WO2020229409A1

WO2020229409A1 - Smf set support over n4 interface

Info

Publication number: WO2020229409A1
Application number: PCT/EP2020/063050
Authority: WO
Inventors: Yong Yang; Jinyin Zhu
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2019-05-10
Filing date: 2020-05-11
Publication date: 2020-11-19

Abstract

Disclosed herein is a method performed by a SMF instance entity (410, 410#1) in a core network (110) of a cellular communications system (100). The method comprises: sending (400a) CP function set information towards a UPF entity (420), to establish or update a PFCP association wherein the CP function set information comprises SMF set information that indicates that the SMF instance entity (410, 410#1) supports a SMF Set feature, in which SMF set any SMF instance of the SMF Set can control any PFCP sessions created by any other SMF instance of the SMF Set.

Description

SMF SET SUPPORT OVER N4 INTERFACE

BACKGROUND

[0001] 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.

[0002] The study of enhanced Service Based Architecture (eSBA) for the Third Generation Partnership Project (3GPP) Fifth Generation (5G) System (5GS) introduces the concept of an Session Management Function (SMF) Set, i.e. functionally equivalent SMF instances that have access to the Session Management (SM) contexts handled by the SMF Set and that can serve SM requests targeting the SMF Set. The SMF Set also has additional requirement on the N4 interface between SMF and User Plane Function (UPF).

[0003] See the following requirements from TS 23.501 V16.0.2:

5.21.3 Network Reliability support with Sets

5.21 .3.1 General

A NF that fails should be replaced by an alternative NF and continue serving the UE without any interruption. The same is also supported for NF Services. This can be achieved when the equivalent NFs and NF Services share the same context data.

Editor's note: Clause 5.21.3 is to be updated if needed based on the outcome of SET concept.

Such a network reliability design shall work in both communication modes, i.e. Direct Communication and Indirect Communication. In the Direct Communication mode, the NF Service consumer is involved in the reliability related procedures. In Indirect Communication mode, the SCP is involved in the reliability related procedures.

5.21 .3.2 NF Set and NF Service Set

Equivalent Control Plane NFs may be grouped into NF Sets, e.g. several SMF instances are grouped into an SMF Set. NFs within a NF Set are interchangeable because they share the same context data, and may be deployed in different locations, e.g. different data centers. A Control Plane NF is composed of one or multiple NF Services. Within a NF a NF service may have multiple instances. These multiple NF Service instances can be grouped into NF Service Set if they are interchangeable with each other because they share the same context data.

NOTE: The actual mapping of instances to a given Set is up to deployment.

5.21.3.3 Reliability of NF instances within the same NF Set

The NF producer instance is the NF instance which host the NF Service Producer. When the NF producer instance is not available, another NF producer instance within the same NF Set is selected.

For Direct Communication mode, the NF Service consumer may subscribe to status change notifications of NF instance from the NRF. If the NF Service consumer is notified by the NRF or detects by itself (e.g. request is not responded) that the NF producer instance is not available anymore, another available NF producer instance within the same NF Set is selected by the NF Service consumer.

For Indirect Communication mode, the SCP selects another NF producer instance within the same NF Set if the original NF producer instance serving the UE is not available anymore.

NOTE: It is up to the implementation on how the SCP knows a NF producer instance is not available anymore.

5.21.3.4 Reliability of NF Services

When multiple NF Service instances within a NF Service Set are exposed to the NF Service consumer or SCP and the failure of NF Service instance is detected, i.e. it is not available anymore, the NF Service consumer or SCP selects another NF Service instance of the same NF Service Set within the NF instance, if available. Otherwise the NF Service consumer or SCP selects a different NF instance within the same NF Set.

NOTE: The NF Producer instance can change the NF Service instance in the response to the service request.

When multiple NF Service instances within a NF Service Set are exposed to the NF Service consumer or SCP as a single NF Service , the reliability, i.e. the selection of an alternative NF Service instance is handled within the NF instance.

SUMMARY

[0004] There currently exist certain challenge(s). The support of SMF set requires that:

a) any SMF instance of an SMF Set can control any Packet Forwarding Control Protocol (PFCP) sessions created by any other SMF instance of the SMF Set; and

b) the UPF can initiate session-related signaling (e.g. PFCP Session Report Request) towards any other SMF instance of the SMF Set, when e.g. the SMF instance that currently serves the session is not responsive or not reachable e.g. due to path failure or internal hardware failure.

[0005] The problem is that the support of SMF set over N4 interface between SMF and UPF is not defined. A solution has been proposed (see CR29.244-0261 from Nokia). However, there are problems with the proposed solution, which are:

1. It is proposed to have a new flag included in each PFCP Session Establishment Request message to indicate the UPF for this PFCP session, in case the SMF is not reachable, any alternative SMF can be selected. Such an approach leads t unnecessary complexities, e.g. impact on the existing PFCP Session establishment procedure.

2. The proposed solution requires UPF (UP function) to perform a Network Repository Function (NRF) or Domain Name System (DNS) procedure via SMF SET Fully Qualified Domain Name (FQDN), where such function is not required as of today.

