.

[0149] That is, unlike the conventional PLMN selection, the PLMN selection in step 371 is performed based on given information (e.g., information that there is an alternative 4G network, such as EPC or eUTRAN, in the case where the 5G network is not available; information that the UE (101) has the ability to use the network or has been notified by the network that the function can be used; or information that causes the 5G network with which there is a roaming agreement to be (temporarily) unavailable).

[0150] The information used at this time may include at least some of the following:

[0151] - Temp information may be available. Temp information may be transmitted. This may be to indicate that the EPC or eUTRAN is being used temporarily.

[0152] - Limited information may be available. This may be to inform the UE (101) that limited services are provided, as the UE (101) is temporarily permitted to use the EPC or eUTRAN.

[0153] - Cause information indicating that there is a 5G network with a roaming agreement, but that the network is (temporarily) unavailable.

[0154] According to one embodiment, the UE (101) may transmit an attach request message to the MME (271) at step 381. For example, the UE (101) may transmit the attach request message to the MME (271) via the eNB (273). For example, the eNB (273) may receive the attach request message from the UE (101), and the eNB (273) may transmit the attach request to the MME (271).

[0155] According to one embodiment, the UE (101) may transmit information to the MME (271) that it is temporarily connected due to the absence of a 5G network in the roaming area. For example, the UE (101) may include information indicating that the UE is temporarily connected in an attach request message and transmit it to the MME (271).

[0156] The information transmitted to MME (271) may include at least some of the following:

[0157] - Temp information may be transmitted. Temp information is intended to indicate temporary use of EPC or eUTRAN.

[0158] - Limited information may be transmitted. Limited information is intended to inform the UE (101) that limited services are provided, as it allows the UE (101) to temporarily use EPC or eUTRAN.

[0159] According to one embodiment, in step 383, the MME (271) may transmit an attach accept message to the UE (101). For example, the MME (271) may transmit an attach accept message to the eNB (273), and the eNB (273) may transmit an attach accept message to the UE (101).

[0160] The information transmitted at this time is as follows:

[0161] Limited information may be transmitted. This is to inform the UE that limited services are provided, as the UE is temporarily permitted to use the EPC or eUTRAN.

[0162] Although FIG. 3 of the present disclosure illustrates that the network with roaming consent is a 5G network and the network replacing the network with roaming consent (e.g., the replacement network) is a 4G network, this is merely an example. For example, the network with roaming consent may be a 4G network and the replacement network may be a 5G network. For example, the network with roaming consent may be a first network that supports 5G, and the replacement network may be a second network that supports 5G. For example, the network with roaming consent may be one of 2G, 3G, 4G, and 5G, and the replacement network may be one of 2G, 3G, 4G, and 5G.

[0163] FIG. 4 is a flowchart illustrating a procedure for smoothly providing a communication service in a 5G network environment and / or a 4G network environment according to one embodiment of the present disclosure.

[0164] Referring to FIG. 4, in step 401 according to one embodiment, the UE (101) may transmit a registration request message to the AMF (111). For example, the UE (101) may transmit a registration request message to the AMF (111) through the base station (103). For example, the base station (103) may receive the registration request message from the UE (101), and the base station (103) may transmit the registration request message to the AMF (111).

[0165] According to one embodiment, in step 405, the AMF (111) may transmit a registration approval message to the UE (101). For example, the base station (103) may receive a registration approval message from the AMF (111), and the base station (103) may transmit the registration approval message to the UE (101).

[0166] Information transmitted to UE (101) may include at least some of the following:

[0167] - PLMN information may be transmitted. For example, the PLMN information may be 5G PLMN information that allows access to a 5G network with a roaming agreement with the operator.

[0168] - D-EPC-PLMN-in roaming information may be transmitted. For example, D-EPC-PLMN-in roaming information may refer to an EPC (e.g., an eUTRAN network) that can be accessed as an alternative to a 5G network with a roaming agreement in the roaming area.

[0169] - d-EPC indicator information may be transmitted. For example, d-EPC information may be indicator information to indicate that an EPC (e.g., an eUTRAN network) that can be accessed as an alternative to a 5G network in the roaming area where there is no 5G network with a roaming agreement is available.

[0170] According to one embodiment, at step 411, the UE (101) may store at least some of the following information:

[0171] - PLMN information. For example, PLMN information may be 5G PLMN information that allows access to a 5G network with a roaming agreement with the carrier.

[0172] - D-EPC-PLMN-in roaming information. For example, D-EPC-PLMN-in roaming information can refer to an EPC or eUTRAN network that can be accessed as an alternative to a 5G network with a roaming agreement in the roaming area.

