SMF deregistration for duplicated PDU session on different access networks

Abstract

Method and apparatus are provided to handle PDU session duplication when a UE has duplicate PDU session over different access networks or systems when the PDU session and the duplicate PDU session are anchored at different session management entities. The method comprises at a UDM detecting duplicate PDU session established over an evolved packet data gateway (ePDG) used to provide access to a UE over non-3GPP access for a UE and notifying the old session management entity anchoring the old / existing PDU session that a duplicate (new) PDU session is setup over an ePDG. Different examples are described as to how that indication is provided. The old session management entity uses the information to initiate release of the PDU session without releasing the PDU session in the UE. A method and apparatus is provided for the SMF that is required to handle the deregistration notification from the UDM.

Description

SMF Deregistration for Duplicated PDU Session on different access networks RELATED APPLICATIONS This application claims the benefit of provisional patent application serial number 63 / 625452 filed on 2024-01-26, and PCT / CN2024 / 084728 filed on 2024-03-29 the disclosure of which are hereby incorporated herein by reference in its entirety. Technical Field

[0001] The present disclosure relates to a cellular communications system and, more particularly, PDU session management and duplicate PDU sessions. Background

[0002] 3GPP Discussion Paper C4-220223 describes the following issue related to duplicated PDU Sessions in the 5G Network. Mainly, in 5G Network, when the Access and Mobility Management Function (AMF) receives request from a UE a request to establish a new PDU session including a PDU session ID that already exists in the UE context within the AMF (e.g. the establishment request may be triggered by the UE that locally removed the PDU session context in the UE), the AMF will attempt to release existing SM Context for the existing PDU Session context in the AMF on the old SMF, and create SM context for the new PDU session (now requested by the UE) on a SMF which may be a different SMF according to the DNN / slice of the new PDU session. If for some reason the AMF cannot successfully release the existing SM Context for the PDU session ID on the old SMF, there will be multiple SM Context with the same PDU session ID existing in the 5G network.

[0003] Figure 4 illustrates the problematic scenario. The potential impact of the above include if the old SMF receive DL data from the AF, it may trigger UP Setup in the RAN, the RAN may setup PDU session resource for the old PDU session which are not expected, or as RAN may already have context resource for the old PDU session, the RAN may reject UP setup for the new PDU session.

[0004] Figure 5 illustrates a proposed solution to the above problem. The solution is adopted by 3GPP specifications and is described as well in 3GPP CT4 C4-220223 and CT4 C4-222407. The solution in Figure 5 is described via the following main steps.1. When the UDM detects duplicate PDU Session, the UDM sends a UECM Deregistration Notification to the old SMF with deregistration reason indicating "Duplicate PDU session" 2. The old SMF shall NOT send a SM Context Status Notify to the AMF as the AMF does not have a duplicate context, to prevent the AMF from triggering any signaling for releasing context associated with the new PDU session established for the PDU session ID towards the RAN node or the UE. 3. The old SMF shall simply clean up core side for the old PDU Session including e.g., N7 (PCF) association deletion, N4 (UPF) association deletion, N40 (CHF) association deletion. Thus, stale session is properly cleaned up and a robust solution is achieved. Summary

[0005] Certain aspects of the present disclosure and their embodiments may provide solutions to the aforementioned or other challenges.

[0006] According to some embodiments, a method performed by a User Data Management (UDM) function or an equivalent function that maintains user data information having or having stored registration information obtained from a first session management function (SMF) for a Packet Data Unit (PDU) session established for a User Equipment (UE). The registration information already stored in or by the UDM include but not limited to a PDU session identifier and a network slice identifier and / or data network name of the PDU session established over a first access (e.g., 3GPP access), the method comprises the step of obtaining from a second session management function (SMF) a registration message indicating that a new PDU session is established by the UE via an evolved packet data gateway (ePDG) providing access to the UE over a non-3GPP access. The ePDG is a well known security access gateway node specified by 3GPP providing UE access over non-3GPP access (e.g., WLAN) to 3GPP Core Networks. The method further comprises the step of sending to the first SMF a deregistration notification comprising deregistration information indicating that a duplicate PDU session is established over the ePDG when the new PDU session established by the second SMF over ePDG has the same PDU session identifier as the PDU session established over the first SMF.

[0007] For example, the registration message received from the second SMF further comprises an access type / RAT type, a network slice identifier (S-NSSAI) and / or a data network name for the new PDU session and the UDM may further determines that the new PDU session is a duplicate when the network slice identifier and / or the data network name of the new PDU session are identical to the network slice identifier and / or the data network name of the PDU session established via the first SMF.

[0008] In some examples, the registration message from the second SMF indicating that a new PDU session is established by the UE via an evolved packet data gateway providing access to the UE over a non-3GPP access corresponds to the registration message comprising an identifier of the ePDG over which the new PDU session is established. The identifier is for example an epdgind information element (IE) which when included indicates a value set to true when the PDU session is established over the ePDG.

[0009] In some examples, the deregistration information included in the deregistration notification from the UDM to the first SMF indicates that a duplicate PDU session is established over the ePDG and is indicated by transmitting both the epdgind IE and a deregistrationreason IE indicating “duplicate PDU session” or is indicated by including only a deregistration reason IE indicating one of “duplicate PDU session on different access” or “duplicate PDU session on non-3GPP access” or “duplicate PDU session ePDG”.

[0010] According to some embodiments, a method performed by a Session Management Function (SMF) having established a PDU session with a PDU session identifier for a UE over a first access network is provided. The method comprises the step of receiving from a User Data Management (UDM) a deregistration notification comprising deregistration information indicating that a duplicate PDU session is established on another SMF for the UE over an evolved packet data gateway (ePDG) used to provide access to the UE over a non-3GPP access, the duplicate PDU session having the same PDU session identifier as the PDU session established over the SMF. The deregistration notification may further include the PDU session identifier of the PDU session established over the SMF, and / or the network slice identifier and / or the DNN associated to the PDU session.

[0011] The method further comprises the step of sending a notification to a network function indicating release of the PDU session due to duplicate PDU session over the ePDG to initiate release of the PDU session at the network function without initiating release of the PDU session in the UE.

[0012] For example, the network function corresponds to an Access and Mobility Management function or an intermediate session management function or a visited session management function.

[0013] For example, the deregistration information indicating that a duplicate PDU session is established on another SMF for the UE over an evolved packet data gateway (ePDG) corresponds to a deregistration cause Information Element IE indicating “DUPLICATE_PDU_SESSION_ePDG” or "DUPLICATE_PDU_SESSION_ ON DIFFERENT ACCESS” or “DUPLICATE_PDU_SESSION_ ON NON-3GPP ACCESS”.

[0014] According to some embodiment, a network node configured to perform the method of any of the embodiments described herein is provided.

[0015] According to some embodiment, a network node comprising one or more processors and memory comprising instructions which when executed by the one or more processors enable the network node to perform the method of any of the embodiments described herein is provided.

[0016] According to some embodiment, a computer readable memory comprising instructions which when executed by one or more processors of one or more servers or nodes configures the one or more servers or nodes to perform the method of any of the embodiments described herein is provided. Brief Description of the Drawings

[0017] The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.

[0018] Figure 1 illustrates one example of a cellular communications system 100 in which embodiments of the present disclosure may be implemented;

[0019] Figures 2 and 3 illustrate example embodiments of the cellular communication system of Figure 1;

[0020] Figure 4 illustrates a flow diagram of stale PDU session context as per the prior art;

[0021] Figures 5 illustrates a flow diagram for a solution to stale PDU session when the UE uses the same access network type as per the prior art;

[0022] Figure 6 illustrates a flow diagram for handling stale PDU sessions over different access networks in accordance with some embodiments.

[0023] Figure 7 illustrates a flow diagram for handling stale PDU sessions over different access networks in accordance with other embodiments.

[0024] Figure 7B illustrates a flow diagram for UDM initiated NF Deregistration in accordance with some embodiments.

[0025] Figure 8 illustrate a flow chart for UDM in accordance with some embodiments;

[0026] Figure 9 illustrate a flow chart for SMF in accordance with some embodiments;

[0027] Figure 10 illustrates a flow diagram for handling stale PDU sessions over different access networks in accordance with other embodiments.

[0028] Figure 11 illustrates a flow diagram for SMF initiating a notification on the status of the PDU session in the NF consumer in accordance with some embodiments.

[0029] Figures 12, 13, and 14 are schematic block diagrams of example embodiments of a network node. Detailed Description

[0030] The embodiments set forth below represent information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure.

[0031] Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Other embodiments, however, are contained within the scope of the subject matter disclosed herein, the disclosed subject matter should not be construed as limited to only the embodiments set forth herein; rather, these embodiments are provided by way of example to convey the scope of the subject matter to those skilled in the art.

[0032] Generally, all terms used herein are to be interpreted according to their ordinary meaning in the relevant technical field, unless a different meaning is clearly given and / or is implied from the context in which it is used. All references to a / an / the element, apparatus, component, means, step, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any methods disclosed herein do not have to be performed in the exact order disclosed, unless a step is explicitly described as following or preceding another step and / or where it is implicit that a step must follow or precede another step. Any feature of any of the embodiments disclosed herein may be applied to any other embodiment, wherever appropriate. Likewise, any advantage of any of the embodiments may apply to any other embodiments, and vice versa. Other objectives, features, and advantages of the enclosed embodiments will be apparent from the following description.

[0033] Radio Node: As used herein, a “radio node” is either a radio access node or a wireless communication device.

[0034] Radio Access Node: As used herein, a “radio access node” or “radio network node” or “radio access network node” is any node in a Radio Access Network (RAN) of a cellular communications network that operates to wirelessly transmit and / or receive signals. Some examples of a radio access node include, but are not limited to, a base station (e.g., a New Radio (NR) base station (gNB) in a Third Generation Partnership Project (3GPP) Fifth Generation (5G) NR network or an enhanced or evolved Node B (eNB) in a 3GPP Long Term Evolution (LTE) network), a high-power or macro base station, a low-power base station (e.g., a micro base station, a pico base station, a home eNB, or the like), a relay node, a network node that implements part of the functionality of a base station (e.g., a network node that implements a gNB Central Unit (gNB-CU) or a network node that implements a gNB Distributed Unit (gNB-DU)) or a network node that implements part of the functionality of some other type of radio access node.

[0035] Core Network Node: As used herein, a “core network node” is any type of node in a core network or any node that implements a core network function. The node can be a server or system of distributed servers. Some examples of a core network node include, e.g., an Access and Mobility Management Function (AMF), a User Plane Function (UPF), a Session Management Function (SMF), and an SMF-packet datagateway control and user plane (SMF+PGW-C, SMF+PGW-U) to support interworking between 5G core network and 4G core network known as Evolved Packet Core network (EPC), a Short message service function (SMSF), an Authentication Server Function (AUSF), a Network Slice Selection Function (NSSF), a Network Exposure Function (NEF), a Network Function (NF) Repository Function (NRF), a Policy Control Function (PCF), a Unified Data Management (UDM), a Network slice Admission Control function (NSACF), an Non-3GPP Interworking function (N3IWF) to support untrusted non-3GPP access or the like, a trusted non-3GPP access network function (TNGF) to support trusted non- 3GPP access networks. The core network may also include 4G network functions including evolved packet data gateway (ePDG) to support untrusted non-3GPP access network. The Core network functions may be virtualized / containerized on a node, server, distributed servers, or implemented as a dedicated function on a dedicated physical node (compute, memory, and network). Other future core network functions in future core networks such as 6G and beyond are also applicable for this invention.

[0036] Communication Device: As used herein, a “communication device” is any type of device that has access to an access network. Some examples of a communication device include, but are not limited to: mobile phone, smart phone, sensor device, meter, vehicle, household appliance, medical appliance, media player, camera, or any type of consumer electronic, for instance, but not limited to, a television, radio, lighting arrangement, tablet computer, laptop, or Personal Computer (PC). The communication device may be a portable, hand-held, computer-comprised, or vehicle- mounted mobile device, enabled to communicate voice and / or data via a wireless or wireline connection.