[0006] Certain aspects of the present disclosure and their embodiments may provide solutions to the aforementioned or other challenges. The present disclosure provides embodiments of a solution, in the 5G Core (5GC) and Evolved Packet Core (EPC) where a Control Plane function has implemented a set concept (e.g., as described in 5.21.3 of TS 23.501 V16.0.2) e.g. in a network virtualization environment, to support separated control plane (CP) and user plane (UP) functions (e.g., to support SMF set over N4 interface between SMF and UPF). In some embodiments, the solution includes:

1. During PFCP association setup and update procedure, in the PFCP Association Setup and/or Update Request and/or Response messages:

a. CP function (e.g. SMF in 5GC) and UP function (e.g. UPF in 5GC) communicate their support of a new Control Plane function feature (preferably called“CP function and SMF Set feature”), which will indicate to the UP function (e.g. a UPF in 5G) to select another Internet Protocol (IP) address pertaining to the PFCP Association (created per CP function set (e.g., created per SMF Set in 5GC)) to communicate to a CP function (e.g., SMF in 5GC) if the originally assigned IP address (e.g., the originally assigned IP address in the Fully Qualified Session Endpoint Identifier (F-SEID)) is not reachable;

b. CP function (e.g. SMF in 5GC) additionally includes the CP function set (e.g., SMF set)

information to UP function (e.g., UPF in 5GC). In other words, the CP function (e.g., SMF in 5GC) additionally includes the CP function set information (e.g., SMF set information in 5GC) in a message sent to the UP function (e.g., UPF in 5GC). The CP function set (e.g., SMF set in 5GC) information includes all available (e.g., N4 in 5GC) interface IP addresses of the CP function set (e.g., SMF Set in 5GC) which can be used by the UP function (e.g., UPF in 5GC) for UP function (e.g., UPF in 5GC) initiated session-related signaling (e.g. PFCP Session Report Request).

2. When UP function (e.g., UPF in 5GC) detects that the IP address (e.g., from CP F-SEID) of the current CP function (e.g., current SMF in 5GC) instance associated with the PFCP session is not responsive (e.g., due to no response from this IP address or due to path failure of this IP address), the UP function (e.g., UPF in 5GC) selects another IP address out of the available CP function (e.g., SMF in 5GC) IP addresses other than the failed one to which to send the session-related signaling (e.g. PFCP Session Report Request). The UP function (e.g., UPF in 5GC) then sends session-related signaling (e.g.,

PFCP Session Report Request) to the CP function (e.g., SMF in 5GC) using the selected IP address.

[0007] Note: For 5GC, there are other changes to support SMF set, but these changes are already captured in 3GPP TS29.244 CR261 and hence are not described in the present disclosure.

[0008] There are, proposed herein, various embodiments which address one or more of the issues disclosed herein.

[0009] Certain embodiments may provide one or more of the following technical advantage(s). For example, for 5GC, embodiments of the present disclosure provide a simple and efficient solution to support SMF set over N4 interface. Compared with the solution provided in 3GPP TS29.244 CR261 , embodiments of the solution described herein are more simple and have less impact on SMF and UPF, e.g.:

1. The proposed new feature“CP function and SMF Set feature” is a node level feature and it is

associated with each PFCP Session of the PFCP Association, so that the UPF can perform necessary actions for all PFCP Sessions associated with the said PFCP Association.

2. The UPF does not need to perform DNS or NRF discovery procedure to find the SMF N4 IP addresses.

3. It works even for the case that an SMF instance has multiple back-end N4 IP addresses for session handling. Normally, the IP address of a SMF provisioned in the NRF or DNS is for creation only. In addition, those IP addresses for handling N4 session may be changed dynamically, especially in a cloud environment, more efficient way to provision these information (e.g. included in PFCP

Association Update Request) is more appreciated than rely on configuration in the DNS or NRF.

4. When the assigned IP address of the SMF (included in the F-SEID received during PFCP Session Creation or Modification) is not reachable, e.g. due to a path failure, the UPF does not need to check each PFCP session to decide whether to trigger restoration procedure.

[0010] A specific embodiment is directed to a method performed by a SMF instance entity in a core network of a cellular communications system. The method comprising: sending CP function set information towards a UPF entity to establish or update a PFCP association wherein the CP function set information comprises SMF set information that indicates that the SMF instance entity supports a SMF Set feature, in which SMF set any SMF instance of the SMF Set can control any PFCP sessions created by any other SMF instance of the SMF Set.

[0011] Another specific embodiment is directed to a network node that implements a SMF instance. The network node comprising: a network interface; and processing circuitry associated with the network interface, the processing circuitry configured to cause the SMF instance to operatively: send CP function set information towards a User UPF entity to establish or update a PFCP association wherein the CP function set information comprises SMF set information that indicates that the SMF instance supports a SMF Set feature, in which SMF set any SMF instance of the SMF Set can control any PFCP sessions created by any other SMF instance of the SMF Set.

[0012] Another specific embodiment is directed to a method performed by UPF entity in a core network of a cellular communications system. The method comprising: receiving CP function set information sent by a SMF instance entity, wherein the CP function set information comprises SMF set information that indicates that the SMF instance entity supports a SMF Set feature, in which SMF set any SMF instance of the SMF Set can control any PFCP sessions created by any other SMF instance of the SMF Set; and storing the CP function set information.

[0013] Another embodiment is directed to a network node that implements a UPF entity, the network node comprising: a network interface; and processing circuitry associated with the network interface, the processing circuitry configured to cause the UPF entity to operatively: receive CP function set information sent by a SMF instance entity, wherein the CP function set information comprises SMF set information that indicates that the SMF instance entity supports a SMF Set feature, in which SMF set any SMF instance of the SMF Set can control any PFCP sessions created by any other SMF instance of the SMF Set; and storing the CP function set information.

BRIEF DESCRIPTION OF THE DRAWINGS

The proposed solutions are now described, by way of example, with reference to the accompanying drawings, in which:

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

Figure 2 illustrates a wireless communication system represented as a 5G network architecture composed of core NFs, where interaction between any two NFs is represented by a point-to-point reference point/interface;

Figure 3 illustrates a 5G network architecture using service-based interfaces between the NFs in the control plane, instead of the point-to-point reference points/interfaces used in the 5G network architecture of Figure 2;

Figure 4 illustrates the operation of an SMF and a UPF to exchange SMF set feature support and the

operation of the SMF to deliver SMF set information to the UPF in accordance with some embodiments of the present disclosure; Figure 5 illustrates the operation of a UPF to use the SMF Set Information to send UPF-initiated signaling to another SMF instance in accordance with some embodiments of the present disclosure;

Figure 6 is a schematic block diagram of a network node 600 according to some embodiments of the

present disclosure;

Figure 7 is a schematic block diagram that illustrates a virtualized embodiment of the network node 600 according to some embodiments of the present disclosure;

Figure 8 is a schematic block diagram of the network node 600 according to some other embodiments of the present disclosure.

