WO2024083362A1

WO2024083362A1 - Method and apparatus for providing user equipment policy sections in an evolved packet system

Info

Publication number: WO2024083362A1
Application number: PCT/EP2023/064600
Authority: WO
Inventors: Roozbeh Atarius; Dimitrios Karampatsis
Original assignee: Lenovo (Singapore) Pte. Ltd.
Priority date: 2023-03-28
Filing date: 2023-05-31
Publication date: 2024-04-25

Abstract

The present application relates to registration and handover techniques in a mobile network. A UE performs a handover from a first to a second mobile network. The mobile networks comprise network entities to perform mobility management, which are incapable of communicating with each other via a direct communication interface to support the handover procedure. In response to a determination to perform the handover, the UE determines whether to perform a UE-initiated UE state indication procedure, create an initial attach request, and transmit it to the second mobile network. The initial attach request includes a request for connectivity comprising an indication that the request for connectivity is part of the handover procedure and an indication that an existing data session is to be transferred. If it is determined not to perform the UE-initiated UE state indication procedure, the request for connectivity lacks a second UE state indication message.

Description

Method and Apparatus for providing User Equipment Policy Sections in an Evolved Packet System

BACKGROUND

Modern 5G System (5GS) networks include two main parts, the access network 5G New Radio (5G NR) and the core network 5G Core Network (5GC or 5GCN). 5GS is an evolution of its predecessor network Evolved Packet System (EPS). EPS also includes an access network called Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) and a core network called Evolved Packet Core (EPC). The 5GC has progressed compared to the EPC in several aspects. Some notable advantages are: the more pronounced separation of the user plane and control plane, the virtualization of network functions (NFs) and the possibility of splitting the network into network slices, which are logically separated, independent parts of the network.

A key component in the 5GCN is the Policy Control Function, which is inter alia responsible for providing UE policy information to a user equipment (UE) that is registered in the 5GS. UE policies provision the registered UE with rules for communicating with the 5GS, thereby enabling the network to adapt the UEs communication behavior to a current network configuration or condition. One aspect of UE policy carried over from EPS is the Access Network Discovery and Selection Policy (ANDSP), which provisions the registered UE with information related to selecting non-3GPP access networks (e.g. Wi-Fi) for accessing the 5GCN. Another important aspect to UE policy is the UE Route Selection Policy (URSP), which provides information to the UE on mapping traffic to network slices and/or Protocol Data Unit (PDU) sessions, which provide connectivity between applications on the UE and a data network (DN).

Fully migrating current mobile networks to 5G is a complex and time-consuming process that effects all parts of the network. Until this process is completed EPS and 5GS networks will coexist and UEs will support these networks to different degrees. Hence, interoperability between 5GS and EPS is a key topic of network expansion. To achieve this interoperability, network architectures have been developed that support interworking of 5GS and EPS including provisioning of UE policies through PCF functionality in EPS for UEs that support UE policy provision in EPS. However, in order to optimize the UE policy provisioning for UEs in EPS, efficient procedures supporting PCF based UE policy provisioning in EPS are needed. SUMMARY

In an aspect of the present disclosure a computer-implemented method for performing a registration procedure for registering a user equipment (UE) to a mobile network is provided. The method is performed by a processor of the UE and comprises creating an initial attach request and transmitting the initial attach request to the mobile network. The initial attach request includes a request for connectivity to a packet data network (PDN). The request for connectivity to the PDN includes a UE state indication message, wherein the UE state indication message lacks an indication that the UE supports provisioning of UE policy section management lists including one or more UE policy rules.

In another aspect of the present disclosure a UE is provided. The UE comprises a processor configured to execute computer-readable instructions for performing a handover procedure from a first mobile network to a second mobile network. The first and second mobile networks each comprise a respective network entity configured to perform mobility management for UEs in the respective mobile network, wherein the respective network entities are incapable of communicating with each other via a direct communication interface to support the handover procedure between the first and second mobile networks. The UE has been registered at the first mobile network by transmitting a first UE state indication message to the first mobile network, wherein the first UE state indication message comprises an indication that the UE supports provisioning of UE policy section management lists including one or more UE policy rules. The computer-readable instructions cause the processor to, in response to a determination of the UE to perform the handover procedure from the first mobile network to the second mobile network, determine whether to perform a UE-initiated UE state indication procedure, create an initial attach request, and transmit the initial attach request to the second mobile network. The initial attach request includes a request for connectivity to a PDN comprising an indication that the request for connectivity is part of the handover procedure and an indication that an existing data session between the UE and the PDN is to be transferred from the first mobile network to the second mobile network. If it is determined not to perform the UE-initiated UE state indication procedure, the request for connectivity to the PDN lacks a second UE state indication message. Alternatively or additionally, if it is determined to perform the UE-initiated UE state indication procedure, the request for connectivity to the PDN includes a second UE state indication message, wherein the second UE state indication message lacks the indication that the UE supports provisioning of UE policy section management lists including one or more UE policy rules. In yet another aspect of the invention a mobile telecommunications network apparatus configured to perform a network function for controlling session management (SM) related policies in a first and a second mobile network is provided. The apparatus comprises a processor configured to execute computer-readable instructions causing the processor to: receive a session management policy update request comprising a UE state indication message from a UE and information indicating that the UE state indication message has been transmitted with an attach request to the second mobile network by the UE during a handover procedure from the first mobile network to the second mobile network; based on the information included in the session management policy update request, determine that the UE performs the handover procedure from the first mobile network to the second mobile network; and based on the determination that the UE performs the handover procedure, establish a UE policy association. The session management policy update request is received from a first network entity implementing a network function for session management in the first and the second mobile network. The UE state indication message is included in the session management policy update request using a first dedicated data type defined for transmitting the UE state indication message with the session management policy update request. The UE policy association is established with a second network entity implementing a network function for controlling UE related policies in the second mobile network, wherein establishing the UE policy association includes transmitting a request message to the second network entity. The request message comprises the UE state indication message and an indication triggering the establishment of the UE policy association, wherein the UE state indication message is transmitted in the request message using a second dedicated data type defined for transmitting the UE state indication message with the request message.

In a further aspect of the present disclosure, a computer-implemented method for performing a handover procedure from a first mobile network to a second mobile network is provided. The first and second mobile networks each comprise a respective network entity configured to perform mobility management for UEs in the respective mobile network, wherein the respective network entities are incapable of communicating with each other via a direct communication interface to support the handover procedure between the first and second mobile networks. A UE has been registered at the first mobile network by transmitting a first UE state indication message to the first mobile network. The first UE state indication message comprises an indication that the UE supports provisioning of UE policy section management lists including one or more UE policy rules, wherein the UE has an existing data session with a PDN, which is to be transferred from the first mobile network to the second mobile network during the handover procedure. The computer-implemented method is performed by the UE, which is configured to include a UE state indication message when attaching to the second mobile network with an access point (AP) having an access point name (APN) in a list of APNs configured in the UE. The method comprises, in response to a determination of the UE to perform the handover procedure from the first mobile network to the second mobile network: determining an APN of an AP of the existing data session; determining that the APN is comprised in the list of APNs configured in the UE; and in response to the determination that the APN is comprised in the list of APNs, determining not to transfer the existing data session to the second mobile network during the handover procedure from the first mobile network to the second mobile network. The method further comprises, after completion of the handover from the first mobile network to the second mobile network, transmitting to the second mobile network, a request for connectivity to the PDN, the request for connectivity comprising an APN of the list of APNs and a second U E state indication message.

