WO2019061400A1

WO2019061400A1 - Enhanced service discovery for network function binding

Info

Publication number: WO2019061400A1
Application number: PCT/CN2017/104767
Authority: WO
Inventors: Yunjie Lu; Yong Yang; Qian Chen
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2017-09-30
Filing date: 2017-09-30
Publication date: 2019-04-04

Abstract

Systems and methods are disclosed herein that provide a mechanism for a first Network Function (NF) to directly or indirectly indicate, to a second NF, a set of NFs of the same type as the first NF that support at least some of the same types of services as the first NF. In some embodiments, a method of operation of a first NF in a core network of a wireless communication system comprise providing, from the first NF to a second NF, information that directly or indirectly indicates a set of NFs of a same NF type as the first NF that support at least some of one or more types of services provided by the first NF. The set of NFs can be used by the second NF when the second NF desires to invoke a service of the first NF, e.g., when the first NF is unavailable.

Description

ENHANCED SERVICE DISCOVERY FOR NETWORK FUNCTION BINDING

Technical Field

The present disclosure relates to Network Functions (NFs) in a core network of a wireless communication system and， in particular， to NF discovery.

Background

Figures 1 and 2 illustrate the non-roaming and roaming Fifth Generation (5G) system architectures as specified by the Third Generation Partnership Project (3GPP) . As illustrated the 5G Core (5GC) network includes a number of Network Functions (NFs) including an Access and Mobility Management Function (AMF) ， 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) ， an Application Function (AF) ， and a Unified Data Management (UDM) function. 3GPP has determined that NFs within the 5GC Control Plane (CP) are to only use service-based interfaces for their interactions， as specified in subclause 4.2.1 of 3GPP Technical Specification (TS) 23.501 V1.3.0. There are typically many instances of each type of NF within the 5GC. The 5G system architecture contains the following service-based interfaces：

● Namf： Service-based interface exhibited by the AMF.

● Nsmf： Service-based interface exhibited by the SMF.

● Nnef： Service-based interface exhibited by the NEF.

● Npcf： Service-based interface exhibited by the PCF.

● Nudm： Service-based interface exhibited by the UDM.

● Naf： Service-based interface exhibited by the AF.

● Nnrf： Service-based interface exhibited by the NRF.

● Nnssf： Service-based interface exhibited by the NSSF.

● Nausf： Service-based interface exhibited by the AUSF.

A CP NF within the 5GC may expose its capabilities as services via its service-based interface， which can be re-used by CP NFs. NF service discovery enables a core network NF to discover NF instance (s) that provide a desired or expected NF service (s) . NF service discovery is implemented via NF discovery functionality.

In subclause 7.1.2 of 3GPP TS 23.501 V1.3.0， 3GPP further specifies NF interactions between a NF service consumer (i.e.， a NF that consumes a service of another NF) and a NF service producer (i.e.， a NF that produces a service consumed by another NF) . Figure 3 illustrates a request-response interaction between a consumer NF (NF A) and a producer NF (NF B) . In this response-request interaction， a CP NF (NF B) receives a request from another CP NF (NF A) to provide a certain NF service to NF A. The NF service may be performing an action， providing information， or both. NF B provides the requested NF service for NF A in response to the request by NF A. In order to fulfill the request， NF B may in turn consume NF services from other NFs. In the request-response mechanism， communication is one-to-one between the two NFs (consumer and producer) ， and a one-time response from the producer NF to a request from the consumer NF is expected within a certain timeframe.

Figures 4 and 5 illustrate a subscribe-notify mechanism. As illustrated in Figure 4， a CP NF (NF A) subscribes to a NF service offered by another CP NF (NF B) . Multiple CP NFs may subscribe to the same service provided by NF B. NF B notifies subscribing NFs of the result of the NF service. The subscription request from NF A may include a request for periodic updates or notification triggered through certain events such as a change in the information subscribed to by NF A， some value reaching a certain threshold， etc. Note that the subscription may be an explicit subscription or an implicit subscription (e.g.， due to a successful registration procedure) . Figure 5 illustrates a subscribe-notify mechanism in which one CP NF (NF A) subscribes to a service provided by NF B on behalf of another CP NF (NF C) .

Within 3GPP， the following requirements for service selection， at least between NFs， e.g. an AMF and a SMF， have also been agreed upon：

1. If there is already a binding between a requester (i.e.， consumer) NF and a provider (i.e.， producer) NF， both NFs consume services from each other. For example， if an AMF (AMF-1) (which is also referred to as an AMF instance) has selected a particular SMF (SMF-1) (which is also referred to as an SMF instance) for a Packet Data Unit (PDU) session establishment， SMF-1 is to use AMF-1′s services for the same PDU session.

2. If there is no binding yet between a requester (i.e.， consumer) NF and a provider (i.e.， producer) NF， the requester NF discovers the NF instances that support a desired or expected NF service according to the principles of subclause 6.8.1.2 of 3GPP TS 23.501 V1.3.0. The requester NF then selects one NF instance among the discovered NF instances.

Note that NF A and NF B may be of different NF types， e.g. communication between an AMF and a SMF， or they may have the same NF type， e.g. communication between v-SMF and h-SMF or communication between the old AMF and new AMF during an AMF relocation procedure. The binding between NF A and NF B implies that the communication between NF A (service consumer， e.g. an AMF) and NF B (service producer) is stateful. In other words， if NF A has invoked a service offered by NF B and the request has been accepted， then the binding between NF A and NF B is established； therefore， if subsequently the NF B desires to invoke a service offered by a NF having the same NF type as NF A， the NF B is to use NF A.

Currently， Hypertext Transfer Protocol Version 2.0 (HTTP/2) is selected to be used for the service-based interfaces between the 5GC NFs. However， the communication in HTTP/2 is unidirectional， i.e. fully bidirectional communication requires two client-server pairs， one per direction. This means that when NF A establishes a binding to NF B by sending an HTTP request to NF B over a Transmission Control Protocol (TCP) connection， NF B needs to send an HTTP request over another TCP connection when NF B desires to invoke a service of NF A.

There is currently no mechanism defined by 3GPP to enable NF B (service producer) to invoke a service on NF A (service consumer) when NF A has already consumed a service of the NF B such that a binding between NF A and NF B has already been established.

Further， in the case of stateless NF with support for Unstructured Data Storage Function (UDSF) (centralized or distributed) ， services offered by a certain type of NF are provided by a group， or set， of NFs. When a particular NF in this group (e.g.， AMF 1 in a group of AMFs) needs to be changed to another NF in the same NF group (e.g.， changed to another AMF in the group of AMFs) for any reason (e.g.， load rebalancing， failure， etc. ) ， there is currently no mechanism defined by 3GPP to enable this change in NFs within the same group.

Summary

Systems and methods are disclosed herein that provide a mechanism for a first Network Function (NF) to directly or indirectly indicate， to a second NF， a set of NFs of the same type as the first NF that support at least some of the same types of services as the first NF. In some embodiments， a method of operation of a first NF in a core network of a wireless communication system comprise providing， from the first NF to a second NF， information that directly or indirectly indicates a set of NFs of a same NF type as the first NF that support at least some of one or more types of services provided by the first NF. The set of NFs can be used by the second NF when the second NF desires to invoke a service of the first NF， e.g.， when the first NF is unavailable. In this manner， NF discovery is enhanced.