DETAILED DESCRIPTION

[0014] 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.

[0015] Radio Node: As used herein, a“radio node” is either a radio access node or a wireless device.

[0016] Radio Access Node: As used herein, a“radio access node” or“radio network node” is any node in a radio access network 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), and a relay node.

[0017] 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. Some examples of a core network node include, e.g., a Mobility Management Entity (MME), a Packet Data Network Gateway (PGW), a Service Capability Exposure Function (SCEF), a Home Subscriber Server (HSS), or the like. Some other examples of a core network node include a node implementing a Access and Mobility Function (AMF), a UPF, a Session Management Function (SMF), an Authentication Server Function (AUSF), a Network Slice Selection Function (NSSF), a Network Exposure Function (NEF), a Network Repository Function (NRF), a Policy Control Function (PCF), a Unified Data Management (UDM), or the like. [0018] Wireless Device: As used herein, a“wireless device” is any type of device that has access to (i.e., is served by) a cellular communications network by wirelessly transmitting and/or receiving signals to a radio access node(s). Some examples of a wireless device include, but are not limited to, a User Equipment device (UE) in a 3GPP network and a Machine Type Communication (MTC) device.

[0019] Network Node: As used herein, a“network node” is any node that is either part of the radio access network or the core network of a cellular communications network/system.

[0020] 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.

[0021] 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.

Figure 1

[0022] 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 NR RAN (i.e., a NR RAN) and a 5GC. However, the embodiments described herein are not limited to the 5GS and may be implemented in other types of wireless communication systems such as, e.g., the Evolved Packet System (EPS) including a LTE RAN. In this example, the RAN includes base stations 102-1 and 102-2, which in 5G NR are referred to as gNBs, 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 Remote Radio Heads (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 network 1 10, which in the 5GS is referred to as the 5G core (5GC). The base stations 102 (and optionally the low power nodes 106) are connected to the core network 1 10. [0023] The base stations 102 and the low power nodes 106 provide service to wireless devices 1 12-1 through 1 12-5 in the corresponding cells 104 and 108. The wireless devices 1 12-1 through 1 12-5 are generally referred to herein collectively as wireless devices 112 and individually as wireless device 1 12. The wireless devices 1 12 are also sometimes referred to herein as UEs.

Figure 2

[0024] 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.

[0025] Seen from the access side the 5G network architecture shown in Figure 2 comprises a plurality of User Equipment (UEs) connected to either a Radio Access Network (RAN) or an Access Network (AN) as well as an Access and Mobility Management Function (AMF). Typically, the R(AN) comprises base stations, e.g. such as evolved Node Bs (eNBs) or 5G base stations (gNBs) or similar. Seen from the core network side, the 5G core NFs shown in Figure 2 include a Network Slice Selection Function (NSSF), an Authentication Server Function (AUSF), a Unified Data Management (UDM), an AMF, a Session Management Function (SMF), a Policy Control Function (PCF), and an Application Function (AF).

[0026] 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 and AMF. The reference points for connecting between the AN and AMF and between the AN and UPF are defined as N2 and N3, respectively. There is a reference point, N11 , between the AMF and SMF, which implies that the SMF is at least partly controlled by the AMF. N4 is used by the SMF and UPF so that the UPF can be set using the control signal generated by the SMF, and the UPF can report its state to the SMF. N9 is the reference point for the connection between different UPFs, and N14 is the reference point connecting between different AMFs, respectively. N15 and N7 are defined since the PCF applies policy to the AMF and SMP, respectively. N12 is required for the AMF to perform authentication of the UE. N8 and N10 are defined because the subscription data of the UE is required for the AMF and SMF.

[0027] The 5G core network aims at separating user plane and control plane. The user plane carries user traffic while the control plane carries signaling in the network. In Figure 2, the UPF is in the user plane and all other NFs, i.e., the AMF, SMF, PCF, AF, AUSF, and UDM, are in the control plane. Separating the user and control planes guarantees each plane resource to be scaled independently. It also allows UPFs to be deployed separately from control plane 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.

[0028] The core 5G network architecture is composed of modularized functions. For example, the AMF and SMF are independent functions in the control plane. Separated AMF and SMF allow independent evolution and scaling. Other control plane functions like the PCF and AUSF can be separated as shown in Figure 2. Modularized function design enables the 5G core network to support various services flexibly.

[0029] 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 control plane, a set of interactions between two NFs is defined as service so that its reuse is possible. This service enables support for modularity. The user plane supports interactions such as forwarding operations between different UPFs.

Figure 3

[0030] Figure 3 illustrates a 5G network architecture using service-based interfaces between the NFs in the control plane, instead of the point-to-point reference points/interfaces used in the 5G network architecture of Figure 2. Flowever, 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 and Nsmf for the service based interface of the SMF etc. The Network Exposure Function (NEF) and the Network Repository Function (NRF) in Figure 3 are not shown in Figure 2 discussed above. Flowever, it should be clarified that all NFs depicted in Figure 2 can interact with the NEF and the NRF of Figure 3 as necessary, though not explicitly indicated in Figure 2.