[0173] - d-EPC indicator information. For example, d-EPC information may be indicator information that indicates that an EPC or eUTRAN network can be accessed as an alternative to a 5G network with a roaming agreement in the roaming area.

[0174] According to one embodiment, in step 431, the UE (101) may transmit a PDU session establishment request message to the SMF (121). For example, the UE (111) may transmit a PDU session establishment request message to the AMF (111) through the base station (103), and the AMF (111) may transmit a PDU session establishment request message to the SMF (121).

[0175] According to one embodiment, in step 433, the SMF (121) may transmit a PDU session establishment response message to the UE (101). For example, the SMF (121) may transmit a PDU session establishment response message to the AMF (111), and the AMF (111) may transmit a PDU session establishment response message to the UE (101) via the base station (103).

[0176] According to one embodiment, in step 451, the UE (101) may select a PLMN. The PLMN selection in step 451 may be different from the existing PLMN selection.

[0177] That is, unlike the conventional PLMN selection, the PLMN selection in step 451 is performed based on given information (e.g., information on whether there is an alternative 4G network (e.g., EPC, eUTRAN) in place of the 5G network if the 5G network is not available, information on whether the network (e.g., 4G network) has the capability to be used, or information on whether the network has notified that the capability is available (e.g., capability information)).

[0178] The information used at this time is as follows:

[0179] - Temp information may be present. For example, Temp information may be transmitted. Temp information is intended to indicate that the EPC or eUTRAN is being used temporarily.

[0180] - Limited information may be available. For example, Limited information may be used to inform the UE (101) that limited services are provided, as it allows the UE (101) to temporarily use EPC or eUTRAN.

[0181] According to one embodiment, the UE (101) may transmit an attach request message to the MME (271) at step 461. For example, the UE (101) may transmit the attach request message to the MME (271) via the eNB (273). For example, the eNB (273) may receive the attach request message from the UE (101), and the eNB (273) may transmit the attach request to the MME (271).

[0182] At this time, the UE (101) can transmit information to the MME (271) that it is temporarily connected because there is no 5G network in the roaming area.

[0183] The information transmitted to MME (271) may include at least some of the following:

[0184] - Temp information may be transmitted. Temp information may be used to indicate temporary use of the EPC or eUTRAN.

[0185] - Limited information may be transmitted. Limited information is intended to inform the UE (101) that limited services are provided, as it allows the UE (101) to temporarily use EPC or eUTRAN.

[0186] According to one embodiment, at step 463, the UE (101) may transmit an attach accept message to the MME (271). For example, the MME (271) may transmit an attach accept message to the eNB (273), and the eNB (273) may transmit an attach accept message to the UE (101).

[0187] The information transmitted to MME (271) may include at least some of the following:

[0188] - Limited information may be transmitted. Limited information is information to inform the UE (101) that limited services are provided, as it allows the UE (101) to temporarily use EPC or eUTRAN.

[0189] According to one embodiment, in step 471, the UE (101) may transmit a TAU (tracking area update) request message to the MME (271). For example, the eNB (273) may receive the TAU request message from the UE (101), and the eNB (273) may transmit the TAU request message to the MME (271).

[0190] In one embodiment, the TAU request message may include information or an information element (IE) or indicator information called "available 5G." However, this is merely an example, and the available 5G information (or IE) may be transmitted in a message separate from the TAU request message.

[0191] For example, available 5G information (or IE) is information that notifies that the UE is able to use the 5G network. For example, available 5G information (or IE) may be information that can indicate that 5G connection of the UE (101) is possible. For example, the UE (101) can notify the network that the UE is able to connect to a 5G network with roaming consent by transmitting available 5G information (or IE) to the network.

[0192] According to one embodiment, in step 473, the MME (271) may transmit a TAU accept message to the UE (101). For example, the MME (271) may transmit a TAU accept message to the eNB (273), and the eNB (273) may transmit the TAU accept message to the UE (101).

[0193] In one embodiment, the TAU Accept message may include information or an information element (IE) or indicator information called "available 5G." However, this is merely an example, and the available 5G information (or IE) may be transmitted in a separate message from the TAU Accept message.

[0194] For example, available 5G information (or IE) is information indicating that a 5G network is available. For example, available 5G information (or IE) may be information indicating that connection of the UE (101) is possible. For example, the UE (101) may identify that it is able to connect to a 5G network with roaming consent based on receiving the available 5G information (or IE). According to one embodiment, the UE (101) may select a PLMN in step 481.

[0195] In one embodiment, a UE (101) that recognizes that 5G is available may select a 5G network. For example, the UE (101) may identify that a 5G network is available based on receiving 5G available information, and the UE (101) may initiate a connection to the 5G network.