In some embodiments， the information that directly or indirectly indicates the set of NFs also directly or indirectly indicates one or more supported services of each NF in the set of NFs including information that indicates how each service can be contacted and consumed.

In some embodiments， providing the information that indicates the set of NFs comprises sending a message from the first NF to the second NF to invoke a service of the second NF， the message comprising the information that directly or indirectly indicates the set of NFs of the same NF type as the first NF that supports at least some of the one or more types of services provided by the first NF.

In some embodiments， the set of NFs comprises one or more NFs. In some embodiments， the set of NFs comprises one or more NFs， but not the first NF. In some other embodiments， the set of NFs comprises the first NF and one or more additional NFs. In some other embodiments， the set of NFs comprise a logical group of NFs that can access User Equipment (UE) context information related to the NF type of the first NF such that NFs in the logical group of NFs are able to serve respective UEs equally.

In some embodiments， the information that directly or indirectly indicates the set of NFs comprises at least one Uniform Resource Indicator (URI) that indirectly indicates the set of NFs， wherein the at least one URI indicates a service instance in a network resource entity from which the second NF can retrieve information that that directly indicates the set of NFs of the same NF type as the first NF. In some other embodiments， the information that indicates directly or indirectly the set of NFs comprises at least one URI that indirectly indicates the set of NFs and their associated services， wherein the at least one URI indicates a service instance in a network resource entity from which the second NF can retrieve information that that directly indicates the set of NFs of the same NF type as the first NF and their associated services. In some embodiments， the instance in a network resource entity comprises an instance of a Network Repository Function (NRF) and the second NF can retrieve the information that that directly indicates the set of NFs of the same NF type as the first NF and their associated services from the NRF using the URI in a service discovery procedure.

In some embodiments， the information that directly or indirectly indicates the set of NFs comprises a separate URI for each NF in the set of NFs； and， for each NF in the set of NFs， the URI for the NF indicates an instance in a network resource entity from which the second NF can retrieve information that directly indicates one or more services of the NF.

In some embodiments， the information that directly or indirectly indicates the set of NFs comprises a set of NF Identifiers (IDs) that directly identify the set of NFs.

In some embodiments， the set of NFs is to be used by the second NF when the second NF desires to invoke a service that is supported by the first NF. In some other embodiments， the set of NFs is to be used by the second NF when the second NF desires to invoke a service that is supported by the first NF and the first NF is unavailable.

In some embodiments， the method further comprises receiving， from the second NF， information that directly or indirectly indicates a set of NFs of a same NF type as the second NF that support at least some of one or more types of services provided by the second NF.

Embodiments of a first NF for a core network of a wireless communication system are also disclosed. In some embodiments， a first NF for a core network of a wireless communication system is adapted to provide， from the first NF to a second NF， information that directly or indirectly indicates a set of NFs of a same NF type as the first NF that support at least some of one or more types of services provided by the first NF.

In some embodiments， a first NF for a core network of a wireless communication system comprises a communication interface and processing circuitry associated with the communication interface， wherein the processing circuitry is operable to cause the first NF to provide， to a second NF via the communication interface， information that directly or indirectly indicates a set of NFs of a same NF type as the first NF that support at least some of one or more types of services provided by the first NF.

In some embodiments， a first NF for a core network of a wireless communication system comprises a processing module operable to cause the first NF to provide， from the first NF to a second NF， information that directly or indirectly indicates a set of NFs of a same NF type as the first NF that support at least some of one or more types of services provided by the first NF.

Embodiments of a method of operation of a second NF in a core network of a wireless communication system are also disclosed. In some embodiments， a second NF in a core network of a wireless communication system comprises receiving， by the second NF from a first NF， information that directly or indirectly indicates a set of NFs of a same NF type as the first NF that support at least some of one or more types of services provided by the first NF. The method further comprises selecting a third NF from the set of NFs and invoking a service of the third NF.

In some embodiments， the method further comprises invoking a service of the first NF upon determining that a service that is supported by the first NF is desired and discovering that the first NF is unavailable. Selecting the third NF from the set of NFs comprises selecting the third NF from the set of NFs upon discovering that the first NF is unavailable.

In some other embodiments， the method further comprises discovering that the first NF is unavailable， wherein selecting the third NF from the set of NFs comprises selecting the third NF from the set of NFs upon discovering that the first NF is unavailable.

In some embodiments， receiving the information that directly or indirectly indicates the set of NFs comprises receiving a message from the first NF that invokes a service of the second NF， the message comprising the information that directly or indirectly indicates the set of NFs of the same NF type as the first NF that support at least some of the one or more types of services provided by the first NF.

In some embodiments， the set of NFs comprises one or more NFs， but not the first NF. In some other embodiments， the set of NFs comprises the first NF and one or more additional NFs. In some other embodiments， the set of NFs comprises a logical group of NFs that can access User Equipment (UE) context information related to the NF type of the first NF such that NFs in the logical group of NFs are able to serve respective UEs equally.

In some embodiments， the information that directly or indirectly indicates the set of NFs comprises a URI for the set of NFs， wherein the URI indicates an instance in a network resource entity from which the second NF can retrieve information that that directly indicates the set of NFs of the same NF type as the first NF. In some other embodiments， the information that directly or indirectly indicates the set of NFs comprises a URI for the set of NFs and their associated services， wherein the URI indicates an instance in a network resource entity from which the second NF can retrieve information that that directly indicates the set of NFs of the same NF type as the first NF and their associated services. In some embodiments， the instance in a network resource entity comprises an instance of a NRF， and the second NF can retrieve the information that directly indicates the set of NFs of the same NF type as the first NF and their associated services from the NRF using the URI in a service discovery procedure.

In some embodiments， the information that directly or indirectly indicates the set of NFs comprises a separate URI for each NF in the set of NFs； and， for each NF in the set of NFs， the URI for the NF indicates an instance in a network resource entity from which the second NF retrieves information that directly indicates one or more services of the NF.

In some embodiments， the information that directly or indirectly indicates the set of NFs comprises a set of NF IDs that directly identify the set of NFs.

Embodiments of a second NF for a core network in a wireless communication system are also disclosed. In some embodiments， a second NF for a core network in a wireless communication system is adapted to receive， by the second NF from a first NF， information that directly or indirectly indicates a set of NFs of a same NF type as the first NF that support at least some of one or more types of services provided by the first NF. The second NF is further adapted to select a third NF from the set of NFs and invoke a service of the third NF.

In some embodiments， a second NF for a core network in a wireless communication system comprises a communication interface and processing circuitry associated with the communication interface， wherein the processing circuitry is operable to cause the second NF to receive， by the second NF from a first NF， information that directly or indirectly indicates a set of NFs of a same NF type as the first NF that support at least some of one or more types of services provided by the first NF， select a third NF from the set of NFs， and invoke a service of the third NF.

In some embodiments， a second NF for a core network in a wireless communication system comprises a receiving module， a selecting module， and an invoking module. The receiving module is operable to receive， from a first NF， information that directly or indirectly indicates a set of NFs of a same NF type as the first NF that support at least some of one or more types of services provided by the first NF. The selecting module is operable to select a third NF from the set of NFs， and the invoking module is operable to invoke a service of the third NF. In some embodiments， a method of operation of a NF in a core network of a wireless communication system comprises receiving an indication that a first NF is out of service or has failed where the first NF is of a same NF type as the NF； and， upon receiving the indication that the first NF is out of service or has failed， sending an indication to a second NF to indicate that the NF is taking over for the NF.

