CN117730569A

CN117730569A - Method and apparatus for providing voice service to user equipment in hybrid mobile communication system

Info

Publication number: CN117730569A
Application number: CN202280053143.1A
Authority: CN
Inventors: 金东妍; 朴重信; 郑相洙
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2021-07-30
Filing date: 2022-07-12
Publication date: 2024-03-19

Abstract

The present disclosure relates to a communication method and system that fuses a fifth generation (5G) communication system for supporting higher data rates than a fourth generation (4G) system with techniques for internet of things (IoT). The present disclosure may be applied to smart services based on 5G communication technology and IoT-related technology, such as smart home, smart building, smart city, smart car, networked car, healthcare, digital education, smart retail, security and security services. A method of controlling a fallback of a User Equipment (UE) by a combined device of a Session Management Function (SMF) and a packet data network gateway (PGW) control plane function (PGW-C) in a hybrid mobile communication system in which a first mobile communication system and a second mobile communication system are interworked is provided.

Description

Method and apparatus for providing voice service to user equipment in hybrid mobile communication system

Technical Field

The present application is based on korean patent application No. 10-2021-0100810 filed at the korean intellectual property office on the day of 7 months 30 in 2021, korean patent application No. 10-2021-0105699 filed at the korean intellectual property office on the day of 8 months 10 in 2021, and korean patent application No. 10-2021-0151800 filed at the korean intellectual property office on the day of 11 months 5 in 2021 and claims priority thereto according to clause 119 (a) of american society of america, the disclosure of each of which is incorporated herein by reference in its entirety.

The present disclosure relates to a method and apparatus for providing a voice service to a User Equipment (UE) in a mobile communication system. More particularly, the present disclosure relates to a method and apparatus for providing a voice service to a UE in a hybrid mobile communication system having different communication protocols.

Background

In order to meet the increased demand for wireless data services since the deployment of fourth generation (4G) communication systems, efforts have been made to develop improved fifth generation (5G) or quasi-5G communication systems. Therefore, a 5G or quasi 5G communication system is also referred to as a "super 4G network" or a "Long Term Evolution (LTE) after-system". A 5G communication system is considered to be implemented in a higher frequency (millimeter wave) band (e.g., 60 gigahertz (GHz) band) in order to achieve higher data rates. In order to reduce propagation loss of radio waves and increase transmission distance, beamforming, massive Multiple Input Multiple Output (MIMO), full-dimensional MIMO (FD-MIMO), array antennas, analog beamforming, massive antenna techniques are discussed in 5G communication systems. In addition, in the 5G communication system, development for system network improvement is performed based on advanced small cells, cloud Radio Access Networks (RANs), ultra dense networks, device-to-device (D2D) communication, wireless backhaul, mobile networks, cooperative communication, coordinated multipoint (CoMP), reception-side interference cancellation, and the like. In the 5G system (5 GS), hybrid Frequency Shift Keying (FSK) and Quadrature Amplitude Modulation (QAM) modulation (FQAM) as Advanced Code Modulation (ACM) and Sliding Window Superposition Coding (SWSC), and Filter Bank Multicarrier (FBMC), non-orthogonal multiple access (NOMA) and Sparse Code Multiple Access (SCMA) as advanced access technologies have been developed.

The internet, which is a human-centric connected network in which humans generate and consume information, is now evolving into the internet of things (IoT) in which distributed entities such as things exchange and process information without human intervention. Internet of everything (IoE) has emerged as a combination of IoT technology and big data processing technology through connection with cloud servers. As IoT implementations have required technical elements such as "sensing technology," "wired/wireless communication and network infrastructure," "service interface technology," and "security technology," sensor networks, machine-to-machine (M2M) communications, machine Type Communications (MTC), etc. have recently been investigated. Such IoT environments may provide intelligent internet technology services that create new value for human life by collecting and analyzing data generated among networking. IoT may be applied in a variety of fields including the following through fusion and combination between existing Information Technology (IT) and various industrial applications: smart home, smart building, smart city, smart car or networking car, smart grid, healthcare, smart home appliances, and advanced medical services.

In keeping with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, techniques such as sensor networks, machine Type Communications (MTC), and machine-to-machine (M2M) communications may be implemented through beamforming, MIMO, and array antennas. The application of cloud Radio Access Networks (RANs) as the big data processing technology described above may also be considered as an example of a convergence between 5G technology and IoT technology.

With recent developments in communication systems, various researches for providing different network slicing modes (or network slices) are being conducted in 5G-based wireless communication systems.

The foregoing information is presented merely as background information to aid in the understanding of the disclosure. As to whether any of the above-described items may be applicable as prior art with respect to the present disclosure, no determination has been made and no assertion has been made.

Disclosure of Invention

Technical problem

The 5GS currently being commercialized and the LTE and long term evolution advanced (LTE-a) systems currently providing mobile communication services are both mobile communication systems providing packet-based services. The 5GS system is being developed to support interworking with the LTE and LTE-a based Evolved Packet System (EPS) (mutual interworking). When a UE that can use wireless communication through 5GS and EPS desires to use voice service through 5GS supporting EPS/5GS interworking, the 5G core network determines whether the UE can use voice service through a next generation radio access network (NG-RAN). When it is determined that the UE cannot use voice service through NG-RAN and 5GS, the 5G core network triggers an EPS fallback (fallback) procedure so that the UE can use voice service through E-UTRAN and EPS. When the UE moves to the EPS through an EPS fallback procedure, the UE registers in the EPS through a Tracking Area Update (TAU) procedure of the EPS and establishes a Packet Data Network (PDN) connection (PDN session), an RRC connection, and a radio bearer for the voice service. This may be referred to as an EPS backoff.

When it is determined that the UE does not use voice service (e.g., does not receive a voice call) for a predetermined time, the UE may switch to an idle state, and the EPS network may release the RRC connection to the UE and induce a return to 5GS.

The UE triggers a registration procedure of a mobility registration update type to return to 5GS, and the 5G core network acquires information such as Mobility Management (MM) context, PDN connection, and EPS bearer related to the UE from the EPS network from which the UE has moved. The 5G core network provides this information to the NG-RAN and makes a request to configure information about the session with the UE. When the EPS network maintains bearer information for the voice service, the NG-RAN may stop the registration procedure that returns the UE to 5GS and move the UE back to the EPS. This may be referred to as a stop of the 5GS move procedure and a secondary EPS backoff.

The UE triggers the TAU procedure to move to the EPS, in which case a 5G globally unique temporary identifier (5G-GUTI) is required to obtain the MM context in the 5GS by the EPS through determination of the access and mobility management function (AMF) address of the 5GS from which the UE has moved, etc. However, since the UE has moved in a state in which the registration procedure has not been successfully completed in 5GS, the UE may not receive allocation of 5G-GUTI from the AMF. In this case, the UE may provide the EPS with the long EPS-GUTI previously allocated by the EPS, and the EPS may reject the TAU procedure because the ESP-GUTI is an invalid UE identifier. Thus, the UE disconnects from the network. That is, the EPS mobility procedure may be stopped and the UE connection may be lost.

Solution scheme

Aspects of the present disclosure are directed to solving at least the problems and/or disadvantages noted above and to providing at least the advantages described below. Accordingly, an aspect of the present disclosure is to provide a method and apparatus for normally performing an EPS mobile procedure by performing a secondary EPS backoff after a 5G-GUTI by completing a registration procedure in 5GS and performing the secondary EPS backoff after receiving the 5G-GUTI when a UE performs the secondary backoff during the mobile procedure to 5GS after the primary EPS backoff.

Another aspect of the present disclosure is to provide a method and apparatus for preventing secondary EPS fallback, in which, when a UE performs EPS fallback in order to use voice service, if the UE does not normally use voice service and moves to 5GS, a connection for voice service remains in the EPS by moving the UE to 5GS after releasing a bearer, RRC connection, and PDN connection established in order to use voice service in the EPS.

Additional aspects will be set forth in part in the description which follows, and in part will be apparent from the description, or may be learned by practice of the presented embodiments.

In accordance with one aspect of the present disclosure, there is provided a method of controlling fallback of a User Equipment (UE) by a combined device of a Session Management Function (SMF) and a packet data network gateway (PGW) control plane function (PGW-C) in a hybrid mobile communication system in which a first mobile communication system and a second mobile communication system are interworked. The method comprises the following steps: receiving a reactivation request for a Packet Data Network (PDN) connection of the UE of the second mobile communication system from an access and mobility management function (AMF) of the first mobile communication system, the reactivation request including a PDN connection context; retrieving a corresponding PDU session based on the PDN connectivity context included in the reactivation request; modifying Evolved Packet System (EPS) bearer identity (EBI) information for IP Multimedia Subsystem (IMS) voice allocated to the UE based on information supported in the first mobile system; establishing a Core Network (CN) tunnel for the PDU session of the UE to a User Plane Function (UPF) and a PGW user plane function (PGW-U) based on the modified EBI information; updating a Session Management (SM) context based on the established CN information; and transmitting a response message including the updated SM context to the AMF in response to the reactivation request.

In accordance with another aspect of the present disclosure, there is provided a combined device of a session management function SMF and a packet data network gateway PGW control plane function PGW-C for controlling fallback of a user equipment UE in a hybrid mobile communication system in which a first mobile communication system and a second mobile communication system are interworked. The combination device includes: a transceiver configured to communicate with a network function of the hybrid mobile communication system; a memory; and a processor configured to control to: receiving a reactivation request for a Packet Data Network (PDN) connection of the UE of the second mobile communication system from an access and mobility management function (AMF) of the first mobile communication system, the reactivation request including a PDN connection context; retrieving a corresponding PDU session based on the PDN connectivity context included in the reactivation request; modifying Evolved Packet System (EPS) bearer identity (EBI) information for IP Multimedia Subsystem (IMS) voice allocated to the UE based on information supported in the first mobile system; establishing a Core Network (CN) tunnel for the PDU session of the UE to a User Plane Function (UPF) and a PGW user plane function (PGW-U) based on the modified EBI information; updating a Session Management (SM) context based on the established CN information; and transmitting a response message including the updated SM context to the AMF in response to the reactivation request.

Advantageous effects of the invention

According to the apparatus and method of various embodiments of the present disclosure, a voice service can be effectively provided in a mobile communication system.

Other aspects, advantages, and salient features of the disclosure will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses various embodiments of the disclosure.

Drawings

The foregoing and other aspects, features, and advantages of certain embodiments of the disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings in which:

fig. 1 illustrates an architecture of a wireless communication system supporting interworking between a 5G system and an EPS system according to an embodiment of the present disclosure;

fig. 2A illustrates a method for registering a UE and managing a session by an NG-RAN through a deferred fallback initiation procedure in accordance with an embodiment of the present disclosure;

fig. 2B illustrates a method for registering a UE and managing a session by an NG-RAN through a deferred fallback initiation procedure in accordance with an embodiment of the present disclosure;

fig. 2C illustrates a method for registering a UE and managing a session by an NG-RAN through a deferred fallback initiation procedure in accordance with an embodiment of the present disclosure;

fig. 2D illustrates a method for registering a UE and managing a session by an NG-RAN through a deferred fallback initiation procedure in accordance with an embodiment of the present disclosure;

Fig. 3A illustrates a method of registering a UE by an AMF through a deferred fallback trigger procedure and managing a session according to an embodiment of the present disclosure;

fig. 3B illustrates a method of registering a UE by an AMF through a deferred fallback trigger procedure and managing a session according to an embodiment of the present disclosure;

fig. 3C illustrates a method for registering a UE and managing a session by an AMF through a deferred fallback trigger procedure according to an embodiment of the present disclosure;

fig. 3D illustrates a method of registering a UE by an AMF through a deferred fallback trigger procedure and managing a session according to an embodiment of the present disclosure;

fig. 4A illustrates a method for registering a UE and managing a session by an MME through a bearer deactivation procedure according to an embodiment of the present disclosure;

fig. 4B illustrates a method for registering a UE and managing a session by an MME through a bearer deactivation procedure according to an embodiment of the present disclosure;

fig. 4C illustrates a method for registering a UE and managing a session by an MME through a bearer deactivation procedure according to an embodiment of the present disclosure;

fig. 4D illustrates a method for registering a UE and managing a session by an MME through a bearer deactivation procedure according to an embodiment of the present disclosure;

fig. 5 shows a configuration of a UE according to an embodiment of the present disclosure;

fig. 6 shows a configuration of a network entity according to an embodiment of the present disclosure;

Fig. 7A illustrates a method for registering a UE and managing a session by an SMF through a delayed fallback trigger procedure according to an embodiment of the present disclosure;

fig. 7B illustrates a method for registering a UE and managing a session by an SMF through a delayed fallback trigger procedure according to an embodiment of the present disclosure;

fig. 7C illustrates a method for registering a UE and managing a session by an SMF through a delayed fallback trigger procedure according to an embodiment of the present disclosure;

fig. 7D illustrates a method for registering a UE and managing a session by an SMF through a delayed fallback trigger procedure according to an embodiment of the present disclosure;

fig. 7E illustrates a method for registering a UE and managing a session by an SMF through a delayed fallback trigger procedure according to an embodiment of the present disclosure;

fig. 8A illustrates a method of registering a UE by an SMF by using a delay of a procedure of triggering a fallback and managing a session according to an embodiment of the present disclosure;

fig. 8B illustrates a method of registering a UE by an SMF by using a delay of a procedure of triggering a fallback and managing a session according to an embodiment of the present disclosure;

fig. 8C illustrates a method of registering a UE and managing a session by an SMF by using a delay of a procedure of triggering a fallback according to an embodiment of the present disclosure;

fig. 8D illustrates a method of registering a UE and managing a session by an SMF by using a delay of a procedure of triggering a fallback according to an embodiment of the present disclosure;

Fig. 8E illustrates a method of registering a UE and managing a session by an SMF using a delay of a procedure of triggering a fallback according to an embodiment of the present disclosure;

fig. 9A illustrates a method of registering a UE and managing a session by maintaining a procedure of triggering a fallback according to an embodiment of the present disclosure;

fig. 9B illustrates a method of registering a UE and managing a session by using maintenance of a procedure of triggering a fallback according to an embodiment of the present disclosure;

fig. 9C illustrates a method of registering a UE and managing a session by using maintenance of a procedure of triggering a fallback according to an embodiment of the present disclosure;

fig. 9D illustrates a method of registering a UE and managing a session by using maintenance of a procedure of triggering fallback according to an embodiment of the present disclosure.