[0196] According to one embodiment, in step 491, the UE (101) may transmit a registration request message to the second AMF (511). For example, the UE (101) may transmit a registration request message to the second base station (503), and the second base station (503) may transmit a registration request message to the second AMF (511).

[0197] According to one embodiment, in step 493, the second AMF (511) may transmit a registration accept message to the UE (101). For example, the second AMF (511) may transmit a registration accept message to the second base station (503), and the second base station (503) may transmit a registration accept message to the UE (101).

[0198] FIG. 5 is a diagram showing the configuration of a terminal according to one embodiment of the present disclosure.

[0199] Referring to FIG. 5, the terminal (101) of the present disclosure may include a transceiver (510), a memory (520), and / or a processor (530). The processor (530), the transceiver (510), and the memory (520) of the terminal may operate according to the communication method of the terminal described above. However, the components of the terminal are not limited to the examples described above. For example, the terminal may include more or fewer components than the components described above. In addition, the processor (530), the transceiver (510), and the memory (520) may be implemented in the form of a single chip. The terminal (101) of FIG. 5 corresponds to the UE (101) of FIGS. 1 to 4.

[0200] According to one embodiment, the transceiver (510) is a general term for the receiver and transmitter of the terminal, and can transmit and receive signals with a base station or a network entity. The signals transmitted and received with the base station may include control information and data. To this end, the transceiver (510) may be configured with an RF transmitter that up-converts and amplifies the frequency of a transmitted signal, and an RF receiver that low-noise amplifies and frequency-downconverts the received signal. However, this is only one embodiment of the transceiver (510), and the components of the transceiver (510) are not limited to the RF transmitter and RF receiver.

[0201] According to one embodiment, the transceiver (510) may include a wired or wireless transceiver and may include various configurations for transmitting and receiving signals.

[0202] According to one embodiment, the transceiver (510) may receive a signal through a wireless channel and output it to the processor (530), and transmit the signal output from the processor (530) through the wireless channel.

[0203] According to one embodiment, the transceiver (510) can receive a communication signal, output the signal to the processor, and transmit the signal output from the processor to a network entity via a wired or wireless network.

[0204] According to one embodiment, the memory (520) may store programs and data necessary for the operation of the terminal. In addition, the memory (520) may store control information or data included in signals obtained from the terminal. The memory (520) may be configured as a storage medium or a combination of storage media, such as a ROM, a RAM, a hard disk, a CD-ROM, and a DVD.

[0205] According to one embodiment, the processor (530) may control a series of processes so that the terminal can operate according to the embodiments of the present disclosure described above. The processor (530) may include at least one processor. For example, the processor (530) may include a communication processor (CP) that performs control for communication and an application processor (AP) that controls upper layers such as application programs.

[0206] FIG. 6 is a diagram illustrating a configuration of a network entity according to one embodiment of the present disclosure.

[0207] Referring to FIG. 6, a network entity of the present disclosure may include a transceiver (610), a memory (620), and / or a processor (630). The processor (630), the transceiver (610), and the memory (620) of the network entity may operate according to the communication method of the network entity described above. However, the components of the network entity are not limited to the examples described above. For example, the network entity may include more or fewer components than the components described above. In addition, the processor (630), the transceiver (610), and the memory (620) may be implemented in the form of a single chip. A network entity may include one of the network functions (NF) described in FIGS. 1 to 5, such as the Access and Mobility Management Function (AMF), the Session Management Function (SMF), the Policy and Charging Function (PCF), the Network Exposure Function (NEF), the Unified Data Management (UDM), or the User Plane Function (UPF). It may also include a base station.

[0208] According to one embodiment, the transceiver (610) is a general term for the receiving unit of a network entity and the transmitting unit of the network entity, and can transmit and receive signals with a terminal or another network entity. At this time, the transmitted and received signals may include control information and data. To this end, the transceiver (610) may be configured with an RF transmitter that up-converts and amplifies the frequency of a transmitted signal, and an RF receiver that low-noise amplifies and frequency-downconverts the received signal. However, this is only one embodiment of the transceiver (610), and the components of the transceiver (610) are not limited to the RF transmitter and RF receiver. The transceiver (610) may include wired and wireless transceivers, and may include various configurations for transmitting and receiving signals.

[0209] According to one embodiment, the transceiver (610) may receive a signal through a communication channel (e.g., a wireless channel) and output the signal to the processor (630), and transmit the signal output from the processor (630) through the communication channel.

[0210] According to one embodiment, the transceiver (610) can receive a communication signal, output it to a processor, and transmit the signal output from the processor to a terminal or network entity via a wired or wireless network.