Brief Description of the Drawings

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.

Figures 1 and 2 illustrate the non-roaming and roaming Fifth Generation (5G) system architectures as specified by the Third Generation Partnership Project (3GPP) .

Figure 3 illustrates a request-response interaction between a consumer Network Function (NF) and a producer NF.

Figures 4 and 5 illustrate a subscribe-notify mechanism in which one NF subscribes to a service of another NF on behalf of itself or yet another NF， respectively.

Figure 6 illustrates one example of a wireless communication system in which embodiments of the present disclosure can be implemented.

Figure 7 illustrates the operation of two NFs according to some embodiments of the present disclosure.

Figures 8A through 8C illustrate one example implementation of the process of Figure 7 with respect to an Access and Mobility Management Function (AMF) and an AMF and a Session Management Function (SMF) with respect to a Packet Data Unit (PDU) session establishment procedure.

Figures 9A through 9C reproduce a diagram for PDU session establishment from 3GPP Technical Specification (TS) 23.501 V1.3.0 in which aspects of Figures 8A through 8C can be implemented.

Figures 10 and 11 illustrate example embodiments of a network node in which a NF (s) is implemented.

Detailed Description

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.

Systems and methods are disclosed herein that provide a mechanism for a first Network Function (NF) to directly or indirectly indicate， to a second NF， a set of NFs of the same type as the first NF that support at least some (but potentially all) of the same types of services as the first NF. The set of NFs can be used by the second NF when the second NF desires to invoke a service of the first NF， e.g.， when the first NF is unavailable. In some embodiments， the first NF establishes a binding to the second NF by invoking (e.g.， subscribing to) a service supported by the second NF and provides a direct or indirect indication of the set of NFs to the second NF when establishing this binding. Note that the service supported by the second NF that is invoked by the first NF is different than the services supported by the set of NFs indicated to the second NF. The first and second NFs may be the same type of NF or different types of NFs (e.g.， a v-SMF (NF A) and a h-SMF (NF B) ， or two AMFs during an AMF relocation procedure) ， and the set of NFs may be used by the second NF when the NF A needs to be changed (e.g.， when NF A has a failure， when NF A is put into maintenance service， or when NF A is put out of service from OAM) .

In this regard， Figure 6 illustrates one example of a wireless communication system 10 in which embodiments of the present disclosure can be implemented. As illustrated， the wireless communication system 10 includes a number of wireless devices 12 served by a Radio Access Network (RAN) that includes a number of radio access nodes 14 having corresponding coverage areas or cells 16. The wireless communication system 10 also includes a core network 18. In the embodiments described herein， the wireless communication system 10 is a Third Generation Partnership Project (3GPP) Fifth Generation (5G) network and， as such， the RAN is a 5G RAN and the core network 18 is a 5G Core (5GC) . The core network 18 includes a number of NFs 20. As illustrated， the NFs 20 include an Access and Mobility Management Function (s) (AMF (s) ) 22， Session Management Function (s) (SMF (s) ) 24， Network Repository Function (s) (NRF (s) ) 26， Network Slice Selection Function (s) (NSSF (s) ) 28， Network Exposure Function (s) (NEF (s) ) 30， Policy Control Function (s) (PCF (s) ) 32， and Application Function (s) (AF (s) ) 34. The NFs 20 are also referred to as NF instances. Thus， as an example， multiple AMFs 22 may be referred to as AMF instances.

Figure 7 illustrates the operation of two NFs 20-A and 20-B according to some embodiments of the present disclosure. Optional steps are represented by dashed lines. The NFs 20-A and 20-B may be different types of NFs (e.g.， an AMF 22 and a SMF 24) or two different instances of the same type of NF (e.g.， two SMFs 24 such as， e.g.， a v-SMF and a h-SMF) .

The NF 20-A provides， to the NF 20-B， information that directly or indirectly indicates a set of NFs of a same type as the NF 20-A that support at least some of the same types of services as the NF 20-A (step 100) . Preferably， the NF 20-A provides the information that indicates the set of NFs to the NF 20-B in a message that the NF 20-A sends to the NF 20-B to invoke a service of NF 20-B. For example， the NF 20-A may subscribe to a particular service supported by the NF 20-B or request a particular service supported by the NF 20-B. The message sent by the NF 20-A to invoke the service of the NF 20-B may be， e.g.， a Hypertext Transfer Protocol (HTTP) request， where the information that indicates the set of NFs is included， e.g.， in a message body of the message or a header of the message.

As used herein， the information directly indicates the set of NFs if the information provided in step 100 itself indicates the set of NFs. For example， the information directly indicates the set of NFs by including NF Identifiers (IDs) of the set of NFs in the information provided in step 100. As used herein， the information indirectly indicates the set of NFs if the information provided in step 100 includes information that can be used by the NF 20-B to retrieve or otherwise obtain information that directly indicates the set of NFs. For example， the information indirectly indicates the set of NFs by including a Uniform Resource Indicator (URI) (e.g.， a Uniform Resource Locator (URL) ) that can be used by the NF 20-B to retrieve information that directly indicates the set of NFs from an instance of a network entity (e.g.， a NRF instance) ， e.g.， using a discovery procedure.

In some embodiments， the set of NFs includes the NF 20-A and one or more additional NFs 20. In some other embodiments， the set of NFs includes one or more NFs 20， but not the NF 20-A. In this case， the NF 20-A may be separately indicated to the NF 20-B， e.g.， in the same message by including a NF ID of the NF 20-A or some other ID of the NF 20-A in the message. As one particular example， the NF 20-A is part of a defined group of NFs 20 (also referred to herein as a logical group of NFs 20) of the same type that support at least some of the same services (e.g.， a group of AMFs 22) and have access to at least some of the same User Equipment (UE) context information， which enables one NF in the group to take over for another NF in the group when the other NF fails or is otherwise unavailable (i.e.， enables NFs in the group to serve the respective UEs equally) . In this case， the set of NFs indicated by the information provided in step 100 is this logical group of NFs includes the NF 20-A. For example， the information indicating the set of NFs may be a set ID assigned to the logical group of NFs or a URI that can be used by the NF 20-B to retrieve information that directly indicates the set of NFs (and optionally their associated services) from， e.g.， the NRF 26.

As stated above， in some preferred embodiments， the information that directly or indirectly indicates the set of NFs is included in the message sent from the NF 20-A to the NF 20-B to invoke a service of the NF 20-B. For example， in some embodiments， the indication of the set of NFs is included in the message sent from the NF 20-A to the NF 20-B to invoke the service of the NF 20-B as， e.g.， an Information Element (IE) . In other words， in some embodiments， providing the information that directly or indirectly indicates the set of NFs in step 100 includes sending a message to invoke a service of the NF 20-B (e.g.， an HTTP request) ， where the message includes the information that directly or indirectly indicates the set of NFs (e.g.， in a message body or header of the HTTP request such as， e.g.， in a new IE included in the body of the HTTP request) .