Like reference numerals are used to denote like elements throughout the figures.

Detailed Description

The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of the various embodiments of the disclosure as defined by the claims and their equivalents. It includes various specific details to aid in this understanding, but these should be considered exemplary only. Accordingly, one of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are not limited to written meanings, but are used only by the inventors to achieve a clear and consistent understanding of the disclosure. Accordingly, it should be apparent to those skilled in the art that the following descriptions of the various embodiments of the present disclosure are provided for illustration only and not for the purpose of limiting the disclosure as defined by the appended claims and their equivalents.

It should be understood that the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a "component surface" includes reference to one or more such surfaces.

In describing embodiments in the present specification, descriptions related to technical contents that are well known in the art and are not directly associated with the present disclosure will be omitted. Such omissions of unnecessary description are intended to prevent confusion and more clear transfer of the main ideas of the present disclosure.

For the same reason, in the drawings, some elements may be exaggerated, omitted, or schematically illustrated. Furthermore, the size of each element does not fully reflect the actual size. In the drawings, the same or corresponding elements are provided with the same reference numerals.

The advantages and features of the present disclosure and the manner in which they are achieved will become apparent by reference to the embodiments as described in detail below in conjunction with the accompanying drawings. However, the present disclosure is not limited to the embodiments set forth below, but may be implemented in various forms. The following examples are provided solely to fully disclose the present disclosure and to inform those of ordinary skill in the art of the scope of the present disclosure, and the present disclosure is limited only by the scope of the appended claims. Throughout the specification, the same or like reference numerals designate the same or like elements.

In this document, it will be understood that each block of the flowchart illustrations, and combinations of blocks in the flowchart illustrations, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart block or blocks. These computer program instructions may also be stored in a computer-usable or computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-usable or computer-readable memory produce an article of manufacture including instruction means that implement the function specified in the flowchart block or blocks. The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operations to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide operations for implementing the functions specified in the flowchart block or blocks.

Furthermore, each block of the flowchart illustrations may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that in some alternative implementations, the functions noted in the blocks may occur out of the order. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved.

As used herein, "unit" refers to a software element or a hardware element, such as a Field Programmable Gate Array (FPGA) or an Application Specific Integrated Circuit (ASIC), that performs a predetermined function. However, the "unit" does not always have a meaning limited to only software or hardware. A "unit" may be structured to be stored in an addressable storage medium or to run one or more processors. Thus, a "unit" includes, for example, software elements, object-oriented software elements, class elements or task elements, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and parameters. The elements and functions provided by a "unit" may be combined into a smaller number of elements or "units" or divided into a larger number of elements or "units". Furthermore, elements and "units" may be implemented to render one or more CPUs within a device or secure multimedia card.

In embodiments of the present disclosure, a base station is an entity that allocates resources to User Equipment (UE) and may be at least one of a gNode B, a gNB, an eNode B, an eNB, a Node B, a Base Station (BS), a radio access unit, a base station controller, and a Node on a network. Further, the base station may be a network entity comprising at least one of: an integrated access and backhaul donor (IAB donor), which is a gNB that provides network access to a UE or terminal(s) via a network of backhaul and access links; and an IAB node, which is a Radio Access Network (RAN) node supporting NR access link(s) to terminal(s) and supporting NR backhaul link to IAB donor or any other IAB node. The terminal may perform wireless access via the IAB nodes and transmit/receive data to/from the IAB donor connected to the at least one IAB node via the backhaul link.

In addition, the UE may include a terminal, a User Equipment (UE), a Mobile Station (MS), a cellular phone, a smart phone, a computer, or various devices capable of performing communication functions. As described above, in the following description, a UE or a terminal may be understood as the same entity.

In the present disclosure, "Downlink (DL)" refers to a wireless link through which a base station transmits signals to a terminal, and "Uplink (UL)" refers to a wireless link through which a terminal transmits signals to a base station. Furthermore, in the following description, an LTE or LTE-a system may be described as an example, but embodiments of the present disclosure may also be applicable to other communication systems having similar technical contexts or channel types. Examples of such communication systems may include fifth generation mobile communication technologies (5G, new radio and NR) developed outside LTE-a, and in the following description, "5G" may be a concept covering existing LTE, LTE-a or other similar services. In addition, embodiments of the present disclosure may also be adapted for use with other communication systems with some modifications based on determinations made by those skilled in the art without departing significantly from the scope of the present disclosure.

Hereinafter, the present disclosure proposes an apparatus and method for providing interworking of network slices (or network slice modes) in a wireless communication system. In particular, a technique for interworking between a 5G network system and an EPS network system to provide a network slicing function in a wireless communication system is described by the present disclosure. In the present disclosure, the 5G network system may be referred to as a first wireless communication system, the EPS network system may be referred to as a second wireless communication system, and both systems may be collectively referred to as wireless communication systems.

In the following description, for convenience, terms referring to signals, terms referring to channels, terms referring to control information, terms referring to network entities, terms referring to device elements, etc. are illustratively used. Further, in the following description, terms used to identify an access node, terms referring to messages, terms referring to interfaces between network entities, terms referring to various information, etc., are illustratively used for convenience. Accordingly, the present disclosure is not limited by terms used below, and other terms referring to a body having an equivalent technical meaning may be used.

In the following description, various embodiments of the present disclosure will be described using terms and names defined in some communication standards, such as the third generation partnership project (3 GPP), but these terms and names are for illustration only. Various embodiments of the present disclosure may be readily adapted for use with other communication systems by way of modification.

In the 3GPP standard, 5G network system architecture and procedures have been standardized. Mobile communication operators can provide various services in 5G networks. In order to provide services, mobile communication operators need to meet different service requirements (e.g., delay time, communication range, data rate, bandwidth, reliability, etc.) of the respective services. The present disclosure describes a technique for supporting various services by using network slices in a wireless communication system.

In a wireless communication system supporting network slicing, traffic for different network slices may be handled by different Protocol Data Unit (PDU) sessions. The PDU session may be an association between a data network providing a PDU connection service and the UE. Network slicing may be understood as a technique for logically configuring a network in a set of Network Functions (NFs) to support various services with different characteristics, such as mission critical services like broadband communication services, large-scale IoT, and V2X, and to divide the different network slices. Therefore, even if any network slice has a communication error, the communication of another network slice is not affected thereby, and thus a stable communication service can be provided. In this disclosure, the term "slice" may be used interchangeably with the term "network slice". A UE receiving various services in such a network environment may access multiple network slices. Further, a Network Function (NF) is a software instance driven in hardware and may be implemented as a function that is instantiated and virtualized in a network element or an appropriate platform.

The mobile communication carrier may configure the network slices and allocate network resources suitable for a specific service according to each network slice or each network slice set. The network resource may be an NF, a logical resource provided by the NF, or an allocation of radio resources of the BS.

For example, a mobile communications carrier may configure network slice a to provide mobile broadband services, network slice B to provide vehicle communications services, and network slice C to provide IoT services. That is, as described above, the 5G network can efficiently provide the corresponding service to the UE through the network slice specialized for the characteristics of each service.

The mobile communication carrier may operate the 5G network and the EPS network (or LTE-based network or 4G network) together. The UE may access the 5G network to use the service and then move to the EPS network. Alternatively, the UE may access the EPS network to use the service and then move to the 5G network. The interworking between networks (systems) related to the movement of the UE may be referred to as 5G core (5 GC) -EPC interworking or 5G system (5 GS) -EPS interworking.

The present disclosure proposes examples of an interworking between a 5G network system and an EPS network system (i.e., 5GS-EPS interworking) or a method of 5GC-EPC interworking providing a network slice function.

Further, the present disclosure describes examples of network operations and UE operations for enabling a UE to use a service without disconnection even if the UE that establishes a session connection in 5GS to use a communication service moves to EPS or the UE that establishes a session connection in EPS to use a communication service moves to 5 GS.

In the present disclosure, the network technology may be referred to by standards defined by the International Telecommunications Union (ITU) or 3GPP (e.g., TS23.501, TS23.502, TS23.503, etc.), and the elements included in the network architecture of fig. 1 may be physical entities, software performing separate functions, or hardware combined with the software. Referring to fig. 1, reference numerals Nx indicating N1, N2, N3,... Hereinafter, in the description of fig. 1, illustration/description of NF not directly related to the present disclosure is omitted.

Fig. 1 shows an example of an interworking architecture of 5GS and EPS in a non-roaming scenario according to an embodiment of the present disclosure.

The 5GS may include a New Radio (NR) base station (e.g., NG Radio Access Node (RAN) or next generation node B (gNB)) 103 and an access and mobility management function (AMF) 105, and further include a Session Management Function (SMF), a User Plane Function (UPF), a Policy Control Function (PCF), a Network Slice Selection Function (NSSF), a Unified Data Management (UDM), and a Unified Data Repository (UDR), which are not shown in fig. 1.

EPS may include E-UTRA base stations (e.g., evolved Universal Mobile Telecommunications System (UMTS) terrestrial radio access network (E-UTRAN) or evolved node B (eNB)) 113, mobility Management Entities (MME) 115, serving Gateway (SGW) 117, packet data network gateway (PGW) (including PGW-U and PGW-C), policy and Charging Rules Function (PCRF), and Home Subscriber Server (HSS).

According to an embodiment, the AMF 105 and MME 115 may be Network Functions (NF) that manage wireless network access and mobility for the UE. The SMF, SGW, and PGW are NFs for managing a session of the UE, and session information may include quality of service (QoS) information, charging information, and information about packet processing. In addition, the UPF and PGW are NFs for handling user plane traffic and are controlled by the SMF and SGW. The PCF and PCRF may be NFs for managing operator policies (and/or PLMN policies) for providing services in the wireless communication system. In addition, PCFs may be divided into PCFs for handling Access and Mobility (AM) policies and UE policies and PCFs for handling Session Management (SM) policies. The PCF for handling AM/UE policies and the PCF for handling SM policies may be logically or physically separate NFs or one NF. The UDM and HSS may be NFs for storing and managing UE subscriber information (UE subscription). The UDR may be an NF or a Database (DB) for storing and managing data. The UDR may store UE subscription information and provide the UE subscription information to the UDM. Further, the UDR may store and provide operator policy information to the PCF. The NSSF may be NF for performing a function of selecting a network slice instance serving the UE or determining Network Slice Selection Assistance Information (NSSAI).

An instance may mean a state in which NF exists in software code and NF functions may be run by allocation of physical or/and logical resources by a computing system to perform NF functions in a physical computing system (e.g., a particular computing system present in a core network). For example, an AMF instance, an SMF instance, or an NSSF instance may refer to a state in which physical resources or/and logical resources may be allocated and used for AMF, SMF, or NSSF operations by a particular computing system present in the core network. Thus, there are cases of AMF, SMF, and NSSF devices, and AMF instances, SMF instances, and NSSF instances where physical resources or/and logical resources are allocated and used for AMF, SMF, and NSSF operations by a particular computing system present in the network may perform the same operations.

The UDM of 5GS and the HSS of the EPS may be configured as one combining node (referred to as hss+udm) 124.Hss+udm 124 may store UE subscriber information. The SMF of 5GS and the PGW-C of the EPS may be configured as one combined node (referred to as smf+pgw-C or PGW-c+smf) 122. The term will indicate that the SMF of 5GS and the PGW-C of EPS are configured as one combined node, so that abbreviations of smf+pgw-C and PGW-c+smf may be used to indicate the same device.

The PCF of 5GS and the PCRF of EPS may be configured as one combined node (referred to as pcf+pcrf) 123. The UPF of 5GS and the PGW-U of EPS may be configured as a combined node (referred to as UPF+PGW-U or PGW-U+UPF) 121. The term will indicate that the UPF of 5GS and the PGW-U of EPS are configured as one combined node, so the abbreviations UPF+PGW-U and PGW-U+UPF can be used to indicate the same device. A User Equipment (UE) 101 may access an MME 115 of EPS through an E-UTRA eNB (i.e., E-UTRAN 113) and use EPS network services. Further, the UE 101 may access the 5GS AMF 105 through the NG-RAN 103 and use 5GS network services. In fig. 1, the same reference numerals are used for the UE 101 accessing the EPS and the UE 101 accessing the 5 GS. This will indicate that the UE 101 is a UE that can access EPS and 5 GS.

As described above, one NF or network entity may support different network systems simultaneously, and NF, network node or network entity may be referred to as a combined node, combined NF, combined node, integrated NF, interworking node, interworking NF, or the like. Furthermore, the functionality of the NF described as a combined node may be implemented by interworking between two or more network entities. In addition, for ease of illustration and description, the symbol "+" or "/" may be used to express NFs that support different network systems simultaneously. For example, when SMF and PGW-C are configured as a combined node, the expression PGW-C/SMF, PGW-C+SMF, SMF/PGW-C, or SMF+PGW-C may be used.

The UE 101 may access a data network (e.g., a network providing internet services) and establish a session through a 5GS or EPS system. At this point, the UE 101 may identify each data network based on an identifier such as a Data Network Name (DNN) or an Access Point Name (APN). To differentiate data networks, DNN may be used in 5GS and APN may be used in EPS. When the UE 101 establishes a session with a network system, the DNN and APN may be used to determine an interface between NFs associated with the user plane, an operator policy, etc. DNN and APN may be understood as equivalent information and may send the same information. The DNN may be used to select, for example, an SMF and UPF(s) for the PDU session and to select interface(s) (e.g., N6 interface) between the data network and the UPF(s) for the PDU session. In addition, the DNN may be used to determine a mobile carrier policy to be applied to the PDU session.

In the following embodiments, for convenience of description, a combined node such as a udm+hss node, a pcf+pcrf node, an smf+pgw-C node, or a upf+pgw-C node is described without a "node". Furthermore, in the following embodiments, the definition of a message defined in one embodiment may be applied as the same meaning to another embodiment using the same message.