In accordance with further aspects of the method of the preceding paragraph, the request for connectivity to the PDN transmitted after completion of the handover may be a second request for connectivity to the PDN and the method may further comprise, in response to determining not to transfer the existing data session to the second mobile network, transmitting during the handover procedure, an initial attach request to the second mobile network including a first request for connectivity to the PDN, wherein the first request for connectivity lacks an identifier for the existing data session. The request for connectivity may comprise an Extended Protocol Configuration Options (ePCO) Information Element (IE) having a length of two octets, wherein the ePCO IE may comprise the second UE state indication message. Additionally or alternatively, the second UE state indication message may comprise the indication that the UE supports provisioning of UE policy section management lists including one or more UE policy rules. In some aspects of the disclosure the first mobile network may be a 5G system (5GS) network and the second mobile network may be an Evolved Packet System (EPS) network. The network entity configured to perform mobility management for UEs in the first mobile network may be an Access and Mobility Function, AMF, and the network entity configured to perform mobility management for UEs in the second mobile network may be a Mobility Management Entity, MME. In aspects of the present disclosure the direct communication interface to support the handover procedure between the first and second mobile networks may be an N26 interface and the AMF and the MME may be incapable of communicating with each other via the N26 interface. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments and aspects of the invention will be described in the following description together with the accompanying drawings, wherein

Fig. 1 shows a non-roaming architecture for policy section delivery to the UE in an EPS network;

Fig. 2 is an exemplary flow diagram showing a first mobility procedure from a 5GS network to an EPS network in accordance with one or more aspects of the present disclosure;

Fig. 3 is an exemplary flow diagram showing a second mobility procedure from a 5GS network to an EPS network in accordance with one or more aspects of the present disclosure;

Fig. 4 shows a mobile telecommunications network apparatus in accordance with one or more aspects of the present disclosure; and

Fig. 5 shows a UE in accordance with one or more aspects of the present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings in which like reference numerals refer to like elements unless specified otherwise.

A UE policy is delivered to the UE in a 5GS by the PCF via the Access and Mobility Management Functions (AMF). The AMF is one of the control plane NFs of the 5GCN. Among other tasks it performs mobility management which includes tracking of the radio access network (RAN) node (e.g. gNB or ng-eNB) to which a UE is currently connected. The AMF is therefore a central part in the communication of the 5GCN and the UE.

The PCF may deliver a UE Policy in several messages to the UE. To facilitate this fragmented delivery and subsequent partial updates of UE policies, a UE policy may be divided into policy sections. The PCF may combine several policy sections into one message as long as a predefined message size limit is observed. A policy section may have a size below a predefined policy section size limit. UE policies are specified in UE policy rules (e.g. URSP rules). A policy section may comprise only complete policy rules. Additionally, the content of a policy section may be provided by a single Public Land Mobile Network (PLMN). A PCF may only determine policy sections of its own PLMN. However, a visited PCF (V-PCF) may forward UE policy sections received from the home PCF (H-PCF) of the UE in a roaming scenario.

Each UE policy section is identified by a UE Policy Section Identifier (UPSI), which may be composed of two parts: (a) a PLMN ID part containing a PLMN identifier (PLMN ID) for the PLMN of the PCF providing the UE policies; and (b) a UE policy section code (UPSC) containing a unique value within the PLMN selected by the PCF. The UE may receive the UE policy sections from the PCF and may store the received UE policy sections and their respective UPSIs.

At the time of initially registering to a 5GS a UE can initiate a UE state indication procedure. The purpose of this UE-initiated procedure is: (a) delivering the UPSIs (UPSIs) of UE policy sections to the PCF, which are (i) identified by a UPSI with a PLMN ID part that indicates the home PLMN (HPLMN) of the UE or the selected PLMN, and stored at the UE, if any; or are (ii) identified by a UPSI with the PLMN ID part indicating the PLMN ID part of the Stand-alone Non-Public Network (SNPN) identity of the selected SNPN and associated with the Network identifier (NID) of the selected SNPN, and stored in the UE, if any; (b) indicating whether the UE supports ANDSP to the PCF; and/or (c) delivering the UE’s one or more Operating System identifiers (OS IDs) to the PCF.

In order to initiate the UE-initiated UE state indication procedure, the UE may create a UE state indication message. The UE may create the UE state indication message by (a) allocating a Procedure Transaction Identity (PTI) value currently not used and setting a PTI Information Element (IE) of the UE state indication message to the allocated PTI value; (b) if not operating in SNPN access operation mode, including the UPSI(s) of the UE policy section(s) which are available in the UE and are identified by a UPSI with the PLMN ID part indicating the HPLMN or the selected PLMN in a UPSI list IE of the UE state indication message; (c) if operating in SNPN access operation mode, including UPSI(s) of the UE policy section(s) which are available in the UE and are identified by a UPSI with the PLMN ID part indicating the Mobile Country Code (MCC) and/or the Mobile Network Code (MNC) of the selected SNPN; and are associated with the NID of the selected SNPN; (d) specifying whether the UE supports ANDSP in a UE policy classmark IE of the UE state indication message; and/or (e) including the UE's one or more OS IDs in a UE OS ID IE of the UE state indication message.

Once created, the UE may send the UE state indication message to the PCF via a RAN node and the AMF. The UE may transport the created UE state indication message using the registration procedure as defined in sub-clause 5.5.1 in 3GPP TS 24.501. Upon receipt of the UE state indication message, the PCF may establish a UE policy association with the AMF to provide the UE with the UE policy sections.

As described above, the UE policy section delivery to a UE is performed by the PCF in cooperation with the AMF and is a feature of the 5GS. However, this feature may be extends to EPS with enhanced UE policy (eUEPO), which allows a UE receiving UE policy sections when the UE registers to the EPS network. Fig. 1 shows an exemplary non-roaming network architecture 100 for policy section delivery to the UE 102 in an EPS network. The network architecture provides the capability to transmit policy sections to the UE 102 when the UE 102 is registered at EPS or at 5GS. Network architecture 100 may provide enhanced interoperability of EPS and 5GS.

A UE 102 may connect to the EPS provided by network architecture 100 using the E- UTRAN 112 air interface to connect to a RAN node (e.g. an eNB). The E-UTRAN 112 (i.e. the eNB) may be connected via the S1-MME interface to the Mobility Management Entity (MME) 120, which is the key control-node in the EPS and may provide inter alia mobility management in the EPS. Like the AMF 130 in the 5GS, the MME 120 in the EPS is a central component in connecting the core network to the UE 102. The Serving Gateway (SGW) 140 may route and forward user data packets in the EPS. It may be connected to the E-UTRAN 112 (i.e. the eNB) via the S1-U interface allowing direct data transfer from the eNB to the SGW 140 for data transfer from the UE 102 to the EPC. Additionally, the SGW 140 may be connected to the MME 120 via the S11 interface for providing data transfer to the UE 102 via the eNB. In the EPS, connectivity to external packet data networks may be provided by a Packet Data Network Gateway (PGW). The PGW may manage EPS Bearers to provide end-to-end connectivity between the UE 102 and an Access Point (AP) identified by an Access Point Name (APN). An AP/APN is a gateway to a PDN (e.g. the internet or a local packet-based network). Each EPS Bearer may support a single QoS profile. The functionality of the PGW may be separated in control and user plane functions. The control plane may be served by the PGW control plane function (PGW-C) and the user plane may be served by the PGW user plane function (PGW-U).

