Mobility management registration in evolved packet system (EPS) to 5G system (5GS) user equipment mobility

Abstract

An access and mobility management function (AMF) 410 of a 5G system (5GS) receives a first registration request message 602 from a user equipment (UE) 504 operating in a single-registration mode. The

Description

TECHNOLOGICAL FIELD

[0001] The present disclosure relates generally to telecommunications and, in particular, to inter-system mobility of a user equipment from an evolved packet system (EPS) to a 5G system (5GS). BACKGROUND

[0002] A telecommunications system can be seen as a facility that enables communication sessions between two or more entities such as user terminals, base stations and / or other nodes by providing carriers between the various entities involved in the communications path. A telecommunications system can be provided for example by means of a communication network and one or more compatible communication devices. The communication sessions may comprise, for example, communication of data for carrying communications such as voice, video, electronic mail (email), text message, multimedia and / or content data and so on. Non-limiting examples of services provided comprise two-way or multi-way calls, data communication or multimedia services and access to a data network system, such as the Internet.

[0003] In a wireless telecommunications system, at least a part of a communication session between at least two stations occurs over a wireless link. Examples of wireless telecommunications systems comprise public land mobile networks (PLMN), satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN). Some wireless systems can be divided into cells, and are therefore often referred to as cellular systems.

[0004] A user can access the telecommunications system by means of an appropriate communication device or terminal. A communication device of a user may be referred to as user equipment (UE) or user device. A communication device is provided with an appropriate signal receiving and transmitting apparatus for enabling communications, for example enabling access to a communication network or communications directly with other users. The communication device may access a carrier provided by a station, for example a base station of a cell, and transmit and / or receive communications on the carrier.

[0005] The telecommunications system and associated devices typically operate in accordance with a given standard or specification which sets out what the various entities associated with the communication system are permitted to do and how operations should be achieved. Communication protocols and / or parameters which shall be used for connection of the various entities are also typically defined. One example of a telecommunications system is the Universal Mobile Telecommunications System (UMTS). Other examples of telecommunications systems are Long-Term Evolution (LTE), LTE Advanced and the so-called 5G or New Radio (NR) networks. NR is being standardized by the 3rd Generation Partnership Project (3GPP). BRIEF SUMMARY

[0006] Example implementations of the present disclosure are directed to telecommunications and, in particular, to inter-system mobility of a user equipment from an evolved packet system (EPS) to a 5G system (5GS). The present disclosure includes, without limitation, the following example implementations.

[0007] Some example implementations provide an apparatus implemented by an access and mobility management function (AMF) of a 5G system (5GS), the apparatus comprising: at least one memory configured to store instructions; and at least one processing circuitry configured to access the at least one memory, and execute the instructions to cause the apparatus to at least: receive a first registration request message from a user equipment (UE) operating in a single-registration mode, the first registration request message for inter-system mobility of the UE from an evolved packet system (EPS) to the 5GS, the first registration request message indicating a mobility management entity (MME) registration exists in the EPS for the UE; make a determination that the AMF is not configured with an interface towards a MME in the EPS; and based on the registration request message and the determination, perform a registration procedure with a unified data management (UDM) in the 5GS to register the AMF in the UDM for the UE, the registration procedure including a second registration request message sent by the AMF to the UDM with an indication to instruct a home subscriber server (HSS) in the EPS not to cancel the MME registration.

[0008] Some example implementations provide an apparatus implemented by an access and mobility management function (AMF) of a 5G system (5GS), the apparatus comprising: means for receiving a first registration request message from an user equipment (UE) operating in a single-registration mode, the first registration request message for inter-system mobility of the UE from an evolved packet system (EPS) to the 5GS, the first registration request message indicating a mobility management entity (MME) registration exists in the EPS for the UE; means for making a determination that the AMF is not configured with an interface towards a MME in the EPS; and based on the registration request message and the determination, means for performing a registration procedure with an unified data management (UDM) in the 5GS to register the AMF in the UDM for the UE, the registration procedure including a second registration request message sent by the AMF to the UDM with an indication to instruct a home subscriber server (HSS) in the EPS not to cancel the MME registration.

[0009] Some example implementations provide a method performed by an access and mobility management function (AMF) of a 5G system (5GS), the method comprising: receiving a first registration request message from a user equipment (UE) operating in a single-registration mode, the first registration request message for inter-system mobility of the UE from an evolved packet system (EPS) to the 5GS, the first registration request message indicating a mobility management entity (MME) registration exists in the EPS for the UE; making a determination that the AMF is not configured with an interface towards a MME in the EPS; and based on the registration request message and the determination, performing a registration procedure with a unified data management (UDM) in the 5GS to register the AMF in the UDM for the UE, the registration procedure including a second registration request message sent by the AMF to the UDM with an indication to instruct a home subscriber server (HSS) in the EPS not to cancel the MME registration.

[0010] Some example implementations provide a computer-readable storage medium that is non-transitory and has instructions stored therein that, in response to execution by at least one processing circuitry, causes an access and mobility management function (AMF) of a 5G system (5GS) to at least: receive a first registration request message from a user equipment (UE) operating in a single-registration mode, the first registration request message for inter-system mobility of the UE from an evolved packet system (EPS) to the 5GS, the first registration request message indicating a mobility management entity (MME) registration exists in the EPS for the UE; make a determination that the AMF is not configured with an interface towards a MME in the EPS; and based on the registration request message and the determination, perform a registration procedure with a unified data management (UDM) in the 5GS to register the AMF in the UDM for the UE, the registration procedure including a second registration request message sent by the AMF to the UDM with an indication to instruct a home subscriber server (HSS) in the EPS not to cancel the MME registration.

[0011] Some example implementations provide an apparatus implemented by unified data management (UDM) of a 5G system (5GS), the apparatus comprising: at least one memory configured to store instructions; and at least one processing circuitry configured to access the at least one memory, and execute the instructions to cause the apparatus to at least: receive a registration request message from an access and mobility management function (AMF) in the 5GS in connection with inter-system mobility of a user equipment (UE) from an evolved packet system (EPS) to the 5GS, the registration request message including a first indication to instruct a home subscriber server (HSS) in the EPS not to cancel a mobility management entity (MME) registration in the HSS for the UE operating in a single-registration mode; register the AMF in the UDM for the UE based on the registration request message; and send a deregistration request message to the HSS, the deregistration request message including a second indication not to cancel the MME registration in the HSS for the UE.

[0012] Some example implementations provide an apparatus implemented by unified data management (UDM) of a 5G system (5GS), the apparatus comprising: means for receiving a registration request message from an access and mobility management function (AMF) in the 5GS in connection with inter-system mobility of an user equipment (UE) from an evolved packet system (EPS) to the 5GS, the registration request message including a first indication to instruct a home subscriber server (HSS) in the EPS not to cancel a mobility management entity (MME) registration in the HSS for the UE operating in a single-registration mode; means for registering the AMF in the UDM for the UE based on the registration request message; and means for sending a deregistration request message to the HSS, the deregistration request message including a second indication not to cancel the MME registration in the HSS for the UE.

[0013] Some example implementations provide a method performed by unified data management (UDM) of a 5G system (5GS), the method comprising: receiving a registration request message from an access and mobility management function (AMF) in the 5GS in connection with inter-system mobility of a user equipment (UE) from an evolved packet system (EPS) to the 5GS, the registration request message including a first indication to instruct a home subscriber server (HSS) in the EPS not to cancel a mobility management entity (MME) registration in the HSS for the UE operating in a single-registration mode; registering the AMF in the UDM for the UE based on the registration request message; and sending a deregistration request message to the HSS, the deregistration request message including a second indication not to cancel the MME registration in the HSS for the UE.

[0014] Some example implementations provide a computer-readable storage medium that is non-transitory and has instructions stored therein that, in response to execution by at least one processing circuitry, causes a unified data management (UDM) of a 5G system (5GS) to at least: receive a registration request message from an access and mobility management function (AMF) in the 5GS in connection with inter-system mobility of a user equipment (UE) from an evolved packet system (EPS) to the 5GS, the registration request message including a first indication to instruct a home subscriber server (HSS) in the EPS not to cancel a mobility management entity (MME) registration in the HSS for the UE operating in a single-registration mode; register the AMF in the UDM for the UE based on the registration request message; and send a deregistration request message to the HSS, the deregistration request message including a second indication not to cancel the MME registration in the HSS for the UE.

[0015] Some example implementations provide an apparatus implemented by a home subscriber server (HSS) of an evolved packet system (EPS), the apparatus comprising: at least one memory configured to store instructions; and at least one processing circuitry configured to access the at least one memory, and execute the instructions to cause the apparatus to at least: receive a deregistration request message from a unified data management (UDM) in a 5G system (5GS) in connection with inter-system mobility of a user equipment (UE) from the EPS to the 5GS, the deregistration request message including an indication not to cancel a mobility management entity (MME) registration in the HSS for the UE operating in a single-registration mode; make a determination not to cancel the MME registration in the HSS for the UE based on the indication in the deregistration request message; and respond to the UDM with a deregistration response message.