[0031] Some properties of the NFs shown in Figures 2 and 3 may be described in the following manner. The AMF provides UE-based authentication, authorization, mobility management, etc. A UE even using multiple access technologies is basically connected to a single AMF because the AMF is independent of the access technologies. The SMF is responsible for session management and allocates Internet Protocol (IP) addresses to UEs. It also selects and controls the UPF for data transfer. If a UE has multiple sessions, different SMFs may be allocated to each session to manage them individually and possibly provide different functionalities per session. The AF provides information on the packet flow to the PCF responsible for policy control in order to support Quality of Service (QoS). Based on the information, the PCF determines policies about mobility and session management to make the AMF and SMF operate properly. The AUSF supports authentication function for UEs or similar and thus stores data for authentication of UEs or similar while the UDM stores subscription data of the UE. The Data Network (DN), not part of the 5G core network, provides Internet access or operator services and similar.

[0032] 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.

Figure 4

[0033] Figure 4 illustrates the operation of an SMF entity 410 (e.g. a SMF instance entity, e.g. a SMF instance entity comprising a first SMF instance 410#1 and a second SMF instance 410#2) and a UPF 420 to exchange SMF set feature support and the operation of the SMF 410 to deliver SMF set information to the UPF entity 420 in accordance with some embodiments of the present disclosure. Note that while this process is described with respect to the SMF 410 and UPF 420, this process is more generally applicable to a CP function and a UP function. The steps of the process of Figure 4 are as follows.

[0034] Steps 400a and 400b: The SMF 410 and the UPF 420 exchange capability information that indicate that they support the SMF Set feature. More specifically, in this example, the SMF 410 sends a PFCP Association Setup Request or PFCP Association Update Request or PFCP Association Setup Response or PFCP Association Update Response to the UPF 420 (step 400a). The PFCP Association Setup Request or PFCP Association Update Request or PFCP Association Setup Response or PFCP Association Update Response includes: (a) information that indicates that the SMF 410 supports the SMF set feature (e.g., a SMF Set feature bit in the CP Function Features that is set to a value that indicates support of the SMF set feature) and (b) SMF Set Information. The SMF Set Information includes all the N4 IP addresses of all SMFs (i.e., all SMF instances) within an SMF set that can be used by the UPF for UPF initiated signaling (e.g. PFCP Session Report Request). In a similar manner, the UPF 420 sends a PFCP Association Setup Request or PFCP Association Update Request or PFCP Association Setup Response or PFCP Association Update Response to the SMF 410 (step 400b), where this message includes information that indicates that the UPF supports the SMF set feature (e.g., an SMF Set feature bit in UP Function Features that is set to a value that indicates that the UP supports the SMF set feature).

[0035] Note that the inclusion of the information that indicates that the SMF 410 supports the SMF set feature in the message of step 400a is optional. In other words, in some embodiments, the message of step 400a may not include this information. Similarly, step 400b is optional in some embodiments. For example, in some embodiments, it may be assumed that both the SMF 410 and the UPF 420 support the SMF set feature. In other embodiments, the SMF 410 and the UPF 420 may obtain this information in a different manner (e.g., from another network node or via a different message). [0036] Step 402: The UPF 420 stores the SMF Set Information. The information can be used when UPF 420 needs to send the UPF initiated signaling (e.g. PFCP Session Report Request) to another SMF instance in the SMF set.

[0037] Step 404 (Optional): The UPF 420 optionally uses the SMF set information for UPF-initiated signaling. For example, the UPF 420 may first attempt to send a UPF-initiated signaling message (e.g., a PFCP Session Report Request) to a particular SMF instance in the SMF set (e.g. SMF 410#1 ). Upon failure of this attempt (e.g., after a timeout period without a response from the SMF instance), the UPF 420 selects an IP address of another SMF instance (e.g. SMF 410#2) in the SMF set from the SMF Set Information and attempts to send the UPF-initiated signaling message to this other SMF instance using the selected IP address. The selected IP address is some IP address in the SMF Set Information other than the IP address of the SMF instance for which the prior attempt failed.

Figure 5

[0038] Figure 5 illustrates the operation of a UPF entity 420 to use the SMF Set Information to send UPF- initiated signaling to another SMF instance 410#2 in accordance with some embodiments of the present disclosure. Note that while this process is described with respect to the SMF entity 410 and UPF entity 420, this process is more generally applicable to a CP function and a UP function. The steps of the process of Figure 5 are as follows.

[0039] Step 500: A PFCP session is established between a first SMF instance (denoted SMF instance 410#1 ) and the UPF, preferably by the SMF instance 410#1 sending a PFCP Association Setup Request to the UPF 420 as in step 400a of Figure 4.

[0040] Step 502: The UPF 420 sends a PFCP Session Report Request to SMF instance 410#1.

[0041] Step 504: The UPF determines that a request has not been received from SMF instance 410#1 via, e.g., a timeout of the request. In other words, a predefined or configured timer is started upon sending the request in step 502 and expires before a response is received from SMF instance 410#1. In other words, the UPF 420 detects that a path failure has occurred between SMF instance 410#1 and the UPF 420. Note that, when path failure is detected towards one SMF IP address, the UPF 420 does not trigger the restoration procedure unless path failure is detected towards all SMF IP addresses.

[0042] Step 506: The UPF 420 selects another SMF instance 410#2 from the stored SMF Set

Information, preferably included in a PFCP Association Setup Request received from a SMF instance 410#1 in the SMF set, e.g. included in the PFCP Association Setup Request sent by the SMF instance 410#1 towards the UPF 420. In this example, the selected SMF instance is SMF instance 410#2. [0043] Step 508: The UPF 420 sends the PFCP Session Report Request to SMF instance 410#2 and receives a corresponding response from SMF instance 410#2.

[0044] Below, an example of a new Information Element (IE) (called“SMF Set information”) in PFCP Association Setup Request, PFCP Association Setup Response, PFCP Association Update Request, and/or PFCP Association Update Response is provided. This IE can be included in the message of step 400a of Figure 4.