In the exemplary network architecture 100, these functions may be provided in the network entities UPF + PGW-U 150 and SMF + PGW-C 160 that are dedicated to interworking between 5GS and EPC. The UPF + PGW-U 150 may combine the EPS functionality of the PGW-U 150 and the 5GS functionality of the User Plane Function (UPF). In the 5GS the UPF may inter alia be responsible for user plane data packet routing, forwarding, and inspection, the user plane part of policy rule enforcement, Quality of Service (QoS) handling for the user plane, and providing interconnectivity to a PDN (e.g. the internet or packed-based local networks). The SMF + PGW-C 160 may combine the EPS functionality of PGW-C and the 5GS functionality of the Session Management Function (SMF). The SMF manages Protocol Data Unit (PDU) sessions, which provide end-to-end user plane connectivity between the UE 102 and a specific Data Network (DN) through the UPF. The DN is identified by a Data Network Name (DNN). A PDU session may support one or more QoS Flows each supporting a single QoS profile. The SMF + PGW-C 160 may be connected to the SGW 140 via the S5-C interface and the UPF + PGW-U 150 may be connected to the SGW 140 via the S5-U interface. The N4 interface may be provided between the SMF + GW-C 160 and the UPF + PGW-U 150 to facilitate efficient communication between these two components. The SMF + PGW-C 160 may manage PDU sessions in accordance with session management related policies provided by the Session Management PCF (SM-PCF) 170, which may be connected to the SMF + PGW-C 160 via the N7 interface.

Network user data including user subscriptions may be controlled in a 5GS by the Unified Data management (UDM) NF. Similar services are provided in an EPS by the Home Subscriber Server (HSS), which may manage user subscriptions and user data in the EPC. The exemplary network architecture 100 may include a HSS + UDM 190 as an interworking entity combining the functions of the HSS in EPS and the UDM in 5GS. The N10 interface may connect the SMF + PGW-C 160 with the HSS + UDM 190, which may be additionally connected to the MME 120 via the S6a interface and to the AMF 130 via the N8 interface.

A UE 106 may connect to the 5GS provided by network architecture 100 using the air interface of the Next Generation RAN (NG-RAN) 116 (i.e. 5G NR) to connect to a NG-RAN node (e.g. a gNB). The NG-RAN 116 (i.e. the gNB) may be connected via the N2 interface to the AMF 130, which is functionally comparable to the MME 120 of the EPS. The UPF + PGW-U 150 and the SMF + PGW-C 160 may provide data connectivity for voice and data services for the UE. In the upload direction, the connection may be provided from the UE 106 over the air interface of the NG-RAN 116 and the N3 interface between the NG-RAN 116 and the UPF + PGW-U 150. In the download direction, the connection to the UE 106 may be supported by the AMF 130, which may connect to the SMF + PGW-C 160 through the N11 interface. The 5GS may additionally include a direct interface N1 between the UE 106, which in the 5GS of network architecture 100 may be technically established via the air interface to the NG-RAN 116 and the N2 interface between the NG-RAN 116 and the AMF 130 but is transparent to the specific radio access network that is used to connect the UE 106 to the AMF 130. Hence, the N1 interface does not rely on the 5G NR access network but could be established via a different radio access network (e.g. a non-3GPP radio access network such as Wi-Fi). UE related policies may be provided to the UE 106 via an established policy association between the LIE-PCF 180 and the AMF. These two NFs may be connected through the N15 interface. In the shown exemplary network architecture 100 the PCF functionality may be split into UE related policy functionality provided by the UE-PCF 180 to the UE 106 via a UE policy association between the UE-PCF 180 and the AMF 130 and SM related policy functionality provided by the SM-PCF 170 to the SMF + PGW-C 160. In order to facilitate efficient communication between the SM-PCF 170 and the UE-PCF 180 an interface (e.g. the Nx interface) may be provided between these two NFs. In some embodiments data exchange between the MME 120 and the AMF 130 may be supported by providing the N26 interface 125 between these two entities. The N26 interface 125 may facilitate interoperability between the EPS and the 5GS and in particular may support performing an efficient handover procedure of a UE 106 from the 5GS to the EPS or of a UE 102 from the EPS to the 5GS by enabling the exchange of data relevant to the handover procedure between the MME 120 and the AMF 130. However, either the MME 120 or the AMF 130 or both may not support the N26 interface 125, therefore leaving the network entities incapable (i.e. unable) of communicating with each other via a direct communication interface (i.e. the N26 interface 125) to support a handover procedure between the EPS and the 5GS.

Turning now to Fig. 2, which illustrates an exemplary flow diagram showing a first mobility (i.e. handover) procedure 200 from a first mobile network (i.e. a 5GS network) to a second mobile network (i.e. an EPS network) in accordance with one or more aspects of the disclosure. The first and second mobile networks may be mobile telecommunication networks. In an aspect of the present disclosure the first mobile network comprises a first network entity (e.g. a NF or a mobile telecommunications network apparatus) configured to perform mobility management (e.g. AMF 130) in the first network. The second network comprises a second network entity (e.g. a NF or a mobile telecommunications network apparatus) performing mobility management (e.g. MME 120 or MME 206) in the second mobile network. The first and second network entities are not connected by a direct communication interface supporting a handover procedure between the first and the second mobile network. Accordingly, the first and second network entities are incapable (i.e. unable) of communicating via a direct communication interface to support the handover procedure between the first and second networks. The first mobile network may be a 5GS network and the second mobile network may be an EPS network. The first mobility management network entity may be an AMF (e.g. AMF 130) and the second mobility management network entity may be a MME (e.g. MME 120 or MME 206). AMF 130 and/or the MME 120 may not support the N26 interface 125. Therefore, the two network entities may not be connected via the N26 interface 125 and may be unable to communicate with each other via the N26 interface 125. In step 220, Fig. 2 shows that a UE 202 has been initially registered in the first network (i.e. a 5GS network) with one or more data sessions (e.g. one or more PDU sessions). The UE 202 may be operating in single registration mode or dual registration mode. In single registration mode, the UE 202 can only be registered to one mobile network at a time (either the first mobile network or the second mobile network). In dual registration mode, the UE 202 can handle independent registrations for the first and the second mobile network at the same time, meaning that the UE 202 can be registered to both mobile networks simultaneously.