[0016] Some example implementations provide an apparatus implemented by a home subscriber server (HSS) of an evolved packet system (EPS), the apparatus comprising: means for receiving a deregistration request message from an unified data management (UDM) in a 5G system (5GS) in connection with inter-system mobility of an user equipment (UE) from the EPS to the 5GS, the deregistration request message including an indication not to cancel a mobility management entity (MME) registration in the HSS for the UE operating in a single-registration mode; means for making a determination not to cancel the MME registration in the HSS for the UE based on the indication in the deregistration request message; and means for responding to the UDM with a deregistration response message.

[0017] Some example implementations provide a method performed by a home subscriber server (HSS) of an evolved packet system (EPS), the method comprising: receiving a deregistration request message from a unified data management (UDM) in a 5G system (5GS) in connection with inter-system mobility of a user equipment (UE) from the EPS to the 5GS, the deregistration request message including an indication not to cancel a mobility management entity (MME) registration in the HSS for the UE operating in a single-registration mode; making a determination not to cancel the MME registration in the HSS for the UE based on the indication in the deregistration request message; and responding to the UDM with a deregistration response message.

[0018] Some example implementations provide a computer-readable storage medium that is non-transitory and has instructions stored therein that, in response to execution by at least one processing circuitry, causes a home subscriber server (HSS) of an evolved packet system (EPS) to at least: receive a deregistration request message from a unified data management (UDM) in a 5G system (5GS) in connection with inter-system mobility of a user equipment (UE) from the EPS to the 5GS, the deregistration request message including an indication not to cancel a mobility management entity (MME) registration in the HSS for the UE operating in a single-registration mode; make a determination not to cancel the MME registration in the HSS for the UE based on the indication in the deregistration request message; and respond to the UDM with a deregistration response message.

[0019] These and other features, aspects, and advantages of the present disclosure will be apparent from a reading of the following detailed description together with the accompanying figures, which are briefly described below. The present disclosure includes any combination of two, three, four or more features or elements set forth in this disclosure, regardless of whether such features or elements are expressly combined or otherwise recited in a specific example implementation described herein. The present disclosure is intended to be read holistically such that any separable features or elements of the disclosure, in any of its aspects and example implementations, should be viewed as combinable unless the context of the disclosure clearly dictates otherwise.

[0020] It will therefore be appreciated that this Brief Summary is provided merely for purposes of summarizing some example implementations so as to provide a basic understanding of some aspects of the disclosure. Accordingly, it will be appreciated that the above described example implementations are merely examples and should not be construed to narrow the scope or spirit of the disclosure in any way. Other example implementations, aspects and advantages will become apparent from the following detailed description taken in conjunction with the accompanying figures which illustrate, by way of example, the principles of some described example implementations. BRIEF DESCRIPTION OF THE FIGURE(S)

[0021] Having thus described example implementations of the disclosure in general terms, reference will now be made to the accompanying figures, which are not necessarily drawn to scale, and wherein:

[0022] FIG. 1 illustrates a telecommunications system that includes one or more public land mobile networks (PLMNs) coupled to one or more external data networks, according to some example implementations of the present disclosure;

[0023] FIG. 2 illustrates a deployment of a PLMN, according to some example implementations;

[0024] FIG. 3 more particularly depicts aspects of a 4G LTE deployment, referred to at times as the evolved packet system (EPS), according to some example implementations;

[0025] FIG. 4 more particularly depicts aspects of a 5G deployment, referred to at times as the 5G system (5GS), according to some example implementations;

[0026] FIG. 5 illustrates an architecture to support inter-system mobility of a user equipment (UE) between the EPS and the 5GS, according to some example implementations;

[0027] FIG. 6 is a signaling chart of UE mobility from EPS to 5GS, according to some example implementations;

[0028] FIG. 7 is a flowchart illustrating various steps in a method performed by an access and mobility management function (AMF) of the 5GS, according to various example implementations;

[0029] FIG. 8 is a flowchart illustrating various steps in a method performed by unified data management (UDM) of a 5GS, according to various example implementations;

[0030] FIGS. 9A and 9B are flowcharts illustrating various steps in a method performed by home subscriber server (HSS) of the EPS, according to various example implementations; and

[0031] FIG. 10 illustrates an apparatus according to some example implementations. DETAILED DESCRIPTION

[0032] Some implementations of the present disclosure will now be described more fully hereinafter with reference to the accompanying figures, in which some, but not all implementations of the disclosure are shown. Indeed, various implementations of the disclosure may be embodied in many different forms and should not be construed as limited to the implementations set forth herein; rather, these example implementations are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like reference numerals refer to like elements throughout.

[0033] Unless specified otherwise or clear from context, references to first, second or the like should not be construed to imply a particular order. A feature described as being above another feature (unless specified otherwise or clear from context) may instead be below, and vice versa; and similarly, features described as being to the left of another feature else may instead be to the right, and vice versa. Also, while reference may be made herein to quantitative measures, values, geometric relationships or the like, unless otherwise stated, any one or more if not all of these may be absolute or approximate to account for acceptable variations that may occur, such as those due to engineering tolerances or the like.

[0034] As used herein, unless specified otherwise or clear from context, the “or” of a set of operands is the “inclusive or” and thereby true if and only if one or more of the operands is true, as opposed to the “exclusive or” which is false when all of the operands are true. Thus, for example, “[A] or [B]” is true if [A] is true, or if [B] is true, or if both [A] and [B] are true. Further, the articles “a” and “an” mean “one or more,” unless specified otherwise or clear from context to be directed to a singular form. Furthermore, it should be understood that unless otherwise specified, the terms “data,” “content,” “digital content,” “information,” and similar terms may be at times used interchangeably. The term “network” may refer to a group of interconnected computers including clients and servers; and within a network, these computers may be interconnected directly or indirectly by various means including via one or more switches, routers, gateways, access points or the like.

[0035] Reference may be made herein to terms specific to a particular system, architecture or the like, but it should be understood that example implementations of the present disclosure may be equally applicable to any of a number of systems, architectures and the like. For example, reference may be made to 3GPP technologies such as Global System for Mobile Communications (GSM), GSM EDGE, UMTS, LTE, LTE Advanced, 5G NR, 5G Advanced and 6G; however, it should be understood that example implementations of the present disclosure may be equally applicable to non-3GPP technologies such as IEEE 802, Bluetooth and Bluetooth Low Energy.

[0036] Further, as used in this application, the term “circuitry” may refer to one or more or all of the following: (a) hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry); (b) combinations of hardware circuits and software, such as (as applicable): (i) a combination of analog and / or digital hardware circuit(s) with software / firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions); or (c) hardware circuit(s) and / or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0037] The above definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0038] FIG. 1 illustrates a telecommunications system 100 according to various example implementations of the present disclosure. The telecommunications system generally includes one or more telecommunications networks. As shown, for example, the system includes one or more public land mobile networks (PLMNs) 102 coupled to one or more other external data networks 104 - notably including a wide area network (WAN) such as the Internet. Each of the PLMNs includes a core network (CN) 106 backbone such as the Evolved Packet Core (EPC) of LTE, the 5G core network (5GC) or the like; and each of the core networks and the Internet are coupled to one or more radio access networks (RANs) 108, air interfaces or the like that implement one or more radio access technologies (RATs). As used herein, a “network device” refers to any suitable device at a network side of a telecommunications network. Examples of suitable network devices are described in greater detail below.

[0039] In addition, the system includes one or more radio units that may be varyingly known as user equipment (UE) 110, terminal device, terminal equipment, mobile station or the like. The UE is generally a device configured to communicate with a network device or a further UE in a telecommunications network. The UE may be a portable computer (e.g., laptop, notebook, tablet computer), mobile phone (e.g., cell phone, smartphone), wearable computer (e.g., smartwatch), or the like. In other examples, the UE may be an Internet of things (loT) device, an industrial loT (11 oT device), a vehicle equipped with a vehicle-to-everythmg (V2X) communication technology, or the like. In some examples, as referenced by 3GPP, the UE may be a narrowband loT (NB-IoT) device, an enhanced machine-type communication (eMTC) device, a reduced capability (RedCap) device, an ambient loT device, or the like.

[0040] In operation, these UEs 110 may be configured to connect to one or more of the RANs 108 according to their particular radio access technologies to thereby access a particular CN 106 of a PLMN 102, or to access one or more of the external data networks 104 (e.g., the Internet). The external data network may be configured to provide Internet access, operator services, 3rd party services, etc. For example, the International Telecommunication Union (ITU) has classified 5G mobile network services into three categories: enhanced mobile broadband (eMBB), ultra-reliable and low-latency communications (URLLC), and massive machine type communications (mMTC) or massive internet of things (MIoT).

[0041] Examples of radio access technologies include 3GPP radio access technologies such as GSM, GSM EDGE, UMTS, LTE, LTE Advanced, 5G NR, 5G Advanced, and 6G. Other examples of radio access technologies include IEEE 802 technologies such as IEEE 802.11 (Wi-Fi), IEEE 802.15 (including 802.15.1 (WPAN / Bluetooth), 802.15.4 (Zigbee) and 802.15.6 (WBAN)), Bluetooth, Bluetooth Low Energy (BLE), ultra wideband (UWB), and the like. Generally, a radio access technology may refer to any 2G, 3G, 4G, 5G, 6G or higher generation mobile communication technology and their different versions, as well as to any other wireless radio access technology that may be arranged to interwork with such a mobile communication technology to provide access to the CN 106 of a mobile network operator (MNO).