Fig. 2A illustrates a method of registering a UE and managing a session through a delayed fallback trigger procedure by an NG-RAN according to an embodiment of the present disclosure, fig. 2B illustrates a method of registering a UE and managing a session through a delayed fallback trigger procedure by an NG-RAN according to an embodiment of the present disclosure, fig. 2C illustrates a method of registering a UE and managing a session through a delayed fallback trigger procedure by an NG-RAN according to an embodiment of the present disclosure, and fig. 2D illustrates a method of registering a UE and managing a session through a delayed fallback trigger procedure by an NG-RAN according to an embodiment of the present disclosure.

Prior to the description of the embodiments of the present disclosure made with reference to fig. 2A-2D, the same reference numerals as those in fig. 1 are used for the respective NF and UE described in fig. 1.

Further, fig. 2A to 2D are described based on sequential flow. For example, the flowchart of fig. 2B is described after the flowchart of fig. 2A, then the flowchart of fig. 2C is described, and finally the flowchart of fig. 2D is described. In a practical implementation, the same order of fig. 2A to 2D as the scheme described in the present disclosure may be used. In another example, only some of fig. 2A to 2D may be sequentially implemented. That is, some of the sequences of fig. 2A-2D may or may not be omitted. In another example, some of the sequences of fig. 2A-2D may be performed in parallel, or the sequences may be changed. Further, the description made with reference to another figure may be inserted in the middle of the flowcharts of fig. 2A to 2D.

In addition, in fig. 2A-2D, operations in blocks between respective NFs may have multiple signal flows between the respective NFs and/or UE and NFs. Referring to fig. 2A to 2D, it should be noted that only a description of overall operation is made in the operations in the blocks, rather than stating all individual signal flows. In the following description, unless fig. 2A, 2B, 2C, and 2D should be distinguished in particular, fig. 2A, 2B, 2C, and 2D are all indicated as fig. 2. In the following description, a specific message may be used without a message/signal, a message, or a signal according to an expression method. For example, RRC connection release may be expressed as "RRC connection release message", "RRC connection release signal" or "RRC connection release", and they should all be understood to have the same meaning.

In operation 1, for a UE 101 connected to 5GS through NG-RAN 103, MO (originated by a mobile originating UE) or MT (terminated by a mobile terminating UE) IP Multimedia Subsystem (IMS) voice session establishment may be initiated.

IMS is a system for providing multimedia services in an IP network and can provide voice, video, messaging, data, web-based wired/wireless technology to users through connections with EPS and 5GS core networks. The proxy call session control function (P-CSCF) of the IMS may be connected to the PCF, PCRF or pcf+pcrf of the 5GS/EPS core network, and the interrogating call session control function (I-CSCF), serving call session control function (S-CSCF) and Application Server (AS) of the IMS may be connected to the HSS, UDM or hss+udm of the 5GS/EPS core network. The UE 101 may be connected to the EPC through an E-UTRAN or an evolved packet data gateway (ePDG) or to the 5GC through NG-RAN 103 or a non-3 GPP interworking function (N3 IWF) to be registered and establish a session, and the EPC/5GC may perform UE registration and session establishment procedures required for entities/functions of the IMS and IMS-based voice services.

In operation 2, the AMF 105 may send an N2 PDU session request message to the NG-RAN 103 through a network-initiated PDU session modification procedure. The N2 PDU session request message may include information requesting for QoS flow setup of the voice service.

In operation 3, when the NG-RAN 103 that receives information requesting QoS flow setting for a voice service is configured to support EPS fallback of IMS voice, the NG-RAN 103 may determine whether to trigger EPS fallback based on the following information. NG-RAN 103 may determine whether to trigger EPS fallback taking into account UE capabilities received from UE 101, indicators from AMF 105 (during initial context setup, handover resource allocation, or path handover request reply procedure) indicating whether redirection of EPS fallback for speech is possible, network configuration (e.g., N26 availability configuration), and radio conditions. When NG-RAN 103 determines that EPS backoff is not triggered, operations following operation 3 may not be performed. Operation 5 may not be performed when the AMF 105 receives an indicator indicating that redirection of EPS fallback for speech is not possible. When NG-RAN 103 does not receive an indicator of redirection of EPS fallback for voice from AMF 105, NG-RAN 103 may exclude network configuration (e.g., N26 availability configuration) from consideration in determining whether to trigger EPS fallback for IMS voice.

In operation 4, NG-RAN 103 may send a response message rejecting the PDU session modification request for QoS flow setup of IMS voice received in operation 2 to smf+pgw-C122 through AMF 105. The response message may include an indicator indicating movement due to fallback of IMS voice. The smf+pgw-C122 that received the response message may maintain Policy and Charging Control (PCC) rule(s) related to QoS flow(s) for IMS voice services. When there is a pcf+pcrf 123 subscribing to the notification of the EPS fallback event, the smf+pgw-C122 may report the EPS fallback event to the corresponding pcf+pcrf 123.

In operation 5, NG-RAN 103 may perform a handover or redirection to EPS according to UE capabilities. When there is a pcf+pcrf 123 subscribing to the notification of the RAT type change event, the smf+pgw-C122 may report the RAT type change event to the corresponding pcf+pcrf 123. When the UE 101 is connected to the EPS, operation 6a or operation 6b may be performed.

In operation 6a, the UE 101 may perform a handover to the EPS or an inter-system redirection using N26. The UE 101 may trigger a Tracking Area Update (TAU) procedure.

In operation 6b, the UE 101 may perform an inter-system redirection without using N26.

In operation 7, the smf+pgw-C122 may restore the setting of the dedicated bearer for IMS voice. smf+pgw-C122 may use information for mapping PCC rule(s) and 5G QoS associated with QoS flows for IMS voice maintained in operation 4 to EPS QoS parameters.

In operation 8, the E-UTRAN 113 may perform a procedure of releasing a Radio Resource Control (RRC) connection with the UE 101 due to the inactivity of the user. Reasons for inactivity of the user may include a situation where the user has not received a voice call for a predetermined time. The E-UTRAN 113 may use the timer to determine the user inactivity.

In operation 9, the E-UTRAN 113 may trigger the movement of the UE 101 to 5GS and the execution of the registration procedure after the procedure of releasing the RRC connection with the UE 101 in operation 8.

In operation 10, the UE 101 may send a registration request message to the NG-RAN 103. The registration request message may include a registration type indicating a mobility registration update. The UE 101 may insert the 5G-GUTI mapped based on an EPS Globally Unique Temporary Identifier (GUTI) as a UE identifier in the EPS that was allocated by the MME 115 through the E-UTRAN 113 prior to operation 10 as an old 5G-GUTI into the registration request message. When there is a 5G-GUTI in the 5GS that is the UE identifier assigned by the AMF 105 through the NG-RAN 103, the UE 101 may insert the 5G-GUTI as a native 5G-GUTI into the registration request message. The UE 101 may insert an indicator indicating a move from EPS to 5GS (e.g., "move from EPS") into the registration request message.

In operation 11, the NG-RAN 103 that received the registration request message including the 5G-GUTI based on the EPS-GUTI map and the mobility registration update type indicating the indicator to move from EPS to 5GS from the UE 101 in operation 10 may select the AMF.

In operation 12, the NG-RAN 103 that selected the AMF in operation 11 may send a registration request message received from the UE 101 to the AMF 105.

In operation 13a, the AMF 105 that received the registration request message in operation 12 may acquire an MME address by using the EPS-GUTI to which the old 5G-GUTI is mapped. The AMF 105 may send a context request message to the MME 115 by using the MME address. The context request message may include a TAU message and an EPS-GUTI to which the old 5G-GUTI is mapped. The MME 115 may determine the validity of the content of the TAU message.

In operation 13b, the MME 115 that received the context request message in operation 13a may send a context response message to the AMF 105. The context response message may include the EPS bearer context(s). The EPS bearer context(s) may include information related to EPS bearers that were not released from EPS before the UE 101 moved to 5GS, and when the dedicated bearer for IMS voice generated in operation 7 is not released, information (context) about the bearer. The dedicated bearer for IMS voice may be configured as a bearer with a QoS Class Identifier (QCI) of 1 (qci=1 bearer). In the present disclosure, a dedicated bearer for IMS voice and a bearer with qci=1 are used interchangeably.

In operation 14, the AMF 105 may perform authentication and/or security procedures required by the network with the UE 101. The AMF 105 may send and receive required information to and from the UE 101, NG-RAN 103, AUSF201, and/or hss+udm 124 to the UE 101, NG-RAN 103, authentication server function (AUSF) 201, and/or hss+udm 124. Specifically, the AMF 105 may perform a UE context setup procedure through a Next Generation Application Protocol (NGAP) together with the NG-RAN 103. The UE context may include a PDU session context, a security key, a mobility restriction list, UE wireless capabilities, and/or UE security capabilities.

In operation 14c-1, the AMF 105 may send an initial context setup request message to the NG-RAN 103. The initial context setup request message may include an indicator indicating whether the UE 101 and/or the network supports EPS backoff. An indicator of redirection for voice EPS fallback may correspond to it and AMF 105 may define the value of the indicator as supported/unsupported, available/unavailable or possible/impossible and send the value to NG-RAN 103. When the UE 101 and/or the network does not support voice services over the 5G system (e.g., when the communication carrier does not support VoNR services), the AMF 105 may send an indicator of redirection for voice EPS fallback to the NG-RAN 103.

Further, when the EPS bearer context is received from the MME 115 in operation 13b, the AMF 105 may insert the EPS bearer context into the initial context setup request message. Specifically, after inserting the EPS bearer context into the PDU session resource setting list, the AMF 105 may send information to the NG-RAN 103 in the form that the PDU session resource setting list is inserted into the initial context setting request message. In operation 13b, the AMF 105 may send an EPS bearer context for a dedicated bearer (or a bearer with QCI 1) for IMS voice to the NG-RAN 103.

In operation 14c-2, the NG-RAN 103 that received the initial context setup request message from the AMF 105 in operation 14c-1 may determine whether to perform EPS backoff. NG-RAN 103 may determine whether to perform EPS fallback in consideration of whether a request for a redirection for voice EPS fallback and/or PDU session resource settings for a dedicated bearer for IMS voice, NG-RAN configuration, etc. is received from AMF 105. For example, NG-RAN 103 determines to perform EPS fallback when the indicator for redirection of voice EPS fallback indicates that EPS fallback is supported and a request for PDU session resource settings for a dedicated bearer for IMS voice is received.

When it is determined to perform EPS backoff, NG-RAN 103 waits a predetermined time instead of immediately triggering an EPS backoff procedure, and then performs a delayed backoff procedure triggering EPS backoff according to a separate request from AMF 105 or the determination of NG-RAN 103. NG-RAN 103 may wait a predetermined time by using a timer (e.g., a delayed back-off timer). The NG-RAN 103 may trigger the deferred fallback procedure when the NG-RAN 103 receives a notification from the AMF 105 indicating that the deferred fallback procedure may be triggered before expiration after the time starts, when the NG-RAN 103 receives a notification indicating that a request from the AMF 105 and/or UE 101 to register the UE is accepted and that 5G-GUTI is assigned to the UE 101, or when the average time required to complete the procedure of registering the UE 101 has elapsed. Upon receiving a request for PDU session resource setting for a dedicated bearer for IMS voice, NG-RAN 103 may configure a timer for triggering a delayed fallback procedure to be longer or shorter than if it was determined to perform EPS fallback for another reason.

In operation 14c-3, the NG-RAN 103 that determined to perform EPS backoff in operation 14c-2 may inform the AMF 105 that the EPS backoff procedure has been triggered. When NG-RAN 103 receives a request for PDU session resource settings for a dedicated bearer for IMS voice or for other reasons desires to trigger EPS fallback after 5G-GUTI is allocated to UE 101, the NG-RAN may inform AMF 105 that a deferred fallback procedure has been triggered. For example, an indicator of the delayed backoff trigger may be inserted into the initial context setup response message and then sent to the AMF 105. The AMF 105, which receives the notification indicating that the deferred fallback procedure has been triggered, may continuously perform the registration procedure corresponding to operations 15 to 24.

When the authentication and/or security procedure (operation 14) is successfully completed in operation 15, the AMF 105, which received a notification from the NG-RAN 103 indicating that the deferred fallback procedure has been triggered in operation 14c-3, may send a context acknowledgement (Ack) signal to the MME 115.

In operation 16, the AMF 105 may make a request to the UE 101 for a subscriber hidden identifier (sui) and receive it.

In operation 17, the AMF 105 may perform a Mobility Equipment (ME) identity check with an Equipment Identity Register (EIR) (or 5G-EIR) 203. The EIR 203 performs the function of checking the permanent device identifier (PEI) of the UE 101 and checks the PEI of the UE 101 during an authentication procedure in the network. A representative example of PEI is International Mobile Equipment Identity (IMEI).

In operation 18, the AMF 105 may select hss+udm 124 by using the sui provided by the UE 101, a subscription permanent identifier (SUPI) converted from the sui, a home network identifier (e.g., MNC and MCC or realm) included in the sui or SUPI, a UDM group ID, or the like.

In operation 19a, the AMF 105 may perform a procedure for registering the UE 101 and the nudm_uecm_registration of the hss+udm 124 selected in operation 18.

In operation 19b, the AMF 105 may perform a process of nudm_sdm_get together with hss+udm 124.

In operation 19c, the AMF 105 may perform a nudm_sdm_subscore procedure together with the hss+udm 124.

In operation 20, the AMF 105 may select the pcf+pcrf 123 by using the SUPI, the S-nsai (S), the PCF group ID included in the SUPI, or the PCF group ID.

In operation 21, the AMF may perform a procedure of AM policy association establishment or AM policy association modification together with the pcf+pcrf 123 selected in operation 20.

In operation 22, the hss+udm 124 may send a cancel location message to the MME 115 and ask the MME 115 to delete or no longer store information such as the MM context of the UE 101.

In operation 23, the MME 115 that received the relocation cancel message from the hss+udm 124 in operation 22 may send a relocation cancel response signal to the hss+udm 124 after deleting information such as MM context of the UE 101.

In operation 23a, the MME 115 may send a delete session request message to the serving gateway when sending a cancel location answer signal to the hss+udm 124 in operation 23.

In operation 24, when it is determined to accept the registration request from the UE 101, the AMF 105 may send a registration accept message to the UE 101 through the NG-RAN 103. The registration accept message may include the 5G-GUTI of the UE 101.

In operation 24a, when the AMF 105 receiving the notification from the NG-RAN 103 that the deferred fallback procedure has been triggered in operation 14c-3 may determine to accept the registration request from the UE 101 and send a 5G-GUTI (operation 24), the AMF may send an indicator to the NG-RAN 103 indicating to stop waiting for the deferred fallback procedure and perform the procedure. For example, a delayed back-off start indicator may be inserted into the N2 request message and sent to NG-RAN 103. The message may be sent when the registration accept message in operation 24 is sent to NG-RAN 103 or before or after the registration accept message.

In operation 24b, the AMF 105 that sent the registration accept message in operation 24 may perform a UE policy association establishment procedure with the PCF.

The above operations 24, 24a, and 24b may be performed in the order described above, or the operation 24a may be performed first, the operation 24 may be performed, and then the operation 24b may be performed. Meanwhile, when the registration rejection message is received in operation 24, operation 24b may be performed without operation 24 a.

In operation 25, the NG-RAN 103 that received the notification from the AMF 105 in operation 24a indicating that the deferred back-off procedure may begin may wait for a predetermined time without beginning the deferred back-off procedure until the UE 101 receives the 5G-GUTI of operation 24. When the operation 24a is performed after the operation 26, the operation 25 may be omitted.

In operation 26, the UE 101 that received the registration accept message from the AMF 105 in operation 24 may send a registration complete message to the AMF 105.

In operation 27, NG-RAN 103 may trigger a delayed fallback procedure.

In operation 28, the NG-RAN 103 may perform a redirection or handoff of the UE 101 to EPS.

In operation 29a-1, the UE 101 may trigger a TAU procedure to connect to the EPS.

In operation 29a-2, the UE 101 may send a TAU request message to the E-UTRAN. The TAU request may include EPS-GUTI converted from the 5G-GUTI received in operation 24 and an indicator that the UE 101 has moved from 5GS to EPS (e.g., "move from 5 GS").

In operation 29a-3, the E-UTRAN 113, which received the TAU request in operation 29a-2, may transmit the TAU request to the MME 115.

In operation 29a-4, the MME 115, which received the TAU request in operation 29a-3, continuously performs the TAU procedure for the UE 101.

In operation 29b, the UE 101 may perform an inter-system redirection without using N26.

In operation 30, smf+pgw-C122 may resume the setting of the dedicated bearer for IMS voice.

Fig. 3A illustrates a method of registering a UE and managing a session through a delayed fallback trigger procedure by an AMF according to an embodiment of the present disclosure, fig. 3B illustrates a method of registering a UE and managing a session through a delayed fallback trigger procedure by an AMF according to an embodiment of the present disclosure, fig. 3C illustrates a method of registering a UE and managing a session through a delayed fallback trigger procedure by an AMF according to an embodiment of the present disclosure, and fig. 3D illustrates a method of registering a UE and managing a session through a delayed fallback trigger procedure by an AMF according to an embodiment of the present disclosure.

Prior to the description of the embodiments of the present disclosure made with reference to fig. 3A-3D, the same reference numerals as those in fig. 1 are used for the respective NF and UE described in fig. 1.

Further, fig. 3A to 3C are described based on the sequential order. For example, the flowchart of fig. 3B is described after the flowchart of fig. 3A, then the flowchart of fig. 3C is described, and finally the flowchart of fig. 3D is described. In a practical implementation, the same order of fig. 3A to 3D as the scheme described in the present disclosure may be used. In another example, only some of fig. 3A to 3D may be sequentially implemented. That is, some of the sequences of fig. 3A through 3D may or may not be omitted. In another example, some of the sequences of fig. 3A through 3D may be performed in parallel, or the sequences may be changed. Further, the description made with reference to another figure may be inserted in the middle of the flowcharts of fig. 3A to 3D.

In addition, in fig. 3A-3D, operations in blocks between respective NFs may have multiple signal flows between the respective NFs and/or UE and NFs. With reference to fig. 3A through 3D, it should be noted that only a description of overall operation is made in the operations in the blocks, rather than stating all individual signal flows. In addition, in the following description, unless fig. 3A, 3B, 3C, and 3D should be distinguished in particular, fig. 3A, 3B, 3C, and 3D are all indicated as fig. 3. In the following description, a specific message may be used without a message/signal, a message, or a signal according to an expression method. For example, RRC connection release may be expressed as "RRC connection release message", "RRC connection release signal" or "RRC connection release", and they should all be understood to have the same meaning.

In operation 1, a Mobile Originated (MO) or Mobile Terminated (MT) IMS voice session setup may be initiated for a UE 101 connected to 5GS through NG-RAN 103.

In operation 3, when the NG-RAN 103 that receives information requesting QoS flow setting for a voice service is configured to support EPS fallback of IMS voice, the NG-RAN 103 may determine whether to trigger EPS fallback. NG-RAN 103 may determine whether to trigger EPS fallback taking into account UE capabilities received from UE 101, indicators from AMF 105 (during initial context setup, handover resource allocation, or path handover request reply procedure) indicating whether redirection of EPS fallback for speech is possible, network configuration (e.g., N26 availability configuration), and radio conditions. When NG-RAN 103 determines that EPS backoff is not triggered, operations following operation 3 may not be performed. Operation 5 may not be performed when the AMF 105 receives an indicator indicating that redirection of EPS fallback for speech is not possible. When NG-RAN 103 does not receive an indicator of redirection of EPS fallback for voice from AMF 105, NG-RAN 103 may exclude network configuration (e.g., N26 availability configuration) from consideration in determining whether to trigger EPS fallback for IMS voice.

In operation 4, NG-RAN 103 may send a response message rejecting the PDU session modification request for QoS flow setup of IMS voice received in operation 2 to smf+pgw-C122 through AMF 105. The response message may include an indicator indicating movement due to fallback of IMS voice. The smf+pgw-C122 that received the response message may maintain PCC rule(s) related to QoS flow(s) for IMS voice services. When there is a pcf+pcrf 123 subscribing to the notification of the EPS fallback event, the smf+pgw-C122 may report the EPS fallback event to the corresponding pcf+pcrf 123.

In operation 6a, the UE 101 may perform a handover to the EPS or an inter-system redirection using N26. The UE 101 may trigger the TAU procedure.

In operation 8, the E-UTRAN 113 may perform a procedure of releasing the RRC connection with the UE 101 due to the inactivity of the user. Reasons for inactivity of the user may include a situation where the user has not received a voice call for a predetermined time. The E-UTRAN 113 may use the timer to determine the user inactivity.

After the E-UTRAN 113 performs the procedure of releasing the RRC connection with the UE 101 in operation 8, the UE 101 moves to 5GS and may perform the registration procedure in operation 9.

In operation 11, the NG-RAN 103 that received the registration request message including the 5G-GUTI based on the EPS-GUTI map and the mobility registration update type indicating the indicator to move from EPS to 5GS from the UE 101 in operation 10 may select the AMF 105.

In operation 12, the NG-RAN 103 that selected the AMF 105 in operation 11 may send a registration request message received from the UE 101 to the AMF 105.

In operation 13b, the MME 115 that received the context request message in operation 13 may send the context request message to the AMF 105. The context response message may include the EPS bearer context(s). The EPS bearer context(s) may include information related to EPS bearers that were not released from EPS before the UE 101 moved to 5GS, and when the dedicated bearer for IMS voice generated in operation 7 is not released, information (context) about the bearer. The dedicated bearer for IMS voice may be configured as a bearer with a QoS Class Identifier (QCI) of 1 (qci=1 bearer). In the present disclosure, a dedicated bearer for IMS voice or a bearer with qci=1 may be used interchangeably.

In operation 14, the AMF 105 may perform authentication and/or security procedures required by the network with the UE 101. The AMF 105 may send and receive the required information to and from the UE 101, NG-RAN 103, AUSF 201, and/or hss+udm 124, to and from the UE 101, NG-RAN 103, AUSF 201, and/or hss+udm 124. Specifically, the AMF 105 may perform a UE context setup procedure through a Next Generation Application Protocol (NGAP) together with the NG-RAN 103. The UE context may include a PDU session context, a security key, a mobility restriction list, UE wireless capabilities, and/or UE security capabilities.

Further, when the EPS bearer context is received from the MME 115 in operation 13b, the AMF 105 may determine whether to insert the EPS bearer context into the initial context setup request message. Specifically, before the 5GS registration procedure of the UE 101 is completed, the AMF 105 may determine not to insert some of the EPS bearer context into the initial context setup request message in case it is considered whether the NG-RAN 103 corresponds to information that may be considered when determining whether to perform EPS backoff and/or whether additional information should be provided to the UE 101 in order to normally perform the EPS registration procedure when EPS backoff is triggered. For example, the AMF 105 receives the EPS bearer context for the dedicated bearer for IMS voice (or the bearer with QCI of 1) in operation 13b, and may not insert the EPS bearer context for the dedicated bearer for IMS voice into the initial context setup request message when the AMF 105 determines that the UE 101 and/or the network supports EPS fallback and determines to inform the NG-RAN 103 of this by using an indicator for redirection of voice EPS fallback.

In operation 14c-2, the NG-RAN 103 that received the initial context setup request message from the AMF 105 in operation 14c-1 may determine whether to perform EPS backoff. NG-RAN 103 may determine whether to perform EPS fallback in consideration of whether a request for a redirection for voice EPS fallback and/or PDU session resource settings for a dedicated bearer for IMS voice, NG-RAN configuration, etc. is received from AMF 105. For example, when the indicator for redirection of voice EPS fallback indicates that EPS fallback is supported and a dedicated bearer for IMS voice is not inserted into the request for PDU session resource setting (example of operation 14 c-1), NG-RAN 103 may determine not to perform EPS fallback. After performing the initial context setup procedure, NG-RAN 103 may send an initial context setup response message to AMF 105. When receiving information indicating that the initial context setup procedure has been normally performed from the NG-RAN 103, the AMF 105 may continuously perform the registration procedure corresponding to operations 15 to 24.

When the authentication and/or security procedure (operation 14) is successfully completed in operation 15, the AMF 105, which received information indicating that the initial context setup procedure has been normally performed from the NG-RAN 103 in operation 14c-2, may send a context answer to the MME 115.

In operation 16, the AMF 105 may make a request for the SUCI to the UE 101 and receive it.

In operation 17, the AMF 105 may perform an ME identity check with the EIR 203.

In operation 18, the AMF 105 may select hss+udm 124 by using the sui provided by the UE 101, the sui converted from the sui, the home network identifier (e.g., MNC and MCC or realm) included in the sui or the SUPI, the UDM group ID, or the like.

In operation 19a, the AMF 105 may perform a nudm_uecm_registration process with the hss+udm 124.

In operation 20, AMF 105 may select pcf+pcrf 123.

In operation 21, the AMF 105 may perform a procedure of AM policy association establishment or AM policy association modification together with the selected pcf+pcrf 123.

After deleting the information such as MM context of the UE 101, the MME 115 that received the relocation cancel message from the hss+udm 124 in operation 22 may send a relocation cancel response signal to the hss+udm 124 in operation 23.

In operation 23a, the MME 115 may send a delete session request to the serving gateway when sending a cancel location answer signal to the hss+udm 124 in operation 23.

Although the EPS bearer context of the IMS voice is received from the MME 115 in operation 13b, the AMF 105, which did not insert information into the initial context setup request message sent to the NG-RAN 103 in operation 14c-1, may make a request to the NG-RAN 103 to perform a delay fallback procedure in operation 24 a. For example, a delayed back off start indicator and/or the reason why a request to perform a delayed back off procedure is made may be inserted into the N2 request message and sent to NG-RAN 103. Reasons for making a request to perform a deferred fallback procedure may include the presence of an EPS bearer context for a dedicated bearer for IMS voice. The message may be sent when the registration accept message in operation 24 is sent to NG-RAN 103 or before or after the registration accept message.

In operation 25, the NG-RAN 103 that received the request from the AMF 105 in operation 24a indicating to perform the deferred fallback procedure may wait for a predetermined time without starting the deferred fallback procedure until the UE 101 receives the 5G-GUTI of operation 24. When the operation 24a is performed after the operation 26, the operation 25 may be omitted.

The NG-RAN 103 may determine not to perform the deferred back-off when there are other reasons such that the reason for making the request for the deferred back-off from the AMF 105 in operation 24a does not match the method by which the NG-RAN 103 determines the EPS back-off, the UE 101 does not support the EPS back-off, the radio conditions are difficult to perform the EPS back-off, or there is a separate configuration in the NG-RAN 103. When NG-RAN 103 does not perform a delayed fallback according to the delayed fallback request of AMF 105, content including a rejection of the delayed fallback request may be sent to AMF 105 via an N2 message. When NG-RAN 103 accepts the delay request of AMF 105, content including the delay request of accepting AMF 105 may be sent to AMF 105 via an N2 message.

In operation 26, the UE that received the registration accept message from the AMF 105 in operation 24 may send a registration complete message to the AMF 105.

In operation 27, NG-RAN 103 may trigger a delayed fallback procedure.

In operation 29a-2, the UE 101 may send a TAU request message to the E-UTRAN 113. The TAU request message may include the EPS-GUTI converted from the 5G-GUTI received in operation 24 and an indicator that the UE 101 has moved from 5GS to EPS (e.g., "move from 5 GS").

In operation 29a-3, the E-UTRAN 113, which received the TAU request message in operation 29a-2, may transmit the TAU request message to the MME 115.

In operation 29a-4, the MME 115, which received the TAU request message in operation 29a-3, continuously performs the TAU procedure for the UE 101.

Fig. 4A illustrates a method of registering a UE and managing a session through a bearer deactivation procedure by an MME according to an embodiment of the present disclosure, fig. 4B illustrates a method of registering a UE and managing a session through a bearer deactivation procedure by an MME according to an embodiment of the present disclosure, fig. 4C illustrates a method of registering a UE and managing a session through a bearer deactivation procedure by an MME according to an embodiment of the present disclosure, and fig. 4D illustrates a method of registering a UE and managing a session through a bearer deactivation procedure by an MME according to an embodiment of the present disclosure.

Prior to the description of the embodiments of the present disclosure made with reference to fig. 4A-4D, the same reference numerals as those in fig. 1 are used for the respective NF and UE described in fig. 1.

Further, fig. 4A to 4D are described based on sequential flow. For example, the flowchart of fig. 4B is described after the flowchart of fig. 4A, then the flowchart of fig. 4C is described, and finally the flowchart of fig. 4D is described. In a practical implementation, the same order of fig. 4A to 4D as the scheme described in the present disclosure may be used. In another example, only some of fig. 4A to 4D may be sequentially implemented. That is, some of the sequences of fig. 4A through 4D may or may not be omitted. In another example, some of the sequences of fig. 4A through 4D may be performed in parallel, or the sequences may be changed. Further, the description made with reference to another figure may be inserted in the middle of the flowcharts of fig. 4A to 4D.

In addition, in fig. 4A-4D, operations in blocks between respective NFs may have multiple signal flows between respective NFs and/or UE and NFs. Referring to fig. 4A to 4D, it should be noted that only a description of overall operation is made in the operations in the blocks, rather than stating all individual signal flows. In the following description, unless fig. 4A, 4B, 4C, and 4D should be distinguished in particular, fig. 4A, 4B, 4C, and 4D are indicated as fig. 4. In the following description, a specific message may be used without a message/signal, a message, or a signal according to an expression method. For example, RRC connection release may be expressed as "RRC connection release message", "RRC connection release signal" or "RRC connection release", and they should be all understood as the same meaning.

In operation 3, when NG-RAN 103 that receives information requesting QoS flow setting for a voice service is configured to support EPS fallback of IMS voice, NG-RAN may determine whether to trigger EPS fallback. NG-RAN 103 may determine whether to trigger EPS fallback taking into account UE capabilities received from UE 101, indicators from AMF 105 (during initial context setup, handover resource allocation, or path handover request reply procedure) indicating whether redirection of EPS fallback for speech is possible, network configuration (e.g., N26 availability configuration), and radio conditions. When NG-RAN 103 determines that EPS backoff is not triggered, operations following operation 3 may not be performed. Operation 5 may not be performed when the AMF 105 receives an indicator indicating that redirection of EPS fallback for speech is not possible. When NG-RAN 103 does not receive an indicator of redirection of EPS fallback for voice from AMF 105, NG-RAN may exclude network configuration (e.g., N26 availability configuration) from consideration in determining whether to trigger EPS fallback for IMS voice.

In operation 6a-1, the UE 101 may perform a handover to EPS or an inter-system redirection using N26. The UE 101 may trigger the TAU procedure.

In operation 6a-2, the UE 101 may send a TAU request message to the E-UTRAN 113.

In operation 6a-3, the E-UTRAN 113 that received the TAU request in operation 6a-2 may transmit a TAU request message to the MME 115.

In operation 6a-4, the MME 115 that received the TAU request message in operation 6a-3 may send a context request message to the AMF 105. The MME 115 may make a request for user information through the message.

In operation 6a-5, the AMF 105 that received the context request message in operation 6a-4 may send a context response message to the MME 115. The AMF 105 may insert an indicator (e.g., voice fallback is triggered) into the context response message indicating that the UE 101 receives a request for information through the context request message and performs EPS fallback of IMS voice.

In operation 6a-6, the MME 115 and the UE 101 that received the context response message may continuously perform the TAU procedure.

In operation 6c, the MME 115 receiving the indicator indicating that the UE 101 made the request for the TAU procedure due to the EPS fallback procedure of IMS voice in operation 6a-5 may transmit the indicator to the E-UTRAN 113. Operation 6c may be performed after operation 6 a-5.

In operation 6d, the E-UTRAN 113 that received the message of operation 6c may determine (or recognize) whether the user has not received a voice call within a predetermined time after the voice back-off procedure is triggered. The E-UTRAN 113 may start a timer to recognize the user inactivity. Operation 6d may be performed after operation 7.

Upon determining (or identifying) that the user is inactive, in operation 8a, the E-UTRAN 113 may make a request to the MME 115 to release the bearer for IMS voice. The request may include an indicator indicating a bearer to be released using an EPS Bearer Identification (EBI) of a bearer for IMS voice or an EBI of a bearer with a QCI value of 1.

In operation 8b, the MME 115 may send a delete bearer command message to the SGW 117.

In operation 8C, the SGW 117 may transmit the delete bearer command message to the PGW-c+smf 122.

In operation 8d, PGW-c+smf 122 and pcf+pcrf 123 may perform the PCEF-initiated procedure for IP-can session modification.

In operation 8e, pcf+pcrf 123 may send a delete-bearer request message to SGW 117.

In operation 8f, the SGW 117 may send a delete bearer request message to the MME 115. In operation 8g, the MME 115 may send a deactivate bearer request message to the E-UTRAN 113.

In operation 8, the E-UTRAN 113 may perform a procedure of releasing or reconfiguring the RRC connection with the UE 101 due to the determination of the cause of the user activity after the voice back-off is triggered.

In operation 8h, the E-UTRAN 113 may send the deactivate bearer response message to the MME 115.

In operation 8i, the MME 115 may send a delete bearer response message to the SGW 117.

In operation 8j, the SGW 117 may send a delete bearer response message to the PGW-c+smf 122.

In operation 10, the UE 101 may send a registration request message to the NG-RAN 103. The registration request message may include a registration type indicating a mobility registration update. The UE 101 may insert the 5G-GUTI mapped based on an EPS Globally Unique Temporary Identifier (GUTI) as a UE identifier in the EPS that was allocated by the MME 115 through the E-UTRAN 113 prior to operation 10 as an old 5G-GUTI into the registration request message. When there is a 5G-GUTI in the 5GS that is the UE identifier assigned by the AMF 105 through the NG-RAN 103, the UE 101 may insert the 5G-GUTI into the registration request as a native 5G-GUTI. The UE 101 may insert an indicator (e.g., "move from EPS") indicating a move from EPS to 5GS into the registration request.

In operation 13b, the MME 115 that received the context request message in operation 13 may send the context request message to the AMF 105. The context response message may include the EPS bearer context(s). The EPS bearer context(s) may include information related to EPS bearers that have not been released in EPS before the UE 101 moves to 5GS, and when a procedure of releasing a bearer for IMS voice is performed in operations 8a to 8j, information on dedicated bearers for IMS voice is not included.

In operation 14c-2, the NG-RAN 103 that received the initial context setup request message from the AMF 105 in operation 14c-1 may determine whether to perform EPS backoff. NG-RAN 103 may determine whether to perform EPS fallback in consideration of whether a request for a redirection for voice EPS fallback and/or PDU session resource settings for a dedicated bearer for IMS voice, NG-RAN configuration, etc. is received from AMF 105. After performing the initial context setup procedure, NG-RAN 103 may send an initial context setup response message to AMF 105. When receiving information indicating that the initial context setup procedure has been normally performed from the NG-RAN 103, the AMF 105 may continuously perform the registration procedure corresponding to operations 15 to 24.

When the authentication and/or security procedure (operation 14) is successfully completed in operation 15, the AMF 105, which received a notification from the NG-RAN 103 indicating that the deferred fallback procedure has been triggered in operation 14c-3, may send a context answer signal to the MME 115.

In operation 17, the AMF 105 may perform an ME identity check with the EIR 203.

In operation 19a, the AMF 105 may perform a nudm_uecm_registration procedure with the hss+udm 124.

In operation 20, AMF 105 may select pcf+pcrf 123.

In operation 23a, the MME 115 may send a delete session request message to the SGW 117 when sending a cancel location answer signal to the hss+udm 124 in operation 23.

Fig. 5 shows a configuration of a UE according to an embodiment of the present disclosure.

Referring to fig. 5, a UE according to the present disclosure may include a transceiver 510, a memory 520, and a processor 530. The processor 530, transceiver 510, and memory 520 of the UE may operate according to the communication method of the UE. However, elements of the UE are not limited to only those illustrated in fig. 5. For example, the UE may include more or fewer elements than illustrated in fig. 5. Further, the processor 530, the transceiver 510, and the memory 520 may be implemented in the form of a single chip.

The transceiver 510 refers collectively to a receiver of a UE and a transmitter of the UE, and may transmit and receive signals to and from a base station or a network entity. The signals transmitted to and received from the base station may include control information and data. To this end, the transceiver 510 may include an RF transmitter for up-converting and amplifying the frequency of a transmitted signal and an RF receiver for low noise amplifying and down-converting the frequency of a received signal. However, this is merely an embodiment of transceiver 510, and elements of transceiver 510 are not limited to RF transmitters and RF receivers.

The transceiver 510 may include a wired/wireless transceiver and various elements for transmitting and receiving signals. The transceiver 510 may receive a signal through a wireless channel, output the signal to the processor 530, and transmit the signal output from the processor 530 through the wireless channel. The transceiver 510 may receive a communication signal, output the communication signal to the processor 530, and transmit the signal output from the processor 530 to a network entity through a wired/wireless network.

The memory 520 may store programs and data required for operation of the UE. The memory 520 may store control information or data included in a signal (or message) acquired by the UE. The memory 520 may be configured by a storage medium or combination of storage media such as ROM, RAM, hard disk, CD-ROM, and DVD.

The processor 530 may control a series of processes for the operation of the UE according to the embodiments of the present disclosure described in the following fig. 2A to 2D, 3A to 3D, 4A to 4D, 7A to 7D, 8A to 8E, and 9A to 9D. Processor 530 may include at least one processor. For example, the processor 530 may include a Communication Processor (CP) performing control such as modulation/demodulation and encoding/decoding of signals/messages/data required for communication and an Application Processor (AP) processing (or controlling) the data/signals/messages processed by the communication processor in a higher layer such as an application.

Further, the UE may include devices such as input/output devices for interfacing with a user and devices such as speakers and microphones for processing voice calls over the VoNR and/or existing wireless networks. The input device may include, for example, at least one of a touch screen, a touch pad, a stylus, keys, a voice recognition device, and a gesture recognition device. The output device may include, for example, at least one of a display, a vibration motor, a speaker, and a lamp.

Fig. 6 shows a configuration of a network entity according to an embodiment of the present disclosure.

Referring to fig. 6, a network entity of the present disclosure may include a transceiver 610, a memory 620, and a processor 630. The network entity according to the present disclosure may perform the operation of the communication method of each of the above-described fig. 2A to 2D, 3A to 3D, and 4A to 4D and/or the operation of the communication method of each of the below-described fig. 7A to 7D, 8A to 8E, and 9A to 9D. The elements of the network entity are not limited to only those illustrated in fig. 6. For example, the network entity may include more or fewer elements than those described above. Further, the processor 630, transceiver 610, and memory 620 may be implemented in the form of a single chip or may be implemented in the form of instances within a particular server. The network entity may be one of the above-mentioned NG-RAN 103, AMF 105, upf+pgw-U121, smf+pgw-C122, pcf+pcrf 123, hss+udm 124, SWG 117, MME 115, E-UTRAN 113, AUSF 201, IMS202, and EIR 203.

Transceiver 610 refers collectively to a receiver of a network entity and a transmitter of a network entity and may transmit signals to and receive signals from another network entity. At this time, the transmitted/received signal/message may include control information and data. When the network entity is, for example, a base station or the like, transceiver 610 may include an RF transmitter configured to up-convert and amplify the frequency of the transmitted signal and an RF receiver configured to low-noise amplify the received signal and down-convert the frequency. However, this is merely an embodiment of transceiver 610, and elements of transceiver 610 are not limited to RF transmitters and RF receivers. When the network entity is an AMF 105, the transceiver 910 may be a device for providing an interface with another network entity.

The memory 520 may store programs and data required for operation of the network entity. The memory 620 may store control information or data included in signals acquired by the network entity. The memory 620 may be configured by a storage medium such as a ROM, RAM, hard disk, CD-ROM, and DVD, or a combination of storage media.

Processor 630 may control a series of processes so that network entities may operate in accordance with embodiments of the disclosure above and/or below. Processor 630 may include at least one processor. The methods according to the embodiments set forth in the claims and/or specification of the present disclosure may be implemented in hardware, software, or a combination of hardware and software.

When the network entity is implemented in software, the network entity can be provided using a computer readable storage medium for storing one or more programs (software modules). One or more programs stored in the computer-readable storage medium may be configured for execution by one or more processors within an electronic device or a particular server. The one or more programs may include instructions for causing the electronic device to perform the methods according to the embodiments set forth in the claims and/or specification of the present disclosure.

The program (software module or software) may be stored in a non-volatile memory comprising: random access memory and flash memory, read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), magnetic disk storage, compact disk-ROM (CD-ROM), digital Versatile Disks (DVD), or other types of optical storage or magnetic cassettes. Alternatively, the program may be stored in a memory configured by a combination of some or all of the enumerated components. Furthermore, the number of memories configured may be plural.

In addition, the program may be stored in an attachable storage device that may perform access through a communication network such as the internet, an intranet, a Local Area Network (LAN), a wide area network (WLAN), and a Storage Area Network (SAN), or a combination thereof. The storage device may access devices that perform embodiments of the present disclosure through an external port. A separate storage device in a communication network may access a device that performs embodiments of the present disclosure.

In the descriptions of fig. 2A-2D, 3A-3D, and 4A-4D, the processes of a-C may be performed when the AMF 105 sends a registration accept operation to the UE 101 (operation 24), rather than as part of the AMF 105 and the UE 101 performing the authentication and/or security procedures required by the network (operation 14).

Procedure of the AMF 105 transmitting the initial context setup request message to the NG-RAN 103.

A procedure in which NG-RAN 103 sends an initial context setup response message to AMF 105.

When it is determined to perform EPS backoff, NG-RAN 103 waits a predetermined time instead of immediately triggering an EPS backoff procedure, and then performs a procedure of triggering a delayed backoff procedure of EPS backoff according to a separate request from AMF 105 or the determination of NG-RAN 103.

Hereinafter, an embodiment corresponding to the case where the operations of a to C are performed when the AMF 105 transmits the operation of registration acceptance (operation 24) to the UE 101.

As an embodiment of the present disclosure, fig. 2A to 2D may be changed as follows.

In operation 1, for a UE 101 connected to 5GS through NG-RAN 103, an IP Multimedia Subsystem (IMS) voice session establishment may be initiated that is terminated by a Mobile Originated (MO) UE or by a Mobile Terminated (MT) UE.

IMS is a system for providing multimedia services in an IP network and can provide voice, video, messaging, data, web-based wired/wireless technology to users through connections with EPS and 5GS core networks. The proxy call session control function (P-CSCF) of the IMS may be connected to the PCF, PCRF or pcf+pcrf of the 5GS/EPS core network, and the interrogating call session control function (I-CSCF), serving call session control function (S-CSCF) and Application Server (AS) of the IMF may be connected to the HSS, UDM or hss+udm of the 5GS/EPS core network. The UE may be connected to the EPC through an E-UTRAN or an evolved packet data gateway (ePDG) or to the 5GS through an NG-RAN or non-3 GPP interworking function (N3 IWF) to be registered and establish a session, and the EPC/5GS may perform an entity/function of the IMS and UE registration and session establishment procedures required for an IMS-based voice service.

In operation 3, when the NG-RAN 103 that receives information requesting QoS flow setting for a voice service is configured to support EPS fallback of IMS voice, the NG-RAN may determine whether to trigger EPS fallback based on the following information. NG-RAN 103 may determine whether to trigger EPS fallback taking into account UE capabilities received from UE 101, indicators from AMF 105 (during initial context setup, handover resource allocation, or path handover request reply procedure) indicating whether redirection of EPS fallback for speech is possible, network configuration (e.g., N26 availability configuration), and radio conditions. When NG-RAN 103 determines that EPS backoff is not triggered, operations following operation 3 may not be performed. Operation 5 may not be performed when the AMF 105 receives an indicator indicating that redirection of EPS fallback for speech is not possible. When NG-RAN 103 does not receive an indicator of redirection of EPS fallback for voice from AMF 105, NG-RAN may exclude network configuration (e.g., N26 availability configuration) from consideration in determining whether to trigger EPS fallback for IMS voice.

In operation 6a, the UE 101 may perform a handover to the EPS or an inter-system redirection using N26. The UE 101 may initiate a Tracking Area Update (TAU) procedure.

After performing the procedure of releasing the RRC connection with the UE 101 in operation 8, the E-UTRAN 113 may trigger the UE 101 to move to 5GS and perform a registration procedure in operation 9.

In operation 13b, the MME 115 that received the context request message in operation 13a may send the context request message to the AMF 105. The context response message may include the EPS bearer context(s). The EPS bearer context(s) may include information related to EPS bearers that were not released from EPS before the UE 101 moved to 5GS, and when the dedicated bearer for IMS voice generated in operation 7 is not released, information (context) about the bearer. The dedicated bearer for IMS voice may be configured as a bearer with a QoS Class Identifier (QCI) of 1 (qci=1 bearer). In the present disclosure, a dedicated bearer for IMS voice or a bearer with qci=1 may be used interchangeably.

The NG-RAN 103 and AMF 105 may directly perform operation 15 without operations 14c-1 through 14 c-3.

When the authentication and/or security procedure (operation 14) has been successfully completed, the AMF 105 may send a context answer signal to the MME 115 in operation 15.

AMF 105 may perform operation 14c-1 concurrently with operation 24 after operation 24.

NG-RAN 103 may insert the registration accept message of operation 24 into the initial context setup request message.

When it is determined to perform EPS backoff, NG-RAN 103 waits a predetermined time instead of immediately initiating an EPS backoff procedure, and then performs a delayed backoff procedure for initiating EPS backoff according to a separate request from AMF 105 or the determination of NG-RAN 103. NG-RAN 103 may wait a predetermined time by using a timer (e.g., a delayed back-off timer). The NG-RAN may initiate the deferred fallback procedure when the NG-RAN 103 receives a notification from the AMF 105 indicating that initiation of the deferred fallback procedure is possible before expiration after the time starts, when the NG-RAN receives a notification indicating that a request from the AMF 105 and/or UE 101 to register the UE is accepted and that 5G-GUTI is assigned to the UE 101, or when the average time required to complete the procedure of registering the UE 101 has elapsed. Upon receiving a request for PDU session resource setting for a dedicated bearer for IMS voice, NG-RAN 103 may configure a timer for initiating a delayed fallback procedure to be longer or shorter than if it was determined to perform EPS fallback for another reason.

In operation 14c-3, the NG-RAN 103 that determined to perform EPS backoff in operation 14c-2 may inform the AMF 105 of the initiation of the EPS backoff procedure. When NG-RAN 103 receives a request for PDU session resource settings for a dedicated bearer for IMS voice or for other reasons desires to initiate EPS fallback after 5G-GUTI is allocated to UE 101, the NG-RAN may inform AMF 105 of the initiation of the deferred fallback procedure. For example, an indicator of the delayed backoff trigger may be inserted into the initial context setup response message and then sent to the AMF 105.

In operation 24a, when the AMF 105 receiving the notification of the initiation of the deferred fallback procedure from the NG-RAN 103 in operation 14c-3 may determine to accept the registration request from the UE 101 and send a 5G-GUTI (operation 24), the AMF may send an indicator to the NG-RAN 103 indicating to stop waiting for the deferred fallback procedure and perform the procedure. For example, a delayed back-off start indicator may be inserted into the N2 request message and sent to NG-RAN 103. The message may be sent when the registration accept message in operation 24 is sent to NG-RAN 103 or before or after the registration accept message.

In operation 25, the NG-RAN 103 that received the notification from the AMF 105 in operation 24a indicating the start of the delayed fallback procedure may wait for a predetermined time without starting the delayed fallback procedure until the UE 101 receives the 5G-GUTI of operation 24. When the operation 24a is performed after the operation 26, the operation 25 may be omitted.

In operation 26, the UE 101 that received the registration accept message from the AMF 105 in operation 24 may send a registration complete message to the AMF 105. The registration accept message may be inserted into an uplink non-access stratum (NAS) message that the UE 101 sends to the network through the NG-RAN 103. Upon receiving the uplink NAS message from the UE 101, the NG-RAN 103 may end waiting for execution of the delayed fallback procedure and perform operation 27.

In operation 27, NG-RAN 103 may trigger a delayed fallback procedure.

As an embodiment of the present disclosure, fig. 3A to 3D may be changed as follows.

When the authentication and/or security procedure (operation 14) has been successfully completed, the AMF 105 may send a context reply to the MME 115 in operation 15.

In operation 17, the AMF 105 may perform an ME identity check with the EIR 203.

In operation 20, AMF 105 may select pcf+pcrf 123.

The AMF 105 may make a request to the PGW-C + SMF 122 to establish and/or reactivate a PDU session. The corresponding PDU session may be determined with reference to PDN connectivity information received from the UE 101 or MME 115. The request for reactivation of the PDU session may be sent by an nsmf_pduse_createsmcontext request message. When including a request to establish and/or re-activate a PDU session corresponding to a PDN connection with a QCI value of 1, PGW-c+smf 122 may reject the request to establish and/or re-activate a PDU session corresponding to a PDN connection with a QCI value of 1, and may send an indicator indicating rejection to AMF 105 via an nsmf_pduse_createsmcontext response message.

Further, when the EPS bearer context is received from the MME 115 in operation 13b, the AMF 105 may determine whether to insert the EPS bearer context into the initial context setup request message. Specifically, before the 5GS registration procedure of the UE101 is completed, the AMF 105 may determine not to insert some of the EPS bearer context into the initial context setup request message in case it is considered whether the NG-RAN 103 corresponds to information that may be considered when determining whether to perform EPS backoff and/or whether additional information should be provided to the UE101 in order to normally perform the EPS registration procedure when EPS backoff is initiated. For example, the AMF 105 receives the EPS bearer context for the dedicated bearer for IMS voice (or the bearer with QCI of 1) in operation 13b, and may not insert the EPS bearer context for the dedicated bearer for IMS voice into the initial context setup request message when the AMF 105 determines that the UE101 and/or the network supports EPS fallback and determines to inform the NG-RAN 103 of this by using an indicator for redirection of voice EPS fallback.

When an indicator indicating a rejection of a request to establish and/or re-activate a PDU session corresponding to a PDN connection with a QCI value of 1 is received from PGW-c+smf 122 in operation 21, AMF 105 may inform NG-RAN 103 of the indicator. In this case, the AMF 105 may not insert the EPS bearer context for the dedicated bearer of the IMS voice into the initial context setup request message.

When an indicator indicating a rejection of a request to establish and/or re-activate a PDU session corresponding to a PDN connection with a QCI value of 1 is received from the PGW-c+smf 122 in operation 21, the AMF 105 may inform the UE 101 of the indicator. In this case, the AMF 105 may transmit an indicator indicating rejection of a request for establishment and/or reactivation of the PDU session corresponding to the PDN connection having the QCI value of 1 through the registration accept message of operation 24 or related information. The related information may be used by an EPS bearer context state Information Element (IE).

Although the EPS bearer context of the IMS voice is received from the MME 115 in operation 13b, the AMF 105, which did not insert information into the initial context setup request message sent to the NG-RAN 103 in operation 14c-1, may make a request to the NG-RAN 103 to perform a delay fallback procedure in operation 24 a. For example, a delayed back off start indicator and/or a reason why a delayed back off procedure was requested may be inserted into the N2 request message and sent to NG-RAN 103. Reasons for making a request to perform a deferred fallback procedure may include the presence of an EPS bearer context for a dedicated bearer for IMS voice. The message may be sent when the registration accept message in operation 24 is sent to NG-RAN 103 or before or after the registration accept message.

The AMF 105 may determine the order of operations 24a and 24 with reference to whether an indicator indicating a rejection of a request to establish and/or re-activate a PDU session corresponding to a PDN connection with a QCI value of 1 was received from the PGW-C + SMF 122 in operation 21. When the indicator is received, operation 24a may be performed after operation 24 is performed.

Fig. 7A illustrates a method of registering a UE and managing a session by an SMF through a delayed fallback trigger procedure according to an embodiment of the present disclosure, fig. 7B illustrates a method of registering a UE and managing a session by an SMF through a delayed fallback trigger procedure according to an embodiment of the present disclosure, fig. 7C illustrates a method of registering a UE and managing a session by an SMF through a delayed fallback trigger procedure according to an embodiment of the present disclosure, and fig. 7D illustrates a method of registering a UE and managing a session by an SMF through a delayed fallback trigger procedure according to an embodiment of the present disclosure, and fig. 7E illustrates a method of registering a UE and managing a session by an SMF through a delayed fallback trigger procedure according to an embodiment of the present disclosure.

In the following description, fig. 7A to 7E are collectively referred to and described as fig. 7. Prior to the description of the embodiments of the present disclosure made with reference to fig. 7A-7E, the same reference numerals as those in fig. 1 are used for the respective NF and UE described in fig. 1. For example, in the examples of fig. 7A to 7E, the operation of fig. 7B may be performed after all operations of fig. 7A or at least one operation thereof. Similarly, the operations of fig. 7C may be performed after at least one or all of the operations of fig. 7B, the operations of fig. 7D may be performed after at least one or all of the operations of fig. 7C, and the operations of fig. 7E may be performed after at least one or all of the operations of fig. 7D. For the operations of fig. 7 described in the present disclosure, for convenience of description and to aid understanding, all the operations will be described. However, at least some operations may be omitted or not performed as appropriate. In a practical implementation, the same order of fig. 7A to 7E as the schemes described in the present disclosure may be used. In another example, only some of the operations of fig. 7A-7E may be implemented according to the illustrated order. That is, some of the sequences of fig. 7A through 7E may or may not be omitted. In another example, some of the sequences of fig. 7A-7E may be performed in parallel or may be changed. Further, competition described with reference to another figure may be included in the middle of the flowcharts in fig. 7A to 7E.

In operation 3, when NG-RAN 103 that receives information requesting QoS flow setting for a voice service is configured to support EPS fallback of IMS voice, NG-RAN may determine whether to trigger EPS fallback. NG-RAN 103 may determine whether to trigger EPS fallback taking into account UE capabilities received from UE 101, indicators from AMF 105 (during initial context setup, handover resource allocation, or path handover request reply procedure) indicating whether redirection of EPS fallback for speech is possible, network configuration (e.g., N26 availability configuration), and radio conditions. When NG-RAN 103 determines that EPS backoff is not triggered, operations following operation 3 may not be performed. When the AMF 105 receives an indicator indicating that redirection of EPS fallback for voice is impossible, the following operation 5 may not be performed. When NG-RAN 103 does not receive an indicator of redirection of EPS fallback for voice from AMF 105, NG-RAN may exclude network configuration (e.g., N26 availability configuration) from consideration in determining whether to trigger EPS fallback for IMS voice.

In operation 4, NG-RAN 103 may send a response message rejecting the PDU session modification request for QoS flow setup of IMS voice received in operation 2 to smf+pgw-C122 through AMF 105. The response message rejecting the PDU session modification request may include an indicator indicating movement due to fallback of IMS voice. The smf+pgw-C122 that receives the response message rejecting the PDU session modification request may maintain PCC rule(s) related to QoS flow(s) for the IMS voice service. When there is a pcf+pcrf 123 subscribing to the notification of the EPS fallback event, the smf+pgw-C122 may report the EPS fallback event to the corresponding pcf+pcrf 123.

In operation 8, the E-UTRAN 113 may perform a procedure of releasing the RRC connection with the UE 101 due to the inactivity of the user. The reason for inactivity of the user in operation 8 may include a case where the user does not receive a voice call for a predetermined time. The E-UTRAN 113 may use the timer to determine the user inactivity. When the dedicated bearer for IMS voice is not released, the E-UTRAN 113 may maintain the RRC connection without releasing the RRC connection. In this case, the operation 8 and the following procedure may be omitted.

In operation 13a, the AMF 105 that received the registration request message in operation 12 may acquire an MME address by using the EPS-GUTI to which the old 5G-GUTI is mapped. The AMF 105 may send a context request message to the MME 115 by using the MME address. The context request message may include a TAU message and an EPS-GUTI to which the old 5G-GUTI is mapped. The MME 115 may determine or identify the validity of the content of the TAU message.

In operation 13b, the MME 115 that received the context request in operation 13 may send a context response message to the AMF 105. The context response message may include the EPS bearer context(s). The EPS bearer context(s) may include information related to EPS bearers that were not released from EPS before the UE 101 moved to 5GS, and when the dedicated bearer for IMS voice generated in operation 7 is not released, information (context) about the bearer. The dedicated bearer for IMS voice may be configured as a bearer with a QoS Class Identifier (QCI) of 1 (qci=1 bearer). In the present disclosure, a dedicated bearer for IMS voice or a bearer with qci=1 may be used interchangeably.

In operation 14, the AMF 105 may determine whether to perform a process of authenticating the UE 101. When the AMF 105 determines to perform a process of authenticating the UE 101, the AMF 105 may perform an authentication and/or security process required by the network with the UE 101. Operation 14 may be omitted when the AMF 105 determines that the process of authenticating the UE 101 is not required.

When the AMF 105 determines to provide service to the UE 101 in operation 13b and accepts the request of the UE 101 in operation 13b, the AMF 105 may send a context reply to the MME 115 in operation 15. The context reply may include a serving GW change indication.

In operation 17, the AMF 105 may perform an ME identity check with the EIR 203.

In operation 20, AMF 105 may select pcf+pcrf 123.

In operation 22a, the AMF 105 may make a request to the smf+pgw-C122 to reactivate the PDU session of the EPS PDN connection. The PDC session requested to be reactivated may be determined based on the information included in the registration request received by AMF 105 from the UE in operation 12. Upon receiving a list of PDU sessions required to be reactivated (provided by the PDU session list to be activated field) from the UE 101 in operation 12, the AMF 105 may make a request to the smf+pgw-C122 to reactivate all corresponding PDU sessions. AMF 105 may send an Nsmf_PDUSation_CreateSMContext message to SMF+PGW-C122. The AMF 105 may provide the UE context received from the MME 115 in operation 13b and/or context information related to the EPS PDN connection to the smf+pgw-C122. Further, the context information received by the AMF 105 in operation 13b may include an EPS bearer context of the qci=1 bearer.

In operation 22b, the smf+pgw-C122 may find a corresponding PDU session based on the PDN connection context included in the request of operation 22 a. The smf+pgw-C122 may modify the content of the allocated EBI information. The smf+pgw-C122 may exclude/remove EBI of the EPS bearer corresponding to the QoS flow that is not supported by 5GS from the allocated EBI information. When 5GS does not support QoS flows for IMS voice, smf+pgw-C122 may exclude/delete EBI of EPS bearers (bearers with qci=1) for IMS voice from the allocated EBI information.

In operation 22C, the smf+pgw-C122 may perform a procedure of N4 session modification together with the upf+pgw-U121 in order to establish a CN tunnel of the PDU session. CN tunnel information for PDU sessions may be allocated by upf+pgw-U121 and provided to smf+pgw-C122.

In operation 22d, the smf+pgw-C122 may update the SM context and provide the updated SM context to the AMF 105. The smf+pgw-C122 may send an nsmf_pduse_createsmcontex response message to the AMF 105. The SM context provided by smf+pgw-C122 to AMF 105 may include a PDU session ID corresponding to the PDN connection context in the request, allocated EBI information (S) and S-nsai for the PDU session, and an N2 SM context corresponding to the PDU session in the list of received PDU sessions to be activated. When the EBI of the EPS bearer corresponding to the QoS flow that is not supported by 5GS is excluded/removed from the allocated EBI information, the smf+pgw-C122 may insert the excluded/removed allocated EBI information into the SM context and transmit the SM context to the AMF 105 in operation 22 b. When the EBI of the EPS bearer (bearer with qci=1) for IMS voice is excluded/removed from the allocated EBI information, the smf+pgw-C122 may provide an indicator indicating that the EPS fallback procedure can be performed to the AMF 105 after the registration procedure is completed in operation 22 b. The indicator may be a delayed back-off start indicator or a delayed back-off trigger indicator. The AMF 105 may store an association between the PDU session ID and the allocated EBI (S) related to the SMF ID, S-nsai, and PDU session ID. The AMF 105 may generate EPS bearer states reflecting all existing EPS bearers based on allocated EBI information received for the UE 101 from all relevant smfs+pgw-C.

In operation 22e, the smf+pgw-C122 may perform a procedure of SM policy association modification together with the pcf+pcrf 123.

In operation 23, the hss+udm 124 may send a cancel location message to the MME 115 and ask the MME 115 to delete or no longer store information such as the MM context of the UE 101.

After deleting the information such as MM context of the UE 101, the MME 115 that received the relocation cancel message from the hss+udm 124 in operation 23 may send a relocation cancel response signal to the hss+udm 124 in operation 24.

In operation 24a, the MME 115 may send a delete session request to the SGW 117 when sending a cancel location answer signal to the hss+udm 124 in operation 23.

In operation 25, when it is determined to accept the registration request from the UE 101, the AMF 105 may send a registration accept message to the UE 101 through the NG-RAN 103. The registration accept message may include the 5G-GUTI of the UE 101.

In operation 25a, the AMF 105, which received an indicator indicating that the EPS fallback procedure can be performed from the smf+pgw-C122 after the completion of the registration procedure in operation 22d, may make a request to the NG-RAN 103 to perform the deferred fallback procedure. For example, a delayed back off start indicator and/or a reason why a delayed back off procedure was requested may be inserted into the N2 request message and sent to NG-RAN 103. Reasons for making a request to perform a deferred fallback procedure may include the presence of an EPS bearer context for a dedicated bearer for IMS voice. The message may be sent when the registration accept message in operation 25 is sent to NG-RAN 103 or before or after the registration accept message.

In operation 25b, the AMF 105 that sent the registration accept message in operation 24 may perform a UE policy association establishment procedure together with the pcf+pcrf 123.

In operation 26, the NG-RAN 103 that received the request from the AMF 105 in operation 25a to perform the deferred fallback procedure may wait a predetermined time without starting the deferred fallback procedure until the UE 101 receives the 5G-GUTI of operation 25. When the operation 25a is performed after the operation 27, the operation 26 may be omitted.

The NG-RAN 103 may determine not to perform the deferred back-off when there are other reasons such that the reason for making the request for the deferred back-off from the AMF 105 in operation 25a does not match the method by which the NG-RAN 103 determines the EPS back-off, the UE 101 does not support the EPS back-off, the radio conditions are difficult to perform the EPS back-off, or there is a separate configuration in the NG-RAN 103. When NG-RAN 103 does not perform a delayed fallback according to the delayed fallback request of AMF 105, content including a rejection of the delayed fallback request may be sent to AMF 105 via an N2 message. When NG-RAN 103 accepts the delay request of AMF 105, content including the delay request of accepting AMF 105 may be sent to AMF 105 via an N2 message.

In operation 27, the UE 101 that received the registration accepted message from the AMF 105 in operation 25 may send a registration complete message to the AMF 105.

In operation 28, NG-RAN 103 may trigger a delayed fallback procedure.

In operation 29, the NG-RAN 103 may perform a redirection or handoff of the UE 101 to EPS.

In operation 30a-1, the UE 101 may trigger a TAU procedure to connect to the EPS.

In operation 30a-2, the UE 101 may send a TAU request message to the E-UTRAN 113. The TAU request message may include the EPS-GUTI converted from the 5G-GUTI received in operation 25 and an indicator that the UE 101 has moved from 5GS to EPS (e.g., "move from 5 GS").

In operation 30a-3, the E-UTRAN 113 that received the TAU request message in operation 30a-2 may transmit the TAU request message to the MME 115.

In operation 30a-4, the MME 115, which received the TAU request message in operation 30a-3, continuously performs the TAU procedure for the UE 101.

In operation 30b, the UE 101 may perform an inter-system redirection without using N26.

In operation 31, the smf+pgw-C122 may restore the setting of the dedicated bearer for IMS voice.

Fig. 8A illustrates a method of registering a UE and managing a session by an SMF by using a delay of a procedure of triggering a fallback according to an embodiment of the present disclosure, fig. 8B illustrates a method of registering a UE and managing a session by an SMF by using a delay of a procedure of triggering a fallback according to an embodiment of the present disclosure, fig. 8C illustrates a method of registering a UE and managing a session by an SMF by using a delay of a procedure of triggering a fallback according to an embodiment of the present disclosure, and fig. 8D illustrates a method of registering a UE and managing a session by an SMF by using a delay of a procedure of triggering a fallback according to an embodiment of the present disclosure.

In the following description, fig. 8A to 8E are collectively referred to and described as fig. 8. Prior to the description of the embodiments of the present disclosure made with reference to fig. 8A-8E, the same reference numerals as those in fig. 1 are used for the respective NF and UE described in fig. 1. For example, in the examples of fig. 8A to 8E, the operation of fig. 8B may be performed after all operations of fig. 8A or at least one operation thereof. Similarly, the operations of fig. 8C may be performed after at least one or all of the operations of fig. 8B, the operations of fig. 8D may be performed after at least one or all of the operations of fig. 8C, and the operations of fig. 8E may be performed after at least one or all of the operations of fig. 8D. For the operations of fig. 8 described in the present disclosure, for convenience of description and to aid understanding, all the operations will be described. However, at least some operations may be omitted or not performed as appropriate. In a practical implementation, the same order of fig. 8A to 8E as the scheme described in the present disclosure may be used. In another example, only some of the operations of fig. 8A through 8E may be implemented according to the illustrated order. That is, some of the sequences of fig. 8A through 8E may or may not be omitted. In another example, some of the sequences of fig. 8A-8E may be performed in parallel or may be changed. Further, competition described with reference to another figure may be included in the middle of the flowcharts in fig. 8A to 8E.

In operation 8, the E-UTRAN 113 may perform a procedure of releasing the RRC connection with the UE 101 due to the inactivity of the user. Reasons for inactivity of the user may include a situation where the user has not received a voice call for a predetermined time. The E-UTRAN 113 may use the timer to determine the user inactivity. When the dedicated bearer for IMS voice is not released, the E-UTRAN 113 may maintain the RRC connection without releasing the RRC connection. In this case, the operation 8 and the following procedure may be omitted.

In operation 14, the AMF 105 may determine whether to perform a process of authenticating the UE 101. When the AMF determines to perform a process of authenticating the UE 101, the AMF 105 may perform an authentication and/or security process required by the network with the UE 101. Operation 14 may be omitted when the AMF 105 determines that the process of authenticating the UE 101 is not required.

When the AMF 105 performs operation 13b to determine to provide service to the UE 101 and to accept the request of the UE 101, the AMF 105 may send a context reply to the MME 115 in operation 15. The context reply may include a serving GW change indication.

In operation 17, the AMF 105 may perform an ME identity check with the EIR 203.

In operation 20, AMF 105 may select pcf+pcrf 123.

In operation 22a, the AMF 105 may make a request to the smf+pgw-C122 to reactivate the PDU session of the EPS PDN connection. The PDC session requested to be reactivated may be determined based on the information included in the registration request received by AMF 105 from UE 101 in operation 12. Upon receiving a list of PDU sessions required to be reactivated (provided by the PDU session list to be activated field) from the UE 101 in operation 12, the AMF 105 may make a request to the smf+pgw-C122 to reactivate all corresponding PDU sessions. AMF 105 may send an Nsmf_PDUSation_CreateSMContext message to SMF+PGW-C122. The AMF 105 may provide the UE context and/or context information related to the EPS PDN connection received from the MME 115 in operation 13b together. Further, the context information received in operation 13b may include an EPS bearer context of the qci=1 bearer.

In operation 22b, the smf+pgw-C122 may find a corresponding PDU session based on the PDN connection context included in the request of operation 22 a. The smf+pgw-C122 may modify the content of the allocated EBI information. The smf+pgw-C122 may exclude/delete EBIs of EPS bearers corresponding to QoS flows not supported by 5GS from the allocated EBI information. When 5GS does not support QoS flows for IMS voice, EBI of EPS bearers (bearers with qci=1) for IMS voice may be excluded/removed from the allocated EBI information.

In operation 22d, the smf+pgw-C122 may update the SM context and provide the updated SM context to the AMF 105. The smf+pgw-C122 may send an nsmf_pduse_createsmcontex response message to the AMF 105. The SM context provided by smf+pgw-C122 to AMF 105 may include a PDU session ID corresponding to the PDN connection context in the request, allocated EBI information (S) and S-nsai for the PDU session, and an N2 SM context corresponding to the PDU session in the list of received PDU sessions to be activated. When the EBI of the EPS bearer corresponding to the QoS flow that is not supported by 5GS is excluded/removed from the allocated EBI information, the excluded/removed allocated EBI information may be inserted into the SM context and transmitted in operation 22 b. Although not shown in fig. 8, when EBI of an EPS bearer (a bearer having qci=1) for IMS voice is excluded/removed from allocated EBI information, the smf+pgw-C122 may provide an indicator indicating that an EPS fallback procedure can be performed to the AMF 105 after the registration procedure is completed in operation 22 b. The indicator may be a delayed back-off start indicator or a delayed back-off trigger indicator. The AMF 105 may store an association between the PDU session ID and the allocated EBI (S) related to the SMF ID, S-nsai, and PDU session ID. The AMF 105 may generate EPS bearer states reflecting all existing EPS bearers based on allocated EBI information received for the UE 101 from all relevant smfs+pgw-C.

In operation 24a, the MME 115 may send a delete session request to the serving gateway when sending a cancel location answer signal to the hss+udm 124 in operation 23.

In operation 26, the UE 101 that received the registration accept message from the AMF 105 in operation 25 may send a registration complete message to the AMF 105.

The waveform shape between operation 26 and operation 27 means that other specific operations may be performed between operation 26 and operation 27. Further, this may mean that a predetermined time has elapsed in time between operation 26 and operation 27.

In operation 27, the E-UTRAN 113 may perform a procedure of releasing the RRC connection with the UE 101 due to the inactivity of the user. Reasons for inactivity of the user may include a situation where the user has not received a voice call for a predetermined time. The E-UTRAN 113 may use the timer to determine the user inactivity.

In operation 28a-1, the UE 101 may send a registration request message to the NG-RAN 103. When there is a 5G-GUTI in the 5GS that is the UE identifier assigned by the AMF 105, the UE 101 may insert the 5G-GUTI as a native 5G-GUTI in the registration request message. The 5G-GUTI may correspond to the 5G-GUTI received in operation 25.

In operation 28a-2, the NG-RAN 103 that received the request from the UE 101 in operation 28a-1 may select the AMF 105.

In operation 28a-3, the NG-RAN 103 that selected the AMF 105 in operation 28a-2 may send a registration request message received from the UE 101 to the AMF 105.

In operation 28b-1, the UE 101 may send a service request message to the NG-RAN 103.

In operation 28b-2, the NG-RAN 103 that received the service request message in operation 28b-1 may send an N2 message to the AMF 105. The N2 message may include all or some of the service requests received in operation 28 b-1.

In operation 29-1, the AMF 105 may send an initial context setup request message to the NG-RAN 103. The initial context setup request message may include an indicator indicating whether the UE 101 and/or the network supports EPS backoff. An indicator of redirection for voice EPS fallback may correspond to it and AMF 105 may define the value of the indicator as supported/unsupported, available/unavailable or possible/impossible and send the value to NG-RAN 103. When the UE 101 and/or the network does not support voice services over the 5G system (e.g., when the communication carrier does not support VoNR services), the AMF 105 may send an indicator of redirection for voice EPS fallback to the NG-RAN 103. NG-RAN 103 may determine whether to perform EPS backoff.

In operation 29-2, the NG-RAN 103 may send an initial context setup response message in response to the request of the AMF 105 of operation 29-1. When it is determined in operation 29-1 that EPS fallback is performed, NG-RAN 103 may inform AMF 105 of the EPS fallback.

When NG-RAN 103 determines to perform an EPS fallback procedure in operation 29-1, NG-RAN 103 may trigger the fallback procedure in operation 30.

In operation 31, the NG-RAN 103 may perform a redirection or handoff of the UE 101 to EPS.

In operation 32a-1, the UE 101 may trigger a TAU procedure to connect to the EPS.

In operation 32a-2, the UE 101 may send a TAU request message to the E-UTRAN 113. The TAU request may include the EPS-GUTI converted from the 5G-GUTI received in operation 25 and an indicator that the UE 101 has moved from 5GS to EPS (e.g., "move from 5 GS").

In operation 32a-3, the E-UTRAN 113 that received the TAU request message in operation 30a-2 may transmit the TAU request message to the MME 115.

In operation 32a-4, the MME 115, which received the TAU request message in operation 32a-3, continuously performs the TAU procedure for the UE 101.

In operation 32b, the UE 101 may perform an inter-system redirection without using N26.

In operation 33, the smf+pgw-C122 may restore the setting of the dedicated bearer for IMS voice.

Fig. 9A illustrates a method of registering a UE and managing a session by using the maintenance of a procedure of triggering a fallback according to an embodiment of the present disclosure, fig. 9B illustrates a method of registering a UE and managing a session by using the maintenance of a procedure of triggering a fallback according to an embodiment of the present disclosure, fig. 9C illustrates a method of registering a UE and managing a session by using the maintenance of a procedure of triggering a fallback according to an embodiment of the present disclosure, and fig. 9D illustrates a method of registering a UE and managing a session by using the maintenance of a procedure of triggering a fallback according to an embodiment of the present disclosure.

In the following description, fig. 9A to 9D are collectively referred to or described as fig. 9. Prior to the description of the embodiments of the present disclosure made with reference to fig. 9A-9D, the same reference numerals as those in fig. 1 are used for the respective NF and UE described in fig. 1. Further, in fig. 9A to 9D, the operation of fig. 9B may be performed after all or at least one of the operations of fig. 9A. Similarly, the operations of fig. 9C may be performed after at least one or all of the operations of fig. 9B, and the operations of fig. 9D may be performed after at least one or all of the operations of fig. 9C. For the operations of fig. 9A to 9D described in the present disclosure, for convenience of description and to aid understanding, all the operations will be described. However, at least some operations may be omitted or not performed as appropriate. In a practical implementation, the same order of fig. 9A to 9D as the scheme described in the present disclosure may be used. In another example, only some of fig. 9A to 9D may be sequentially implemented. That is, some of the sequences of fig. 9A through 9D may or may not be omitted. In another example, some of the sequences of fig. 9A through 9D may be performed in parallel, or the sequences may be changed. Further, the description made with reference to another figure may be inserted in the middle of the flowcharts of fig. 9A to 9D.

In operation 13b, the MME 115 that received the context request in operation 13a may send a context response message to the AMF 105. The context response message may include the EPS bearer context(s). The EPS bearer context(s) may include information related to EPS bearers that were not released from EPS before the UE 101 moved to 5GS, and when the dedicated bearer for IMS voice generated in operation 7 is not released, information (context) about the bearer. The dedicated bearer for IMS voice may be configured as a bearer with a QoS Class Identifier (QCI) of 1 (qci=1 bearer). In the present disclosure, a dedicated bearer for IMS voice or a bearer with qci=1 may be used interchangeably.

In operation 14c-2, the NG-RAN 103 that received the initial context setup request message from the AMF 105 in operation 14c-1 may determine whether to perform EPS backoff. NG-RAN 103 may determine whether to perform EPS fallback in consideration of whether a request for a redirection for voice EPS fallback and/or PDU session resource settings for a dedicated bearer for IMS voice, NG-RAN configuration, etc. is received from AMF 105. For example, NG-RAN 103 determines to perform EPS fallback when the indicator for redirection of voice EPS fallback indicates that EPS fallback is supported and a request for PDU session resource settings for a dedicated bearer for IMS voice is received. After performing the initial context setup procedure, NG-RAN 103 may send an initial context setup response message to AMF 105. When determining to perform EPS fallback, NG-RAN 103 may inform AMF 105 of the EPS fallback.

When the authentication and/or security procedure (operation 14) has been successfully completed in operation 14c-2, the AMF105 may determine whether to send a context response signal to the MME 115, and when it is determined to send the context response signal, may send the context response signal to the MME 115 in operation 15. The AMF105 may not transmit the context answer signal when a notification indicating that the EPS backoff procedure has been triggered is received from the NG-RAN 103 in operation 14 c-2.

In operation 15a, the AMF105 may make a request to the MME 115 to remove or not modify information such as MM context of the UE 101. The AMF105 may also send a reason indicating that the EPS fallback procedure is to be performed or that the EPS fallback procedure starts when a notification indicating that the EPS fallback procedure has been triggered is received from the NG-RAN 103 in operation 14 c-2.

In operation 15b, the MME 115 may extend a timer that determines a point in time when information about the MM context of the UE 101 is deleted or modified. The timer may be started when a request of the AMF105 of operation 13a is received or a response of operation 13b is transmitted. The MME 115 may use an identifier such as IMSI when identifying the UE 101 to which the extended timer is to be applied. When the MME 115 receives a request from the AMF105 in operation 15a or when the UE 101 uses IMS voice services, the timer may be extended if the execution of the EPS back-off procedure is known.

In operation 15c-1, the MME 115 may make a request to the hss+udm 124 to not remove or modify information such as MM context of the UE 101 or to not remove or modify registration status or registration information of the MME 115. When the MME 115 receives a request from the AMF 105 in operation 15a, the MME 115 may also send to the hss+udm 124 a reason indicating that the EPS fallback procedure is to be performed or that the EPS fallback procedure starts, when the UE 101 uses IMS voice services, or when it may be known that the execution of the EPS fallback procedure is.

In operation 15c-2, the hss+udm 124 that received the request of operation 15c-1 may maintain information such as the MM context of the UE 101 and the registration state or registration information of the MME 115 without removing or modifying the information.

When NG-RAN 103 determines to perform an EPS fallback procedure in operation 14c-2, NG-RAN 103 may trigger the fallback procedure in operation 18.

In operation 19, the NG-RAN 103 may perform a redirection or handoff of the UE 101 to EPS.

In operation 20a-1, the UE 101 may trigger a TAU procedure to connect to the EPS.

In operation 20a-2, the UE 101 may send a TAU request message to the E-UTRAN 113. The TAU request message may include EPS-GUTI. The EPS-GUTI may correspond to the EPS-GUTI determined in operations 6A through 6B.

In operation 20a-3, the E-UTRAN 113, which received the TAU request in operation 21a-2, may transmit the TAU request to the MME 115.

In operation 20a-4, the MME 115 may not reject the TAU request of the UE for reasons that the context request, the context response, and/or the context answer procedure have been performed with the MME or the AMF prior to operation 20a-4 based on the information of operations 15 a-15 b.

In operation 20a-5, the MME 115, which received the TAU request message in operation 20a-3, continuously performs the TAU procedure for the UE 101.

In operation 21, the hss+udm 124 may send a cancel location message to the MME 115 and ask the MME 115 to delete or no longer store information such as the MM context of the UE 101. The hss+udm 124 may not transmit the cancel location message based on the information of the above operations 15c-1 to 15c-2, in which case the operations 21, 21a, 22 and 22a may be omitted.

In operation 21a, the MME 115 may ignore the cancel location request of operation 21 based on the information of operations 15a to 15 b.

In operation 22, the MME 115 may not remove information such as MM context of the UE 101 based on the information of operations 15a to 15 b. The MME 115 may not transmit a delete session request message to the serving gateway based on the information of operations 15a to 15 b. The MME 115 may or may not send a relocation acknowledge signal to the hss+udm 124, whether information such as MM context is removed or whether a delete session request message is sent to the serving gateway.

In operation 22a, the HSS+UDM 124 may ignore the relocation answer of operation 22d based on the information of operations 15c-1 to 15 c-2.

In operation 20a-6, the UE 101 may perform an inter-system redirection without using N26.

In operation 23, the smf+pgw-C122 may restore the setting of the dedicated bearer for IMS voice.

In the above detailed embodiments of the present disclosure, elements included in the present disclosure are expressed in singular or plural according to the presented detailed embodiments. However, for convenience of description, the singular or plural form is appropriately selected depending on the presented situation, and the present disclosure is not limited by elements expressed in the singular or plural. Accordingly, an element expressed in a plurality may also include a single element, or an element expressed in the singular may also include a plurality of elements.

While the present disclosure has been shown and described with reference to various embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure as defined by the appended claims and their equivalents.

INDUSTRIAL APPLICABILITY

The present disclosure may be used when providing voice services to UEs in a hybrid mobile communication system having different communication protocols.

Claims

1. A method of controlling fallback of a user equipment, UE, by a combined device of a session management function, SMF, and a packet data network, PGW, control plane function, PGW-C, in a hybrid mobile communication system in which a first mobile communication system and a second mobile communication system are interworked, the method comprising:

receiving a reactivation request for a packet data network, PDN, connection of the UE for the second mobile communication system from an access and mobility management function, AMF, of the first mobile communication system, the reactivation request comprising a PDN connection context;

retrieving a corresponding protocol data unit, PDU, session based on the PDN connectivity context included in the reactivation request;

modifying Evolved Packet System (EPS) bearer identification (EBI) information allocated to the UE for an Internet Protocol (IP) multimedia subsystem (IMS) voice based on information supported in the first mobile communication system;

establishing a core network CN tunnel for the PDU session of the UE to a user plane function UPF and a PGW user plane function PGW-U based on the modified EBI information;

updating a session management SM context based on the established CN tunnel; and

and responding to the reactivation request, and sending a response message comprising the updated SM context to the AMF.

2. The method of claim 1, wherein the reactivation request further comprises a list of PDU sessions received from the UE that are required to be reactivated.

3. The method of claim 1, wherein the reactivation request further comprises at least one of a UE context or context information related to an EPS PDN connection received from a mobility management entity MME of the second mobile communication system.

4. The method of claim 1, wherein modifying the EBI information comprises: the EBI of the EPS bearer corresponding to the quality of service QoS flow not supported in the first mobile communication system is removed from the allocated EBI information.

5. The method of claim 1, wherein modifying the EBI information comprises: the EBI of the EPS bearer for the IMS voice is removed from the allocated EBI information based on a quality of service QoS flow for the IMS voice that is not supported in the first mobile communication system.

6. The method of claim 1, wherein the response message further comprises an indicator indicating that an EPS backoff procedure can be performed after the procedure of registering the UE in the first mobile communication system is completed.

7. The method of claim 6, wherein the indicator is a delayed back off start indicator or a delayed back off trigger indicator.

8. A combined device of a session management function SMF and a packet data network gateway PGW control plane function PGW-C for controlling a fallback of a user equipment UE in a hybrid mobile communication system in which a first mobile communication system and a second mobile communication system are interworked, the combined device comprising:

a transceiver configured to communicate with a network function of the hybrid mobile communication system;

a memory; and

a processor configured to:

9. The combination of claim 8, wherein the reactivation request further comprises a list of PDU sessions received from the UE that are required to be reactivated.

10. The combination of claim 8, wherein the reactivation request further comprises at least one of a UE context received from a mobility management entity, MME, of the second mobile communication system or context information related to an EPS PDN connection.

11. The combination of claim 8, wherein the processor is further configured to: as at least part of modifying the EBI information, an EBI of an EPS bearer corresponding to a quality of service QoS flow not supported in the first mobile communication system is removed from the allocated EBI information.

12. The combination of claim 8, wherein the processor is further configured to: an EBI for an EPS bearer of the IMS voice is removed from the allocated EBI information as at least part of modifying the EBI information based on a quality of service QoS flow for the IMS voice that is not supported in the first mobile communication system.

13. The combination of claim 8, wherein the response message further comprises an indicator indicating that an EPS backoff procedure can be performed after the procedure of registering the UE in the first mobile communication system is completed.

14. The combination of claim 13, wherein the indicator is a delayed back off start indicator or a delayed back off trigger indicator.