New Information Element in a PFCP Association Setup Request, PFCP Association Setup Response, PFCP Association Update Request, PFCP

Association Update Response

[0045] Below, an example of a new feature bit (called“SMFSET”) in CP Function Features for SMF Set feature in accordance with some embodiments of the present disclosure. This feature bit can be included in the message of step 400a of Figure 4, e.g. as a part of or associated with the SMF Set Information. New feature bit in CP Function Features for SMF Set feature

[0046] In some embodiments, the PFCP session response message (e.g., in step 506 of Figure 5), the replacement (also referred to as alternative) SMF instance (i.e., SMF instance 410#2 in the example of Figure 5) provides a local F-TEID (referred to as“CP N4-u F-TEID” in the example below) on the user plane (so called

NR-u between SMF and UPF) to allow the UPF to forward user plane traffic to the SMF. This local F-TEID may be in addition to the F-TEID (referred to as“CP F-TEID” in the example below). One example implementation of this as a change to 3GPP TS 29.244 V15.5.0 is shown below:

7.5.9 PFCP Session Report Response

7.5.9.1 General

The PFCP Session Report Response shall be sent over the Sxa, Sxb, Sxc and N4 interface by the CP function to the UP function as a reply to the PFCP Session Report Request.

Table 7.5.9.1-1 : Information Elements in a PFCP Session Report Response

Figure 6

[0048] Figure 6 is a schematic block diagram of a network node 600 according to some embodiments of the present disclosure. The network node 600 may be, for example, a NF (e.g., SMF, UPF, or the like) in the core network 110 or a network node implementing a NF (e.g., SMF, UPF, or the like) in the core network 1 10. As illustrated, the network node 600 includes one or more processors 604 (e.g., Central Processing Units (CPUs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), and/or the like), memory 606, and a network interface 608. The one or more processors 604 are also referred to herein as processing circuitry. The one or more processors 604 operate to provide one or more functions of a network node 600 as described herein (e.g., one or more functions of an SMF or UPF as described herein, e.g., with respect to Figures 4 and 5). In some embodiments, the function(s) are implemented in software that is stored, e.g., in the memory 606 and executed by the one or more processors 604.

Figure 7

[0049] Figure 7 is a schematic block diagram that illustrates a virtualized embodiment of the network node 600 according to some embodiments of the present disclosure. A used herein, a“virtualized” network node is an implementation of the network node 600 in which at least a portion of the functionality of the network node 600 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 600 includes one or more processors 704 (e.g., CPUs, ASICs, FPGAs, and/or the like), memory 706, and a network interface 708. In this example, functions 710 of the network node 600 described herein (e.g., one or more functions of an SMF or UPF as described herein, e.g., with respect to Figures 4 and 5) are implemented at the one or more processing nodes 700. In some particular embodiments, some or all of the functions 710 of the network node 600 described herein (e.g., one or more functions of an SMF or UPF as described herein, e.g., with respect to Figures 4 and 5) are implemented as virtual components executed by one or more virtual machines implemented in a virtual environment(s) hosted by the processing node(s) 700.

[0050] 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 600 or a node (e.g., a processing node 700) implementing one or more of the functions 710 of the network node 600 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).

Figure 8

[0051] Figure 8 is a schematic block diagram of the network node 600 according to some other embodiments of the present disclosure. The network node 600 includes one or more modules 800, each of which is implemented in software. The module(s) 800 provide the functionality of the network node 600 described herein (e.g., one or more functions of an SMF or UPF as described herein, e.g., with respect to Figures 4 and 5). This discussion is equally applicable to the processing node 700 of Figure 7 where the modules 800 may be implemented at one of the processing nodes 700 or distributed across multiple processing nodes 700 and/or distributed across the processing node(s) 700 and the control system 602.

[0052] 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 Processor (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.

[0053] 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.).

[0054]

Some embodiments described above may be summarized in the following manner:

1. A method performed by Control Plane, CP, function instance (e.g., SMF instance) in a core network of a cellular communications system, the method comprising:

sending (400a) CP function set information to a User Plane, UP (e.g. UPF and/or UPF instance), function, wherein the CP function set information comprises information related to a CP function set.

2. The method of embodiment 1 wherein the CP function set is a set of two or more CP function instances of a particular CP function.

3. The method of embodiment 2 wherein the two or more CP function instances in the CP function set are functionally equivalent. 4. The method of embodiment 2 or 3 wherein the CP function set information comprises IP addresses of the two or more CP function instances.

5. The method of embodiment 2 or 3 wherein:

the CP function set is an SMF set;

the CP function set information is SMF set information; and

the two or more CP function instances are two or more SMF instances having access to Session Management, SM, contexts handled by the SMF set that can serve SM requests that target the SMF set.

6. The method of embodiment 5 wherein the SMF set information comprises N4 IP addresses of the two or more SMF instances comprised in the SMF set.

7. The method of embodiment 5 or 6 wherein the UP function is a UPF.

8. The method of any one of embodiments 1 to 6 wherein sending (400a) the CP function set information comprises: sending a PFCP Association Setup Request that comprises the CP function set information to the UP function;

sending a PFCP Association Update Request that comprises the CP function set information to the UP function;

sending a PFCP Association Setup Response that comprises the CP function set information to the UP function; or

sending a PFCP Association Update Response that comprises the CP function set information to the UP function.

9. The method of any one of embodiments 1 to 8 further comprising sending (400a), to the UP function, information that indicates that the CP function supports a CP function set feature.

10. The method of any one of embodiments 1 to 9 further comprising receiving (400b), from the UP function, information that indicates that the UP function supports a CP function set feature. 1 1. A network node that implements a CP function instance adapted to perform the method of any one of embodiments 1 to 10.