The information that indicates the set of NFs can take many different forms， depending on the particular embodiment. In some embodiments， the information that indicates the set of NFs is information that indirectly indicates the set of NFs. Further， in some embodiments， the information that indirectly indicates the set of NFs includes one or more URIs (e.g.， one or more URLs) that can be used by the NF 20-B to obtain information that directly indicates the set of NFs and， in some particular embodiments， their associated services. More specifically， in some embodiments， the NF 20-A is part of a logical group of NFs that have access to at least some of the same UE context information， and the set of NFs indicated by the information provided from the NF 20-A to the NF 20-B in step 100 is the logical group of NFs. The URI (s) then include a URL that includes a set ID that identifies the logical group of NFs and can be used by the NF 20-B to query the NRF 26 (e.g.， using a HTTP GET) to obtain information that directly identifies the NFs 20 in the set of NFs and， in some embodiments， one or more services supported by those NFs. For instance， by querying the NRF 26， e.g.， using an extended discovery mechanism and the URL containing the NF set ID， the NF 20-B obtains information that indicates the NFs 20 in the set that are available and， optionally， the services supported by the available NFs in the set.

In some other embodiments， the information that indicates the set of NFs includes one or more URIs (e.g.， one or more URLs) for one or more NFs 20 configured as backup NFs for the NF 20-A that can be used by the NF 20-B to query an instance of a network entity (e.g.， used to query the NRF 26， e.g.， using a discovery mechanism) to obtain information that directly indicates the set of NFs and， in some embodiments， the services provided by those NFs. For example， if there is one backup NF configured for the NF 20-A， then the information includes one URI (e.g.， one URL) for that backup NF that can be used by the NF 20-B to query， e.g.， the NRF 26 to determine whether the backup NF is available and， optionally， obtain information that indicates one or more services supported by the backup NF. If there are two or more backup NFs for the NF 20-A， then the information may include a single URI (e.g.， a single URL) that can be used by the NF 20-A to query， e.g.， the NRF 26 to determine which of the backup NFs is (are) available and， optionally， obtain information that indicates the services supported by the available backup NFs. Alternatively， the information may include a separate URI (e.g.， a separate URL) for each backup NF that can be used by the NF 20-B to query， e.g.， the NRF 26 to determine whether that backup NF is available and， optionally， the services supported by that backup NF.

In some other embodiments， the information that indicates the set of NFs is information that directly indicates the set of NFs. For example， the information that directly indicates the set of NFs includes IDs of the NFs (NF IDs of the NFs) . The IDs of the NFs can， for example， be used by the NF 20-B to query， e.g.， the NRF 26 to determine whether the NFs are available and， optionally， obtain information that indicates the services supported by those NFs. As one alternative， the information that directly indicates the set of NFs may also include information regarding the services supported by those NFs.

In some embodiments， the NFs in the set of NFs indicated by the information provided from the NF 20-A to the NF 20-B in step 100 may be prioritized. For example， in embodiments where the set of NFs includes the NF 20-A and one or more additional NFs， the NF 20-A may be prioritized such that， if the service (s) of the NF 20-A is needed by the NF 20-B， the NF 20-B first attempts to invoke the service (s) of the NF 20-A and only invokes the service (s) of one of the other NFs in the set if the NF 20-A is unavailable (e.g.， due to failure) .

In some embodiments， the NF 20-B also provides， to the NF 20-A， information that directly or indirectly indicates a set of NFs that are of the same type as the NF 20-B and support at least some of the same services of the NF 20-B (step 102) . In some embodiments， the information provided in step 100 is provided within a message from the NF 20-A to the NF 20-B in which the NF 20-A invokes a service of the NF 20-B， as described above. Then， in step 102， the NF 20-B provides the information that that directly or indirectly indicates a set of NFs that are of the same type as the NF 20-B and support at least some of the same services of the NF 20-B in a response sent to the NF 20-B to acknowledge receipt of the invocation message from the NF 20-A.

In some embodiments， whether or not the NF 20-A is included in the set of NFs indicated in the information of step 100， the NF 20-B first attempts to invoke a service of the NF 20-A upon determining that the service of the NF 20-A is needed. In this regard， upon determining that it desires to invoke a service supported by the NF 20-A (which is different than the type of service of the NF 20-B that is being consumed by the NF 20-A) ， the NF 20-B invokes the service of the NF 20-A (step 104) . For example， the NF 20-B may subscribe to the service of the NF 20-A or request the service of the NF 20-A. In some embodiments， as an alternative to providing such information in step 102， the NF 20-B provides， within a message information that that directly or indirectly indicates a set of NFs that are of the same type as the NF 20-B and support at least some of the same services of the NF 20-B. In this example， the NF 20-A is able to provide the service and， as such， returns a response to the NF 20-B that acknowledges receipt of the message invoking the service of the NF 20-A (step 106) .

In this example， sometime thereafter while the NF 20-B is consuming the service of the NF 20-A， the NF 20-B discovers that the NF 20-A is unavailable (step 108) . The manner in which the NF 20-B discovers that the NF 20-A is unavailable varies depending on the particular embodiment and the type of NFs 20-A and 20-B. For example， the NF 20-B may discover that the NF 20-A is unavailable while consuming the service of the NF 20-A if the NF 20-B receives no response to the invocation request from the NF 20-A or if if the NF 20-A responds to the invocation request by indicating that that the NF 20-A is unavailable. Alternatively， the NF 20-B may discover that the NF 20-A is unavailable prior to consuming the service of the NF 20-A. For example， the NF 20-B may discover that the NF 20-A is unavailable prior to sending the request of step 104 by using a discovery mechanism of the NRF 26. Upon discovering that the NF 20-A is unavailable， the NF 20-B selects a NF (in this example NF 20-C) from the set of NFs indicated by the information provided by the NF 20-A in step 100 (step 110) . In some embodiments， the NF 20-B selects any one of the NFs in the set. In some other embodiments， the NF 20-B uses information about the services supported by the NFs in the set of NFs to select one of the NFs 20 from the set that supports the particular service desired by the NF 20-B. For example， the NF 20-B may query the NRF 26 to determine which of the NFs in the set is (are) currently available to provide the desired service and then select one of those NFs as the NF 20-C from which to invoke the service. The NF 20-B then invokes the service of the NF 20-C (step 112) and receives a response from the NF 20-C that accepts the request to invoke the service of the NF 20-C (step 114) .

Note that in some other embodiments， the NF 20-B does not necessarily invoke the desired service from the NF 20-A without first considering the full set of NFs. For example， after receiving the information that indicates the set of NFs in step 100， the NF 20-B may decide that it desires to invoke a service of the NF 20-A. Rather than initially invoking the service from the NF 20-A， the NF 20-B may select one of the NFs from the set of NFs (i.e.， the NF 20-C in the example of Figure 7) ， which may or may not be the NF 20-A， and invoke the service from the selected NF. In this case， the NF 20-A may also be included in the set and may or may not be selected by the NF 20-B from the set as the NF from which to invoke the service.