[0042] In various examples, a RAN 108 may be configured as one or more macrocells, microcells, picocells, femtocells or the like. The RAN may generally include one or more radio access nodes that are configured to interact with UEs 110. In various examples, a radio access node may be referred to as a base station (BS), access point (AP), base transceiver station (BTS), Node B (NB), evolved NB (eNB), macro BS, NB (MNB) or eNB (MeNB), home BS, NB (HNB) or eNB (HeNB), next generation NB (gNB), enhanced gNB (en-gNB), next generation eNB (ng-eNB), or the like. The RAN may include some type of network controlling / governing entity responsible for control of the radio access nodes. The network controlling / governing entity and radio access node may be separate or integrated into a single apparatus. The network controlling / governing entity may include processing circuity configured to carry out various management functions, etc. The processing circuity may be associated with a memory, computer-readable storage medium or database for maintaining information required in the management functions.

[0043] A RAN 108 may be centralized or distributed. In various examples, components of a RAN may be interconnected by Ethernet, Gigabit Ethernet, Asynchronous Transfer Mode (ATM), optical fiber, dark fiber, passive wavelength division multiplexing (WDM), WDM passive optical network (WDM-PON), optical transport network (OTN), time sensitive networking (TSN) and / or any other data link layer network, possibly including radio links. The RAN may be connected to a CN 106 through one or more gateways, network functions or the like.

[0044] As will be appreciated, a PLMN 102 may be deployed in a number of different manners. In a GSM EDGE deployment, for example, the GSM EDGE radio access network (GERAN) is the RAN 108. In a UMTS deployment, the UMTS terrestrial radio access network (UTRAN) is the RAN.

[0045] FIG. 2 illustrates a deployment 200 of a PLMN, such as a 4G LTE, 5G or 6G deployment, according to some example implementations. As shown, the deployment includes a CN 106, and RAN 108 with one or more radio access nodes 202 configured to interact with UEs 110. In a 4G LTE deployment, the EPC is the CN, and the evolved UTRAN (E-UTRAN) is the RAN; and the E-UTRAN includes one or more eNBs (radio access nodes) configured to connect UEs to the E-UTRAN to thereby access the EPC. Similarly, in a 5G deployment, the 5GC is the CN 106, and the next generation (NG) radio access network (NG-RAN) is the RAN 108; and the NG-RAN includes one or more gNBs (radio access nodes) configured to connect UEs 110 to the NG-RAN to thereby access the 5GC (at times referred to as the NGC). The term ‘gNB’ in 5G may correspond to the eNB in 4G LTE.

[0046] In some deployments, operations of the radio access node 202 may be carried out, at least partly, in a centra 1 / centralized unit (CU), such as a server, host or node, operationally coupled to a distributed unit (DU), such as a radio head node. It is also possible that node operations may be distributed among a plurality of servers, hosts or nodes.

[0047] It should also be understood that the distribution of work between CN 106 operations and radio access node 202 operations may vary depending on implementation. Thus, a 5G network architecture may be based on a so-called CU-DU split. One gNB-CU (central node) may control one or more gNB-DUs. The gNB-CU may control a plurality of spatially separated gNB-DUs, acting at least as transmit / receive (Tx / Rx) nodes. In some example implementations, however, the gNB-DUs (also called DU) may include, for example, a radio link control (REC), medium access control (MAC) layer and a physical (PHY) layer, whereas the gNB-CU (also called a CU) may include the layers above the RLC layer, such as a packet data convergence protocol (PDCP) layer, a radio resource control (RRC), and an IP layer. Other functional splits are also possible. It is considered that a skilled person is familiar with the open systems interconnection (OSI) model and the functionalities within each layer.

[0048] In some example implementations, the server or CU may generate a virtual network through which the server communicates with the radio node. In general, virtual networking may involve a process of combining hardware and software network resources and network functionality into a single, software-based administrative entity, a virtual network. Such virtual network may provide flexible distribution of operations between the server and the radio head / node. In practice, any digital signal processing task may be performed in either the CU or the DU, and the boundary where the responsibility is shifted between the CU and the DU may be selected according to implementation.

[0049] Some deployments of 4G LTE and 5G in particular are considered standalone (SA) deployments. Other deployments combine 4G LTE and 5G technologies, and are referred to as non-standalone (NSA) deployments. In some deployments, the E-UTRAN includes one or more ng-eNBs that are configured to communicate with the 5GC, and that may also be configured to communicate with one or more gNBs. Similarly, in another deployment, the NG-RAN may include one or more en-gNBs that are configured to communicate with the EPC, and that may also be configured to communicate with one or more eNBs. In various instances, a single UE 110, a dual-mode or multimode UE, may support multiple (two or more) RANs—thereby being configured to connect to multiple RANs, such as 4G LTE and 5G.

[0050] FIG. 3 more particularly depicts aspects of a 4G LTE deployment for a mobile network operator (MNO), which may correspond to deployment 200, according to some example implementations. This deployment is at times referred to as the evolved packet system (EPS) 300. As shown, the EPS includes an EPC 302, and an E-UTRAN 304 with one or more eNBs 306 configured to connect UEs 308 to the E-UTRAN to thereby access the EPC. The EPC may include, for example, a mobility management entity (MME) 310, a home subscriber server (HSS) 312, a serving gateway (SGW) 314, a home subscriber server (HSS) 314, a packet data network gateway (PGW) 316, and the like.

[0051] The MME 310 handles the control plane within the EPC 302. For example, the MME handles the signaling related to mobility and security for E-UTRAN access. The MME is responsible for tracking and paging the UE 308 in idle mode. The MME may also provide the control plane function for mobility between different radio access technologies (e.g., LTE and 3G). The HSS is a master user database that stores subscription-related information such as subscriber profiles associated with the UE. The HSS also performs authentication and authorization of users and provides location and Internet Protocol (IP) information for the user.

[0052] The SGW 314 and PGW 316 handle the user plane. The SGW and PGW transport data traffic between the UE 308 and external data networks (DN or Packet Data Network (PDN)). The SGW is the point of interconnect between the radio side and EPC 302, and serves the UE by routing incoming and outgoing IP packets. The SGW is also the anchor point for the intra-LTE mobility (i.e., in case of handover between eNBs 306), and between LTE and 3G or other 3GPP access. The PGW is the point of interconnect between the EPC and external data networks (i.e., point of ingress or egress for a data network), and routes packets to and from the data network.

[0053] FIG. 4 more particularly depicts aspects of a 5G deployment for a MNO, which may correspond to deployment 200, according to some example implementations. This deployment is at times referred to as the 5G system (5GS) 400. As shown, the 5GS includes a 5GC 402, and NG-RAN 404 with one or more gNBs 406 configured to connect UEs 408 to the NG-RAN to thereby access the 5GC. The 5GC may include a number of network functions (NFs) divided between the control plane and the user plane. In particular, the 5GC may include, for example, an access and mobility management function (AMF) 410, a unified data management (UDM) 412, a policy control function (PCF) 414, a session management function (SMF) 416, a user plane function (UPF) 418, and the like.

[0054] In the control plane, the AMF 410 is configured to provide UE-based authentication, authorization, mobility management, etc. The UDM 412 processes credentials, location management, subscription management, and the like. The UDM stores data including user subscription data, such as subscription identifiers, security credentials, access and mobility related subscription data, and session related subscription data. The PCF 414 is responsible for policy enforcement and management, controlling Quality of Service (QoS), charging, and resource allocation for subscribers. The PCF may facilitate efficient resource utilization, optimizing network performance, and delivering a quality user experience.

[0055] The SMF 416 is configured to provide various functionality including session management (SM), UE Internet Protocol (IP) address allocation and management, selection and control of UPF(s) 418, control part of policy application and QoS, lawful intercept, termination of SM parts of non-access stratum (NAS) messages, Downlink Data Notification (DNN), roaming functionality, handle local enforcement to apply QoS for Service Level Agreements (SLAs), charging data collection and charging interface, etc. If the UE 408 has multiple sessions, different SMFs may be allocated to each session to manage them individually and possibly provide different functionalities per session.

[0056] The UPF 418 supports various user plane operations and functionalities, such as packet routing and forwarding, traffic handling (e.g., QoS enforcement), an anchor point for intra-RAT / inter-RAT mobility (when applicable), packet inspection and policy rule enforcement, lawful intercept (UP collection), traffic accounting and reporting, etc. Similar to the PGW 316 in the EPC 302, the UPF is the point of interconnect between the 5GC and external data networks (i.e., point of ingress or egress for a data network), and routes packets to and from the data network. As explained above, data network may be configured to provide Internet access, operator services, 3rd party services, etc.

[0057] FIG. 5 schematically shows an architecture 500 to support inter-system mobility between the EPS 300 and the 5GS 400. For EPS interworking, an SMF 416 may be co-located with a PGW control plane (PGW-C). The PGW-C represents the control plane part of the PGW 316. In some of the following examples, the SMF located with the PGW-C may be labeled as SMF+PGW-C 502. The SMF+PGW-C is a combined network entity that acts as an SMF for 5GC peers, and as a PGW-C for EPC peers. In other examples, the SMF and PGW are deployed as separate network entities, as shown in FIGS. 3 and 4. An N26 interface may be supported between a MME 310 and an AMF 410 for inter-system mobility, although inter-system mobility may also be supported without an N26 interface between the MME and the AMF.