12. The network node of embodiment 1 1 comprising:

a network interface; and

processing circuitry associated with the network interface, the processing circuitry configured to cause the network function to implement the CP function instance.

13. A method performed by User Plane, CP, function in a core network of a cellular communications system, the method comprising:

receiving (400a) CP function set information from a Control Plane, CP, function instance, wherein the CP function set information comprises information related to a CP function set; and

storing (402) the CP function set information.

14. The method of embodiment 13 further comprising using (402) the CP function set information (e.g., to send a UP function initiated signaling message to an CP function instance in the CP function set).

15. The method of embodiment 14 wherein:

the CP function set is a set of two or more CP function instances of a particular CP function; and using (402) the CP function set information comprises:

attempting (502) to send a UP initiated message to a first CP function instance from among the set of two or more CP function instances;

determining (504) that the attempt to send the UP initiated message to the first CP function instance failed;

selecting (506) a second CP function instance from among the set of two or more CP function instances, the second CP function instance being different than the first CP function instance; and attempting (506) to send the UP initiated message to the second CP function instance (e.g., using information related to the second CP function instance comprised in the CP function set information (e.g., an IP address of the second CP function instance comprised in the CP function set information)). 16. The method of embodiment 13 or 14 wherein the CP function set is a set of two or more CP function instances of a particular CP function.

17. The method of embodiment 15 or 16 wherein the two or more CP function instances in the CP function set are functionally equivalent.

18. The method of any one of embodiments 15 to 17 wherein the CP function set information comprises IP addresses of the two or more CP function instances.

19. The method of any one of embodiments 15 to 17 wherein:

the CP function set is an SMF set;

the CP function set information is SMF set information; and

20. The method of embodiment 19 wherein the SMF set information comprises N4 IP addresses of the two or more SMF instances comprised in the SMF set.

21. The method of embodiment 19 or 20 wherein the UP function is a UPF.

22. The method of any one of embodiments 13 to 21 wherein receiving (400a) the CP function set information comprises:

receiving a PFCP Association Setup Request that comprises the CP function set information from the CP function instance;

receiving a PFCP Association Update Request that comprises the CP function set information from the CP function instance;

receiving a PFCP Association Setup Response that comprises the CP function set information from the CP function instance; or

receiving a PFCP Association Update Response that comprises the CP function set information from the CP function instance. 23. The method of any one of embodiments 13 to 22 further comprising receiving (400a), from the CP function instance, information that indicates that the CP function instance supports a CP function set feature.

24. The method of any one of embodiments 13 to 23 further comprising sending (400b), to the CP function instance, information that indicates that the UP function supports a CP function set feature.

25. A network node that implements a UP function adapted to perform the method of any one of embodiments 13 to 24.

26. The network node of embodiment 25 comprising:

a network interface; and

processing circuitry associated with the network interface, the processing circuitry configured to cause the network function to implement the UP function.

[0055]

Some other embodiments described above may be summarized in the following manner:

1. A method performed by a Session Management Function, SMF, instance entity (410, 410#1 ) in a core network (1 10) of a cellular communications system (100), the method comprising:

sending (400a) CP function set information towards a User Plane, UP, Function, UPF, entity, (420), to establish or update a Packet Forwarding Control Protocol, PFCP, association wherein the CP function set information comprises SMF set information that indicates that the SMF instance entity (410, 410#1 ) supports a SMF Set feature, in which SMF set any SMF instance of the SMF Set can control any PFCP sessions created by any other SMF instance of the SMF Set.

2. The method of embodiment 1 wherein the SMF Set is a set of two or more SMF instances (410#1 ,

410#2).

3. The method of embodiment 2 wherein the two or more SMF instances (410#1 , 410#2) are functionally equivalent. 4. The method of embodiment 2 or 3 wherein the SMF set information comprises IP addresses of the two or more SMF instances (410#1 , 410#2).

5. The method of embodiment 2 or 4 wherein:

the two or more SMF instances (410#1 , 410#2) have access to Session Management, SM, contexts handled by the SMF set that can serve SM requests that target the SMF set.

6. The method of embodiment 4 or 5 wherein the SMF set information comprises N4 IP addresses of the two or more SMF instances comprised in the SMF set.

7. The method of any one of embodiments 1 to 6 wherein sending (400a) the CP function set information comprises:

sending a PFCP Association Setup Request that comprises the CP function set information towards the UPF entity; or

sending a PFCP Association Update Request that comprises the CP function set information towards the UPF entity.

8. A network node that implements a Session Management Function, SMF, instance entity (410, 410#1 ) adapted to perform the method of any one of claim 1 to 7.

9. A network node that implements a Session Management Function, SMF, instance entity (410, 410#1 ), the network node comprising:

a network interface; and

processing circuitry associated with the network interface, the processing circuitry configured to cause the SMF instance entity to operatively:

send (400a) CP function set information towards a User Plane, UP, Function, UPF, entity, (420), to establish or update a Packet Forwarding Control Protocol, PFCP, association wherein the CP function set information comprises SMF set information that indicates that the SMF instance entity supports a SMF Set feature, in which SMF set any SMF instance of the SMF Set can control any PFCP sessions created by any other SMF instance of the SMF Set. 10. The network node of embodiment 9 wherein the SMF Set is a set of two or more SMF instances (410#1 , 410#2).

1 1. The network node of embodiment 10 wherein the two or more SMF instances (410#1 , 410#2) are functionally equivalent.

12. The network node of embodiment 10 or 11 wherein the SMF set information comprises IP addresses of the two or more SMF instances (410#1 , 410#2).

13. The network node of embodiment 10 or 12 wherein:

14. The network node of embodiment 12 or13 wherein the SMF set information comprises N4 IP addresses of the two or more SMF instances comprised in the SMF set.