Figures 8A through 8C illustrate one example implementation of the process of Figure 7 with respect to an AMF 22-1 and an SMF 24-1 with respect to a PDU session establishment procedure. As illustrated， as part of a UE (i.e.， a wireless device) initiated PDU Session Establishment procedure， the AMF 22-1 needs to select a SMF 24 to establish a N11 session for the PDU session to be established. In this example， the AMF 22-1 selects the SMF 24-1. So， the AMF 22-1 invokes an SMF service (Nsmf_PDU_Session_Create SM Context) of the SMF 24-1 (step 200) . The AMF 22-1 invokes the SMF service in a corresponding HTTP Post message that is used to create the resource， e.g. the resource for the N11 session in the SMF 24-1. The HTTP Post message includes information that directly or indirectly indicates a set of AMFs 22 that also support at least some of the services supported by the AMF 22-1. For example， if the AMF 22-1 is part of a group of AMFs 22， e.g. identified by AMF Set ID， that also have the UE context of the UE for which the PDU session is being established or is configured to know which AMFs 22 can serve as back-up AMF (s) for the AMF 22-1 (e.g.， configured to know which AMFs 22 also have the UE context of the UE for which the PDU session is being established and， therefore， can serve the UE equally) ， the set of AMFs indicated by the information included in the HTTP Post message includes some or all of those other AMFs. In this example， the information that indicates the set of AMFs is a new IE， preferably called ″AMF Service Information ″ that indirectly indicates the set of AMFs including a URL pointing to the NRF 26， e.g. as www. nrf. mnc. mcc. gprsnetworks/amf/？ amf_set_id ＝ <SET ID> when the AMF belongs to a AMF set or www. nrf. mnc. mcc. gprsnetworks/amf/？ amf_id ＝ <AMF ID of AMF 22-1> & amf_id ＝ <AMF ID of AMF 22-n> when the AMF 22-n is configured as the back-up AMF for the AMF 22-1. If an AMF has geo- redundancy， e.g. AMF 1， AMF 2... AMF 10 are using the same Unstructured Data Storage Function (UDSF) (or distributed UDSF is used where certain UE context is stored in a specific AMF in the AMF group/set) ， and the AMF is completely stateless， one of the AMFs， e.g. AMF 1， could tell the SMF： www. nrf. mnc. mcc. gprsnetworks/amf/？ amf_id ＝ < [AMF 1>] & amf_id ＝ < [AMF 2] >1-10. This is an example of the URI indicating a set of AMFs to be used by the SMF for the binding and it also indicates that AMF 1 is the preferred AMF (i.e.， the default AMF) .

The SMF 24-1 sends a response to the request (step 202) . In this example， the response includes information that directly or indirectly indicates a set of SMFs that also support at least some of the services (including the invoked service) of the SMF 24-1. For example， the information that indicates the set of SMFs may be a new IE ( “SMF Service Information” ) included in the response (e.g.， in the message body of the response) . The new IE may include， for example， a URL for the set of SMFs if the SMF 24-1 is part of a SMF set (e.g.， www. nrf. mnc. mcc. gprsnetworks/smf/？ smf_set_id ＝ < SMF SET ID>) a URL (s) for a particular SMF (s) configured as a backup (s) for the SMF 24-1 (e.g.， www. nrf. mnc. mcc. gprsnetworks/smf/？ smf_id ＝ <SMF ID of SMF 24-1> & smf_id ＝ <SMF ID of SMF 24-n>) .

When the SMF 24-1 needs to consume AMF services， e.g. Namf_Communication_N1N2 message transfer， the SMF 24-1 uses the AMF service information (e.g.， use HTTP GET with the URL provided in the AMF service information) to get a list of the AMFs in the set and the associated AMF services by consuming an Nnrf service. Preferably， the SMF 24-1 primarily uses the services offered by the AMF 22-1； but， if the AMF 22-1 is not reachable， the SMF 24-1 uses another AMF 22 in the set. For example， the SMF 24-1 may determine that the AMF 22-1 is unreachable when the SMF 24-1 performs service discovery using the AMF service information (e.g.， uses HTTP GET www. nrf. mnc. mcc. gprsnetworks/amf/？ amf_set_id ＝ <AMF SET ID>) and the AMF 22-1 is not on the list of AMF candidates (i.e.， list of available AMFs) .

In this example， the AMF 22-1 is able to serve the SMF 24-1. As such， the SMF 24-1 invokes the AMF service of the AMF 22-1 (step 204) ， and the AMF 22-1 acknowledges the request (step 206) .

If the AMF 22-1 fails or if the AMF 22-1 is put into maintenance mode， in some embodiments， the AMF 22-1 informs an AMF 22-n in the same AMF set or configured as a backup AMF for the AMF 22-1 that the AMF 22-1 is out of service and： (a) requests that the AMF 22-n take over its AMF services and (b) informs the AMF 22-n if there is a need to consume the SMF service of the SMF 24-1 (step 208) . The AMF 22-n consumes the SMF service， e.g. Nsmf_PDU_Session_Create SM Context， by sending a corresponding request to the SMF 24-1 to invoke the SMF service (step 210) . In the request， the AMF 22-n can include an indication to indicate to the SMF 24-1 that the AMF 22-n has taken over the UE session. The SMF 24-1 is able to provide the requested SMF service， and the SMF updates the binding towards the AMF 22-n and use this AMF 22-n as primary AMF for this session (step 212) .

Alternatively， if the SMF 24-1 detects that the AMF 22-1 failed (step 214) ， e.g. when the SMF 24-1 needs consume AMF services， e.g. Namf_Communication_N1N2 message transfer， the SMF 24-1 uses another AMF (e.g.， the AMF 22-n) in the set of AMFs indicated by the AMF service information received by the SMF 24-1 in step 200 (step 216) . In other words， the SMF 24-1 invokes the AMF service of the other AMF 22-n. The AMF 22-n is able to provide AMF service， and the SMF 24-1 updates the binding towards the AMF 22-n and uses it as the primary AMF for the session (step 218) .

Similarly， if the SMF 24-1 thereafter fails or if the SMF 24-1 is put into maintenance mode， in some embodiments， the SMF 24-1 sends a request to the SMF 24-n to take over for the SMF 24-1 and informs the SMF 24-n if the SMF 24-4 needs to consume an AMF service (step 220) . The alternative SMF 24-n invokes an AMF service， e.g. Namf_Communication_N1N2 message transfer， of the AMF 22-n (step 222) . In the message invoking the AMF service， the SMF 24-n includes a new indication that indicates that the SMF 24-n is taking over for the session. The AMF 22-n is able to provide AMF service， and the AMF 22-n updates the binding towards the SMF 24-n and uses this SMF 24-n as the primary SMF for this session (step 224) .

Alternatively， in the subsequent signaling， the AMF 22-n discovers that the SMF 24-1 has failed (step 226) . The AMF 22-n then tries another SMF 24-n obtained from the SMF assistance information (e.g.， retrieved by using the URL included in the SMF assistance information using， e.g.， HTTP GET www. nrf. mnc. mcc. gprsnetworks/smf/？ smf_set_id ＝ <SMF SET ID>) (step 228) . In particular， upon discovering the SMF 24-n using the SMF service information received in step 202， the AMF 22-n invokes the SMF service of the SMF 24-n. Note that the AMF 22-n may obtain the SMF service assistance information in any suitable manner. For example， the SMF service assistance information may be stored as part of the UE context， which is accessible to the AMF 22-n. The SMF 24-n is able to provide SMF service， and the AMF 22-n updates the binding towards the SMF 24-n and use this SMF 24-n as the primary SMF for this session (step 230) .