[0037] Wireless Communication Device: One type of communication device is a wireless communication device, which may be any type of wireless device that has access to (i.e., is served by) a wireless network (e.g., a cellular network). Some examples of a wireless communication device include, but are not limited to: a User Equipment device (UE) in a 3GPP network, a Machine Type Communication (MTC) device, and an Internet of Things (IoT) device. Such wireless communication devices may be, or may be integrated into, a mobile phone, smart phone, sensor device, meter, vehicle, household appliance, medical appliance, media player, camera, or any type of consumer electronic, for instance, but not limited to, a television, radio, lighting arrangement, tablet computer, laptop, or PC. The wireless communication device maybe a portable, hand-held, computer-comprised, or vehicle-mounted mobile device, enabled to communicate voice and / or data via a wireless connection.

[0038] Network Node: As used herein, a “network node” is any node that is either part of the RAN or the core network of a cellular communications network / system.

[0039] Note that the description given herein focuses on a 3GPP cellular communications system and, as such, 3GPP terminology or terminology similar to 3GPP terminology is oftentimes used. However, the concepts disclosed herein are not limited to a 3GPP system.

[0040] Note that, in the description herein, reference may be made to the term “cell”; however, particularly with respect to 5G NR concepts, beams may be used instead of cells and, as such, it is important to note that the concepts described herein are equally applicable to both cells and beams.

[0041] Figure 1 illustrates one example of a cellular communications system 100 in which embodiments of the present disclosure may be implemented. In the embodiments described herein, the cellular communications system 100 is a 5G system (5GS) including a Next Generation RAN (NG-RAN) and a 5G Core (5GC); however, the present disclosure is not limited thereto. In this example, the RAN includes base stations 102-1 and 102-2, which in the 5GS include NR base stations (gNBs) and optionally next generation eNBs (ng-eNBs) (e.g., LTE RAN nodes connected to the 5GC), controlling corresponding (macro) cells 104-1 and 104-2. The base stations 102- 1 and 102-2 are generally referred to herein collectively as base stations 102 and individually as base station 102. Likewise, the (macro) cells 104-1 and 104-2 are generally referred to herein collectively as (macro) cells 104 and individually as (macro) cell 104. The RAN may also include a number of low power nodes 106-1 through 106-4 controlling corresponding small cells 108-1 through 108-4. The low power nodes 106-1 through 106-4 can be small base stations (such as pico or femto base stations) or RRHs, or the like. Notably, while not illustrated, one or more of the small cells 108-1 through 108-4 may alternatively be provided by the base stations 102. The low power nodes 106-1 through 106-4 are generally referred to herein collectively as low power nodes 106 and individually as low power node 106. Likewise, the small cells 108-1 through 108-4 are generally referred to herein collectively as small cells 108 and individually as small cell 108. The cellular communications system 100 also includes a core network110, which in the 5G System (5GS) is referred to as the 5GC. The base stations 102 (and optionally the low power nodes 106) are connected to the core network 110.

[0042] The base stations 102 and the low power nodes 106 provide service to wireless communication devices 112-1 through 112-5 in the corresponding cells 104 and 108. The wireless communication devices 112-1 through 112-5 are generally referred to herein collectively as wireless communication devices 112 and individually as wireless communication device 112. In the following description, the wireless communication devices 112 are oftentimes UEs and as such sometimes referred to herein as UEs 112, but the present disclosure is not limited thereto.

[0043] Figure 2 illustrates a wireless communication system represented as a 5G network architecture composed of core Network Functions (NFs), where interaction between any two NFs is represented by a point-to-point reference point / interface. Figure 2 can be viewed as one particular implementation of the system 100 of Figure 1. The embodiments in the reminder of these document are described within the context of 5G network architecture using the 5G terminology, but the embodiments are also applicable to other systems / networks using network slicing, admission control of network slicing and on-demand network slicing can. Example of those systems / networks may be 6G systems / networks and beyond.

[0044] Seen from the access side the 5G network architecture shown in Figure 2 comprises a plurality of UEs 112 connected to either a RAN 102 or an Access Network (AN) as well as an AMF 200. Typically, the R(AN) 102 comprises base stations, e.g. such as eNBs or gNBs or similar. Seen from the core network side, the 5GC NFs shown in Figure 2 include a NSSF 202, an AUSF 204, a UDM 206, the AMF 200, a SMSF 220, a SMF 208, a SMF-PGW-C 208I, N3IWF, TNGF, ePDG, a PCF 210, and an Application Function (AF) 212.

[0045] Reference point representations of the 5G network architecture are used to develop detailed call flows in the normative standardization. The N1 reference point is defined to carry signaling between the UE 112 and AMF 200. The reference points for connecting between the AN 102 and AMF 200 and between the AN 102 and UPF 214 are defined as N2 and N3, respectively. There is a reference point, N11, between the AMF 200 and SMF 208, which implies that the SMF 208 is at least partly controlled by the AMF 200. N4 is used by the SMF 208 and UPF 214 so that the UPF 214 can be set using the control signal generated by the SMF 208, and the UPF 214 can report its stateto the SMF 208. The SMSF 220 communicates with the AMF 200 over the N20 reference point, and with UDM 206 over the N21 reference point, and AMF 200 communicates with UDM 206 over the N8 reference point as illustrated in Figure 2. N9 is the reference point for the connection between different UPFs 214, and N14 is the reference point connecting between different AMFs 200, respectively. N15 and N7 are defined since the PCF 210 applies policy to the AMF 200 and SMF 208, respectively. N12 is required for the AMF 200 to perform authentication of the UE 112. N8 and N10 are defined because the subscription data of the UE 112 is required for the AMF 200 and SMF 208.

[0046] The 5GC network aims at separating UP and CP. The UP carries user traffic while the CP carries signaling in the network. In Figure 2, the UPF 214 is in the UP and all other NFs, i.e., the AMF 200, SMF 208, SMF-PGW-C, PCF 210, AF 212, NSSF 202, AUSF 204, and UDM 206, are in the CP. Separating the UP and CP guarantees each plane resource to be scaled independently. It also allows UPFs to be deployed separately from CP functions in a distributed fashion. In this architecture, UPFs may be deployed very close to UEs to shorten the Round Trip Time (RTT) between UEs and data network for some applications requiring low latency. To support non-3GPP access networks N3IWF, TNGF, ePDG are special functions that provide access to core network resources and services and they handle both User plane and control plane capabilities.

[0047] The 5G core network architecture is composed of modularized functions. For example, the AMF 200, SMF 208 / SMF+PGW-C are independent functions in the CP. Separated AMF 200 and SMF 208 / SMF+PGW-C allow independent evolution and scaling. Other CP functions like the PCF 210 and AUSF 204 can be separated as shown in Figure 2. Modularized function design enables the 5GC network to support various services flexibly.

[0048] Each NF interacts with another NF directly. It is possible to use intermediate functions to route messages from one NF to another NF. In the CP, a set of interactions between two NFs is defined as service so that its reuse is possible. This service enables support for modularity. The UP supports interactions such as forwarding operations between different UPFs.

[0049] Figure 3 illustrates a 5G network architecture using service-based interfaces between the NFs in the CP, instead of the point-to-point reference points / interfaces used in the 5G network architecture of Figure 2. However, the NFs described above with reference to Figure 2 correspond to the NFs shown in Figure 3. The service(s) etc.that a NF provides to other authorized NFs can be exposed to the authorized NFs through the service-based interface. In Figure 3 the service based interfaces are indicated by the letter “N” followed by the name of the NF, e.g. Namf for the service based interface of the AMF 200 and Nsmf for the service based interface of the SMF 208, Nsmsf for service based interface exposing services of SMSF 220, etc. Any NFs depicted in Figure 2 can interact with the NEF 216 and / or NRF 218 of Figure 3 as necessary, though not explicitly indicated in Figure 2.

[0050] Some properties of the NFs shown in Figures 2 and 3 may be described in the following manner. The AMF 200 provides UE-based authentication, authorization, mobility management, etc. A UE 112 even using multiple access technologies is basically connected to a single AMF 200 because the AMF 200 is independent of the access technologies. The SMF 208 and SMF-PGW-C are responsible for session management and allocates Internet Protocol (IP) addresses to UEs. It also selects and controls the UPF 214 for data transfer. More particularly the SMF+PGW-C supports session management interworking between 5G core network and evolved packet core (4G) to support session continuity for a UE moving between 5G core network and 4G core network (EPC) including between NR and LTE access networks. If a UE 112 has multiple sessions, different SMFs 208 may be allocated to each session to manage them individually and possibly provide different functionalities per session. The AUSF 204 supports authentication function for UEs or similar and thus stores data for authentication of UEs or similar while the UDM 206 stores subscription data of the UE 112. The functionality of N3IWF in the case of untrusted non-3GPP access includes support of IPsec tunnel establishment with the UE where the N3IWF terminates the IKEv2 / IPsec protocols with the UE over NWu and relays over N2 the information needed to authenticate the UE and authorize its access to the 5G Core Network, it also terminates N2 and N3 interfaces to 5G Core Network for control - plane and user-plane respectively, relay uplink and downlink control-plane NAS (N1) signalling between the UE and AMF, Handling of N2 signalling from SMF (relayed by AMF) related to PDU Sessions and QoS. The N3IWF also establishment the IPsec Security Association (IPsec SA) to support PDU Session traffic as well as relays uplink and downlink user-plane packets between the UE and UPF. The functionality of the TNGF in the case of trusted non-3GPP access includes terminates the N2 and N3 interfaces and the EAP-5G signalling and behaves as authenticator when the UE attempts to register to 5GC via theTNAN. The TNGF performs AMF selection procedure and transparently relays NAS messages between the UE and the AMF, via NWt. The TNGF also handles N2 signalling with SMF (relayed by AMF) for supporting PDU sessions and QoS.

[0051] The ePDG which is known as a 4G function / gateway to enable the UE to access the core network via untrusted WLAN (considered the legacy function of N3IWF), supports establishment of the IPSec tunnel and establishment of the PDN connection / PDU session with a SMF+PGW-C / SMF when the UE requests IP connectivity service via IKE / IPSec tunnel. When using an ePDG, NAS signalling is not used and hence AMF is not used, unlike N3IWF.

[0052] Many NFs including AMF 200, SMF 208 communicate with UDM 206 to obtain subscription data and / or notification of UE availability for reachability or SMS availability. The Data Network (DN), not part of the 5GC network, provides Internet access or operator services and similar.

[0053] An NF may be implemented either as a network element on a dedicated hardware, as a software instance running on a dedicated hardware, or as a virtualized function instantiated on an appropriate platform, e.g., a cloud infrastructure. Certain aspects of the present disclosure and their embodiments may provide solutions to the aforementioned or other challenges. The solution as previously described in Figure 5 assumes that duplicate PDU session can only happen while the UE is within the same access type, such as, 3GPP access, where the UE uses N1 to access the 5G Core network and request establishment of PDU session. The AMF is likely common to both PDU Sessions (old and new) and consequently AMF can detect the duplication and clean up the access resources and its own resources associated with the stale PDU session. The stale PDU session is on the old SMF which includes associations to PCF (policy function), UPF (User plane function) and even CHF (charging function) However, the solution above illustrated in Figure 5 does not handle the problem when the second (the new) PDU session can be initiated by the UE on a different access network (e.g., non-3GPP such as wireless LAN when an existing PDU session is on 3GPP access). For example, the old PDU session could be on 3GPP N1 access / AMF (if 5G), while the new PDU Session could be on non-3GPP untrusted Wi-Fi access / ePDG or N3IWF (untrusted non-3GPP interworking function) or could also be over trusted Wi-Fi access / TNGF (trusted non-3GPP gateway function). In this scenario, the AMF will not be able to detect the duplication to clean up its context and 3GPP RAN resources associated with the PDU session ID. Only the UDM 206 can detect the duplicate PDUSession (assuming the two sessions are anchored on two different SMFs – SMF1208-1 for N1 / AMF access and SMF2208-2 for Wi-Fi / ePDG access. The opposite scenario also applies, i.e., the old session is from WLAN / ePDG or N3IWF / TNGF and the new session is established over 3GPP N1 access connecting to an AMF in 5G or 3GPP S1 access to MME in 4G. Note that other generation of access and core network are not precluded, such as 3G, 6G and beyond. The solution in Figure 5 described above cannot solve this scenario. Since in the solution above, SMF1 cannot clean up any AMF / RAN resources associated with the old stale session.

[0054] Embodiments of the solutions described herein an SMF hosting stale PDU session context to determine that the AMF and optionally RAN include state PDU session context as well that needs to be cleaned up. The proposed solution described within the context of 5G core network functions extends UECM deregistration mechanism at the UDM 206, which is responsible for subscription and context data management, with a new deregistration reason “Duplicate PDU Session on different access”.

[0055] Mainly, when UDM 206 detects duplicate PDU session is initiated by a UE but on a different access, it notifies the (old) SMF 208-1 to deregister the old PDU Session (with the same PDU session ID as the new duplicated one) with a specific deregistration reason “Duplicate PDU Session on different access”. This would result in that the SMF 208-1 initiates cleaning up not only the core side associated with the old PDU Session (cleaning up associations with PCF, CHF, UPF), but also the access side associated with the old PDU Session (AMF and RAN), either the AMF triggers the RAN clean up or the old SMF 208-1 sends an N2 message to the RAN node via the AMF.

[0056] Having a specific deregistration reason for duplicate PDU session deregistration notification can differentiate the two scenarios – (i) duplicate PDU sessions are in same access (e.g., both sessions are on N1 access) as per prior art (Figures 4 and 5) and (ii) duplicate PDU sessions are in different accesses (e.g., old PDU session with PDU session ID1 is on N1 access / 3GPP access, and the new PDU session with also PDU session ID1 is on untrusted Wi-Fi access (either over ePDG or over N3IWF when connected to a different AMF). This may also apply for when the new PDU session is on trusted WiFi access as well.

[0057] This distinction by the UDM 206 of the deregistration reason in the deregistration notification allows SMF 208-1 to treat the two scenarios differently andthus enabling clean-up of resources accordingly when associated with the stale old session.

[0058] Figure 6 illustrates duplicate PDU session release of stale resources when an intermediate SMF (I-SMF) is not deployed. Figure 6 is illustrated with an ePDG, but it could be an N3IWF using a different AMF than the initial AMF used in the previous PDU session establishment.

[0059] Step 1: UE has an existing PDU Session on SA access (3GPP access) with SMF1208-1. SMF1208-1 registers with UDM 206. It indicates PDU session ID1 and may indicate the access type as well.

[0060] Step 2-4 UE moves to non-3GPP access (WiFi) and connects to ePDG or N3IWF (or even TNGF) and initiates establishment of the same PDU Session with same PDU Session ID. This time SMF2208-2 is selected for the PDU session by ePDG or another AMF (when N3IWF / TNGF is used). This could be due to wrong implementation or misconfiguration in the UE. As SMF2208-2 does not have any subscription data, it registers with the UDM 206 by sending a UECM-Registration where it indicates UE accessing via ePDG or N3IWF or TNGF or simply access type over non-3GPP access. Note that indication of ePDG ot N3IWF or TNGF are also indication of non-3GPP access by the UE.

[0061] On detection by the UDM 206 of duplicate PDU session ID1 on a different access, the UDM 206 sends a deregistration notification to the old SMF (SMF1208-1). It also includes a new deregistration reason (“Duplicate PDU Session on different access” or “Duplicate PDU Session on non-3GPP access) is provided by the UDM 206 if previous access was on 3GPP access. It may also include the PDU session ID (PDU session ID1) that is duplicated. One or more PDU session IDs may be included. Of more than one is duplicated. Note that the Vice versa is also applicable, i.e., if previous access was on non-3GPP access, the UDM 206 may indicates “duplicate PDU session on 3GPP access”. A person skilled in the art would understand the different permutation and that the deregistration reason needs to identify duplication when UE requesting same PDU session with same PDU session ID over a different access network type, to make sure that all resources including access network resources including access network function resources are appropriately released in the access network and optionally indicating to the UE that PDU session context for PDU session ID1 is released over 3GPP access.

[0062] Step 5-8. Based on the received deregistration reason, SMF1208-1 initiates deletion of the old stale PDU Session in SMF1 (including UPF, PCF, CHF, not shown). Optionally, it may use N1N2 Message Transfer mechanism or other appropriate mechanism to trigger the AMF to release access resources associated to PDU session ID1 in RAN node previously serving the UE and optionally it may inform the UE that PDU session ID1 over 3GPP access is finally released or deleted. For example, the N1N2 Message Transfer message includes N1 resources release (in UE) and / or N2 session release (in gNB) request.

[0063] Step 9. SMF1208-1 sends SM context status notify to AMF (with cause =” Duplicate PDU Session on different access” or “Duplicate PDU session on non-3GPP access) to enable AMF to release any context associated with the old PDU Session stored in the AMF. Note that this step may be combined with steps 5-8 above as well. In which case, the AMF may also then trigger a release context in the RAN node, e.g., transferring a session management N2 message or using an appropriate message over N2 to release the associated PDU session context in the RAN node. The AMF may also trigger a notification to the UE over NAS that the PDU session context associated to PDU session ID1 is released over 3GPP access.

[0064] Figure 7 illustrates duplicate PDU session release of stale resources when an intermediate SMF is deployed. Figure 7 is illustrated with an ePDG, but it could be an N3IWF using a different AMF than the initial AMF used in the previous PDU session establishment.

[0065] Step 1: UE has an existing PDU Session on SA access (3GPP access) with SMF1208-1. SMF1208-1 registers with UDM 206. It indicates PDU session ID1 and may indicate the access type as well.

[0066] Step 2-4 UE moves to non-3GPP access (WiFi) and connects to ePDG or N3IWF (or even TNGF) and initiates establishment of the same PDU Session with same PDU Session ID. This time SMF2208-2 is selected for the PDU session by ePDG or another AMF (when N3IWF / TNGF is used). This could be due to wrong implementation or misconfiguration in the UE. As SMF2208-2 does not have any subscription data, it registers with the UDM 206 by sending a UECM-Registration where it indicates UE accessing via ePDG or N3IWF or TNGF or simply access type over non-3GPP access. Note that indication of ePDG ot N3IWF or TNGF are also indication of non-3GPP access by the UE.

[0067] On detection by the UDM 206 of duplicate PDU session ID1 on a different access, the UDM 206 sends a deregistration notification to the old SMF (SMF1208-1). It also includes a new deregistration reason (“Duplicate PDU Session on different access” or “Duplicate PDU Session on non-3GPP access) is provided by the UDM 206 if previous access was on 3GPP access. It may also include the PDU session ID (PDU session ID1) that is duplicated. One or more PDU session IDs may be included. Of more than one is duplicated. Note that the Vice versa is also applicable, i.e., if previous access was on non-3GPP access, the UDM 206 may indicates “duplicate PDU session on 3GPP access”. A person skilled in the art would understand the different permutation and that the deregistration reason needs to identify duplication when UE requesting same PDU session with same PDU session ID over a different access network type, to make sure that all resources including access network resources including access network function resources are appropriately released in the access network and optionally indicating to the UE that PDU session context for PDU session ID1 is released over 3GPP access.

[0068] Step 5-9. Based on the received deregistration reason, SMF1208-1 initiates deletion of the old stale PDU Session in SMF1208-1 (including UPF, PCF, CHF, not shown) and in I-SMF using PDU session update. Optionally, the PDU session update includes N1 information indicating PDU session ID1 resources release (in UE) and / or N2 session release (in gNB) request. The I-SMF may use N1N2 Message Transfer mechanism or other appropriate mechanism to trigger the AMF to release access resources associated to PDU session ID1 in RAN node previously serving the UE and optionally it may inform the UE that PDU session ID1 over 3GPP access is finally released or deleted.

[0069] Step 9-10. SMF1208-1 sends SM context status notify to I-SMF (with cause =” Duplicate PDU Session on different access” or “Duplicate PDU session on non-3GPP access) to enable - (i) I-SMF to release SM Context and (ii) I-SMF to send SM Context Status Notify to AMF including the same cause as received by the I-SMF from SMF1 208-1. The AMF on receiving the SM context notify releases any context associated with the old PDU Session stored in the AMF. Note that this step may be combined with steps 5-9 above as well. In which case, the AMF may also then trigger a release context in the RAN node, e.g., transferring a session management N2 message or using an appropriate message over N2 to release the associated PDU session context in the RANnode. The AMF may also trigger a notification to the UE over NAS indicating that the PDU session context associated to PDU session ID1 is released over 3GPP access.

[0070] Figure 7B illustrates a more detailed flow diagram based on Figure 6 and 7 of the interaction between UDM 206 and service consumer (SMF 208) based on 3GPP 5G service based interface (SBI) procedure. More specifically the procedure is described as UDM 206 initiated NF Deregistration, where the UDM 206 initiates the deregistration procedures towards the SMF 208 of the old PDU session when a new PDU session has been established with the same PDU session ID from a different SMF, during SM Context Transfer procedure (see clause 4.26.5.3 of 3GPP TS 23.502 incorporated by reference) or when duplicated PDU sessions existing in the network (e.g. the AMF failed to release the old PDU session before creation of the new PDU session with the same PDU session ID or the new PDU session with the same PDU session ID is created on a different access type).

[0071] Step 1. The UDM 206 sends a POST request to the deregCallbackUri as provided by the NF service consumer during the registration.

[0072] If the SMF deregistration is triggered by SM Context Transfer procedure, i.e. the UDM 206 has received a registration request with registrationReason IE set to the value "SMF_CONTEXT_TRANSFERRED" from another SMF, the UDM 206 shall set the deregReason IE to the value "SMF_CONTEXT_TRANSFERRED". If the SMF deregistration is due to duplicated PDU sessions in the network, i.e. the UDM 206 has received a registration request from another SMF without registrationReason IE set to the value "SMF_CONTEXT_TRANSFERRED", the UDM 206 shall set the deregReason IE to the value "DUPLICATE_PDU_SESSION".

[0073] If the SMF deregistration is due to an UDM-triggered PDU session release with re-activation, the UDM shall set the deregReason attribute in DeregistrationData to the value "PDU_SESSION_REACTIVATION_REQUIRED"; in this case, the SMF shall trigger a network-initiated PDU session release procedure (see clause 4.3.4 of 3GPP TS 23.502, incorporated by reference) with 5GSM cause "Reactivation requested" (see clause 8.3.14 of 3GPP TS 24.501, incorporated by reference)

[0074] If the UDM 206 has received a registration request from another SMF on a different access type, such as over WLAN and ePDG (ePDG being the security gateway that supports access to EPS via LWAN), the registration request in UDM 206 includes the access type and / or epdgindicator (epdgind) information element set to true, theUDM 206 shall set the deregReason IE to the value "DUPLICATE_PDU_SESSION_ DIFFERENT_ACCESS " or "DUPLICATE_PDU_SESSION_ EPDG " or "DUPLICATE_PDU_SESSION_ non-3gpp access "

[0075] 2a. On success, the NF service consumer responds with "204 No Content".

[0076] An SMF received the deregistration notification without with deregReason IE set to the value "DUPLICATE_PDU_SESSION_ DIFFERENT_ACCESS " or "DUPLICATE_PDU_SESSION_ non-3GPP access" or "DUPLICATE_PDU_SESSION_ on ePDG" indicating the duplicate PDU session is on a different access then the current one, or with deregReason IE set to "DUPLICATE_PDU_SESSION” it shall release the PDU session but shall not send a SM Context Status Notification to the AMF. For a PDU session with I-SMF or V-SMF, the anchor SMF shall send a Status Notification to the I- SMF or V-SMF indicating that the PDU session is released due to duplicated PDU sessions.

[0077] An SMF receiving the deregistration notification with deregReason IE set to the value "DUPLICATE_PDU_SESSION_ DIFFERENT_ACCESS " or "DUPLICATE_PDU_SESSION_ non-3GPP access" or "DUPLICATE_PDU_SESSION_ on ePDG" indicating the duplicate PDU session is on a different access then the current one, it shall release the PDU session, release any access specific resource, and shall send a SM Context Status Notification to the AMF. For a PDU session with I-SMF or V- SMF, the anchor SMF shall send a resources release request to the access and a Status Notification to the I-SMF or V-SMF indicating that the PDU session is released due to duplicated PDU sessions on different access.

[0078] 2b. On failure or redirection, one of the appropriate HTTP status code listed in Table 6.2.5.2-3 of TS 29.503 (incorporated by reference) shall be returned. For a 4xx / 5xx response, the message body may contain appropriate additional error information.

[0079] The enumeration DeregistrationReason represents the reason for the Deregistration Notification. It shall comply with the provisions defined in table 1 below.Table 1: Enumeration DeregistrationReason Enumeration value Description "UE_INITIAL_REGISTRATION" When sent by the HSS; indicates that the deregistration towards the UDM is due to an initial attach in EPS. When sent by the UDM; indicates that the deregistration in the old AMF is due to a new AMF serving the UE during an initial registration See 3GPP TS 23.502 [3] and 3GPP TS 23.632

[0032] . "UE_REGISTRATION_AREA_CHANGE" see 3GPP TS 23.502 [3] "SUBSCRIPTION_WITHDRAWN" see 3GPP TS 23.502 [3] "5GS_TO_EPS_MOBILITY" see 3GPP TS 23.502 [3] and 3GPP TS 23.632

[0032] . "5GS_TO_EPS_MOBILITY_UE_INITIAL_REGISTRATION" This value shall only be sent by the UDM. It indicates that the deregistration in AMF is due to an initial attach in EPS, See 3GPP TS 23.502 [3] and 3GPP TS 23.632

[0032] . "REREGISTRATION_REQUIRED" see 3GPP TS 23.502 [3] "SMF_CONTEXT_TRANSFERRED" see 3GPP TS 23.502 [3] "DUPLICATE_PDU_SESSION" This value shall only be sent by the UDM to an SMF. It indicates that the deregistration in the SMF is due to a new PDU session with the same PDU session ID has been established in another SMF on same access type. "PDU_SESSION_REACTIVATION_REQUIRED" This value shall only be sent by the UDM to an SMF. It indicates that the PDU session being released is requested to be re-activated. "DISASTER_CONDITION_TERMINATED" This value shall be used by the UDM when the disaster condition ceases. "DUPLICATE_PDU_SESSION_DIFFERENT_ACCESS"or all indicating the duplicate PDU "DUPLICATE_PDU_SESSION_ non-3GPP access" or session is on a different access "DUPLICATE_PDU_SESSION_ on ePDG" then the existing PDU session. This value shall only be sent by the UDM to an SMF. It indicates that the deregistration in the SMF is due to a new PDU session with the same PDU session ID has been established in another SMF on a different access type.

[0080] Figure 8 illustrates a flow chart for one or more embodiments of a method in UDM 206 based on embodiments described in Figures 6, 7 and 7B. The UDM receives from a first session management function a registration to register the first session management function for the UE / PDU session identified by a PDU session ID (ID1) when the first session management function receives a request to establish the PDU session from the UE over the 3GPP access network. The registration may indicate the PDU session ID (ID1), the access type or RAT type (e.g., 3GPP access type) for the PDU session, network slice identifier (S-NSSAI) and / or Data Network Name (DNN).

[0081] When the UE moves to non-3GPP access and initiates establishment of a PDU session indicating the same PDU session (ID1) (using procedures described in the 3GPP standard, TS 23.502 incorporated by reference) involving a second session management function, the UDM receives from the second session management function another registration message indicating registration of SMF2, same PDU session ID (ID1), network slice (S-NSSAI) and / or DNN and indication that UE is accessing via non-3GPP access, such as for example access via ePDG or N3IWF or TNGF or an indication of non- 3GPP access. The UDM then determines that ID1 is a duplicate PDU session established over a different access network, i.e., over non-3GPP access as the first one is over 3GPP access and sends a deregistration notification to the first session management function including a deregistration reason indicating duplicate PDU session on different access or duplicate PDU session over non-3GPP access or any appropriate reason indicating duplicate PDU session over two different access networks (e.g., 3GPP and non-3GPP access networks).

[0082] In some examples, the UDM detects the duplication by determining that the PDU session ID was previously registered by the first session management function as established over a different access / RAT (e.g., 3GPP access technology), where the first session management function may also register with the PDU session ID at the UDM the network slice (S-NSSAI) and DNN.

[0083] The UDM then determines whether the PDU session ID, S-NSSAI and DNN as provided by the first session management function for the PDU session are the same as the PDU session ID, S-NSSAI and DNN provided by the second session management function.

[0084] Figure 9 illustrates a flow chart for one or more embodiments of a method in a first session management function (SMF) based on embodiments described in Figures 6,7 and 7B. The first session management function initially receiving from the AMF or intermediate SMF a request to establish the PDU session with PDU session ID (ID1) on a network slice (S-NSSAI) and DNN and originated by the UE over the 3GPP access network. The first session management function sends to a User Data Management (UDM) a registration to register the first session management function for the UE / PDU session identified by the PDU session ID (ID1). The registration may indicate the PDU session ID (ID1), the access type or RAT type (e.g., 3GPP access type) for the PDU session, network slice identifier (S-NSSAI) and / or Data Network Name (DNN).

[0085] When the UE moves to non-3GPP access and initiates establishment of a PDU session indicating the same PDU session (ID1) (using procedures described in the 3GPP standard, TS 23.502 incorporated by reference) involving a second session management function, the first session management receives a deregistration notification from the UDM, the deregistration notification including a deregistration reason indicating duplicate PDU session on different access or duplicate PDU session over non-3GPP access or any appropriate reason indicating duplicate PDU session over two different access networks (e.g., 3GPP and non-3GPP access networks), and may include the PDU session ID (ID1) that is duplicated. More than one PDU session ID may be included if more than one is determined to be duplicated by the UDM.

[0086] The first session management function notifies the AMF (when no Intermediate SMF (I-SMF) is deployed) or notifies the I-SMF (when I-SMF is deployed) that the PDU session ID (ID1) is duplicated causing the corresponding resources in AMF and I-SMF to be released. If the first session management function notifies the I-SMF (in case of I-SMF deployment), the I-SMF then notifies the AMF after releasing the context associated to the duplicated PDU session ID. The notification from first session management function to I-SMF or AMF or from I-SMF to AMF includes the reason or cause indicating release due duplicate PDU session on different access or duplicate PDU session over non-3GPP access or any appropriate reason indicating duplicate PDU session over two different access networks (e.g., 3GPP and non-3GPP access networks) and may include the PDU session ID and / or S-NSSAI and / or DNN to enable the AMF to release the duplicate context for the PDU session ID for the UE. For example, the notification is a status notify message in Figures 6 and 7 and comprising a cause value. The following table list the duplication reason as one additional cause value to be specified in the standard: The enumeration Cause indicates a cause information. It shall comply with the provisions defined in table 2 based on table 6.1.6.3.8-1 of TS 29.518 (incorporated by reference).Table 2: Enumeration Cause Enumeration value Description ---- Some parts not shown (part of TS 29.518) "REL_DUE_TO_SLICE_NOT_AVAILABLE" Release due to the associated S- NSSAI becomes no longer available (e.g. the validity time of the S-NSSAI expires, or the S-NSSAI is decommissioned, etc.). "REL_DUE_TO_DUPLICATE_SESSION_ID" Release due to a UE request to establish a new PDU session with an identical PDU session Id. "REL_DUE_TO_DUPLICATE_SESSION_ID_DIFFERENT Release due to a UE request to ACCESS" or "DUPLICATE_PDU_SESSION_ non-3GPP establish a new PDU session with access" or "DUPLICATE_PDU_SESSION_ on ePDG" an identical PDU session Id on a different access. ---- Some parts not shown (part of TS 29.518)

[0087] The notification may potentially trigger the AMF to release access network resources associated with the PDU session ID and may also trigger the AMF to inform the UE that PDU session ID (ID1) is released in the 3GPP access network (previous access network). Alternatively, the first session management function may alternatively send a separate message to trigger the AMF to release the access network resources and to notify the UE of the PDU session ID context release. The separate message may be an N1N2 message transfer.

[0088] The deregistration notification from UDM to the old SMF may include one or more parameters / information elements to indicate that the same PDU session is established on a different access network / core network. For example, the indication of duplicate PDU session over different access may be indicated as one parameter, deregistration reason “Duplicate PDU Session on different access” or “Duplicate PDU Session on non-3GPP access” or Duplicate PDU Session_ePDG” or two parameters / IEs can be used such as in the example below illustrated in Figure 10 where the two parameters may be the existing deregistration reason “DUPLICATE PDU session” and another new parameter included in the deregistrationnotification to the old SMF being the epdgind IE indicating the PDU session is established over ePDG as provided to the UDM from the new SMF. Alternatively, the two parameters are the existing deregistration reason indicating duplicate PDU session and the access type or Radio access technology type or both over which the duplicated PDU session is established in the new access / system.

[0089] Figure 10 can be implemented through various examples as described here in. For example in Figure 10, the epdgind IE to indicate that the ePDG is used for the PDU session can be included in the registration request from the new SMF (SMF-2208-2), oran indication of the access type and / or RAT type to indicate the PDU session the RAT / access type used by the UE for the new PDU session (either parameters above is included in the registration request of the new SMF 208-2 to the UDM 206 and in the deregistration notification from the UDM 206 to the old SMF, SMF1208-1). The behaviour of the old SMF 208-1 when receiving a deregistration notification from UDM comprising the access type / RAT type of the duplicated PDU session together with the deregistration reason (duplicate PDU Session) and the PDU session ID is the same as receiving a deregistration notification comprising either: a. a Epdgind IE set to true and a deregistration reason set to duplicate pdu session, and PDU session ID or b. a Deregistration reason set to “Duplicate PDU Session on different access” or “Duplicate PDU Session on non-3GPP access” or Duplicate PDU Session ePDG” and the PDU session ID. In this case, the deregistration notification does not need to include the access type / RAT type oor the epdgind IE.

[0090] Figure 10 illustrates an example for the same embodiment with the difference that two parameters are used as an indication for duplicate PDU session to trigger appropriate resource release in the old system.

[0091] Step 1: UE has an established PDU session over SMF1208-1, then later establishes the same PDU session over SMF2208-2 (e.g., changed radio access / core network to for eg. WLAN / ePDG). The SMF2 208-2 (which may be a PGW-C+SMF or PGW-C or just SMF (connected to ePDG)) sends a UECM Registration Request to UDM 206 as per current 3GPP TS 23.502 procedure for PDU session establishment and includes the PDU session ID. If the UE has established the duplicate PDU session over WLAN access such as ePDG / WLAN where ePDG is the WLAN gateway described in 4G standard TS 23.402, SMF2 208-2 includes an epdgind IE with value set to “true”, else it may omit the IE or include it with value “false” if the new session is established over 3GPP access / AMF (N1 mode).

[0092] Step 2: may be done together with Step 3. The UDM 206 does the duplicated PDU session detection based on the PDU session ID.

[0093] Step 3: The UDM 206 finds there is a duplicated PDU session which registered from SMF1208-1. The UDM 206 prepares the UECM DeregistrationNotification Request. Beside the legacy logic, if new session UECM Registration Request contains the epdgIndIE with value set to “true”, the UDM 206 sets the epdgInd IE in UECM DeregistrationNotification Request to value “true”, otherwise, the UDM 206 does not include the epdgInd IE in UE DeregistrationNotification Request or include it with value set to “false”. The UDM 206 will also set the deregReason IE to the value "DUPLICATE_PDU_SESSION.

[0094] Step 4: the UDM 206 sends the UECM DeregistrationNotification Request to SMF1.

[0095] Step 5: when the SMF1208-1 (which may be a PGW-C+SMF as well) receives the UECM deregistration notification with deregReason IE set to the value "DUPLICATE_PDU_SESSION", the SMF1208-1: 1. shall release the old PDU session if the old PDU session is via the access from AMF: a. If epdgInd IE is not included or epdgInd IE included with value set to “false”, the SMF1 shall not send a SM Context Status Notification to the AMF to trigger release of resources associated to the PDU session. For a PDU session with I-SMF or V-SMF, the SMF1208-1 which is the anchor SMF shall send a Status Notification to the I- SMF or V-SMF indicating that the PDU session is released due to duplicated PDU session. b. If the epdgInd IE is included with value set to “true”, the SMF1 208-1 shall not involve UE. 2. shall initiate the PDN connection release if the old session is via the access from SGW-C (or other 3GPP Access node rather than AMF) a. If epdgInd IE not included or epdgInd IE included with value set to “false”, SMF1 does not notify SGW-C. b. If the epdgInd IE is included with value set to “true”, notify the SGW-C so resources are released in SGW-C. 3. shall initiate the PDN connection release if the old session is via the access from ePDG (WLAN / ePDG) c. The SMF1208-1 shall initiate the PDN connection release and notify the ePDG.

[0096] In yet another aspect based on Figure 10,

[0097] Step 1: UE has an established PDU session over SMF1208-1, then later establishes the same PDU session over SMF2208-2 and ePDG (e.g., changed radio access / core network to for eg. WLAN). The SMF2 208-2 (which may be a PGW-C+SMF or PGW-C or just SMF (connected to ePDG)) sends a UECM Registration Request to UDM 206 as per current 3GPP TS 23.502 procedure for PDU session establishment and includes the PDU session ID. If the UE has established the duplicate PDU session over WLAN access such as ePDG / WLAN where ePDG is the WLAN gateway described in 4G standard TS 23.402, SMF2208-2 includes an epdgind IE with value set to “true”, else it may omit the IE or include it with value “false” if the new session is established over 3GPP access / AMF (N1 mode).

[0098] Step 2: may be done together with Step 3. The UDM 206 does the duplicated PDU session detection based on the PDU session ID.

[0099] Step 3: The UDM 206 finds that the new PDU session over SMF2208-2 is a duplicated PDU session to the PDU session included in the previous registration from SMF1208-1. The UDM 206 prepares the UECM DeregistrationNotification Request. If the UECM Registration Request from SMF2208-2 contains the epdgInd IE with value set to “true”, the UDM 206 sets the deregReason IE to the value "DUPLICATE_PDU_SESSION_ePDG” or "DUPLICATE_PDU_SESSION_ on different access” or “Duplicate PDU Session on non-3GPP access” or appropriate reason indicating duplicate PDU session is on different access than the existing one in the UECM DeregistrationNotification message to SMF1208-1.

[0100] Step 4: the UDM 206 sends the UECM DeregistrationNotification Request to SMF1208-1 including the deregReason IE.

[0101] Step 5: The SMF1 (which may be a PGW-C+SMF as well) receiving the UECM deregistration notification with deregReason IE set to the value "DUPLICATE_PDU_SESSION_ePDG” or "DUPLICATE_PDU_SESSION_ on different access” or “Duplicate PDU Session on non-3GPP access” or appropriate reason indicating duplicate PDU session is on different access than the existing one, shall release the PDU session in SMF1 208-1 and release the RAN resource by sending an appropriate N2 message via AMF. The SMF shall also send a SM Context Status Notify for the released PDU session to the AMF. For a PDU session with I-SMF or V-SMF, the anchor SMF1 shall send a Status Notification to the I-SMF or V-SMF indicating that thePDU session is released due to duplication session established via ePDG or different access or non-3GPP access.

[0102] The following embodiments provides further examples of Figure 10 with as proposed changes (underlined) to the 3GPP standard procedures illustrating only two examples of how to indicate duplicate PDU session over a different access. For example, the following alternative can be implemented in the standard based on slightly different aspects of the embodiments described with Figure 10: Alternative 1) changes to 3GPP TS 29.502 and TS 29.503 5.2.2.8.3.3 Network (e.g. H-SMF, SMF) or UE requested PDU session release The requirements specified in clause 5.2.2.8.3.1 shall apply with the following modifications. 1. Same as step 1 of Figure 5.2.2.8.3.1-1 in TS 29.502 (or step 4 in figure 10), with the following modifications. The requestIndication shall be set to NW_REQ_PDU_SES_REL or UE_REQ_PDU_SES_REL for a Network requested PDU session release or UE requested PDU session release respectively. If the session release is triggered by UECM DeregistrationNotification with deregReason IE set to DUPLICATED_PDU_SESSION, the cause shall be set to REL_DUE_TO_DUPLICATE_SESSION_ID. If the UECM DeregistrationNotification contains the epdgInd IE with the value “true”, the epdgInd in VsmfUpdateData shall be set to true, otherwise the epdgInd IE in VsmfUpdateData shall not be present or present with value set to false. Alternatively (to including the epdgind IE), if deregReason IE is set to one of “duplicate PDU session on different access” or “duplicate PDU session on non-3GPP access” or “duplicate PDU session on 3GPP access” or “duplicate PDU session ePDG”, the epdgInd IEis not required to be included in the notification payload. 2. Same as step 2 of Figure 5.2.2.8.3.1-1 of TS 29.502 ( ), with the following modifications. If the requestIndication in the request is set to NW_REQ_PDU_SES_REL or UE_REQ_PDU_SES_REL, - If the cause is set to REL_DUE_TO_DUPLICATE_SESSION_ID: - If the epdgInd IE in VsmfUpdateData is set to true, the V-SMF or I-SMF shall initiate the release of the RAN resources allocated for the PDU session if any and shall not send a PDU Session release command to the UE. - or if the cause is set to of “duplicate PDU session on different access” or “duplicate PDU session on non- 3GPP access” or “duplicate PDU session on 3GPP access” or “duplicate PDU session ePDG” the V-SMF or I-SMF shall initiate the release of the AMF and / or RAN resources allocated for the PDU session if any and shall not send a PDU Session release command to the UE, Otherwise, if the received cause is simply REL_DUE_TO_DUPLICATE_SESSION_ID the V-SMF or I-SMF shall initiates the release of the resource allocated for the PDU session. The V-SMF or I-SMF shall not send an N1N2 Message Transfer request and a SMContextStatusNotification to AMF, and the V-SMF or I-SMF shall not send a PDU Session release command to the UE. - Otherwise, the V-SMF or I-SMF shall initiate the release of RAN resources allocated for the PDU session if any and shall send a PDU session release command to the UE. The V-SMF or I-SMF shall not release the SM context for the PDU session. NOTE: The SM context will be released when receiving Status notification from the H-SMF or SMF indicating the PDU session is released in the H-SMF or SMF.Additional change to 3GPP TS 29.502 as a further example for Figure 10, step 5): 5.2.2.10 Notify Status service operation 5.2.2.10.1 General The Notify Status service operation shall be used to notify the NF Service Consumer about status changes of a PDU session (e.g. when the PDU session is released and the release is not triggered by a Release Request, or when the PDU session is moved to another system, or when the control of the PDU session is taken over by another anchor SMF), for a HR PDU session or a PDU session involving an I-SMF. It is used in the following procedures: - Home network requested PDU Session release (see clause 4.3.4.3 of 3GPP TS 23.502 [3]), e.g. H-SMF initiated release; - SMF requested PDU session release, for a PDU session involving an I-SMF (see clause 4.23 of 3GPP TS 23.502 [3]); - Handover of a PDU Session procedure from 3GPP to untrusted non-3GPP access (see clauses 4.9.2.4.2 and 4.23.16.2 of 3GPP TS 23.502 [3]); - Interworking procedures without N26 interface, e.g.5GS to EPS Mobility (see clause 4.11.2.2 of 3GPP TS 23.502 [3]); - Handover from 5GC-N3IWF to EPS (see clause 4.11.3.2 of 3GPP TS 23.502 [3]); - Handover from 5GS to EPC / ePDG (see clause 4.11.4.2 of 3GPP TS 23.502 [3]); - The control of PDU session is taken over by a new anchor SMF within the same SMF set (see clause 5.22 of 3GPP TS 29.244

[0029] ), and the new SMF instance decides to notify the change of SMF; - SMF triggered I-SMF selection or removal (see clause 4.23.5.4 of 3GPP TS 23.502 [3]); - Change of SSC mode 2 PDU Session Anchor with different PDU Sessions (see clause 4.3.5.1 of 3GPP TS 23.502 [3]); - Change of SSC mode 3 PDU Session Anchor with multiple PDU Sessions (see clause 4.3.5.2 of 3GPP TS 23.502 [3]). The SMF (i.e. H-SMF for a HR PDU session, or SMF for a PDU session involving an I-SMF) shall notify the NF Service Consumer (i.e. V-SMF for a HR PDU session, or I-SMF for a PDU session involving an I-SMF) by using the HTTP POST method as shown in Figure 5.2.2.10-1 of TS 29.502, herein presented as Figure 11. According to Figure 11: 1. The SMF shall send a POST request (part of step 5 of figure 10) to the resource representing the individual PDU session resource in the NF Service Consumer. The payload body of the POST request shall contain the notification payload, with the status information. If the notification is triggered by PDU session handover to release resources of the PDU Session in the source access, the notification payload shall contain the resourceStatus IE with the value "RELEASED" and the Cause IE with value "PDU_SESSION_HANDED_OVER" as specified in clause 4.2.9.4.2 of 3GPP TS 23.502 [3]. If the notification is triggered by PDU session handover to release only the SM Context with the I-SMF in the source access but without releasing the PDU session in the AMF, the notification payload shall contain the resourceStatus IE with the value "UPDATED" and the Cause IE with the value "PDU_SESSION_HANDED_OVER" as specified in clause 4.23.16.2 of 3GPP TS 23.502 [3]. If the notification is triggered by SMF for I-SMF selection or removal for the current PDU session, or SMF selection during PDU Session re-establishment for SSC mode 2 / 3, the notification payload shall contain the resourceStatus IE with the value "UNCHANGED", the Cause IE with the value "TARGET_DNAI_NOTIFICATION" and the targetDnaiInfo IE. The targetDnai IE in the targetDnaiInfo IE shall be absent if the I-SMF removal is triggered due to the DNAI currently served by the I-SMF being no longer used for the PDU Session. If the notification is triggered for SMF selection during PDU Session re-establishment for SSC mode 3, the notification payload may also contain the oldPduSessionRef IE as specified in clause 4.3.5.2 of 3GPP TS 23.502 [3]. If the notification is triggered by PDU session handover to release resources of the PDU Session in the target access due to handover failure between 3GPP access and non-3GPP access, the notification payload shall contain the resourceStatus IE with the value "RELEASED" and the Cause IE with the value "PDU_SESSION_HAND_OVER_FAILURE". If the NF Service Consumer indicated support of the HOFAIL feature (see clause 6.1.8) and if the notification is triggered by PDU session handover to update access type of the PDU Session due to handover failure between 3GPP access and non-3GPP access, the notification payload shall contain the resourceStatus IE with the value "UPDATED", the anType IE with the value "3GPP" or "NON_3GPP" indicating the access type of the PDU session after the handover failure scenario and the Cause IE with the value "PDU_SESSION_HAND_OVER_FAILURE". If upon a change of anchor SMF, the new anchor SMF instance decides to notify the change of anchor SMF, then the notification payload shall contain the resourceStatus IE with the value "UPDATED" and the Cause IE with the value "CHANGED_ANCHOR_SMF". In addition, the new anchor SMF instance shall include its SMF Instance ID in the notification payload, and / or carry an updated binding indication in the HTTP headers to indicate the change of anchor SMF (as per step 6 of clause 6.5.3.3 of 3GPP TS 29.500 [4]). If the PDU session may be moved to EPS with N26 and the EPS PDN Connection Context information of the PDU session on the new anchor SMF is different from the one on the old anchor SMF, the payload shall also include the "epsPdnCnxInfo" IE including the updated EPS PDN Connection Context information. The NF Service consumer shall overwrite the locally stored EPS PDN Connection Context information with the new one if received. If the notification is triggered by a PDU session release due to slice inactivity as specified in clause 5.15.15.3 of 3GPP TS 23.501 [2], the notification payload shall contain the resourceStatus IE with the value "RELEASED" and the Cause IE with the value "REL_DUE_TO_SLICE_INACTIVITY". If the notification is triggered by a PDU session release due to UECM DeregistrationNotification with deregReason IE set to “DUPLICATE_PDU_SESSION”, the notification payload shall contain the resourceStatus IE with the value "RELEASED" and the Cause IE with the value " REL_DUE_TO_DUPLICATE_SESSION_ID". If the epdgInd IE is present with value set to “true” in UECM DeregistrationNotification, the notification payload shall contain the epdgInd IE with the value “true”, otherwise the NF consumer shall not contain the epdgInd IE or contains epdgInd IE with the value “false”. Alternatively, if deregReason IE is set to one of “duplicate PDU session on different access” or “duplicate PDU session on non-3GPP access” or “duplicate PDU session on 3GPP access” or “duplicate PDU session ePDG” the epdgInd IEis not required to be included in the notification payload. 2a. On success, "204 No Content" shall be returned and the payload body of the POST response shall be empty. If the SMF indicated in the request that the PDU session in the SMF is released, the NF Service Consumer shall release the SM context for the PDU session. If the SMF indicated in the request that the PDU session in the SMF is released with Cause IE with value "REL_DUE_TO_DUPLICATE_SESSION_ID", the NF Service Consumer shall release PDU session. If the epdgInd IE with value “true” or the deregReason IE is set to one of “duplicate PDU session on different access” or “duplicate PDU session on non-3GPP access” or “duplicate PDU session on 3GPP access” or “duplicate PDU session ePDG” in the notification payload, the NF service consumer shall not send a PDU session release command to the UE and may send an N1N2 notification to the AMF to release associated resources for the PDU session. Otherwise, the NF service consumer shall not send an N1N2 Message Transfer request and a SMContextStatusNotification to AMF, and the V-SMF shall not send a PDU Session release command to the UE. If the SMF indicated in the request that the SM context resource is updated with the anType IE, the NF Service Consumer shall change the access type of the PDU session with the value of anType IE. 2b. On failure or redirection, one of the HTTP status code listed in Table 6.1.3.7.3.1-2 shall be returned. For a 4xx / 5xx response, the message body shall contain a ProblemDetails structure with the "cause" attribute set to one of the application errors listed in Table 6.1.3.7.3.1-2.Finally, the following changes are proposed to 3GPP TS 29.503 as examples of figure 10 step 4 or figure 7B, step 1): 5.3.2.3.2 UDM initiated NF Deregistration Figure 5.3.2.3.2-1 shows a scenario where the UDM notifies the registered NF about its deregistration (see also 3GPP TS 23.502 [3] figure 4.2.2.2.2-1 step 14, 3GPP TS 23.502 [3] figure 4.2.2.3.3-1 step 1 and 3GPP TS 23.502 [3] figure 4.26.4.1.1-1 step 14). The request contains the deregCallbackUri URI for deregistration notification as received by the UDM during registration, and Deregistration Data. The UDM initiates the deregistration procedure when the UE is registered to the AMF which does not support CAG feature and the CAG subscription of the UE changes and it is allowed to access the 5GS via CAG cell(s) only. The UDM also initiates deregistration notification when UE moves to different AMF within same AMF-Set. The UDM may also initiate deregistration notification for the disaster inbound roaming UE when a disaster condition is no longer being applicable. Deregistration notification shall not be sent if the nfInstanceId of the AMF initiating registration is same as the old AMF already registered in UDM (e.g. when multiple PLMNs are hosted on same AMF and UE moves across PLMNs). The UDM also initiates the deregistration procedures towards the SMF of the old PDU session when a new PDU session has been established with the same PDU session ID from a different SMF, during SM Context Transfer procedure (see clause 4.26.5.3 of 3GPP TS 23.502 [3]) or when duplicated PDU sessions existing in the network (e.g. the AMF failed to release the old PDU session before creation of the new PDU session with the same PDU session ID). In accordance with Figure 7B or Figure 10 Step 4: 1. The UDM sends a POST request to the deregCallbackUri as provided by the NF service consumer during the registration. If the SMF deregistration is triggered by SM Context Transfer procedure, i.e. the UDM has received a registration request with registrationReason IE set to the value "SMF_CONTEXT_TRANSFERRED" from another SMF, the UDM shall set the deregReason IE to the value "SMF_CONTEXT_TRANSFERRED". If the SMF deregistration is due to duplicated PDU sessions in the network, i.e. the UDM has received a registration request from another SMF without registrationReason IE set to the value "SMF_CONTEXT_TRANSFERRED", the UDM shall set the deregReason IE to the value "DUPLICATE_PDU_SESSION", if new session UECM Registration Request contains the epdgInd IE with value set to “true” or an indication of the access type used for the PDU session, the UDM shall either set the epdgInd IE to the value “true” in UECM DeregistrationNotification Request, or set the deregReason IE to one of “duplicate PDU session on different access” or “duplicate PDU session on non-3GPP access” or “duplicate PDU session on 3GPP access” or “duplicate PDU session ePDG”, otherwise, the UDM shall not include the epdgInd IE in UE DeregistrationNotification Request or include it with value set to “false” (if the epdgind indicator solution is used) or just indicate deregReason IE to"DUPLICATE_PDU_SESSION" If the SMF deregistration is due to an UDM-triggered PDU session release with re-activation, the UDM shall set the deregReason attribute in DeregistrationData to the value "PDU_SESSION_REACTIVATION_REQUIRED"; in this case, the SMF shall trigger a network-initiated PDU session release procedure (see clause 4.3.4 of 3GPP TS 23.502 [3]) with 5GSM cause "Reactivation requested" (see clause 8.3.14 of 3GPP TS 24.501

[0027] ) 2a. On success, the NF service consumer responds with "204 No Content" if no information is to be sent to the UDM. Otherwise, if the "DeregistrationResponseBody" feature is supported by both the UDM and the NF consumer, the NF service consumer (e.g. the SMF) responds with "200 OK" with the response body including the information to the UDM (e.g. the indication that the SMF event subscription on the SMF for the UE have been implicitly removed).An SMF receiving the deregistration notification with deregReason IE set to the value "DUPLICATE_PDU_SESSION" shall release the PDU session: - If epdgInd IE is not included or epdgInd IE is included with value set to “false”, the SMF shall not send a SM Context Status Notification and an N1N2 Message Transfer request to the AMF. For a PDU session with I-SMF or V-SMF, the anchor SMF shall send a Status Notification to the I-SMF or V- SMF indicating that the PDU session is released due to duplicated PDU session. - If the epdgInd IE is included with value set to “true”, or deregReason IE set to one of “duplicate PDU session on different access” or “duplicate PDU session on non-3GPP access” or “duplicate PDU session on 3GPP access” or “duplicate PDU session ePDG”, the SMF shall not send a PDU session release command to UE. 2b. On failure or redirection, one of the appropriate HTTP status code listed in Table 6.2.5.2-3 shall be returned. For a 4xx / 5xx response, the message body may contain appropriate additional error information. The following table illustrates the change in the HTTP message for deregistration notification from the UDM to the SMF: Table 6.2.6.2.5-1: Definition of type DeregistrationData Attribute name Data type P Cardinality Description deregReason DeregistrationReason M 1 String; see clause 6.2.6.3.3 Could indicate (“duplicate PDU session on different access” or “duplicate PDU session on non-3GPP access” or “duplicate PDU session on 3GPP access”, or “duplicate PDU session ePDG” accessType AccessType C 0..1 Access type where the UE is deregistered. Shall be present in Deregistration Notifications sent to the AMF. pduSessionId PduSessionId C 0..1 It shall be present if the deregistration of SMF happens. If present, indicates PDU Session ID for which old SMF is deregistered. newSmfInstanceId NfInstanceId O 0..1 NF Instance Id of the new SMF to which the SMF context is transferred. epdgInd boolean O 0..1 included when deregReason indicates DUPLICATED_PDU_SESSION When present, it indicates whether access of new session is from ePDG. true: access from ePDG. false or absent: access not from ePDG (optional if deregistration registration indicate any of “duplicate PDU session on different access” or “duplicate PDU session on non-3GPP access” or “duplicate PDU session on 3GPP access” or “duplicate PDU session ePDG” Alternative 2: changes to TS 29.502 & TS 29.503 based on other aspects in accordance with Figure 11. 5.2.2.10.1 General The Notify Status service operation shall be used to notify the NF Service Consumer about status changes of a PDU session (e.g. when the PDU session is released and the release is not triggered by a Release Request, or when the PDU session is moved to another system, or when the control of the PDU session is taken over by another anchor SMF), for a HR PDU session or a PDU session involving an I-SMF. It is used in the following procedures: - Home network requested PDU Session release (see clause 4.3.4.3 of 3GPP TS 23.502 [3]), e.g. H-SMF initiated release;- SMF requested PDU session release, for a PDU session involving an I-SMF (see clause 4.23 of 3GPP TS 23.502 [3]); - Handover of a PDU Session procedure from 3GPP to untrusted non-3GPP access (see clauses 4.9.2.4.2 and 4.23.16.2 of 3GPP TS 23.502 [3]); - Interworking procedures without N26 interface, e.g.5GS to EPS Mobility (see clause 4.11.2.2 of 3GPP TS 23.502 [3]); - Handover from 5GC-N3IWF to EPS (see clause 4.11.3.2 of 3GPP TS 23.502 [3]); - Handover from 5GS to EPC / ePDG (see clause 4.11.4.2 of 3GPP TS 23.502 [3]); - The control of PDU session is taken over by a new anchor SMF within the same SMF set (see clause 5.22 of 3GPP TS 29.244