[0058] On the EPS side of FIG. 5, a UE 504 (e g., UE 308, 408) is connected to an E-UTRAN 304. The E-UTRAN is connected to the MME 310. The MME is connected to a SGW 314 by an SI 1 interface, and the MME is connected to a HSS + UDM 506 via a S6a interface. The SGW 314 is connected to the SMF+PGW-C 502 via an S5-C interface, and the SGW is connected to a UPF+PGW-U 508 via an S5-U interface.

[0059] Similar to SMF+PGW-C 502, the HSS+UDM 506 is a combined network entity in which the HSS 312 is co-located with the UDM 412. The HSS+UDM acts as an HSS for EPC peers, and acts as a UDM for 5GC peers. In other examples, the HSS and UDM are deployed as separate network entities, as shown in FIGS. 3 and 4. Likewise, the UPF+PGW-U 508 is a combined network entity in which the UPF 418 is co-located with a PGW user plane (PGW-U), which represents the user plane part of the PGW 316. The UPF+PGW-U acts as a UPF for 5GC peers, and acts as a PGW-U for EPC peers. In other examples, the UPF and PGW are deployed as separate network entities.

[0060] On the 5GS side, a UE 504 (e.g., UE 308, 408) is connected to an NG-RAN 404. The further UE is also connected to the AMF 410 via an N1 interface. The NG-RAN is also connected to the AMF via an N2 interface. The NG-RAN is connected to the UPF+PGW-U 508 via an N3 interface. The AMF is connected to the SMF+PGW-C 502 via an Nil interface. The AMF is also connected to a PCF 414, and the AMF is connected to the HSS+UDM 506 via an N8 interface.

[0061] The UPF+PGW-U 508 is connected to the SMF+PGW-C 502 via N4 interface. The SMF+PGW-C is connected to the PCF 414 via an N7 interface. And the SMF+PGW-C is connected to the HSS+UDM 506 via an N10 interface.

[0062] A UE 504 may need to register with the EPC 302 / 5GC 402 to establish UE context in the network and receive services that require registration. In order to interwork between EPC and 5GC, a UE that supports both 5GC and EPC NAS may operate in a single-registration mode or a dual-registration mode.

[0063] In single-registration mode, the UE 504 may have only one active mobility management (MM) state (either registration management (RM) state in 5GC 402 or EPS mobility management (EMM) state in EPC 302), and the UE may be in either 5GC NAS mode (when connected to 5GC) or EPC NAS mode (when connected to EPC). The UE may maintain a single coordinated registration for 5GC and EPC, and map between respective globally unique temporary identifiers (GUTIs) during mobility between EPC and 5GC. To enable re-use of a previously established 5G security context when returning to 5GC, the UE may also keep the native 5G-GUTI and the native 5G security context when moving from 5GC to EPC.

[0064] In dual-registration mode, the UE 504 may handle independent registrations for the 5GC 402 and the EPC 302 using separate RRC connections. In dual-registration mode, the UE may independently maintain a 5G-GUH and an EPS-GUTI. The UE may provide its native 5G-GUTI (if previously allocated) for registrations towards the 5GC, and provide its native EPS-GUTI (if previously allocated) for attach / tracking area update (TAU) towards the EPC. In dual-registration mode, the UE may be registered to the 5GC only, the EPC only, or to both the 5GC and the EPC.

[0065] When the UE 504 (e.g., UE 308) moves from EPS 300 to 5GS 400, there may be scenarios in which UE context may need to be retained in both EPC 302 and 5GC 402 when the UE 504 (e.g., UE 308) moves from EPS 300 to 5GS 400. In this regard, there may be a need to retain an MME registration in the EPS (in the HSS 312) for the UE in order to preserve the UE context in the MME 310 for some time after the UE moves to the 5GS in case the UE would quickly move back to the EPS. One of these scenarios is when the UE is in single-registration mode, the N26 interface (between the AMF 410 and MME) is not supported, and the UE performs a registration (mobility-registration) procedure for inter-system mobility from the EPS to 5GS m which the UE indicates that an MME registration exists in the EPS (in the HSS) for the UE. When this MME registration exists, the UE may be viewed as EMM registered.

[0066] A solution currently does not exist to prevent cancelation of the MME registration by the HSS 314 in the above scenario. That is, when EPS-5GS interworking with the N26 interface unsupported, and a UE 504 operates in single-registration mode, during the UE mobility from EPS 300 to 5GS 400, there is currently no solution to prevent the cancelation of the MME registration by the HSS 312. This results in the 5GS systematically canceling the MME registration in this use case, and accordingly to the MME 310 deleting the corresponding UE context. This in turn results in the absence of an available UE context at the MME if the UE moves back to the MME (EPS) shortly after the EPS to 5GS mobility, preventing seamless service continuity.

[0067] Some example implementations of the present disclosure provide a solution to prevent the cancelation of the MME registration by the UDM 412 and HSS 312 (or HSS+UDM 506) when EPS-5GS interworking with the N26 interface unsupported, the UE 504 (e.g., UE 308) is operating in single-registration mode, and the AMF 410 receives a mobility registration request from the UE indicating that the UE is EMM registered (e.g., by a UE status information element (IE) in the mobility registration request). In some examples, the AMF may provide an indication to the UDM (which, in turn, communicates with the HSS) to prevent cancelation of the MME registration by the HSS. The decision to trigger or avoid cancelation of the MME registration may depend on receipt of this indication by the UDM.

[0068] More particularly, for example, in some scenarios when EPS-5GS interworking with the N26 interface not supported, the UE 504 is operating in singleregistration mode, and the AMF 410 receives a mobility registration request from the UE containing the UE status IE indicating that the UE is in the EMM-registered state. In these scenarios, the AMF may send a UECMRegistrationRequest to the UDM 412 with an attribute (e.g., Eps5gsmobilityWithoutN26IwkInd) to indicate that the UE is performing an EPS 300 to 5GS 400 mobility in single-registration mode without the N26 interface. Upon receiving the indication from the AMF, the UDM may send a Nhss^UECM^SNDeregistration to the HSS 312 with information to not cancel the EPS registration towards the MME 310 (e.g., EPS5GSMOBILITYWITHOUTN26JWK). Based on the reception or not of the indication / information, the UDM / HSS may determine whether or not to cancel the EPS registration towards the MME.

[0069] According to some example implementations, then, an AMF 410 may receive a (first) registration request message from a UE 504 (e.g., UE 308) operating in a singleregistration mode. The first registration request message may be for inter-system mobility of the UE from the EPS 300 to the 5GS 400 (a mobility registration request), and indicate a MME registration exists in the EPS (in the HSS 312) for the UE. In this regard, in some examples, the registration request message from the UE may includes a UE status IE set to indicate the MME registration exists in the EPS for the UE (UE status IE = EMM-Registered). The AMF may determine that the AMF is not configured with an interface (N26 interface) towards a MME 310 in the EPS 300.

[0070] Based on the registration request message and the determination that the (N26) interface is not configured, the AMF 410 may perform a registration procedure with a UDM 412 (or HSS+UDM 506) in the 5GS 400 to register the AMF 410 in the UDM for the UE 504. In this regard, the AMF may send a (second) registration request message (Nudm UECM Registration Request) to the UDM to register the AMF in the UDM for the UE 504.

[0071] The registration request from the AMF 410 may include a (first) indication to instruct a HSS 312 (or HSS+UDM 506) in the EPS 300 not to cancel the MME registration. In some examples, this registration request message includes an indication the UE is operating in the single-registration mode, and an indication the registration request message is related to the inter-system mobility of the UE from the EPS 300 to the 5GS 400. In various examples, the indication the UE is opeating in the single-registration mode may be a dual-registration flag (drFlag) that is not set or set to false, or that is not included in the registration request message. The indication the registration request message is related to the inter-system mobility of teh UE may be an initial registration flag that is not set or set to false, or that is not included in the registration request message. The registration request message may also include an IE (e.g., eps5gsmobilityWithoutN26IwkInd) set with the indication to instruct the HSS 312 not to cancel the MME registration for the UE.

[0072] The UDM 412 may receive the registration request message from the AMF 410, and register the AMF in the UDM for the UE 504 based on the registration request message. The UDM may send a deregistration request message (Nhss^UECM^SNDeregistration) to the HSS 312 for support node deregistration. The deregistration request message from the UDM may include an (second) indication not to cancel the MME registration in the HSS for the UE . In some examples, the indication in the deregistration request message may be provided by a deregistration reason (DeregistrationReason) that is due to EPS 300 to 5GS 400 mobility without the (N26) interface between the AMF in the 5GS and MME 310 in the EPS (e.g., EPS5GSMOB1I^

[0073] The HSS 312 may receive the deregistration request message from the UDM 412 (or HSS+UDM 506), and make a determination not to cancel the MME registration in the HSS for the UE 504 based on the indication not to cancel the MME registration in the deregistration request message. In examples in which the UE also has GERAN / UTRAN access, the HSS may have a serving general packet radio service (GPRS) support node (SGSN) registration in the HSS 312 for the UE 504. In some of these examples, the indication in the degregistration request may also be to cancel the SGSN registration in the HSS for the UE. The HSS may cancel the SGSN registration in the HSS for the UE based on the indication in the deregistration request message. The HSS may then respond to the UDM with a deregistration response message.