Note that the mechanism used to enable the AMF 22-n to have the UE context as in the AMF 22-1 can be any suitable mechanism. For example， this can be done using an UDSF connected to the AMFs， or the AMF 22-1 can push the UE context to the AMF 22-n either when the failure (or by Operation and Maintenance (O&M) ) takes place， or before that. The same is true for the SMF 24-1 and the SMF 24-n.

In above example， the URL that is referring to the NRF 26 pointing to a list of services of the NF and the equivalent NF (within the same NF group or configured as a backup NF (s) ) is assumed to be provided in the HTTP message body. However， as alternative， such URL can be embedded in a NEW custom HTTP header. For example， if HTTP GET is used to initiate a communication between NF A and NF B， the URL is placed in the HTTP header， which is particularly beneficial since a HTTP GET does not have a message body.

Tables 1 and 2 below are reproductions of tables from 3GPP Technical Specification (TS) 23.502 V1.2.0 that gives a list of currently defined SMF and AMF services. Table 1 is SMF services from chapter 5.2.8 of 3GPP TS 23.502 V1.2.0， and Table 2 is AMF services from chapter 5.2.2 of 3GPP TS 23.502 V1.2.0. Other types of NFs 20 provide other types of services. Further， additional or alternative services may be defined in the future.

Table 1： NF Services Provided by the SMF

Table 2： List of AMF Services

For context， Figures 9A through 9C reproduce the diagram for PDU session establishment from 3GPP TS 23.501 V1.3.0. These figures are for context only and are to illustrate that

steps

200 and 202 correspond to steps 3 and 10 in Figures 9A through 9C. The remaining steps are well known to those of skill in the art and， therefore， the details of those steps are not provided.

It should be noted that the process of Figures 8A through 8C is only one example implementation of the process of Figure 7. The process of Figure 7 can be utilized for any type of procedure in the core network 18 in which one NF 20 invokes the service of another NF 20.

Figure 10 illustrates one example of a network node 36 in which a NF (s) 20 may be implemented according to some embodiments of the present disclosure. As illustrated， the network node 36 comprises hardware 38 including a communication interface 40 configured to set up and maintain a wired or wireless connection with an interface of a different network node of the wireless communication system 10. The network node 36 further comprises processing circuitry 42， which may have storage and/or processing capabilities. In particular， the processing circuitry 42 may comprise one or more programmable processors， application specific integrated circuits， field programmable gate arrays， or combinations of these (not shown) adapted to execute instructions. The network node 36 further comprises software 44， which is stored in or is accessible by the network node 36 and executable by the processing circuitry 42. The software 44 includes an application 46. The application 46 may， for example， be a software application that provides one or more NFs 20 of the same NF type or different NF types.

Figure 11 illustrates the network node 36 in accordance with some other embodiments of the present disclosure. As illustrated， the network node 36 includes one or more modules 48， each of which is implemented in software. As an example， if the network node 36 implements the NF 20-A， then the modules 48 include a providing module that provides the information that indicates the set of NFs to the NF 20-B as described above with respect to， e.g.， Figure 7. As another example， if the network node 36 implements the NF 20-B， then the modules 48 include a receiving module that receives， from the NF 20-A， the information that indicates the set of NFs， a selecting function that operates to select a NF from the set of NFs when the NF 20-B desires to invoke a service of the NF 20-A， and an invoking module that operates to invoke the service， as described above with respect to， e.g.， Figure 7.

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

Item 1 is directed to method of operation of a first NF in a core network of a wireless communication system， which method comprises：

providing， from the first NF to a second NF， information that directly or indirectly indicates a set of NFs of a same NF type as the first NF that support at least some of one or more types of services provided by the first NF.

Item 2 is directed to the method of item 1 wherein the information that directly or indirectly indicates the set of NFs also directly or indirectly indicates one or more supported services of each NF in the set of NFs including information that indicates how each service can be contacted and consumed.

Item 3 is directed to the method of

item

1 or 2 wherein providing the information that indicates the set of NFs comprises：

sending a message from the first NF to the second NF to invoke a service of the second NF， the message comprising the information that directly or indirectly indicates the set of NFs of the same NF type as the first NF that support at least some of the one or more types of services provided by the first NF.

Item 4 is directed to the method of any one of item 1 to 3 wherein the set of NFs comprises one or more NFs.

Item 5 is directed to the method of any one of item 1 to 3 wherein the set of NFs comprises the first NF and one or more additional NFs.

Item 6 is directed to the method of any one of item 1 to 3 wherein the set of NFs comprise a logical group of NFs that can access User Equipment， UE， context information related to the NF type of the first NF such that NFs in the logical group of NFs are able to serve respective UEs equally.

Item 7 is directed to the method of any one of item 1 to 6 wherein the information that directly or indirectly indicates the set of NFs comprises at least one Uniform Resource Indicator， URI， that indirectly indicates the set of NFs， wherein the at least one URI indicates a service instance in a network resource entity from which the second NF can retrieve information that that directly indicates the set of NFs of the same NF type as the first NF.

Item 8 is directed to the method of any one of item 1 to 6 wherein the information that indicates directly or indirectly the set of NFs comprises at least one Uniform Resource Indicator， URI， that indirectly indicates the set of NFs and their associated services， wherein the at least one URI indicates a service instance in a network resource entity from which the second NF can retrieve information that that directly indicates the set of NFs of the same NF type as the first NF and their associated services.

Item 9 is directed to the method of item 8 wherein the instance in the network resource entity comprises an instance of a Network Repository Function， NRF， and the second NF can retrieve the information that that directly indicates the set of NFs of the same NF type as the first NF and their associated services from the NRF using the URI in a service discovery procedure.

Item 10 is directed to the method of any one of item 1 to 6 wherein：

the information that directly or indirectly indicates the set of NFs comprises a separate Uniform Resource Indicator， URI， for each NF in the set of NFs； and

for each NF in the set of NFs， the URI for the NF indicates an instance in a network resource entity from which the second NF can retrieve information that that directly indicates one or more services of the NF.

Item 11 is directed to the method of any one of item 1 to 6 wherein the information that directly or indirectly indicates the set of NFs comprises a set of NF Identifiers， IDs， that directly identify the set of NFs.

Item 12 is directed the method of any one of item 1 to 11 wherein the set of NFs is to be used by the second NF when the second NF desires to invoke a service that is supported by the first NF.

Item 13 is directed to the method of any one of item 1 to 11 wherein the set of NFs is to be used by the second NF when the second NF desires to invoke a service that is supported by the first NF and the first NF is unavailable.

Item 14 is directed to the method of any one of item 1 to 13 further comprising：

receiving， from the second NF， information that directly or indirectly indicates a set of NFs of a same NF type as the second NF that support at least some of one or more types of services provided by the second NF.

Item 15 is directed to a first NF for a core network of a wireless communication system， the first NF adapted to operatively：

provide， from the first NF to a second NF， information that directly or indirectly indicates a set of NFs of a same NF type as the first NF that support at least some of one or more types of services provided by the first NF.

Item 16 is directed to the first NF of item 15 wherein the first NF is further adapted to perform the method of any one of item 2 to 14.