When registering to the first mobile network, the UE 202 may have initiated a state indication procedure by transmitting a UE state indication message to the first mobile network. The transmitted UE state indication message included an indication that the UE 202 supports provisioning of UE policy section management lists (UPSMLs) including one or more UE policy rules in the second network (e.g. in the EPS network). Each UPSML may include one or more UE policy sections with each UE policy section identified by a UPSI. Each UE policy section may include one or more UE policy rules. The one or more policy rules may comprise one or more URSP rules. In an aspect, the indication that the UE 202 supports provisioning of UPSMLs includes an indication of a capability of the UE 202 to support URSP provisioning in EPS. The first mobile network may store the support of the UE 202 for provisioning of UPSMLs including one or more UE policy rules provisioning in a data repository of the first network for the UE 202. The data repository may be a Unified Data Repository, which is a central data repository for storing user data and subscription data in an EPS network and/or a 5GS network. In some embodiments, the capability of UE 202 to support URSP provisioning in EPS is stored in the UDR for the UE 202.

The UE 202 may determine to perform a handover procedure. At the time of mobility (i.e. handover) to the second mobile network (e.g. an EPS network), the UE 202 performs a tracking area update (TAU) procedure in the second network. The UE 202 may send a TAU request at step 224 to a RAN node (e.g. eNB 204), which may forward the request to the second network entity (e.g. MME 206). This TAU procedure may be performed according to clause 5.3.3.1 in 3GPP TS 23.401 by providing an EPS Globally Unique Temporary Identity (EPS-GUTI) mapped to a 5G- GUTI. Based on the EPS-GUTI mapped to the 5G-GUTI, the MME 206 may determine the AMF (e.g. AMF 130) and thereby the support 5GS-EPS interworking architecture (e.g. network architecture 100) without an N26 interface. Based on this determination the MME 206 may send a TAU reject to the UE 202 via the MME 206 in step 226.

Based on the determination to perform a handover procedure to the second mobile network, the UE 202 determines whether to perform a UE-initiated UE state indication procedure. The UE 202 creates an initial attach request. The attach request includes a request for connectivity to a PDN (e.g. a PDN connectivity request) which comprises an indication that the request for connectivity is part of a handover procedure. Additionally, the request for connectivity to the PDN comprises an indication that an existing data session between the UE 202 and the PDN is to be transferred form the first mobile network to the second mobile network. The existing data session is a data session between the UE 202 and the PDN that has been established within the first mobile network and exists and is active within the first mobile network when the UE 202 decides to perform the handover procedure.

Based on the UE 202 having already performed the UE-initiated UE state indication procedure when registered to the first network (e.g. the 5GS network) and the UE 202 requesting the transfer of the existing data session between the UE 202 and the PDN to the second network EPS, the UE 202 may determine not to perform the UE-initiated UE state indication procedure. In this case, the created attach request includes the request for connectivity to the PDN, which lacks a UE state indication message (i.e. the request for connectivity to the PDN does not include a UE state indication message). The request for connectivity may be a PDN connectivity request and may not include an ePCO IE including a UE state indication message.

Alternatively or additionally, when the UE 202 determines to perform the UE-initiated state indication procedure the created attach request includes the request for connectivity to the PDN comprising a UE state indication message. However, unlike the state indication message that has been provided by the UE 202 during registration to the first network, the UE state indication message comprised in the request for connectivity to the PDN lacks an indication that the UE 202 supports provisioning of UPSMLs including one or more policy rules in the second mobile network (i.e. the UE state indication message does not include an indication that the UE 202 supports provisioning of UPSMLs including one or more policy rules in the second mobile network). In an aspect, the UE state indication message lacking the indication that the UE 202 supports provisioning of UPSMLs comprises that the UE state indication message lacks an indication of a capability of the UE 202 to support URSP provisioning in EPS. The request for connectivity to the PDN may be a PDN connectivity request and may include an ePCO IE comprising the UE state indication message. The ePCO IE may have a length of two octets as defined in clause 10.5.6.3A in 3GPP TS 24.008. A PCO IE may have a length of one octet.

The PDN connectivity request message may initiate a PDN connectivity procedure for setting up a default EPS Bearer for end-to-end communication of the UE 202 with a PDN. The PDN connectivity request may comprise a DNN/APN and/or a PDU session ID of a PDU session that is to be transferred to the EPS network. The PDN connectivity request message may be of a type indicating that the PDN connectivity request is part of the handover procedure. More specifically, the PDN connectivity request may include a type field, which is set to a value indicating that the PDN connectivity request is part of the handover procedure (i.e. a value “handover”). The DNN/APN and the PDU session ID may be comprised in a PCO IE or an ePCO IE. Accordingly, the PDN connectivity request may comprise the PCO IE or the ePCO IE comprising the PDU session ID of the PDU session to be transferred to the EPS.

In other embodiments, the PDN connectivity request may comprise an ePCO IE comprising the PDU session ID of the PDU session to be transferred to the EPS network in addition to the UE network capability IE with respective bits set to indicate the support for the respective UE capabilities.

In step 230 the UE 202 initiates an attach procedure to the second mobility management entity of the second mobile network by sending the created attach request to the RAN node (e.g. eNB 204). The attach request may be comprised in an RRC request. The UE 202 may use the RRC request message including the attach request to the network for an RRC connection. The RRC request message may be transmitted via a Radio Access Network, RAN, node of the second mobile network using an air interface of the RAN.

The attach request is transmitted from the UE 202 to the RAN node (e.g. eNB 204) using the RRC request in step 230 and from the RAN node to the second mobile management network entity (e.g. MME 206) via an initial UE message in step 232. The attach request may include an identity of the UE 202 (e.g. a unique identifier such as an International Mobile Subscriber Identity, IMSI) and the PDN connectivity request message. The PDN connectivity request message may be contained in a EPS Session Management (ESM) message container IE of the PDN connectivity request message.

In an alternative embodiment, if the UE 202 chooses to perform the UE-initiated UE state indication procedure, the UE 202 may be required to transmit the UE state indication message comprising (a) a UPSI list; (b) an indication that the UE 202 supports the provision of UPSMLs including respective indications that the UE 202 supports ANDSP and has the capability for receiving URSP rules in EPS (e.g. within a UE policy classmark IE); and/or one or more OS IDs of the UE 202.

In step 232, upon receipt of the attach request within an RRC Request message by the eNB 204, the eNB 204 may select the MME 206 from the RRC request message carrying the old Globally Unique Mobility Management Entity Identifier (GUMMEI) comprising a PLMN identity, an MME group identity and an MME code where the MME code may be used by the Non-Access Stratum (NAS) node selection function of the eNB 204, to select the MME.

If the MME 206 is not associated with the eNB 204 or the old GUMMEI is not available, the eNB 204 selects an MME 206 using a MME selection function described in clause 4.3.8.3 of 3GPP TS 24.301. According to that clause, the eNB 204 makes selection of the MME 206 based on the GUMMEI with or without distinguishing whether the GUMMEI is mapped from a Packet Temporary Mobile Subscriber Identity (P-TMSI) and/or a Routing Area Identification (RAI) or is a native GUMMEI. If a Dedicated Core Network (DCN) is deployed and the UE assisted DCN selection feature is supported, the UE 202 may provide a DCN-ID to the eNB 204 to be used by the eNB 204 for MME selection to maintain the same DCN when the serving MME is not available.

The MME 206 may request for the UE's IMSI and the network may authenticate the UE 202. The MME 206 may select the SGW 208 based on network topology, i.e. the selected SGW 208 may serve the UE's location and for overlapping SGW service areas, the selection may prefer SGWs 208 with service areas that reduce the probability of changing the SGW 208.