[0074] To further illustrate some exampe implementations, FIG. 6 is a signaling chart 600 of UE mobility from EPS 300 to 5GS 400, according to some example implementations. As shown, the a UE 504 of a subscriber registers to the EPS. The UE at steps 601 and 602 moves from EPS to 5GS. The UE operates m single-registration mode, and EPS-5GS interworking is supported without an N26 interface between the MME 310 and AMF 410. The UE indicates to the AMF that it is EMM registered.

[0075] The AMF 410 at step 603 sends a NudmUECMRegistration request to the UDM 412 for 3GPP access containing a subscription permanent identifier (SUPI) of the subscriber. If EPS interworking without N26 is supported, and the UE status IE is present with 'EMM-REGISTERED ' value m the UE’s mobility registration request, the AMF includes the “Eps5gsmobilityWithoutN26IwkInd” IE set to true in the Nudm UECM Registration request to the UDM. The UDM at step 604 sends a Nudm UECM Registration response to the AMF.

[0076] The UDM 412 at step 605 send a Nhss^UECM^SNDeregistration request message to the HSS 312. The request message includes DeregistrationReason set to EPS_5GS_MOBILITY_WITHOUT_N26_IWK; and as a result, the HSS does not cancel the MME registration in the HSS for the UE 504. The HSS at step 606 sends a Nhss UECM SNDeregistration response message to the UDM.

[0077] FIG. 7 is a flowchart illustrating various steps in a method 700 performed by an access and mobility management function (AMF) of a 5G system (5GS), according to various example implementations. The method includes receiving a first registration request message from a user equipment (UE) operating in a single-registration mode, as shown at block 702. The first registration request message is for inter-system mobility of the UE from an evolved packet system (EPS) to the 5GS, and the first registration request message indicates a mobility management entity (MME) registration exists in the EPS for the UE. The method includes making a determination that the AMF is not configured with an interface towards a MME in the EPS, as shown at block 704. And based on the registration request message and the determination, the method includes performing a registration procedure with a unified data management (UDM) in the 5GS to register the AMF in the UDM for the UE, as shown at block 706. The registration procedure includes a second registration request message sent by the AMF to the UDM with an indication to instruct a home subscriber server (HSS) in the EPS not to cancel the MME registration.

[0078] In some examples, the first registration request message from the UE includes a UE status information element set to indicate the MME registration exists in the EPS for the UE.

[0079] In some examples, the second registration request message includes an indication the UE is operating in the single-registration mode. In some of these examples, the second registration request message also includes an indication the second registration request message is related to the inter-system mobility of the UE from the EPS to the 5GS.

[0080] In some examples, the second registration request message includes an information element set with the indication to instruct the HSS not to cancel the MME registration for the UE.

[0081] FIG. 8 is a flowchart illustrating various steps in a method 800 performed by unified data management (UDM) of a 5G system (5GS), according to various example implementations. The method includes receiving a registration request message from an access and mobility management function (AMF) in the 5GS in connection with intersystem mobility of a user equipment (UE) from an evolved packet system (EPS) to the 5GS, as shown at block 802. The registration request message includes a first indication to instruct a home subscriber server (HSS) in the EPS not to cancel a mobility management entity (MME) registration in the HSS for the UE operating m a singleregistration mode. The method includes registering the AMF in the UDM for the UE based on the registration request message, as shown at block 804. And the method includes sending a deregistration request message to the HSS, the deregistration request message including a second indication not to cancel the MME registration in the HSS for the UE, as shown at block 806.

[0082] In some examples, the registration message is received at block 802 from the AMF that is not configured with an interface towards a MME in the EPS.

[0083] In some examples, the registration request message includes an indication the UE is operating in the single-registration mode, In some of these examples, the registration request message also includes an indication the registration request message is related to the inter-system mobility of the UE from the EPS to the 5GS.

[0084] In some examples, the registration request message includes an information element set with the indication to instruct the HSS not to cancel the MME registration in the HSS for the UE.

[0085] FIGS. 9A and 9B are flowcharts illustrating various steps in a method 900 performed by home subscriber server (HSS) of an evolved packet system (EPS), according to various example implementations. The method includes receiving a deregistration request message from a unified data management (UDM) in a 5G system (5GS) in connection with inter-system mobility of a user equipment (UE) from the EPS to the 5GS, as shown at block 902 of FIG. 9A. The deregistration request message includes an indication not to cancel a mobility management entity (MME) registration in the HSS for the UE operating in a single-registration mode. The method includes making a determination not to cancel the MME registration in the HSS for the UE based on the indication m the deregistration request message, as shown at block 904. And the method includes responding to the UDM with a deregistration response message, as shown at block 906.

[0086] In some examples, the indication is provided by a deregistration reason that is due to EPS to 5GS mobility without an interface between an access and mobility management function (AMF) in the 5GS and a MME in the EPS.

[0087] In some examples, the indication in the deregistration request message is also to cancel a serving general packet radio service (GPRS) support node (SGSN) registration in the HSS for the UE. In some of these examples, the method 900 further includes canceling the SGSN registration in the HSS for the UE based on the indication in the deregistration request message, as shown at block 908 of FIG. 9B.

[0088] According to example implementations of the present disclosure, a telecommunications system 100 or PLMN 102, and its components such as a UE 110, 308, 408, 504, CN 106, RAN 108, radio access node 202, EPC 302, E-UTRAN 304, eNB 306, MME 310, HSS 312, SGW 314, PGW 316, 5GC 402, NG-RAN 404, gNB 406, AMF 410, UDM 412, PCF 414, SMF 416, UPF 418, SMF+PGW-C 502, HSS+UDM 506 and / or UPF+PGW-U 508, may be implemented by various means. Means for implementing the system and its components may include hardware, firmware, software, or combinations thereof. In some examples, one or more apparatuses may be configured to function as or otherwise implement the system and its components shown and described herein. In examples involving more than one apparatus, the respective apparatuses may be connected to or otherwise in communication with one another in a number of different manners, such as directly or indirectly via a wired or wireless network or the like.

[0089] According to some example implementations, at least some of the method 700 described with respect to FIG. 7 may be carried out by an apparatus comprising means for performing functions corresponding steps of the method. Similarly, at least some of the method 800 described with respect to FIG. 8 may be carried out by an apparatus comprising means for performing functions corresponding steps of the method. Likewise, at least some of the method 900 described with respect to FIGS. 9Aand 9B may be carried out by an apparatus comprising means for performing functions corresponding steps of the method. Examples of a suitable apparatus may include an AMF, UDM, HSS or any suitable apparatus, such as a server, host or node.

[0090] FIG. 10 illustrates an apparatus 1000 in which means for performing various functions includes hardware, alone or under direction of one or more computer programs from a computer-readable storage medium or other memory, such as computer memory, according to some example implementations of the present disclosure. The apparatus may include one or more of each of a number of components such as, for example, processing circuitry 1002 connected to computer-readable storage medium or other memory 1004.

[0091] The processing circuitry 1002 may be composed of one or more processors alone or in combination with one or more computer-readable storage media. The processing circuitry is generally any piece of computer hardware that is capable of processing information such as, for example, data, computer programs and / or other suitable electronic information. The processing circuitry is composed of a collection of electronic circuits some of which may be packaged as an integrated circuit or multiple interconnected integrated circuits (an integrated circuit at times more commonly referred to as a “chip”). The processing circuitry may be configured to execute computer programs, which may be stored onboard the processing circuitry or otherwise stored in the memory 1004 (of the same or another apparatus).

[0092] The processing circuitry 1002 may be a number of processors, a multi-core processor or some other type of processor, depending on the particular implementation. Further, the processing circuitry may be implemented using a number of heterogeneous processor systems in which a main processor is present with one or more secondary processors on a single chip. As another illustrative example, the processing circuitry may be a symmetric multi-processor system containing multiple processors of the same type. In yet another example, the processing circuitry may be embodied as or otherwise include one or more ASICs, FPGAs or the like. Thus, although the processing circuitry may be capable of executing a computer program to perform one or more functions, the processing circuitry of various examples may be capable of performing one or more functions without the aid of a computer program. In either instance, the processing circuitry may be appropriately programmed to perform functions or operations according to example implementations of the present disclosure.

[0093] The memory 1004 is generally any piece of computer hardware that is capable of storing information such as, for example, data, computer programs, instructions 1006 (e.g., computer-readable program code) and / or other suitable information either on a temporary basis and / or a permanent basis. The memory may include volatile and / or nonvolatile memory, and may be fixed or removable. Examples of suitable memory include recording media, random access memory (RAM), read-only memory (ROM), a hard drive, a flash memory, a thumb drive, a removable computer diskette, an optical disk or some combination thereof.