Item 17 is directed to a first NF 20-A for a core network 18 of a wireless communication system 10， comprising：

a communication interface 40； and

processing circuitry 42 associated with the communication interface， wherein the processing circuitry is operable to cause the first NF to provide， to a second NF 20-B via the communication interface， information that directly or indirectly indicates a set of NFs of a same NF type as the first NF that support at least some of one or more types of services provided by the first NF.

Item 18 is directed to the first NF of item 17 wherein the processing circuitry is further operable to cause the first NF to perform the method of any one of item 2 to 14.

Item 19 is directed to a first NF 20-A for a core network of a wireless communication system， the first NF comprises：

a processing module 48 operable to cause the first NF to provide， from the first NF to a second NF 20-B， information that directly or indirectly indicates a set of NFs of a same NF type as the first NF that support at least some of one or more types of services provided by the first NF.

Item 20 is directed to a method of operation of a second NF in a core network of a wireless communication system， comprising：

receiving， by the second NF from a first NF， information that directly or indirectly indicates a set of NFs of a same NF type as the first NF that support at least some of one or more types of services provided by the first NF；

selecting a third NF from the set of NFs； and

invoking a service of the third NF.

Item 21 is directed to the method of item 20 further comprising：

invoking a service of the first NF upon determining that a service that is supported by the first NF is desired； and

discovering that the first NF is unavailable；

wherein selecting the third NF from the set of NFs comprises selecting the third NF from the set of NFs upon discovering that the first NF is unavailable.

Item 22 is directed to the method of item 20 further comprising：

discovering that the first NF is unavailable；

Item 23 is directed to the method of any one of item 20 to 22 wherein receiving the information that directly or indirectly indicates the set of NFs comprises：

receiving a message from the first NF (20-A) that invokes a service of the second NF， the message comprising the information that directly or indirectly indicates the set of NFs of the same NF type as the first NF that support at least some of the one or more types of services provided by the first NF.

Item 24 is directed to the method of any one of item 20 to 23 wherein the set of NFs comprises one or more NFs.

Item 25 is directed to the method of any one of item 20 to 23 wherein the set of NFs comprises the first NF and one or more additional NFs.

Item 26 is directed to the method of any one of item 20 to 23 wherein the set of NFs comprises a logical group of NFs that can access User Equipment， UE， context information related to the NF type of the first NF such that NFs in the logical group of NFs are able to serve respective UEs equally.

Item 27 is directed to the method of any one of item 20 to 26 wherein the information that directly or indirectly indicates the set of NFs comprises at least one Uniform Resource Indicator， URI， for the set of NFs， wherein the at least one URI indicates a service instance in a network resource entity from which the second NF can retrieve information that that directly indicates the set of NFs of the same NF type as the first NF.

Item 28 is directed to the method of any one of item 20 to 26 wherein the information that directly or indirectly indicates the set of NFs comprises at least one Uniform Resource Indicator， URI， for the set of NFs and their associated services， wherein the at least one URI indicates a service instance in a network resource entity from which the second NF can retrieve information that that directly indicates the set of NFs of the same NF type as the first NF and their associated services.

Item 29 is directed to the method of item 28 wherein the instance in the network resource entity comprises an instance of a Network Repository Function， NRF， and the second NF can retrieve the information that that directly indicates the set of NFs of the same NF type as the first NF and their associated services from the NRF using the URI in a service discovery procedure.

Item 30 is directed to the method of any one of item 20 to 26 wherein：

Item 31 is directed to the method of any one of item 20 to 26 wherein the information that directly or indirectly indicates the set of NFs comprises a set of NF Identifiers， IDs， that directly identify the set of NFs.

Item 32 is directed to a second NF for a core network of a wireless communication system， the second NF adapted to：

receive， by the second NF from a first NF， information that directly or indirectly indicates a set of NFs of a same NF type as the first NF that support at least some of one or more types of services provided by the first NF；

select a third NF from the set of NFs； and

invoke a service of the third NF.

Item 33 is directed to the second NF of item 32 wherein the second NF is further adapted to perform the method of any one of item 21 to 31.

Item 34 is directed to a second NF 20-B for a core network 18 of a wireless communication system 10， comprising：

a communication interface 40； and

processing circuitry 42 associated with the communication interface， wherein the processing circuitry is operable to cause the second NF to：

receive， by the second NF from a first NF 20-A， information that directly or indirectly indicates a set of NFs of a same NF type as the first NF that support at least some of one or more types of services provided by the first NF；

select a third NF 20-C from the set of NFs； and

invoke a service of the third NF.

Item 35 is directed to the second NF of item 34 wherein the processing circuitry is further operable to cause the second NF to perform the method of any one of item 21 to 31.

Item 36 is directed to a second NF for a core network of a wireless communication system， comprising：

a receiving module operable to receive， from a first NF， information that directly or indirectly indicates a set of NFs of a same NF type as the first NF that support at least some of one or more types of services provided by the first NF；

a selecting module operable to select a third NF from the set of NFs； and

an invoking module (48) operable to invoke a service of the third NF.

Item 37 is directed to a method of operation of a NF in a core network of a wireless communication system， comprising：

receiving an indication that a first NF is out of service or has failed， the first NF being of a same NF type as the NF； and

upon receiving the indication that the first NF is out of service or has failed， sending an indication to a second NF to indicate that the NF is taking over for the NF.

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) .

● 3GPP Third Generation Partnership Project

● 5G Fifth Generation

● 5GC Fifth Generation Core

● AF Application Function

● AMF Access and Mobility Management Function

● AUSF Authentication Server Function

● CP Control Plane

● HTTP/2 Hypertext Transfer Protocol Version 2.0

● ID Identifier

● IE Information Element

● NEF Network Exposure Function

● NF Network Function

● NRF Network Repository Function

● NSSF Network Slice Selection Function

● O&M Operation and Maintenance

● PCF Policy Control Function

● PDU Packet Data Unit

● RAN Radio Access Network

● SMF Session Management Function

● TCP Transmission Control Protocol

● TS Technical Specification

● UDM Unified Data Management

● UDSF Unstructured Data Storage Function

● UE User Equipment

● URI Uniform Resource Indicator

● URL Uniform Resource Locator

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

A method of operation of a first Network Function， NF， (20-A) in a core network (18) of a wireless communication system (10) ， comprising：

providing (100) ， from the first NF (20-A) to a second NF (20-B) ， information that directly or indirectly indicates a set of NFs of a same NF type as the first NF (20-A) that support at least some of one or more types of services provided by the first NF (20-A) .
The method of claim 1 wherein the information that directly or indirectly indicates the set of NFs also directly or indirectly indicates one or more supported services of each NF in the set of NFs including information that indicates how each service can be contacted and consumed.
The method of claim 1 or 2 wherein providing (100) the information that indicates the set of NFs comprises：