[0211] According to one embodiment, the memory (620) may store programs and data necessary for the operation of the network entity. In addition, the memory (620) may store control information or data included in signals obtained from the network entity. The memory (620) may be configured as a storage medium or a combination of storage media, such as a ROM, a RAM, a hard disk, a CD-ROM, and a DVD.

[0212] According to one embodiment, the processor (630) may control a series of processes so that a network entity can operate according to the embodiments of the present disclosure described above. The processor (630) may include at least one processor. The methods according to the embodiments described in the claims or specification of the present disclosure may be implemented in the form of hardware, software, or a combination of hardware and software.

[0213] FIG. 7 illustrates a base station according to one embodiment of the present disclosure.

[0214] Referring to FIG. 7, the configuration illustrated in FIG. 7 according to one embodiment may be understood as a configuration of the RAN (103) of FIG. 1 and / or the RAN (503) (e.g., gNB, eNB) of FIG. 3. Terms such as "...unit" and "...unit" used hereinafter mean a unit that processes at least one function or operation, which may be implemented by hardware, software, or a combination of hardware and software.

[0215] According to one embodiment, the base station includes a transceiver (710), a memory (720), and / or a processor (730).

[0216] The transceiver (710) performs functions for transmitting and receiving signals via a wireless channel. For example, the transceiver (710) performs a conversion function between a baseband signal and a bit stream according to the physical layer specifications of the system. For example, when transmitting data, the transceiver (710) generates complex symbols by encoding and modulating a transmission bit stream. In addition, when receiving data, the transceiver (710) restores a reception bit stream by demodulating and decoding a baseband signal. In addition, the transceiver (710) upconverts a baseband signal to an RF band signal and transmits it through an antenna, and downconverts an RF band signal received through the antenna to a baseband signal. For example, the transceiver (710) may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc.

[0217] In addition, the transceiver (710) may include multiple transceiver paths. Furthermore, the communication unit (405) may include at least one antenna array composed of multiple antenna elements. In terms of hardware, the transceiver (710) may be composed of digital circuits and analog circuits (e.g., radio frequency integrated circuits (RFIC)). Here, the digital circuits and analog circuits may be implemented in a single package. In addition, the transceiver (710) may include multiple RF chains. Furthermore, the transceiver (710) may perform beamforming.

[0218] The transceiver (710) transmits and receives signals as described above. Accordingly, all or part of the transceiver (710) may be referred to as a "transmitter," a "receiver," or a "transmitter-receiver." Furthermore, in the following description, the term "transmission and reception" performed via a wireless channel is used to mean that the transceiver (710) performs the processing described above.

[0219] The memory (720) stores data such as basic programs, application programs, and setting information for the operation of the base station. The memory (720) may be composed of volatile memory, nonvolatile memory, or a combination of volatile and nonvolatile memory. In addition, the memory (720) provides stored data upon request from the processor (730).

[0220] The processor (730) controls the overall operations of the base station. For example, the processor (730) transmits and receives signals through the transceiver (710). In addition, the processor (730) records and reads data from the memory (720). In addition, the processor (730) can perform the functions of the protocol stack required by the communication standard. To this end, the processor (730) may include at least one processor or microprocessor, or may be a part of a processor. In addition, a part of the transceiver (710) and the processor (730) may be referred to as a CP (communication processor). According to various embodiments, the processor (730) may control synchronization using a wireless communication network. For example, the processor (730) may control the base station to perform operations according to the various embodiments described above.

[0221] When implemented in software, a computer-readable storage medium storing one or more programs (software modules) may be provided. The one or more programs stored in the computer-readable storage medium are configured for execution by one or more processors within an electronic device. The one or more programs include instructions that cause the electronic device to execute methods according to the embodiments described in the claims or specification of the present disclosure.

[0222] These programs (software modules, software) may be stored in random access memory, non-volatile memory including flash memory, read only memory (ROM), electrically erasable programmable read only memory (EEPROM), magnetic disc storage devices, compact disc-ROMs (CD-ROMs), digital versatile discs (DVDs) or other forms of optical storage devices, magnetic cassettes, or may be stored in memories formed by a combination of some or all of these. In addition, each configuration memory may include multiple copies.

[0223] Additionally, the program may be stored on an attachable storage device that is accessible via a communication network, such as the Internet, an intranet, a local area network (LAN), a wide area network (WAN), a storage area network (SAN), or a combination thereof. Such a storage device may be connected to a device performing an embodiment of the present disclosure via an external port. Additionally, a separate storage device on the communication network may be connected to a device performing an embodiment of the present disclosure.