The UE 208 may have included the APN/DNN for the transferring the PDU session in the PDN connectivity request. The included APN/DNN may be used to identify the SMF+PGW-C 210. The subscription context, which is provided by the HSS, for the UE 202 may include one or more APNs for one or more PDNs for the services. The subscription context may be provided by the HSS if the APN/DNN and the PDN connectivity request provided by the UE 202 are in subscription contexts.

In case the request type of the attach request is "initial request", the UE 202 has not provided any APN, and the subscription context from HSS contains a PDN Gateway (PDN GW) identity corresponding to the default APN, the MME 208 may use the PDN GW corresponding to the default APN for default bearer activation. In case the UE 202 provided an APN and the APN is for transferring the PDU session, the MME 206 may select the SMF+PGW-C 210 for the default bearer activation. If a DCN with a dedicated SGW 208 and PDN GW is used, the Domain Name System (DNS) procedure for SGW 208 and SMF+PGW-C 210 selections may be used such that a SGW 208 and the SMF+PGW-C 210 both belong to a DCN serving the UE 202.

If the MME 206 supports ePCO, an extended PCO support indication may be set to 1 on the S11 interface by the MME 206 to inform the SGW 208 that ePCO is supported by the UE 202 and the MME 206. In step 234 a create session request message may be transmitted for the MME 206 to the SGW 208. The MME 206 may also use the kind of the container ID within the ePCO IE, which is specifically intended for the PDU session ID to indicate that the attach request is for transferring the existing PDU session with the provided PDU session ID to the EPS.

Upon receiving the create session request message, the SGW 208 may create a new entry in its EPS Bearer context table and may transmit in step 236 the create session request message comprising the APN of the existing PDU session, the SGW address, PDN address, subscribed APN and protocol configuration options towards the SMF+PGW-C 210 indicated by the SMF+PGW-C address received in the previous step. If the SGW 208 supports ePCO, the SGW 208 sets extended PCO support indication to 1 on S5 interfaces (and/or on S8 interfaces) as to show the support for ePCO by the UE 202, MME 206 and SWG 208 to SMF + PGW-C 210. The SGW 208 may also use the kind of the container ID within the ePCO IE, which is specifically intended for the PDU session ID to indicate that the attach request is for transferring the existing PDU session with the provided PDU session ID to the EPS.

Upon receipt of the create session request message and realizing that the included ePCO IE is for establishing a PDN connection for transferring the PDU session with the identity equal to PDU session ID, the SMF+PGW-C 210, after determination that the policy control request is met, may construct an HTTP POST request for the update of session management policy control by updating Radio Access Technology (RAT) type, EPS bearer QoS information, user location information of EPC, etc. e.g. according to 3GPP TS 29.512. In step 240, SMF + PGW-C 210 may transmit the constructed HTTP POST request as a SM policy control update request to the SM- PCF 212. In case the UE 202 included the UE state indication message with the PDN connectivity request in step 230 (e.g. within the ePCO IE in the PDN connectivity request), the SMF+PGW-C 210 may send the UE state indication message to the SM-PCF 212. In order for the SMF+PGW- C 210 to do that, the SM policy update context data (SmPolicyUpdateContextData) as described e.g. in table 5.6.2.19-1 in 3GPP TS 29.512 may need to be updated with supporting a new data type specifically adapted for transmitting the UE state indication message with the SM policy control update request to the SM-PCF 212.

In the case that the UE 202 included the UE state indication message lacking the indication that the UE 202 supports provisioning of UPSMLs including one or more UE policy rules in the second network, the SMF+PGW-C 210 may ignore that the indication of the supported provision of UPSMLs is missing from the UE state indication message and proceed under the assumption that the UE 202 does support this feature. In an aspect, if the UE 202 included the UE state indication message lacking the indication of a capability of the UE 202 to support the provisioning of URSP (i.e. URSP rules) in EPS UPSMLs including one or more UE policy rules, the SMF+PGW- C 210 may ignore that the indication of the supported provision LIRSP in EPS is missing from the UE state indication message and proceed under the assumption that the UE 202 does support this feature.

The SM-PCF 212, based on the information provided by the SMF+PGW-C 210 in step 240, may determine that the UE 202 performs a handover procedure from the first mobile network (e.g. a 5GS network) to the second mobile network (e.g. an EPS network). In such a case, the SM-PCF 212 may determine whether the UE 202 supports provisioning of UPSMLs including one or more UE policy rules in the second mobile network (e.g. whether UE 202 supports provisioning of URSP rules in EPS) by checking UE context policy control subscription information stored in UDR, the policy control subscription information having been stored in UDR during the registration procedure of the UE 202 with the first mobile network (e.g. the 5GS network). Based on the result of this determination the SM-PCF 212 may determine whether to establish a UE policy association towards the UE-PCF 214 at step 244. In an alternative embodiment the SM-PCF 212 may determine to establish a UE policy association in step 244 based on receiving from the SMF+PGW-C 210 the UE state indication message included in the SM policy control update request and conveyed by the new data type specifically adapted for transmitting the UE state indication message with the SM policy control update request to the SM-PCF 212.

In step 248, the UE-PCF 214 may maintain a UE policy association with a first mobility management entity (e.g. the AMF 130) of the first network. The maintained UE policy association may have been established when the UE 202 registered to the 5GS. Alternatively, the maintained UE policy association may be based on a UE policy association that has been established when the UE 202 registered to the 5GS (e.g. the maintained UE policy association may be similar to, derived from, or equal to a UE policy association that has been established when the UE 202 registered to the 5GS). This may be the case when (a) the UE 202 is in dual registration mode, where the UE 202 is connected to the EPS and the 5GS simultaneously; or (b) the UE-PCF 214 has not deleted the UE policy association due to: (i) the UE's request at the time of release from the 5GS; (ii) a configured period of time when the UE releases from the 5GS not having passed; or (iii) the UE 202 having lost the 5GS connection abruptly due to e.g. bad coverage and the UE- PCF 214 not having been updated with respect to UE's release form the 5GS. The maintained UE policy association may be equal to the

The SM-PCF 212 may discover and select a UE-PCF 214 and may establish a UE policy association with the selected UE-PCF 214. The SM-PCF 212 may transmit a UE policy control create request at step 252 and may include the policy container received from the SMF+PGW-C 210. If the UE 202 included the UE state indication message with the PDN connectivity request in step 230 (e.g. within the ePCO of the PDN connectivity request), the SM-PCF 212 may send the UE state indication message to the UE-PCF 214 in addition to an indication about the trigger for the UE Policy association establishment (e.g. "5GS to EPC handover"). In order for the SM-PCF 212 to send the UE state indication message with the UE policy control create request, a new data type needs to be introduced specifically adapted for transmitting the UE state indication message with the UE policy control create request to the UE-PCF 214.

In step 254, the UE policy association between the SM-PCF 212 and the UE-PCF 214 may be established and regular procedure may now be followed to determine the UE policy sections. In case the UE-PCF 214 has maintained a previously established UE policy association with the AMF 130 as described above, the UE policy association between the SM-PCF 212 and the UE- PCF 214 may be established based on the maintained UE policy association (e.g. the UE policy association between the SM-PCF 212 and the UE-PCF 214 may be derived from the maintained UE policy association). In step 256, The UE-PCF 214 may transmit a UE policy control create response message to the SM-PCF 212 (e.g. Npcf_UEPolicyControl create answer).

The SMF + PGW-C 210 may receive the create session request message comprising the ePCO IE in step 236. If the establishment of the PDN connection is successful, the SMF-PGW-C 210 may create a new entry in its EPS Bearer context table and may return a create session response message in step 260. The create session response message may comprise the SMF + PGW-C address for the user plane, PDN address and ePCO support. The create session response message may be transmitted from the SMF + PGW-C 210 to the SGW 208.

In step 262, the SGW 208 may return a create session response message to the MME 206 comprising the ePCO. The SGW 208 may buffer any data downlink packets it may receive from SMF + PGW-C 210 until it may receive a modify bearer request message (e.g. in step 286) from the MME 206.

The MME 206 may sends to the eNB 204, in step 264, an attach accept message comprising a session management request message used to establish a PDN connection which may be an ESM message container compromising (a) an Active Default EPS Bearer Context Request message; and/or (b) the EPS network feature support comprising ePCO support for the network. The attach accept request is transmitted within an S1AP initial context setup request message. Upon receiving, by the eNB 204, the S1AP initial context setup request message, the eNB 204 may send the RRC connection reconfiguration message including the attach accept message comprising ePCO support, in step 270, to the UE 202.

In step 270, the UE 202, upon receipt of the RRC connection reconfiguration message, may send the RRC connection reconfiguration complete message to eNB 204, which may trigger the eNB transmitting initial context setup response message in step 280 to the MME 206.

The UE 202 may send a direct transfer message to the eNB 204 in step 282, including the attach complete message comprising the Activate Default EPS Bearer Context Accept message, contained in the ESM message container IE. In step 284, the eNB 204 may use an uplink NAS transport message to send the attach complete to the MME 206. The MME 206 may use a modify bearer request message at step 286 to enable the SWG 208 to transmit downlink data to the UE 202. The SGW 208 may answer the modify bearer request message in step 288 with a modify bearer response message to the MME 206. Finally, in step 290, a PCF initiated URSP update procedure may be performed according to clause 6.16.2.2 of 3GPP TR 23.700-85.

In an embodiment, a mobile telecommunications network apparatus is provided which will now be described in relation to the network entities and procedure steps a depicted in Fig. 2. The mobile telecommunications network apparatus is configured to perform a network function (e.g. SM-PCF 212 or SM.PCF 170) for controlling session management related policies in the first mobile network and the second mobile network. The apparatus comprises a processor configured to execute computer-readable instructions causing the processor to receive (e.g. at step 240), from a session management network entity implementing a NF for session management in the first mobile network and the second mobile network (e.g. SMF + PGW-C 210 or SMF + PGW-C 160), a session management policy update request (e.g. the SM policy control update request i.e. the constructed HTTP POST request for the update of session management policy control). The session management policy update request comprises a UE state indication message provided to the second mobile network in the attach request at step 230. The session management policy update request further comprises information indicating that the UE state indication message has been transmitted with the attach request to the second mobile network during a handover procedure from the first mobile network to the second mobile network. The state indication message is included in the session management policy update request using a first dedicated data type defined for transmitting the UE state indication message with the session management policy update request. The instructions further cause the processor to, based on the information included in the session management policy update request, determine (e.g. in step 244) that the UE 202 performs the handover procedure from the first mobile network to the second mobile network; and based on the determination that the UE performs the handover procedure, establish (e.g. step 254) a UE policy association with a second network entity implementing a network function (e.g. UE-PCF 214) for controlling UE related policies in the second mobile network. Establishing the UE policy association includes transmitting (e.g. step 252) a request message (e.g. UE policy control create request) to the second network entity, the request message comprising the UE state indication message and an indication triggering the establishment of the UE policy association, wherein the UE state indication message is transmitted in the request message using a second dedicated data type defined for transmitting the UE state indication message with the request message. The second network entity may also implement the network function for controlling UE related policies in the first mobile network (e.g. the 5GS network) and may maintain a previously established UE policy association (e.g. in step 248) for the UE 202 during the handover procedure of the UE 202 from the first mobile network to the second mobile network, the previously established UE policy association having been established in the first mobile network during registration of the UE 202 with the first mobile network.

The above discussion was related to a handover process performed by a UE 202 from a first mobile network to a second mobile network. However, the present invention may also be applied advantageously to situations where a simple registration is performed in a mobile network without the requirement of a previous registration to another mobile network or a handover to another mobile network. In this embodiment, a computer-implemented method for performing a registration procedure for registering a UE (e.g. UE 202 or UE 102), to the second mobile network (e.g. the EPS network) within an interoperability network architecture (e.g. network architecture 100) is provided. The method is performed by a processor of the UE 102, 202. In a first step an initial attach request is created including a request for connectivity to a PDN (e.g. a PDN connectivity request). The request for connectivity to the PDN includes a UE state indication message. The UE state indication message lacks an indication that the UE supports provisioning of UE policy section management lists including one or more UE policy rules. In a second step the created initial attach request is transmitted to the second mobile network. The request for connectivity may comprise an ePCO IE, which may include the UE state indication message. The ePCO IE may have a length of two octets. The one or more UE policy rules may comprise one or more URSP rules. Transmitting the initial attach request to the second mobile network may comprise transmitting the initial attach request to a network entity configured to perform mobility management for UEs in the mobile network using an RRC request message, wherein the RRC request massage is transmitted via a Radio Access Network, RAN, node of the mobile network using an air interface of the RAN. An alternative embodiment for a handover procedure of a UE 302 from the first mobile network to the second mobile network is now discussed with reference to Fig. 3, which illustrates an exemplary flow diagram showing a second mobility (i.e. handover) procedure 300 from a first mobile network (i.e. a 5GS network) to a second mobile network (i.e. a EPS network) in accordance with one or more aspects of the disclosure. The first and second mobile networks may be mobile telecommunication networks. In an aspect of the present disclosure the first mobile network comprises a first network entity (e.g. a NF or a mobile telecommunications network apparatus) configured to perform mobility management (e.g. AMF 130) in the first mobile network. The second network comprises a second network entity (e.g. a NF or a mobile telecommunications network apparatus) performing mobility management (e.g. MME 120 or MME 206) in the second mobile network. The first and second network entities are not connected by a direct communication interface supporting a handover procedure between the first and the second mobile network. Accordingly, the first and second network entities are incapable (i.e. unable) of communicating via a direct communication interface to support the handover procedure between the first and second networks. The first mobile network may be a 5GS network and the second mobile network may be an EPS network. The first mobility management network entity may be an AMF (e.g. AFM 130) and the second mobility management network entity may be a MME (e.g. MME 120 or MME 306) and the AMF 130 and/or the MME 306 may not support the N26 interface 125. The two network entities may therefore not be connected via the N26 interface 125 and may be unable to communicate with each other via the N26 interface 125.

The UE 302 has been initially registered in the first network (i.e. a 5GS network) with one or more data sessions (e.g. one or more PDU sessions). The UE 302 may be operating in single registration mode or dual registration mode. When registering to the first mobile network, the UE 302 may have initiated a state indication procedure by transmitting a UE state indication message to the first mobile network. The transmitted UE state indication message included an indication that the UE 302 supports provisioning of UPSMLs including one or more UE policy rules in the second network (e.g. in the EPS network). Each UPSML may include one or more UE policy sections, wherein each UE policy section is identified by a UPSI. Each UE policy section may include one or more UE policy rules. The one or more UE policy rules may comprise one or more URSP rules. In an aspect, the indication that the UE 302 supports the provisioning of UPSMLs includes an indication of a capability of the UE 302 to support URSP provisioning in EPS. The first mobile network may store the support of the UE 302 for provisioning of UPSMLs including one or more UE policy rules provisioning in a data repository of the first network for the UE 302. The data repository may be a Unified Data Repository, which is a central data repository for storing user data and subscription data in an EPS network or a 5GS network. In some embodiments, the capability of UE 302 to support LIRSP provisioning in EPS is stored in the UDR for the UE 302.

A computer-implemented method is performed by the UE 302, which is configured to include a UE state indication message when attaching to the second mobile network with an AP having an APN in a list of APNs configured in the UE 302. The UE 302 may be configured with the list of APNs to send a UE state indication message when the UE 302 attaches in EPS to an APN of the list of APNs. At step 320 the UE 302 decides to handover from the first mobile network to which the UE 320 has been registered in a previous step to the second mobile network. Subsequently, a TAU procedure is performed in step 325. The TAU procedure may be performed in accordance with steps 224 and 226 of Fig. 2 or steps 0-4 of Fig. 4.11.2.2-1 of 3GPP TS 23.502 for 5GS to EPS mobility when the N26 interface is not supported.

In response to the determination of the UE 302 to perform the handover procedure from the first mobile network to the second mobile network the UE 302 at step 330 determines an APN of an AP of the existing active data session (an existing active PDU session to be transferred to EPS) that is to be transferred and determines that the APN is comprised in the list of APNs configured in the UE 302. In step 335, in response to the determination that the APN is comprised in the list of APNs, the UE 302 determines not to transfer the existing data session to the second mobile network during the handover procedure from the first mobile network to the second mobile network. The UE may send an initial attach request without including the PDU session ID of the PDU session if the APN of the PDU session is configured in the UE 302 to include a UE state indication message when attaching in EPS. The handover to EPS may continue and complete at step 340. The handover may continue and complete as per steps 5-13 of Fig. 4.11 .2.2-1 of 3GPP TS 23.502.

At step 345, after completion of the handover from the first mobile network to the second mobile network, the UE 302 may determine to request connectivity to the PDN. At step 350, the UE 302 transmits, to the second mobile network, a request for connectivity to the PDN, the request for connectivity comprising an APN of the list of APNs and a second UE state indication message. The UE 302, after handover to the second mobile network completes, may transmit a request for connectivity to the PDN (e.g. a separate PDN connectivity request) including in the request the second UE state indication message. The UE state indication message may be comprised in an ePCO IE of the PDN connectivity request. The UE state indication message includes an indication that the UE 302 supports provisioning of UPSMLs including one or more UE policy rules. The UE policy rules may comprise one or more URSP rules. In some embodiments, the UE state indication message may include a capability of the UE 302 to support URSP provisioning in EPS.

At step 354, the SMF-PGW-C 310 updates an existing SM policy association with the SM- PCF and includes the policy container received by the UE 302. The SM-PCF 312 acknowledges the request in step 356. The UE requested PDN connectivity continues and completes in step 360. The SM-PCF 312 at step 370 determines to establish a UE policy association with the UE-PCF 314 based on the policy container received from the SMF-PGW-C 310 and selects a UE-PCF 314. In step 374, the SM-PCF 312 establishes a UE policy association and includes the policy container. The UE-PCF 314 acknowledges the request in step 374.

The UE 302 may initiate the handover procedure from the first mobile network to the second mobile network as per steps 220 to 234 of Fig. 2. Then if the UE 302 needs to transfer existing active data sessions (e.g. a PDU session) to the second mobile network (e.g. as part of step 320 in Fig. 3), the UE 302 may determine whether the APN/DNN of the data session to be transferred is included in the list of APNs configured in the UE 302 to include the UE state indication message when attaching in the second mobile network. If the APN/DNN of the data session is included in the configured list of APNs then the UE 302 may not include the data session ID in the list of data sessions to be transferred in a request for connectivity to a PDN (e.g. a PDN connectivity request) included in the initial attach message.

The request for connectivity to the PDN transmitted after completion of the handover may be a second request for connectivity to the PDN and, in response to determining not to transfer the existing data session to the second mobile network, the UE 302 may transmit, during the handover procedure, an initial attach request to the second mobile network including a first request for connectivity to the PDN. The first request for connectivity may lack an identifier for the existing data session (e.g. a PDU session ID). The request for connectivity may comprise an Extended Protocol Configuration Options (ePCO) Information Element (IE), having a length of two octets, wherein the ePCO IE may comprise the second UE state indication message. Additionally or alternatively, the second UE state indication message may comprise the indication that the UE 302 supports provisioning of UE policy section management lists including one or more UE policy rules. In some aspects of the disclosure the first mobile network may be a 5G system (5GS) network and the second mobile network may be an Evolved Packet System (EPS) network. The network entity configured to perform mobility management for UEs in the first mobile network may be an Access and Mobility Function, AMF, and the network entity configured to perform mobility management for UEs in the second mobile network may be a Mobility Management Entity, MME. In aspects of the present disclosure the direct communication interface to support the handover procedure between the first and second mobile networks may be an N26 interface 125 and the AMF 130 and the MME 306 may be incapable of communicating with each other via the N26 interface.

With respect to Figs. 1 , 2 and 3 a person skilled in the art recognizes that the presented network entities may correspond with each other in certain embodiments. In particular, UEs 202 and 302 may correspond to UE 102 and UE 106, MME 306 and MME 206 may correspond to MME 120, SGW 208 may correspond to SGW 140, SMF + PGW-C 210 and 310 may correspond to SMF + PGW-C 160, SM-PCF 212 and 312 may correspond to SM-PCF 170 and UE-PCF 214 and 314 may correspond to UE-PCF 180.

Turning briefly to Figs. 4 and 5, Fig. 4 shows a mobile telecommunications network apparatus 400 in accordance with one or more aspects of the present disclosure. Specifically, Fig. 4 shows a mobile telecommunications network apparatus 400 having one or more processors 410 and a memory 420. The memory 420 may have stored computer-executable instructions that, when executed by the one or more processors, cause the processor to perform one of the methods with regard to Figs. 2 and 3 that are performed by one of the core network components (e.g. core network components 206, 208, 210, 212, 214, 306, 310, 312, or 314). The memory may have also stored computer-executable instructions for implementing any of the MME (e.g. MME 206 or 306), SGW (e.g. SGW 208), SMF+PGW-C (e.g. SMF-PGW-C 210 or 310), SM-PCF (e.g. SM-PCF 212 or 312), and/or UE-PCF (e.g. UE-PCF 214 or 314) described in this specification. The memory 420 is coupled to the one or more processors 410.

Fig. 5 shows a UE 500 in accordance with one or more aspects of the present disclosure. Specifically, Fig. 5 shows a UE 500 having one or more processors 510 and a memory 520. The memory 520 may have stored computer-executable instructions that, when executed by the one or more processors, cause the one or more processors to perform one of the methods described with regard to Figs. 2 and 3 that are performed by the UE (e.g. UE 202 or 302). The memory 520 is coupled to the one or more processors 510.

While the present disclosure has been described with respect to the physical embodiments constructed in accordance therewith, it will be apparent to those skilled in the art that various modifications, variations and improvements of the present disclosure may be made in light of the above teachings and within the purview of the appended claims without departing from the spirit and intended scope of the disclosure. In addition, those areas in which it is believed that those of ordinary skill in the art are familiar, have not been described herein in order to not unnecessarily obscure the present disclosure described herein. Accordingly, it is to be understood that the present disclosure is not to be limited by the specific illustrative embodiments, but only by the scope of the appended claims.

Claims

1. A computer-implemented method for performing a registration procedure for registering a user equipment, UE, to a mobile network, wherein the method is performed by a processor of the UE, the method comprising: creating an initial attach request including a request for connectivity to a packet data network, PDN, wherein the request for connectivity to the PDN includes a UE state indication message, the UE state indication message lacking an indication that the UE supports provisioning of UE policy section management lists including one or more UE policy rules; and transmitting the initial attach request to the mobile network.

2. The method of claim 1 , wherein the request for connectivity comprises an Extended Protocol Configuration Options, ePCO, Information Element, IE, which includes the UE state indication message.

3. The method of claim 1 , wherein the ePCO IE has a length of two octets.

4. The method of claim 1 , wherein the mobile network is an Evolved Packet System, EPS, network.

5. The method of claim 4, wherein the one or more UE policy rules comprise one or more UE Route Selection Policy, URSP, rules.

6. The method of claim 1 , wherein transmitting the initial attach request to the mobile network comprises transmitting the initial attach request to a network entity configured to perform mobility management for UEs in the mobile network using an RRC request message, wherein the RRC request massage is transmitted via a Radio Access Network, RAN, node of the mobile network using an air Interface of the RAN.

7. A user equipment, UE, comprising: a processor configured to execute computer-readable instructions for performing a handover procedure from a first mobile network to a second mobile network, wherein the first and second mobile networks each comprise a respective network entity configured to perform mobility management for UEs in the respective mobile network, wherein the respective network entities are incapable of communicating with each other via a direct communication interface to support the handover procedure between the first and second mobile networks, wherein the UE has been registered at the first mobile network by transmitting a first UE state indication message to the first mobile network, the first UE state indication message comprising an indication that the UE supports provisioning of UE policy section management lists including one or more UE policy rules, wherein the computer-readable instructions cause the processor to, in response to a determination of the UE to perform the handover procedure from the first mobile network to the second mobile network: determine whether to perform a UE-initiated UE state indication procedure; create an initial attach request including a request for connectivity to a packet data network, PDN, wherein the request for connectivity comprises an indication that the request for connectivity is part of the handover procedure and an indication that an existing data session between the UE and the PDN is to be transferred from the first mobile network to the second mobile network; and transmit the initial attach request to the second mobile network, wherein, if it is determined not to perform the UE-initiated UE state indication procedure, the request for connectivity to the PDN lacks a second UE state indication message, and/or wherein, if it is determined to perform the UE-initiated UE state indication procedure, the request for connectivity to the PDN includes a second UE state indication message, the second UE state indication message lacking the indication that the UE supports provisioning of UE policy section management lists including one or more UE policy rules. The UE of claim 7, wherein the first mobile network is a 5G system, 5GS, network and the second mobile network is an Evolved Packet System, EPS, network. The UE of claim 8, wherein the one or more UE policy rules comprise one or more UE Route Selection Policy, URSP, rules. The UE of claim 7, wherein the first mobile network is a 5G system, 5GS, network and the network entity configured to perform mobility management for UEs in the first mobile network is an Access and Mobility Function, AMF. The UE of claim 7, wherein the second mobile network is an Evolved Packet System network and the network entity configured to perform mobility management for UEs in the second mobile network is a Mobility Management Entity, MME. The UE of claim 7, wherein the network entity configured to perform mobility management for UEs in the first mobile network is an Access and Mobility Function, AMF and network entity configured to perform mobility management for UEs in the second mobile network is a Mobility Management Entity, MME, wherein the direct communication interface to support the handover procedure between the first and second mobile networks is an N26 interface and wherein the AMF and the MME are incapable of communicating with each other via the N26 interface. The UE of claim 7, wherein the request for connectivity to a PDN is a PDN connectivity request and the existing data session is a Protocol Data Unit, PDU, session. The UE of claim 13, wherein the PDN connectivity request is of a type indicating that the PDN connectivity request is part of the handover procedure. The UE of claim 13, wherein the PDN connectivity request includes a PDU session ID of the existing data session, the PDU session ID indicating the existing data session is to be transferred from the first mobile network to the second mobile network. The UE of claim 15, the PDU session ID is comprised in a Protocol Configuration Options, PCO, Information Element, IE, having a length of a single octet or in an Extended PCO, ePCO, IE having a length of two octets. The UE of claim 7, wherein registering the UE at the first mobile network included performing a UE-initiated UE state indication procedure including transmitting the first UE state indication message to the first mobile network. The UE of claim 7, wherein transmitting the initial attach request to the second mobile network comprises transmitting the initial attach request to the network entity configured to perform mobility management for UEs in the second mobile network using a RRC request message, the RRC request message being transmitted via a Radio Access Network, RAN, node of the second mobile network using an air interface of the RAN. A mobile telecommunications network apparatus configured to perform a network function for controlling session management related policies in a first and a second mobile network, the apparatus comprising: a processor configured to execute computer-readable instructions causing the processor to: receive, from a first network entity implementing a network function for session management in the first and the second mobile network, a session management policy update request comprising a user equipment, UE, state indication message, from a UE and information indicating that the UE state indication message has been transmitted with an attach request to the second mobile network by the UE during a handover procedure from the first mobile network to the second mobile network, wherein the UE state indication message is included in the session management policy update request using a first dedicated data type defined for transmitting the UE state indication message with the session management policy update request; based on the information included in the session management policy update request, determine that the UE performs the handover procedure from the first mobile network to the second mobile network; based on the determination that the UE performs the handover procedure, establish a UE policy association with a second network entity implementing a network function for controlling UE related policies in the second mobile network, wherein establishing the UE policy association includes transmitting a request message to the second network entity, the request message comprising the UE state indication message and an indication triggering the establishment of the UE policy association, wherein the UE state indication message is transmitted in the request message using a second dedicated data type defined for transmitting the UE state indication message with the request message. The mobile telecommunications network apparatus of claim 19, wherein the second network entity further implements the network function for controlling UE related policies in the first mobile network and wherein the second network entity maintains a UE policy association similar to, modified of, or equal to a previously established UE policy association for the UE during the handover procedure from the first mobile network to the second mobile network, the previously established UE policy association having been established in the first mobile network during registration of the UE with the first mobile network.