sending (100) a message from the first NF (20-A) to the second NF (20-B) to invoke a service of the second NF (20-B) ， the message comprising the information that directly or indirectly indicates the set of NFs of the same NF type as the first NF (20-A) that support at least some of the one or more types of services provided by the first NF (20-A) .
The method of any one of claims 1 to 3 wherein the set of NFs comprises one or more NFs.
The method of any one of claims 1 to 3 wherein the set of NFs comprises the first NF (20-A) and one or more additional NFs.
The method of any one of claims 1 to 3 wherein the set of NFs comprise a logical group of NFs that can access User Equipment， UE， context information related to the NF type of the first NF (20-A) such that NFs in the logical group of NFs are able to serve respective UEs equally.
The method of any one of claims 1 to 6 wherein the information that directly or indirectly indicates the set of NFs comprises at least one Uniform Resource Indicator， URl， that indirectly indicates the set of NFs， wherein the at least one URl indicates a service instance in a network resource entity (26) from which the second NF (20-B) can retrieve information that that directly indicates the set of NFs of the same NF type as the first NF (20-A) .
The method of any one of claims 1 to 6 wherein the information that indicates directly or indirectly the set of NFs comprises at least one Uniform Resource Indicator， URl， that indirectly indicates the set of NFs and their associated services， wherein the at least one URl indicates a service instance in a network resource entity (26) from which the second NF (20-B) can retrieve information that that directly indicates the set of NFs of the same NF type as the first NF (20-A) and their associated services.
The method of claim 8 wherein the instance in the network resource entity (26) comprises an instance of a Network Repository Function， NRF， and the second NF (20-B) can retrieve the information that that directly indicates the set of NFs of the same NF type as the first NF (20-A) and their associated services from the NRF using the URl in a service discovery procedure.
The method of any one of claims 1 to 6 wherein：

the information that directly or indirectly indicates the set of NFs comprises a separate Uniform Resource Indicator， URl， for each NF in the set of NFs； and

for each NF in the set of NFs， the URl for the NF indicates an instance in a network resource entity (26) from which the second NF (20-B) can retrieve information that that directly indicates one or more services of the NF.
The method of any one of claims 1 to 6 wherein the information that directly or indirectly indicates the set of NFs comprises a set of NF Identifiers， IDs， that directly identify the set of NFs.
The method of any one of claims 1 to 11 wherein the set of NFs is to be used by the second NF (20-B) when the second NF (20-B) desires to invoke a service that is supported by the first NF (20-A) .
The method of any one of claims 1 to 11 wherein the set of NFs is to be used by the second NF (20-B) when the second NF (20-B) desires to invoke a service that is supported by the first NF (20-A) and the first NF (20-A) is unavailable.
The method of any one of claims 1 to 13 further comprising：

receiving (102， 104) ， from the second NF (20-B) ， information that directly or indirectly indicates a set of NFs of a same NF type as the second NF (20-B) that support at least some of one or more types of services provided by the second NF (20-B) .
A first Network Function， NF， (20-A) for a core network (18) of a wireless communication system (10) ， the first NF (20-A) adapted to：

provide， from the first NF (20-A) to a second NF (20-B) ， information that directly or indirectly indicates a set of NFs of a same NF type as the first NF (20-A) that support at least some of one or more types of services provided by the first NF (20-A) .
The first NF (20-A) of claim 15 wherein the first NF (20-A) is further adapted to perform the method of any one of claims 2 to 14.
A method of operation of a second Network Function， N F， (20-B) in a core network (18) of a wireless communication system (10) ， comprising：

receiving (100) ， by the second NF (20-B) from a first NF (20-A) ， information that directly or indirectly indicates a set of NFs of a same NF type as the first NF (20-A) that support at least some of one or more types of services provided by the first NF (20-A) ；

selecting (110) a third NF (20-C) from the set of NFs； and

invoking (112) a service of the third NF (20-C) .
The method of claim 17 further comprising：

invoking (104) a service of the first NF (20-A) upon determining that a service that is supported by the first NF (20-A) is desired； and

discovering (108) that the first NF (20-A) is unavailable；

wherein selecting (110) the third NF (20-C) from the set of NFs comprises selecting (110) the third NF (20-C) from the set of NFs upon discovering (108) that the first NF (20-A) is unavailable.
The method of claim 17 further comprising：

discovering (108) that the first NF (20-A) is unavailable；

wherein selecting (110) the third NF (20-C) from the set of NFs comprises selecting (110) the third NF (20-C) from the set of NFs upon discovering (108) that the first NF (20-A) is unavailable.
The method of any one of claims 17 to 19 wherein receiving (100) the information that directly or indirectly indicates the set of NFs comprises：

receiving (100) a message from the first NF (20-A) that invokes a service of the second NF (20-B) ， the message comprising the information that directly or indirectly indicates the set of NFs of the same NF type as the first NF (20-A) that support at least some of the one or more types of services provided by the first NF (20-A) .
The method of any one of claims 17 to 20 wherein the set of NFs comprises one or more NFs.
The method of any one of claims 17 to 20 wherein the set of NFs comprises the first NF (20-A) and one or more additional NFs.
The method of any one of claims 17 to 20 wherein the set of NFs comprises a logical group of NFs that can access User Equipment， UE， context information related to the NF type of the first NF (20-A) such that NFs in the logical group of NFs are able to serve respective UEs equally.
The method of any one of claims 17 to 23 wherein the information that directly or indirectly indicates the set of NFs comprises at least one Uniform Resource Indicator， URl， for the set of NFs， wherein the at least one URl indicates a service instance in a network resource entity (26) from which the second NF (20-B) can retrieve information that that directly indicates the set of NFs of the same NF type as the first NF (20-A) .
The method of any one of claims 17 to 23 wherein the information that directly or indirectly indicates the set of NFs comprises at least one Uniform Resource Indicator， URl， for the set of NFs and their associated services， wherein the at least one URl indicates a service instance in a network resource entity (26) from which the second NF (20-B) can retrieve information that that directly indicates the set of NFs of the same NF type as the first NF (20-A) and their associated services.
The method of claim 25 wherein the instance in the network resource entity (26) comprises an instance of a Network Repository Function， NRF， and the second NF (20-B) can retrieve the information that that directly indicates the set of NFs of the same NF type as the first NF (20-A) and their associated services from the NRF using the URl in a service discovery procedure.
The method of any one of claims 17 to 23 wherein：

the information that directly or indirectly indicates the set of NFs comprises a separate Uniform Resource Indicator， URl， for each NF in the set of NFs； and

for each NF in the set of NFs， the URl for the NF indicates an instance in a network resource entity (26) from which the second NF (20-B) can retrieve information that that directly indicates one or more services of the NF.
The method of any one of claims 17 to 23 wherein the information that directly or indirectly indicates the set of NFs comprises a set of NF Identifiers， IDs， that directly identify the set of NFs.
A second Network Function， NF， (20-B) for a core network (18) of a wireless communication system (10) ， the second NF (20-B) adapted to：

receive， by the second NF (20-B) from a first NF (20-A) ， information that directly or indirectly indicates a set of NFs of a same NF type as the first NF (20-A) that support at least some of one or more types of services provided by the first NF (20-A) ；

select a third NF (20-C) from the set of NFs； and

invoke a service of the third NF (20-C) .
The second NF (20-B) of claim 29 wherein the second NF (20-B) is further adapted to perform the method of any one of claims 21 to 31.
A method of operation of a Network Function， NF， (22-n) in a core network (18) of a wireless communication system (10) ， comprising：

receiving (208) an indication that a first NF (22-1) is out of service or has failed， the first NF (22-1) being of a same NF type as the NF (22-n) ； and

upon receiving (208) the indication that the first NF (22-1) is out of service or has failed， sending (210) an indication to a second NF (24-1) to indicate that the NF (22-n) is taking over for the NF (22-1) .