[0094] The memory 1004 is a non-transitory device capable of storing information. One example of a suitable memory is a computer-readable storage medium, which is distinguishable from a computer-readable transmission medium capable of carrying information from one location to another. Examples of suitable computer-readable transmission media comprise electronic carrier signals, telecommunications signals, or some combination thereof. As used herein, the term “non-transitory” is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM versus ROM). A computer-readable medium as described herein generally refers to a computer-readable storage medium or computer-readable transmission medium. A computer-readable medium is any entity or device capable in which information, such as one or more computer programs or portions thereof, may be stored and carried.

[0095] In addition to the memory 1004 (e.g., computer-readable storage medium), the processing circuitry 1002 may also be connected to one or more interfaces for displaying, transmitting and / or receiving information. The interfaces may include a communications interface 1008 and / or one or more user interfaces (e.g., display, user input interface). The communications interface may be configured to transmit and / or receive information, such as to and / or from other apparatus(es), network(s) or the like. The communications interface may be configured to transmit and / or receive information by physical (wired) and / or wireless communications links. Examples of suitable communication interfaces include a network interface controller (NIC), wireless NIC (WNIC) or the like.

[0096] Execution of the instructions 1006 by the processing circuitry 1002, or storage of the instructions in the memory 1004, supports combinations of operations for implementing example implementations of the present disclosure. In this manner, an apparatus 1000 may comprise at least one processing circuitry and at least one memory coupled to the at least one processing circuitry, where the at least one processing circuitry is configured to execute instructions stored in the at least one memory. It will also be understood that one or more functions, and combinations of functions, may be implemented by special purpose hardware-based computer systems and / or processing circuitry which perform the specified functions, or combinations of special purpose hardware and program code instructions.

[0097] Some example implementations of the present disclosure may also be carried out in the form of a computer process defined by one or more computer programs or portions thereof. Example implementations of the present disclosure may be carried out by executing at least one portion of a computer program comprising instructions. The computer program may be in source code form, object code form, or in some intermediate form. The computer program may be stored in a computer-readable medium that is readable by a computer, processing circuitry or other suitable apparatus. As indicated above, for example, the computer program may be stored in a memory, such as a computer-readable storage medium. Additionally or alternatively, for example, the computer program may be stored in a computer-readable transmission medium. The coding of software for carrying out example implementations of the present disclosure is well within the scope of a person of ordinary skill in the art.

[0098] As will be appreciated, any suitable instructions may be loaded onto a computer, a processing circuitry or other programmable apparatus from a memory or a computer-readable medium (e.g., computer-readable storage medium, computer-readable transmission medium) to produce a particular machine, such that the particular machine becomes a means for implementing the functions specified herein. The instructions may also be stored in a computer-readable medium that can direct a computer, a processing circuitry or other programmable apparatus to function in a particular manner to thereby generate a particular machine or particular article of manufacture. In some examples, the instructions stored in the computer-readable medium may produce an article of manufacture, where the article of manufacture becomes a means for implementing functions described herein. The instructions may be retrieved from a computer-readable medium and loaded into a computer, processing circuitry or other programmable apparatus to configure the computer, processing circuitry or other programmable apparatus to execute operations to be performed on or by the computer, processing circuitry or other programmable apparatus.

[0099] Retrieval, loading and execution of instructions comprising program code instructions may be performed sequentially such that one instruction is retrieved, loaded and executed at a time. In some example implementations, retrieval, loading and / or execution may be performed in parallel such that multiple instructions are retrieved, loaded, and / or executed together. Execution of the program code instructions may produce a computer-implemented process such that the instructions executed by the computer, processing circuitry or other programmable apparatus provide operations for implementing functions described herein.

[0100] As explained above and reiterated below, the present disclosure includes, without limitation, the following example implementations.

[0101] Clause 1. An apparatus implemented by an access and mobility management function (AW) of a 5G system (5GS), the apparatus comprising: at least one memory configured to store instructions; and at least one processing circuitry configured to access the at least one memory, and execute the instructions to cause the apparatus to at least: receive a first registration request message from a user equipment (UE) operating in a single-registration mode, the first registration request message for inter-system mobility of the UE from an evolved packet system (EPS) to the 5GS, the first registration request message indicating a mobility management entity (MME) registration exists in the EPS for the UE; make a determination that the AMF is not configured with an interface towards a MME in the EPS; and based on the registration request message and the determination, perform a registration procedure with a unified data, management (UDM) in the 5GS to register the AMF in the UDM for the UE, the registration procedure including a second registration request message sent by the AMF to the UDM with an indication to instruct a home subscriber server (HSS) in the EPS not to cancel the MME registration.

[0102] Clause 2. The apparatus of clause 1, wherein the first registration request message from the UE includes a. UE status information element set to indicate the MME registration exists m the EPS for the UE.

[0103] Clause 3. The apparatus of clause 1 or clause 2, wherein the second registration request message includes an indication the UE is operating in the singleregistration mode, and an indication the second registration request message is related to the inter-system mobility of the UE from the EPS to the 5GS.

[0104] Clause 4 The apparatus of any of clauses 1 to 3, wherein the second registration request message includes an information element set with the indication to instruct the HSS not to cancel the MMF registration for the UE.

[0105] Clause 5. An apparatus implemented by an access and mobility management function (AMP) of a 5G system (5GS), the apparatus comprising: means for receiving a first registration request message from an user equipment (UE) operating in a singleregistration mode, the first registration request message for inter-system mobility of the UE from an evolved packet system (EPS) to the 5GS, the first registration request message indicating a mobility’ management entity’ (AIME) registration exists in the EPS for the UE; means for making a determination that the AMF is not configured with an interface towards a MME in the EPS; and based on the registration request message and the determination, means for performing a registration procedure with an unified data management (UDM) in the 5GS to register the AMF in the UDM for the UE, the registration procedure including a second registration request message sent by the AMF to the UDM with an indication to instruct a home subscriber server (HSS) in the EPS not to cancel the MME registration.

[0106] Clause 6. The apparatus of clause 5, wherein the first registration request message from the UE includes a UE status information element set to indicate the MME registration exists in the EPS for the UE.

[0107] Clause 7. The apparatus of clause 5 or clause 6, wherein the second registration request message includes an indication the UE is operating in the single-registration mode, and an indication the second registration request message is related to the inter-system mobility of the UE from the EPS to the 5GS.

[0108] Clause 8. The apparatus of any of clauses 5 to 7, wherein the second registration request message includes an information element set with the indication to instruct the HSS not to cancel the MME registration for the UE.

[0109] Clause 9. A method performed by an access and mobility management function (AMF) of a 5G system (5GS), the method comprising: receiving a first registration request message from a user equipment (UE) operating in a single-registration mode, the first registration request message for inter-system mobility of the UE from an evolved packet system (EPS) to the 5GS, the first registration request message indicating a mobility management entity (MME) registration exists in the EPS for the UE; making a determination that the AMF is not configured with an interface towards a MME in the EPS; and based on the registration request message and the determination, performing a registration procedure with a unified data management (UDM) in the 5GS to register the AMF in the UDM for the UE, the registration procedure including a second registration request message sent by the AMF to the UDM with an indication to instruct a home subscriber server (HSS) in the EPS not to cancel the MME registration.

[0110] Clause 10. The method of clause 9, wherein the first registration request message from the UE includes a UE status information element set to indicate the MME registration exists m the EPS for the UE.

[0111] Clause 11. The method of clause 9 or clause 10, wherein the second registration request message includes an indication the UE is operating in the singleregistration mode, and an indication the second registration request message is related to the inter-system mobility of the UE. from the EPS to the 5GS.

[0112] Clause 12 The method of any of clauses 9 to 11, wherein the second registration request message includes an information element set with the indication to instruct the HSS not to cancel the MME registration for the UE.

[0113] Clause 13. A computer-readable storage medium that is non-transitory and has instructions stored therein that, in response to execution by at least one processing circuitry', causes an access and mobility management function (AMF) of a 5G system (5GS) to at least: receive a first registration request message from a user equipment (UE) operating in a single-registration mode, the first registration request message for intersystem mobility of the UE from an evolved packet system (EPS) to the 5GS, the first registration request message indicating a. mobility management entity (MME) registration exists in the EPS for the UE; make a determination that the AMF is not configured with an interface towards a MME in the EPS; and based on the registration request message and the determination, perform a registration procedure with a unified data management (UDM) in the 5GS to register the AMF in the UDM for the UE, the registration procedure including a second registration request message sent by the AMF to the UDM with an indication to instruct a home subscriber server (HSS) in the EPS not to cancel the MME registration.

[0114] Clause 14. The computer-readable storage medium of clause 13, wherein the first registration request message from the UE includes a UE status information element set to indicate the MME registration exists in the EPS for the UE.

[0115] Clause 15. The computer-readable storage medium of clause 13 or clause 14, wherein the second registration request message includes an indication the UE is operating in the single-registration mode, and an indication the second registration request message is related to the inter-system mobility of the UE from the EPS to the 5GS.

[0116] Clause 16. The computer-readable storage medium of any of clauses 13 to 15, wherein the second registration request message includes an information element set with the indication to instruct the HSS not to cancel the MME registration for the UE.

[0117] Clause 17. A apparatus comprising means for performing the method of any of clauses 9 to 12.

[0118] Clause 18. A computer-readable medium comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of clauses 9 to 12.

[0119] Clause 19. A computer-readable storage medium comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of clauses 9 to 12.