15. A method performed by User Plane Function, UPF, entity (420) in a core network (1 10) of a cellular communications system (100), the method comprising:

receiving (400a) CP function set information sent by a Session Management Function, SMF, instance entity (410. 410#1 ), wherein the CP function set information comprises SMF set information that indicates that the SMF instance entity (410. 410#1 ) supports a SMF Set feature, in which SMF set any SMF instance of the SMF Set can control any PFCP sessions created by any other SMF instance of the SMF Set; and

storing (402) the CP function set information.

16. The method of embodiment 15, wherein the SMF set is a set of two or more SMF instances (410#1 ,

410#2); the method further comprising:

attempting (402, 502) to send a UPF initiated message (e.g. a PFCP Session Report Request) to a first SMF instance (410#1 ) from among the set of two or more SMF instances (410#1 , 410#2); determining (402, 504) that the attempt to send the UPF initiated message to the first SMF instance failed;

selecting (402, 506) a second SMF instance (410#2) from among the set of two or more SMF instances, the second SMF (410#2) instance being different than the first SMF instance (410#1 ); and attempting (402, 506) to send the UPF initiated message to the second SMF instance (e.g., using information related to the second SMF instance comprised in the CP function set information (e.g., an IP address of the second SMF instance comprised in the CP function set information)).

17. The method of embodiment 16 wherein the SMF set is a set of two or more SMF instances (410#1 ,

410#2) of a particular SMF (410).

18. The method of embodiment 16 or 17 wherein the two or more CP function instances (410#1 , 410#2) in the CP function set are functionally equivalent.

19. The method of any one of embodiments 16 to 18 wherein the CP function set information comprises IP addresses of the two or more CP function instances (410#1 , 410#2).

20. The method of any one of embodiments 16 to 18 wherein:

the two or more CP function instances (410#1 , 410#2) are two or more SMF instances having access to Session Management, SM, contexts handled by the SMF set that can serve SM requests that target the SMF set.

21. The method of embodiment 19 wherein the SMF set information comprises N4 IP addresses of the two or more SMF instances (410#1 , 410#2) comprised in the SMF set.

22. The method of any one of embodiments 16 to 21 wherein receiving (400a) the CP function set information comprises:

receiving a PFCP Association Setup Request that comprises the CP function set information from the SMF instance entity (410, 410#1 ); or

receiving a PFCP Association Update Request that comprises the CP function set information from the SMF instance entity.

23. A network node that implements a User Plane Function, UPF, entity (420) adapted to perform the method of any one of embodiments 15 to 22. 24. A network node that implements a User Plane Function, UPF, entity (420), the network node comprising:

a network interface; and

processing circuitry associated with the network interface, the processing circuitry configured to cause the UPF entity to operatively:

receive (400a) CP function set information sent by a Session Management Function, SMF, instance entity (410. 410#1 ), wherein the CP function set information comprises SMF set information that indicates that the SMF instance entity (410. 410#1 ) supports a SMF Set feature, in which SMF set any SMF instance of the SMF Set can control any PFCP sessions created by any other SMF instance of the SMF Set; and storing (402) the CP function set information.

25. The network node of embodiment 24 wherein:

the SMF set is a set of two or more SMF instances (410#1 , 410#2); and wherein UPF entity operatively:

attempts (402, 502) to send a UPF initiated message to a first SMF instance (410#1 ) from among the set of two or more SMF instances(410#1 , 410#2);

determines (402, 504) that the attempt to send the UPF initiated message to the first SMF instance failed;

selects (402, 506) a second SMF instance (410#2) from among the set of two or more SMF instances, the second SMF (410#2) instance being different than the first SMF instance (410#1 ); and attempts (402, 506) to send the UPF initiated message to the second SMF instance (e.g., using information related to the second SMF instance comprised in the CP function set information (e.g., an IP address of the second SMF instance comprised in the CP function set information)).

26. The network node of embodiment 24 wherein the SMF set is a set of two or more SMF instances (41 o#1 , 410#2) of a particular SMF (410).

27. The network node of embodiment 25 or 26 wherein the two or more CP function instances (410#1 ,

410#2) in the CP function set are functionally equivalent.

28. The network node of any one of embodiments 25 to 27 wherein the CP function set information comprises IP addresses of the two or more CP function instances (410#1 , 410#2). 29. The network node of any one of embodiments 26 to 28 wherein:

30. The network node of embodiment 28 wherein the SMF set information comprises N4 IP addresses of the two or more SMF instances (410#1 , 410#2) comprised in the SMF set. 31. The network node of any one of embodiments 25 to 30 wherein receiving (400a) the CP function set information comprises:

Abbreviations

At least some of the following abbreviations may be used in this disclosure. If there is an inconsistency between abbreviations, preference should be given to how it is used above. If listed multiple times below, the first listing should be preferred over any subsequent listing(s).

• 3G Third Generation

• 3GPP Third Generation Partnership Project

• 4G Fourth Generation

• 5G Fifth Generation

• AF Application Function

• AMF Access and Mobility Management Function

• AN Access Network

• AUSF Authentication Server Function

• BS Base Station

• DL Downlink

• DN Data Network

• eNB Enhanced or Evolved Node B

• E-UTRA Evolved Universal Terrestrial Radio Access

• E-UTRAN Evolved Universal Terrestrial Radio Access Network

• GERAN Global System for Mobile (GSM) Communications Enhanced Data Rates for GSM Evolution Radio Access Network