[0029] ), and the new SMF instance decides to notify the change of SMF; - SMF triggered I-SMF selection or removal (see clause 4.23.5.4 of 3GPP TS 23.502 [3]); - Change of SSC mode 2 PDU Session Anchor with different PDU Sessions (see clause 4.3.5.1 of 3GPP TS 23.502 [3]); - Change of SSC mode 3 PDU Session Anchor with multiple PDU Sessions (see clause 4.3.5.2 of 3GPP TS 23.502 [3]); - Network slice usage behaviour control, i.e. SMF initiated PDU session release due to slice inactivity, see clause 5.15.15.3 of 3GPP TS 23.501 [2]. The SMF (i.e. H-SMF for a HR PDU session, or SMF for a PDU session involving an I-SMF) shall notify the NF Service Consumer (i.e. V-SMF for a HR PDU session, or I-SMF for a PDU session involving an I-SMF) by using the HTTP POST method as shown in Figure 5.2.2.10-1. In accordance with Figure 11 : 1. The SMF shall send a POST request to the resource representing the individual PDU session resource in the NF Service Consumer. The content of the POST request shall contain the notification content, with the status information. If the notification is triggered by PDU session handover to release resources of the PDU Session in the source access, the notification content shall contain the resourceStatus IE with the value "RELEASED" and the Cause IE with value "PDU_SESSION_HANDED_OVER" as specified in clause 4.2.9.4.2 of 3GPP TS 23.502 [3]. If the notification is triggered by PDU session handover to release only the SM Context with the I-SMF in the source access but without releasing the PDU session in the AMF, the notification content shall contain the resourceStatus IE with the value "UPDATED" and the Cause IE with the value "PDU_SESSION_HANDED_OVER" as specified in clause 4.23.16.2 of 3GPP TS 23.502 [3]. If the notification is triggered by SMF for I-SMF selection or removal for the current PDU session, or SMF selection during PDU Session re-establishment for SSC mode 2 / 3, the notification content shall contain the resourceStatus IE with the value "UNCHANGED", the Cause IE with the value "TARGET_DNAI_NOTIFICATION" and the targetDnaiInfo IE. The targetDnai IE in the targetDnaiInfo IE shall be absent if the I-SMF removal is triggered due to the DNAI currently served by the I-SMF being no longer used for the PDU Session. If the notification is triggered for SMF selection during PDU Session re- establishment for SSC mode 3, the notification content may also contain the oldPduSessionRef IE as specified in clause 4.3.5.2 of 3GPP TS 23.502 [3]. If the notification is triggered by PDU session handover to release resources of the PDU Session in the target access due to handover failure between 3GPP access and non-3GPP access, the notification content shall contain the resourceStatus IE with the value "RELEASED" and the Cause IE with the value "PDU_SESSION_HAND_OVER_FAILURE". If the NF Service Consumer indicated support of the HOFAIL feature (see clause 6.1.8) and if the notification is triggered by PDU session handover to update access type of the PDU Session due to handover failure between 3GPP access and non-3GPP access, the notification content shall contain the resourceStatus IE with the value "UPDATED", the anType IE with the value "3GPP" or "NON_3GPP" indicating the access type ofthe PDU session after the handover failure scenario and the Cause IE with the value "PDU_SESSION_HAND_OVER_FAILURE". If upon a change of anchor SMF, the new anchor SMF instance decides to notify the change of anchor SMF, then the notification content shall contain the resourceStatus IE with the value "UPDATED" and the Cause IE with the value "CHANGED_ANCHOR_SMF". In addition, the new anchor SMF instance shall include its SMF Instance ID in the notification content, and / or carry an updated binding indication in the HTTP headers to indicate the change of anchor SMF (as per step 6 of clause 6.5.3.3 of 3GPP TS 29.500 [4]). If the PDU session may be moved to EPS with N26 and the EPS PDN Connection Context information of the PDU session on the new anchor SMF is different from the one on the old anchor SMF, the content shall also include the "epsPdnCnxInfo" IE including the updated EPS PDN Connection Context information. The NF Service consumer shall overwrite the locally stored EPS PDN Connection Context information with the new one if received. If the notification is triggered by a PDU session release due to slice inactivity as specified in clause 5.15.15.3 of 3GPP TS 23.501 [2] and clause 5.11.2 of 3GPP TS 29.244

[0029] , the notification content shall contain the resourceStatus IE with the value "RELEASED" and the Cause IE with the value "REL_DUE_TO_SLICE_INACTIVITY". If the notification is triggered by duplicated PDU session detected during Create operation (see clause 5.2.2.7.1) or SMF deregistration from UDM due to duplicated pdu sessions (see clause 5.3.2.3 of 3GPP TS 29.503

[0046] ), the request body shall include cause IE with the value "REL_DUE_TO_DUPLICATE_SESSION_ID". Upon receipt of such a status notification, the V-SMF or I-SMF shall not send SM context status notification to the AMF. If the notification is triggered SMF deregistration from UDM due to duplicated pdu session established via ePDG (see clause 5.3.2.3 of 3GPP TS 29.503

[0046] ), the request body shall include cause IE with the value "REL_DUE_TO_DUPLICATE_SESSION_EPDG" (see additional enumeration cause in the table below). Upon receipt of such a status notification, the V-SMF or I-SMF shall release the PDU session and also clean up the PDU session resources in AMF and RAN (if needed), but shall not release the PDU session in the UE. 2a. On success, "204 No Content" shall be returned and the content of the POST response shall be empty. If the SMF indicated in the request that the PDU session in the SMF is released, the NF Service Consumer shall release the SM context for the PDU session. If the SMF indicated in the request that the SM context resource is updated with the anType IE, the NF Service Consumer shall change the access type of the PDU session with the value of anType IE. 2b. On failure or redirection, one of the HTTP status code listed in Table 6.1.3.7.3.1-2 shall be returned. For a 4xx / 5xx response, the message body shall contain a ProblemDetails structure with the "cause" attribute set to one of the application errors listed in Table 6.1.3.7.3.1-2. 6.1.6.3.8 Enumeration: Cause The enumeration Cause indicates a cause information. It shall comply with the provisions defined in table 6.1.6.3.8- 1.Table 6.1.6.3.8-1: Enumeration Cause Enumeration value Description […] […] "REL_DUE_TO_DUPLICATE_SESSION_EPDG" Release due to a a new PDU session with an identical PDU session Id was established from another anchor SMF via ePDG. Changes to TS 29.503 for Alternative 2 5.3.2.3.2 UDM initiated NF Deregistration Figure 5.3.2.3.2-1 shows a scenario where the UDM notifies the registered NF about its deregistration (see also 3GPP TS 23.502 [3] figure 4.2.2.2.2-1 step 14, 3GPP TS 23.502 [3] figure 4.2.2.3.3-1 step 1 and 3GPP TS 23.502 [3] figure 4.26.4.1.1-1 step 14). The request contains the deregCallbackUri URI for deregistration notification as received by the UDM during registration, and Deregistration Data. The UDM initiates the deregistration procedure when the UE is registered to the AMF which does not support CAG feature and the CAG subscription of the UE changes and it is allowed to access the 5GS via CAG cell(s) only. The UDM also initiates deregistration notification when UE moves to different AMF within same AMF-Set. The UDM may also initiate deregistration notification for the disaster inbound roaming UE when a disaster condition is no longer being applicable. Deregistration notification shall not be sent if the nfInstanceId of the AMF initiating registration is same as the old AMF already registered in UDM (e.g. when multiple PLMNs are hosted on same AMF and UE moves across PLMNs). The UDM also initiates the deregistration procedures towards the SMF of the old PDU session when a new PDU session has been established with the same PDU session ID from a different SMF, during SM Context Transfer procedure (see clause 4.26.5.3 of 3GPP TS 23.502 [3]) or when duplicated PDU sessions existing in the network (e.g. the AMF failed to release the old PDU session before creation of the new PDU session with the same PDU session ID). In accordance with figure 7B: 1. The UDM sends a POST request to the deregCallbackUri as provided by the NF service consumer during the registration. If the SMF deregistration is triggered by SM Context Transfer procedure, i.e. the UDM has received a registration request with registrationReason IE set to the value "SMF_CONTEXT_TRANSFERRED" from another SMF, the UDM shall set the deregReason IE to the value "SMF_CONTEXT_TRANSFERRED". If the SMF deregistration is due to a duplicated PDU session established via ePDG, i.e. the UDM has received a registration request from another SMF with epdgInd IE set to the value true, the UDM shall set the deregReason IE to the value "DUPLICATE_PDU_SESSION_EPDG". If the SMF deregistration is due to duplicated PDU sessions in the network, i.e. the UDM has received a registration request from another SMF without registrationReason IE set to the value "SMF_CONTEXT_TRANSFERRED" and without epdgInd set to the value true, the UDM shall set the deregReason IE to the value "DUPLICATE_PDU_SESSION". If the SMF deregistration is due to an UDM-triggered PDU session release with re-activation, the UDM shall set the deregReason attribute in DeregistrationData to the value "PDU_SESSION_REACTIVATION_REQUIRED".; in this case, the SMF shall trigger a network-initiated PDU session release procedure (see clause 4.3.4 of 3GPP TS 23.502 [3]) with 5GSM cause "Reactivation requested" (see clause 8.3.14 of 3GPP TS 24.501

[0027] ) 2a. On success, the NF service consumer responds with "204 No Content" if no information is to be sent to the UDM. Otherwise, if the "DeregistrationResponseBody" feature is supported by both the UDM and the NF consumer, the NF service consumer (e.g. the SMF) responds with "200 OK" with the response body including the information to the UDM (e.g. the indication that the SMF event subscription on the SMF for the UE have been implicitly removed).If the deregistration reason is "PDU_SESSION_REACTIVATION_REQUIRED", the SMF receiving the deregistration notification shall trigger a network initiated PDU session release procedure (see clause 4.3.4 of 3GPP TS 23.502 [3]) with 5GSM cause "Reactivation requested" (see clause 8.3.14 of 3GPP TS 24.501

[0027] ). If the deregistration reason is "SMF_CONTEXT_TRANSFERRED" or "DUPLICATE_PDU_SESSION", the SMF receiving the deregistration notification shall release the PDU session but shall not send a SM Context Status Notification to the AMF. For a PDU session with I-SMF or V- SMF, the anchor SMF shall send a Status Notification to the I-SMF or V-SMF indicating that the PDU session is released due to duplicated PDU sessions. If the deregistration reason is "DUPLICATE_PDU_SESSION_EPDG", the SMF receiving the deregistration notification shall release the PDU session in SMF and release the RAN resource if needed. The SMF shall also send a SM Context Status Notify for the released PDU session to the AMF. For a PDU session with I-SMF or V-SMF, the anchor SMF shall send a Status Notification to the I- SMF or V-SMF indicating that the PDU session is released due to duplication session established via ePDG. 2b. On failure or redirection, one of the appropriate HTTP status code listed in Table 6.2.5.2-3 shall be returned. For a 4xx / 5xx response, the message body may contain appropriate additional error information. Enumeration: DeregistrationReason The enumeration DeregistrationReason represents the reason for the Deregistration Notification. It shall comply with the provisions defined in table 6.2.6.3.3-1 of TS 29.503.Table 6.2.6.3.3-1: Enumeration DeregistrationReason Enumeration value Description "UE_INITIAL_REGISTRATION" When sent by the HSS; indicates that the deregistration towards the UDM is due to an initial attach in EPS. When sent by the UDM; indicates that the deregistration in the old AMF is due to a new AMF serving the UE during an initial registration See 3GPP TS 23.502 [3] and 3GPP TS 23.632

[0032] . "UE_REGISTRATION_AREA_CHANGE" see 3GPP TS 23.502 [3] "SUBSCRIPTION_WITHDRAWN" see 3GPP TS 23.502 [3] "5GS_TO_EPS_MOBILITY" see 3GPP TS 23.502 [3] and 3GPP TS 23.632

[0032] . "5GS_TO_EPS_MOBILITY_UE_INITIAL_REGISTRATION" This value shall only be sent by the UDM. It indicates that the deregistration in AMF is due to an initial attach in EPS, See 3GPP TS 23.502 [3] and 3GPP TS 23.632

[0032] . "REREGISTRATION_REQUIRED" see 3GPP TS 23.502 [3] "SMF_CONTEXT_TRANSFERRED" see 3GPP TS 23.502 [3] "DUPLICATE_PDU_SESSION" This value shall only be sent by the UDM to an SMF. It indicates that the deregistration in the SMF is due to a new PDU session with the same PDU session ID has been established in another SMF. "PDU_SESSION_REACTIVATION_REQUIRED" This value shall only be sent by the UDM to an SMF. It indicates that the PDU session being released is requested to be re- activated. "DISASTER_CONDITION_TERMINATED" This value shall be used by the UDM when the disaster condition ceases. "OPERATOR_DETERMINED_BARRING" This value indicates that the deregistration is due to ODB (see 3GPP TS 23.015

[0071] ). "DUPLICATE_PDU_SESSION_EPDG" This value shall only be sent by the UDM to an SMF. It indicates that the deregistration in the SMF is due to a new PDU session with the same PDU session ID has been established in another SMF via ePDG. Further Description

[0103] Figure 12 is a schematic block diagram of a network node 1100 according to some embodiments of the present disclosure. Optional features are represented by dashed boxes. The network node 1100 may be, for example, a core network node that implements a NF (e.g., AMF 200, SMF 206, SMSF220, NSACF 207, UDM 406, or the like). As illustrated, the network node 1100 includes a one or more processors 1104 (e.g., Central Processing Units (CPUs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), and / or the like), memory 1106, and a network interface 1108. The one or more processors 1104 are also referred to herein as processing circuitry. The one or more processors 1104 operate to provide one or more functions of the network node 1100 as described herein (e.g., one or morefunctions of the AMF 200, SMF 206, SMSF220, NSACF 207, UDM 406, ePDG, N3IWF, TNGF or the like, as described herein. In some embodiments, the function(s) are implemented in software that is stored, e.g., in the memory 1106 and executed by the one or more processors 1104.