[0120] Clause 20. A computer program comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of clauses 9 to 12.

[0121] Clause 21. An apparatus implemented by unified data management (UDM) of a 5G system (5GS), the apparatus comprising: at least one memory configured to store instructions; and at least one processing circuitry configured to access the at least one memory, and execute the instructions to cause the apparatus to at least: receive a registration request message from an access and mobility management function (AMF) in the 5GS in connection with inter-system mobility of a user equipment (UE) from an evolved packet system (EPS) to the SOS, the registration request message including a first indication to instruct a home subscriber server (HSS) in the EPS not to cancel a mobility management entity' (MME) registration in the HSS for the UE operating in a single-registration mode; register the AMF in the UDM for the UE based on the registration request message, and send a deregistration request message to the HSS, the deregistration request message including a second indication not to cancel the MME registration in the HSS for the UE.

[0122] Clause 22. The apparatus of clause 21, wherein the registration message is received from the AMF that is not configured with an interface towards a MME in the EPS.

[0123] Clause 23. The apparatus of clause 21 or clause 22, wherein the registration request message includes an indication the UE is operating in the single-registration mode, and an indication the registration request message is related to the inter-system mobility' of the UE from the EPS to the 5GS.

[0124] Clause 24 The apparatus of any of clauses 21 to 23, wherein the registration, request message includes an information element set with the indication to instruct the HSS not to cancel the MME registration in the HSS for the UE.

[0125] Clause 25. An apparatus implemented by unified data management (UDM) of a 5G system (5GS), the apparatus comprising: means for receiving a registration request message from an access and mobility' management function (AMF) in the 5GS in connection with inter-system mobility of an user equipment (UE) from an evolved packet system (EPS) to the 5GS, the registration request message including a first indication to instruct a home subscriber server (HSS) in the EPS not to cancel a mobility management entity (MME) registration in the HSS for the UE operating in a single-registration mode; means for registering the AMF in the UDM for the UE based on the registration request message; and means for sending a deregistration request message to the HSS, the deregistration request message including a second indication not to cancel the MME registration in the HSS for the UE,

[0126] Clause 26. The apparatus of clause 25, wherein the registration message is received from the AMF that is not configured with an interface towards a MME in the EPS.

[0127] Clause 27. The apparatus of clause 25 or clause 26, wherein the registration request message includes an indication the UE is operating in the single-registration mode, and an indication the registration request message is related to the inter-system mobility of the UE from the EPS to the 5GS.

[0128] Clause 28. The apparatus of any of clauses 25 to 27, wherein the registration request message includes an information element set with the indication to instruct the HSS not to cancel the MME registration in the HSS for the UE.

[0129] Clause 29. A method performed by unified data management (UDM) of a 5G system (5GS), the method comprising: receiving a registration request message from an access and mobility management function (AMF) in the 5GS m connection with inter system mobility of a user equipment (UE) from an evolved packet system (EPS) to the 5GS, the registration request message including a first indication to instruct a home subscriber server (HSS) in the EPS not to cancel a mobility management entity (MME) registration in the HSS for the UE operating in a single-registration mode; registering the AMF in the UDM for the LIE based on the registration request message; and sending a deregistration request message to the HSS, the deregistration request message including a second indication not to cancel the MME registration in the HSS for the UE,

[0130] Clause 30. The method of clause 29, wherein the registration message is received from the AMF that is not configured with an interface towards a MME in the EPS.

[0131] Clause 31. The method of clause 29 or clause 30, wherein the registration request message includes an indication the UE is operating in the single-registration mode, and an indication the registration request message is related to the inter-system mobility of the UE from the EPS to the 5GS.

[0132] Clause 32. The method of any of clauses 29 to 31, wherein the registration request message includes an information element set with the indication to instruct the HSS not to cancel the MME registration m the HSS for the UE.

[0133] Clause 33. A computer-readable storage medium that is non-transitory and has instructions stored therein that, in response to execution by at least one processing circuitry, causes a unified data, management (UDM) of a 5G system (5GS) to at least: receive a registration request message from an access and mobility management function (AMF) in the 5GS in connection with inter-system mobility of a user equipment (UE) from an evolved packet system (EPS) to the 5GS, the registration request message including a first indication to instruct a home subscriber server (HSS) in the EPS not to cancel a mobility management entity (MME) registration in the HSS for the UE operating in a single-registration mode; register the AMF in the UDM for the UE based on the registration request message; and send a deregistration request message to the HSS, the deregistration request message including a second indication not to cancel the AIME registration in the HSS for the UE.

[0134] Clause 3-4. The computer-readable storage medium of clause 33, wherein the registration message is received from the AMF that is not. configured with an interface towards a MME m the EPS.

[0135] Clause 35. The computer-readable storage medium of clause 33 or clause 34, wherein the registration request message includes an indication the UE is operating in the single-registration mode, and an indication the registration request message is related to the inter-system mobility of the UE from the EPS to the 5GS.

[0136] Clause 36. The computer-readable storage medium of any of clauses 33 to 35, wherein the registration request message includes an information element set with the indication to instruct the HSS not to cancel the MME registration in the HSS for the UE.

[0137] Clause 37. A apparatus comprising means for performing the method of any of clauses 29 to 32.

[0138] Clause 38. A computer-readable medium comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of clauses 29 to 32.

[0139] Clause 39. A computer-readable storage medium comprising instructions that, in response to execution by at least one processing circuitry', causes an apparatus to perform the method of any of clauses 29 to 32.

[0140] Clause 40. A computer program comprising instructions that, in response to execution by at least, one processing circuitry, causes an apparatus to perform the method of any of clauses 29 to 32. [0141 ] Clause 41. An apparatus implemented by a home subscriber server (HSS) of an evolved packet system (EPS), the apparatus comprising: at least one memory configured to store instructions; and at least one processing circuitry configured to access the at least one memory', and execute the instructions to cause the apparatus to at least: receive a deregistration request message from a unified data management (UDM) m a 5G system (5GS) in connection with inter-system mobility' of a user equipment (UE) from the EPS to the 5GS, the deregistration request message including an indication not to cancel a mobility management entity’ (MME) registration m the HSS for the UE operating in a single-registration mode; make a determination not to cancel the MME registration in the HSS for the UE based on the indication in the deregistration request message: and respond to the UDM with a deregistration response message.

[0142] Clause 42. The apparatus of clause 41, wherein the indication is provided by a deregistration reason that is due to EPS to 5GS mobility without an interface between an access and mobility management function (AMF) in the 5GS and a MME in the EPS.

[0143] Clause 43. The apparatus of clause 41 or clause 42, wherein the indication in the deregistration request message is also to cancel a serving general packet radio service (GPRS) support node (SGSN) registration in the HSS for the UE, and wherein the at least one processing circuitry is configured to execute the instructions to cause the apparatus to further cancel the SGSN registration in the HSS for the UE based on the indication in the deregistration request message.

[0144] Clause 44. An apparatus implemented by a home subscriber server (HSS) of an evolved packet system (EPS), the apparatus comprising: means for receiving a deregistration request message from an unified data management (UDM) m a 5G system (5GS) in connection with inter-system mobility of an user equipment (UE) from the EPS to the 5GS, the deregistration request message including an indication not to cancel a mobility management entity (MME) registration m the HSS for the UE operating in a single-registration mode; means for making a determination not to cancel the MME registration in the HSS for the UE based on the indication in the deregistration request message; and means for responding to the UDM with a deregistration response message.

[0145] Clause 45. The apparatus of clause 44, wherein the indication is provided by a deregistration reason that is due to EPS to 5GS mobility without an interface between an access and mobility’ management function (AMF) in the 5GS and a MME in the EPS.

[0146] Clause 46. The apparatus of clause 44 or clause 45, wherein the indication in the deregistration request message is also to cancel a serving general packet radio service (GPRS) support node (SGSN) registration in the HSS for the UE, and wherein the apparatus further comprises means for canceling the SGSN registration in the HSS for the UE based on the indication in the deregistration request message.

[0147] Clause 47. A method performed by a home subscriber server (HSS) of an evolved packet system (EPS), the method comprising: receiving a deregistration request message from a unified data management (UDM) in a 5G system (5GS) in connection with inter-system mobility of a user equipment (UE.) from the EPS to the 5GS, the deregistration request message including an indication not to cancel a mobility management entity (MME) registration in the HSS for the UE operating in a singleregistration mode; making a determination not to cancel the MME- registration m the HSS for the UE- based on the indication in the deregistration request message; and responding to the UDM with a deregistration response message. [014S] Clause 48. The method of clause 47. wherein the indication is provided by a deregistration reason that is due to EPS to 5GS mobility without an interface between an access and mobility management function (AMF) in the 5GS and a MME in the EPS.

[0149] Clause 49. The method of clause 47 or clause 48, wherein the indication in the deregistration request message is also to cancel a serving general packet radio service (GPRS) support node (SGSN) registration in the HSS for the UE, and wherein the method further comprises canceling the SGSN registration in the HSS for the UE based on the indication in the deregistration request message.

[0150] Clause 50. A computer-readable storage medium that is non-transitory and has instructions stored therein that, in response to execution by at least one processing circuitry, causes a home subscriber server (HSS) of an evolved packet system (EPS) to at least: receive a deregistration request message from a unified data management (UDM) in a 5G system (5GS) in connection with inter-system mobility of a user equipment (UE) from the EPS to the 5GS, the deregistration request message including an indication not to cancel a mobility management entity (MME) registration in the HSS for the UE operating in a single-registration mode; make a determination not to cancel the MME registration in the HSS for the UE based on the indication in the deregistration request message; and respond to the UDM with a deregistration response message.

[0151] Cla use 51. The computer-readable storage medium of clause 50, wherein the indication is provided by a deregistration reason that is due to EPS to 5GS mobility without an interface between an access and mobility' management function (AMF) in the 5GS and a MME in the EPS.

[0152] Clause 52. The computer-readable storage medium of clause 50 or clause 51, wherein the indication in the deregistration request message is also to cancel a serving general packet radio service (GPRS) support node (SGSN) registration in the HSS for the UE, and wherein the computer-readable storage medium, has further instructions stored therein that, in response to execution by the at least one processing circuitry, causes the apparatus to further cancel the SGSN registration in the HSS for the UE based on the indication in the deregistration request message.

[0153] Clause 53 A apparatus comprising means for performing the method of any of clauses 47 to 49.

[0154] Clause 54. A computer-readable medium comprising instructions that, in response to execution by at least one processing circuitry', causes an apparatus to perform the method of any of clauses 47 to 49.

[0155] Clause 55. A computer-readable storage medium comprising instructions that, in response to execution by at least one processing circuitry', causes an apparatus to perform the method of any of clauses 47 to 49.

[0156] Clause 56. A computer program comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of clauses 47 to 49.

[0157] Many modifications and other implementations of the disclosure set forth herein will come to mind to one skilled in the art to which the disclosure pertains having the benefit of the teachings presented in the foregoing description and the associated figures. Therefore, it is to be understood that the disclosure is not to be limited to the specific implementations disclosed and that modifications and other implementations are intended to be included within the scope of the appended claims. Moreover, although the foregoing description and the associated figures describe example implementations in the context of certain example combinations of elements and / or functions, it should be appreciated that different combinations of elements and / or functions may be provided by alternative implementations without departing from the scope of the appended claims. In this regard, for example, different combinations of elements and / or functions than those explicitly described above are also contemplated as may be set forth in some of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. An apparatus implemented by an access and mobility management function (AMF) of a 5G system (5GS), the apparatus comprising:means for receiving a first registration request message from an user equipment (UE) operating in a single-registration mode, the first registration request message for inter-system mobility of the UE from an evolved packet system (EPS) to the 5GS, the first registration request message indicating a mobility management entity (MME) registration exists in the EPS for the UE;means for making a determination that the AMF is not configured with an interface towards a MME in the EPS; and based on the registration request message and the determination,means for performing a registration procedure with an unified data management (UDM) in the 5GS to register the AMF in the UDM for the UE, the registration procedure including a second registration request message sent by the AMF to the UDM with an indication to instruct a home subscriber server (HSS) m the EPS not to cancel the MME registration.

2. The apparatus of claim 1, wherein the first registration request message from the UE includes a UE status information element set to indicate the MME registration exists in the EPS for the UE.

3. The apparatus of claim 1 or claim 2, wherein the second registration request message includes an indication the UE is operating in the single-registration mode, and an indication the second registration request message is related to the intersystem mobility of the UE from the EPS to the 5GS.

4. The apparatus of any of claims 1 to 3, wherein the second registration request message includes an information element set with the indication to instruct the HSS not to cancel the MME registration for the UE.

5. A method performed by an access and mobility management function (AMF) of a 5G system (5GS), the method comprising:receiving a first registration request message from a user equipment (UE) operating in a single-registration mode, the first registration request message for intersystem mobility of the UE from an evolved packet system (EPS) to the 5GS, the first registration request message indicating a mobility management entity (MME) registration exists in the EPS for the UE;making a determination that the AMF is not configured with an interface towards a MME in the EPS; and based on the registration request message and the determination, performing a registration procedure with a unified data management (UDM) in the 5GS to register the AMF in the UDM for the UE, the registration procedure including a second registration request message sent by the AMF to the UDM with an indication to instruct a home subscriber server (HSS) in the EPS not to cancel the MME registration.

6. The method of claim 5, wherein the first registration request message from the UE includes a UE status information element set to indicate the MME registration exists in the EPS for the UE.

7. The method of claim 5 or claim 6, wherein the second registration requestmessage includes an indication the UE is operating in the single-registration mode, and an indication the second registration request message is related to the inter-system mobility of the UE from the EPS to the 5GS.

8. The method of any of claims 5 to 7, wherein the second registration request message includes an information element set with the indication to instruct the HSS not to cancel the MME registration for the UE.

9. A computer program comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of claims 5 to 8.

10. An apparatus implemented by unified data management (UDM) of a 5G system (5GS), the apparatus comprising:means for receiving a registration request message from an access and mobility management function (AMF) in the 5GS in connection with inter-system mobility of an user equipment (UE) from an evolved packet system (EPS) to the 5GS, the registration request message including a first indication to instruct a home subscriber server (HSS) in the EPS not to cancel a mobility management entity (MME) registration in the HSS for the UE operating in a single-registration mode;means for registering the AMF in the UDM for the UE based on the registration request message; andmeans for sending a deregistration request message to the HSS, the deregistration request message including a second indication not to cancel the MME registration in the HSS for the UE.

11. The apparatus of claim 10, wherein the registration message is received from the AMF that is not configured with an interface towards a MME in the EPS.

12. The apparatus of claim 10 or claim 11, wherein the registration request message includes an indication the UE is operating in the single-registration mode, and an indication the registration request message is related to the inter-system mobility of the UE from the EPS to the 5GS.

13. The apparatus of any of claims 10 to 12, wherein the registration request message includes an information element set with the indication to instruct the HSS not to cancel the MME registration in the HSS for the UE.

14. A method performed by unified data management (UDM) of a 5G system (5GS), the method comprising:receiving a registration request message from an access and mobility management function (AMF) in the 5GS in connection with inter-system mobility of a user equipment (UE) from an evolved packet system (EPS) to the 5GS, the registration request messageincluding a first indication to instruct a home subscriber server (HSS) in the EPS not to cancel a mobility management entity (MME) registration in the HSS for the UE operating in a single-registration mode;registering the AMF in the UDM for the UE based on the registration request message; andsending a deregistration request message to the HSS, the deregistration request message including a second indication not to cancel the MME registration in the HSS for the UE.

15. The method of claim 14, wherein the registration message is received from the AMF that is not configured with an interface towards a MME in the EPS.

16. The method of claim 14 or claim 15, wherein the registration request message includes an indication the UE is operating in the single-registration mode, and an indication the registration request message is related to the inter-system mobility of the UE from the EPS to the 5GS.

17. The method of any of claims 14 to 16, wherein the registration request message includes an information element set with the indication to instruct the HSS not to cancel the MME registration in the HSS for the UE.

18. A computer program comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of claims 14 to 17.

19. An apparatus implemented by a home subscriber server (HSS) of an evolved packet system (EPS), the apparatus comprising:means for receiving a deregistration request message from an unified data management (UDM) in a 5G system (5GS) in connection with inter-system mobility of an user equipment (UE) from the EPS to the 5GS, the deregistration request messageincluding an indication not to cancel a mobility management entity (MME) registration in the HSS for the UE operating in a single-registration mode;means for making a determination not to cancel the MME registration in the HSS for the UE based on the indication in the deregistration request message; andmeans for responding to the UDM with a deregistration response message.

20. The apparatus of claim 19, wherein the indication is provided by a deregistration reason that is due to EPS to 5GS mobility without an interface between an access and mobility management function (AMF) in the 5GS and a MME in the EPS.

21. The apparatus of claim 19 or claim 20, wherein the indication in the deregistration request message is also to cancel a serving general packet radio service (GPRS) support node (SGSN) registration in the HSS for the UE, andwherein the apparatus further comprises means for canceling the SGSN registration m the HSS for the UE based on the indication in the deregistration request message.

22. A method performed by a home subscriber server (HSS) of an evolved packet system (EPS), the method comprising:receiving a deregistration request message from a unified data management (UDM) in a 5G system (5GS) in connection with inter-system mobility of a user equipment (UE) from the EPS to the 5GS, the deregistration request message including an indication not to cancel a mobility management entity (MME) registration in the HSS for the UE operating in a single-registration mode;making a determination not to cancel the MME registration in the HSS for the UE based on the indication in the deregistration request message; andresponding to the UDM with a deregistration response message.

23. The method of claim 22, wherein the indication is provided by a deregistration reason that is due to EPS to 5GS mobility without an interface between an access and mobility management function (AMF) in the 5GS and a MME in the EPS.

24. The method of claim 22 or claim 23, wherein the indication in the deregistration request message is also to cancel a serving general packet radio service (GPRS) support node (SGSN) registration in the HSS for the UE, andwherein the method further comprises canceling the SGSN registration in the HSS for the UE based on the indication in the deregistration request message.

25. A computer program comprising instructions that, in response to execution by at least one processing circuitry, causes an apparatus to perform the method of any of claims 22 to 24.

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