[0224] In the specific embodiments of the present disclosure described above, components included in the disclosure are expressed in the singular or plural form, depending on the specific embodiment presented. However, the singular or plural expressions are selected to suit the presented situation for convenience of explanation, and the present disclosure is not limited to singular or plural components. Components expressed in the plural form may be composed of singular elements, or components expressed in the singular form may be composed of plural elements.

[0225] While the detailed description of this disclosure has described specific embodiments, it should be understood that various modifications are possible without departing from the scope of this disclosure. Therefore, the scope of this disclosure should not be limited to the described embodiments, but should be defined not only by the scope of the claims described below, but also by equivalents thereof.

Claims

1. In a method performed by UE (user equipment), A step of sending a registration request message to an AMF (access and mobility management function) entity; A step of receiving a registration acceptance message from the AMF entity, the registration acceptance message including first information about a 5G (generation) PLMN (public land mobile network) of the roaming area and second information about an EPC (evolved packet core) PLMN of the roaming area; If the 5G PLMN is unavailable, a step of identifying the EPC PLMN associated with the MME (mobility management entity) based on the second information; and A method comprising the step of transmitting, to the MME, an attach request message including an indicator indicating temporary access to the EPC PLMN.

2. In claim 1, The registration acceptance message includes at least one of the first information about the 5G PLMN, the second information about the EPC PLMN, or third information indicating whether the EPC PLMN is accessible, A method wherein the second information about the EPC PLMN includes information about a 4G PLMN that can replace the 5G PLMN in the roaming area.

3. In claim 2, A method further comprising the step of storing at least one of the first information, the second information, or the third information.

4. In claim 1, Further comprising the step of receiving an attach acceptance message from the MME, A method wherein the above attach acceptance message includes information indicating that a limited service is provided to the UE.

5. In claim 1, A step of sending a PDU (protocol data unit) session establishment request message to an SMF (session management function) entity after the registration procedure is completed; and A method comprising the step of receiving a PDU session establishment response message from the above SMF.

6. In claim 1, A method wherein the above attach request message includes information about the cause of accessing the EPC PLMN.

7. In claim 1, The method wherein the above 5G PLMN is a PLMN with a roaming agreement in the above roaming area.

8. In UE (user equipment), At least one transceiver; At least one processor communicatively coupled to said at least one transceiver; and At least one memory communicatively coupled to said at least one processor and storing instructions, The above instructions are executed individually or in any combination by the at least one processor so that the UE: Send a registration request message to the AMF (access and mobility management function) entity, Receive a registration acceptance message from the AMF entity, the registration acceptance message including first information about a 5G (generation) PLMN (public land mobile network) of the roaming area and second information about an EPC (evolved packet core) PLMN of the roaming area, If the above 5G PLMN is unavailable, the EPC PLMN associated with the MME (mobility management entity) is identified based on the second information, A UE that causes the MME to transmit an attach request message including an indicator indicating temporary access to the EPC PLMN.

9. In claim 8, The registration acceptance message includes at least one of the first information about the 5G PLMN, the second information about the EPC PLMN, or third information indicating whether the EPC PLMN is accessible, The second information about the EPC PLMN includes information about a 4G PLMN that can replace the 5G PLMN in the roaming area.

10. In claim 9, The above commands cause the UE to: A UE configured to store at least one of the first information, the second information, or the third information.

11. In claim 8, The above commands cause the UE to: To receive an attach acceptance message from the above MME, The above attach acceptance message includes information indicating that a limited service is provided to the UE.

12. In claim 8, The above commands cause the UE to: To the SMF (session management function) entity, a PDU (protocol data unit) session establishment request message is sent after the registration procedure is completed, A UE configured to receive a PDU session establishment response message from the above SMF.

13. In claim 8, The above attach request message includes information about the cause of accessing the EPC PLMN.

14. In claim 8, The above 5G PLMN is a UE that has a roaming agreement in the above roaming area.

15. One or more non-transitory computer-readable storage media storing computer-executable instructions, wherein when the computer-executable instructions are individually or collectively executed by at least one processor of a user equipment (UE), the UE: Send a registration request message to the AMF (access and mobility management function) entity, Receive a registration acceptance message from the AMF entity, the registration acceptance message including first information about a 5G (generation) PLMN (public land mobile network) of the roaming area and second information about an EPC (evolved packet core) PLMN of the roaming area, If the above 5G PLMN is unavailable, the EPC PLMN associated with the MME (mobility management entity) is identified based on the second information, A recording medium that causes the MME to perform operations of transmitting an attach request message including an indicator indicating temporary access to the EPC PLMN.

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