[0104] Figure 13 is a schematic block diagram that illustrates a virtualized embodiment of the network node 1100 according to some embodiments of the present disclosure. Again, optional features are represented by dashed boxes. As used herein, a “virtualized” network node is an implementation of the network node 1100 in which at least a portion of the functionality of the network node 1100 is implemented as a virtual component(s) (e.g., via a virtual machine(s) executing on a physical processing node(s) in a network(s)). As illustrated, in this example, the network node 1100 includes one or more processing nodes 1200 coupled to or included as part of a network(s) 1202. Each processing node 1200 includes one or more processors 1204 (e.g., CPUs, ASICs, FPGAs, and / or the like), memory 1206, and a network interface 1208. In this example, functions 1210 of the network node 1100 described herein (e.g., one or more functions of the AMF 200, SMF 206, SMSF220, NSACF 207, UDM 406, ePDG, N3IWF, TNGF or the like, as described herein) are implemented at the one or more processing nodes 1200 or distributed across the two or more processing nodes 1200 in any desired manner. In some particular embodiments, some or all of the functions 1210 of the network node 1100 described herein are implemented as virtual components executed by one or more virtual machines implemented in a virtual environment(s) hosted by the processing node(s) 1200.

[0105] In some embodiments, a computer program including instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of the network node 1100 or a node (e.g., a processing node 1200) implementing one or more of the functions 1210 of the network node 1100 in a virtual environment according to any of the embodiments described herein is provided. In some embodiments, a carrier comprising the aforementioned computer program product is provided. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium such as memory).

[0106] Figure 14 is a schematic block diagram of the network node 1100 according to some other embodiments of the present disclosure. The network node 1100 includesone or more modules 1300, each of which is implemented in software. The module(s) 1300 provide the functionality of the network node 1100 described herein. This discussion is equally applicable to the processing node 1200 of Figure 13 where the modules 1300 may be implemented at one of the processing nodes 1200 or distributed across multiple processing nodes 1200.

[0107] Any appropriate steps, methods, features, functions, or benefits disclosed herein may be performed through one or more functional units or modules of one or more virtual apparatuses. Each virtual apparatus may comprise a number of these functional units. These functional units may be implemented via processing circuitry, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include Digital Signal Processors (DSPs), special-purpose digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as Read Only Memory (ROM), Random Access Memory (RAM), cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory includes program instructions for executing one or more telecommunications and / or data communications protocols as well as instructions for carrying out one or more of the techniques described herein. In some implementations, the processing circuitry may be used to cause the respective functional unit to perform corresponding functions according one or more embodiments of the present disclosure.

[0108] While processes in the figures may show a particular order of operations performed by certain embodiments of the present disclosure, it should be understood that such order is exemplary (e.g., alternative embodiments may perform the operations in a different order, combine certain operations, overlap certain operations, etc.).

[0109] Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein.

[0110] Some example embodiments of the present disclosure are as follows: Embodiment 1. A method performed by a User Data Management (UDM) comprising:- obtaining from a second session management function a registration message indicating a PDU session ID and an indication that the UE has established the associated PDU session over a new RAT (e.g., non-3GPP access technology); - Upon detecting the PDU session ID is duplicate over two different access types or different RATs, sending a deregistration notification to a first session management function comprising information indicating the deregistration notification is due duplicate PDU session or PDU session ID on different access / RAT. Embodiment 2. The method of embodiment 1 wherein the registration message comprises one or more of an access type / RAT type, network slice identifier (S- NSSAI) and data network name. Embodiment 3. The method of embodiment 1 wherein the registration message comprises an epdgind information element (IE) to indicate whether the UE has established the PDU session over an ePDG. Embodiment 4. The method of embodiment 3 wherein the epdgind IE includes a value set to true when the PDU session is established over the ePDG. Embodiment 5. The method of embodiment 3 wherein the information in the deregistration notification includes the epdgind IE and the deregistrationreason IE indicating “duplicate PDU session”. Embodiment 6. The method of embodiment 1 wherein the information in the deregistration notification comprises a deregistration reason IE indicating one of “duplicate PDU session on different access” or “duplicate PDU session on non- 3GPP access” or “duplicate PDU session ePDG”. Embodiment 7. The method of any one of embodiments 5 or 6 wherein the information in the deregistration notification comprises the PDU session ID. Embodiment 8. The method of embodiment 1 wherein the step of detecting further comprises: - determining that the PDU session ID was previously registered by the first session management function as established over a different access / RAT (e.g., 3GPP access technology). Embodiment 9. The method of embodiment 1 wherein the step of detecting further comprises:- determining that the PDU session ID was previously registered by the first session management function for an associated network slice identifier (S- NSSAI) and / or DNN. Embodiment 10. The method of embodiment 9 wherein the step of detecting further comprises: - determining that the PDU session ID, S-NSSAI and DNN as provided by the first session management function for the PDU session are the same as the PDU session ID, S-NSSAI and DNN provided by the second session management function. Embodiment 11. A method performed by a Session Management Function (SMF) having established a PDU session with PDU session ID for a UE over a first access network / RAT (e.g., 3GPP access), the method comprising: - receiving from a User Data Management (UDM) a deregistration notification comprising information indicating the deregistration notification is due to duplicate PDU session / PDU session ID on different access / RAT; and - sending a notification to a network function indicating release of the PDU session due to duplicate PDU session over the ePDG to initiate release of the PDU session at the network function without initiating release of the PDU session in the UE. Embodiment 12. The method of embodiment 11 wherein the network function corresponds to an Access and Mobility Management function or an intermediate session management function. Embodiment 13. The method of any one of embodiments 11-12 wherein the deregistration notification further comprises one or more of network slice identifier and DNN for the PDU session. Embodiment 14. The method of any one of embodiments 11-13 wherein the method further comprises sending a message to the network function to trigger release of resources associated with the PDU session in the network function and / or first access network. Embodiment 15. The method of embodiments 14, wherein the method further comprises sending an N1 message to notify the UE of release of the PDU session resources in the first access network.Embodiment 16. The method of embodiment 11 wherein the information indicating the deregistration notification is due duplicate PDU session or PDU session ID on different access / RAT comprises a deregistration reason IE indicating one of “duplicate PDU session on different access” or “duplicate PDU session on non-3GPP access” or “duplicate PDU session ePDG”. Embodiment 17. A network node configured to perform the method of any one of embodiments 1 to 16. Embodiment 18. A network node comprising one or more processors and memory comprising instructions which when executed by the one or more processors enable the network node to perform the method of any one of embodiments 1 to 16. Embodiment 19. A computer readable memory comprising instructions which when executed by one or more processors of one or more servers configures the one or more servers to perform the method of any one of embodiments 1 to 16.

[0111] Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein.

Claims

Claims:

1. A method performed by a User Data Management (UDM) having registration information obtained from a first session management function (SMF) for a Packet Data Unit (PDU) session established for a User Equipment (UE), the registration information comprising a PDU session identifier and a network slice identifier and / or data network name of the PDU session established over a first access, the method comprising: - obtaining from a second session management function a registration message indicating that a new PDU session is established by the UE via an evolved packet data gateway (ePDG) providing access to the UE over a non- 3GPP access; and - sending to the first SMF a deregistration notification comprising deregistration information indicating that a duplicate PDU session is established over the ePDG when the new PDU session established by the second SMF over the ePDG has the same PDU session identifier as the PDU session established over the first SMF.

2. The method of claim 1 wherein the registration message comprises one or more of an access type / RAT type, a network slice identifier (S-NSSAI) and / or a data network name for the new PDU session. wherein the duplicate PDU session further corresponds to the new PDU session with the network slice identifier and / or the data network name are identical to the network slice identifier and / or the data network name of the PDU session.

3. The method of claim 1 wherein the registration message indicating that a new PDU session is established by the UE via an evolved packet data gateway providing access to the UE over a non-3GPP access corresponds to the registration message comprising an identifier of the ePDG over which the new PDU session is established.

4. The method of claim 3 wherein the identifier of the ePDG is comprised in an epdgind information element (IE).

5. The method of claim 4 wherein the epdgind IE includes a value set to true when the PDU session is established over the ePDG.

6. The method of claim 3 wherein the deregistration information indicating that a duplicate PDU session is established over the ePDG comprises the epdgind IE and a deregistrationreason IE indicating “duplicate PDU session”.

7. The method of claim 1 wherein the deregistration information indicating that a duplicate PDU session is established over the ePDG corresponds to a deregistration reason IE indicating one of “duplicate PDU session on different access” or “duplicate PDU session on non-3GPP access” or “duplicate PDU session ePDG”.

8. The method of claim 1 and 2 wherein the duplicate PDU session is identified when the network slice identifier and / or the data network name of the new PDU session are identical to the network slice identifier and / or the data network name of the PDU session.

9. A method performed by a Session Management Function (SMF) having established a PDU session with a PDU session identifier for a UE over a first access network, the method comprising: - receiving from a User Data Management (UDM) a deregistration notification comprising deregistration information indicating that a duplicate PDU session is established on another SMF for the UE over an evolved packet data gateway (ePDG) used to provide access to the UE over a non-3GPP access, the duplicate PDU session having the same PDU session identifier as the PDU session established over the SMF; and - sending a notification to a network function indicating release of the PDU session due to duplicate PDU session over the ePDG to initiate release of the PDU session at the network function without initiating release of the PDU session in the UE.

10. The method of claim 9 wherein the network function corresponds to an Access and Mobility Management function or an intermediate session management function or a visited session management function.

11. The method of claim 9 wherein the deregistration information indicating that a duplicate PDU session is established on another SMF for the UE over an evolved packet data gateway (ePDG) corresponds to a deregistration cause Information Element IE indicating “DUPLICATE_PDU_SESSION_ePDG” or "DUPLICATE_PDU_SESSION_ ON DIFFERENT ACCESS” or “DUPLICATE_PDU_SESSION_ ON NON-3GPP ACCESS”.

12. The method of claim 9 wherein the deregistration notification further comprises one or more of the PDU session identifier, network slice identifier and DNN associated to the PDU session.

13. A network node configured to perform the method of any one of claims 1 to 12.

14. A network node comprising one or more processors and memory comprising instructions which when executed by the one or more processors enable the network node to perform the method of any one of claims 1 to 12.

15. A computer readable memory comprising instructions which when executed by one or more processors of one or more servers configures the one or more servers to perform the method of any one of claims 1 to 12.

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