• gNB New Radio Base Station

• GSM Global System for Mobile Communications

• HO Flandover

• IP Internet Protocol

• LAN Local Area Network

• LTE Long Term Evolution

• MME Mobility Management Entity

• NEF Network Exposure Function

• NF Network Function

• NR New Radio

• NRF Network Repository Function NSSF Network Slice Selection Function

O&M Operation and Maintenance

PCF Policy Control Function

P-GW Packet Data Network Gateway

PLMN Public Land Mobile Network

QoS Quality of Service

RAN Radio Access Network

RAT Radio Access Technology

RNC Radio Network Controller

SCEF Service Capability Exposure Function

S-GW Serving Gateway

SIM Subscriber Identity Module

SMF Session Management Function

UDM Unified Data Management

UE User Equipment

UL Uplink

UMTS Universal Mobile Telecommunications System

USIM Universal Subscriber Identity Module

UTRA Universal Terrestrial Radio Access

UTRAN Universal Terrestrial Radio Access Network

VNE Virtual Network Element

VNF Virtual Network Function

WCDMA Wideband Code Division Multiple Access WD Wireless Device

Claims

2. The method of claim 1 wherein the SMF Set is a set of two or more SMF instances (410#1 , 410#2).

3. The method of claim 2 wherein the two or more SMF instances (410#1 , 410#2) are functionally equivalent.

4. The method of claim 2 or 3 wherein the SMF set information comprises IP addresses of the two or more SMF instances (410#1 , 410#2).

5. The method of claim 2 or 4 wherein:

6. The method of claim 4 or 5 wherein the SMF set information comprises N4 IP addresses of the two or more SMF instances comprised in the SMF set.

7. The method of any one of claim 1 to 6 wherein sending (400a) the CP function set information comprises:

9. A network node that implements a Session Management Function, SMF, instance (410, 410#1 ), the network node comprising:

a network interface; and

processing circuitry associated with the network interface, the processing circuitry configured to cause the SMF instance to operatively:

send (400a) CP function set information towards a User Plane, UP, Function, UPF, entity, (420), to establish or update a Packet Forwarding Control Protocol, PFCP, association wherein the CP function set information comprises SMF set information that indicates that the SMF instance supports a SMF Set feature, in which SMF set any SMF instance of the SMF Set can control any PFCP sessions created by any other SMF instance of the SMF Set.

10. The network node of claim 9 wherein the SMF Set is a set of two or more SMF instances (410#1 ,

410#2).

1 1. The network node of claim 10 wherein the two or more SMF instances (410#1 , 410#2) are functionally equivalent.

12. The network node of claim 10 or 1 1 wherein the SMF set information comprises IP addresses of the two or more SMF instances (410#1 , 410#2).

13. The network node of claim 10 or 12 wherein:

14. The network node of claim 12 or13 wherein the SMF set information comprises N4 IP addresses of the two or more SMF instances comprised in the SMF set.

15. A method performed by User Plane Function, UPF, entity (420) in a core network (1 10) of a cellular communications system (100), the method comprising: receiving (400a) CP function set information sent by a Session Management Function, SMF, instance entity (410. 410#1 ), wherein the CP function set information comprises SMF set information that indicates that the SMF instance entity (410. 410#1 ) supports a SMF Set feature, in which SMF set any SMF instance of the SMF Set can control any PFCP sessions created by any other SMF instance of the SMF Set; and

storing (402) the CP function set information.

16. The method of claim 15, wherein the SMF set is a set of two or more SMF instances (410#1 , 410#2); the method further comprising:

attempting (402, 502) to send a UPF initiated message to a first SMF instance (410#1 ) from among the set of two or more SMF instances (410#1 , 410#2);

determining (402, 504) that the attempt to send the UPF initiated message to the first SMF instance failed;

17. The method of claim 16 wherein the SMF set is a set of two or more SMF instances (410#1 , 410#2) of a particular SMF (410).

18. The method of claim 16 or 17 wherein the two or more CP function instances (410#1 , 410#2) in the CP function set are functionally equivalent.

19. The method of any one of claim 16 to 18 wherein the CP function set information comprises IP addresses of the two or more CP function instances (410#1 , 410#2).

20. The method of any one of claim 16 to 18 wherein:

21. The method of claim 19 wherein the SMF set information comprises N4 IP addresses of the two or more SMF instances (410#1 , 410#2) comprised in the SMF set.

22. The method of any one of claim 16 to 21 wherein receiving (400a) the CP function set information comprises:

23. A network node that implements a User Plane Function, UPF, entity (420) adapted to perform the method of any one of claim 15 to 22.

24. A network node that implements a User Plane Function, UPF, entity (420), the network node comprising:

a network interface; and

25. The network node of claim 24 wherein:

attempts (402, 502) to send a UPF initiated message to a first SMF instance (410#1 ) from among the set of two or more SMF instances (410#1 , 410#2);

determines (402, 504) that the attempt to send the UPF initiated message to the first SMF instance failed; selects (402, 506) a second SMF instance (410#2) from among the set of two or more SMF instances, the second SMF (410#2) instance being different than the first SMF instance (410#1 ); and attempts (402, 506) to send the UPF initiated message to the second SMF instance (e.g., using information related to the second SMF instance comprised in the CP function set information (e.g., an IP address of the second SMF instance comprised in the CP function set information)).

26. The network node of claim 24 wherein the SMF set is a set of two or more SMF instances (410#1 ,

410#2) of a particular SMF (410).

27. The network node of claim 25 or 26 wherein the two or more CP function instances (410#1 , 410#2) in the CP function set are functionally equivalent.

28. The network node of any one of claim 25 to 27 wherein the CP function set information comprises IP addresses of the two or more CP function instances (410#1 , 410#2).

29. The network node of any one of claim 26 to 28 wherein:

30. The network node of claim 28 wherein the SMF set information comprises N4 IP addresses of the two or more SMF instances (410#1 , 410#2) comprised in the SMF set.

31. The network node of any one of claim 25 to 30 wherein receiving (400a) the CP function set information comprises: