Patent Description:
In <NUM> telecommunications networks, a network node that provides service is referred to as a producer network function (NF). A network node that consumes services is referred to as a consumer NF. A network function can be both a producer NF and a consumer NF depending on whether it is consuming or providing service.

A given producer NF may have many service endpoints, where a service endpoint is a combination of IP address and port number on a network node that hosts a producer NF. Producer NFs register with a network function repository function (NRF). The NRF maintains an NF profile of available NF instances and their supported services. Consumer NFs can subscribe to receive information about producer NF instances that have registered with the NRF.

One example of an NF that provides services to user equipment (UE) devices, such as Internet of Things (IoT) devices, is the access and mobility management function or AMF. The AMF provides registration management, connection management, reachability management, mobility management, and other services for UE devices. The AMF serves as the point of contact between the radio access network and the remaining nodes in the <NUM> core network. The AMF also serves as the point of access to network slice services.

There may be many AMFs serving a particular transfer area (TA) in which a UE is located. It is desirable to optimize AMF resource utilization and, in particular, if network slicing is implemented. Network slicing is a service provided in <NUM> networks where network resources are logically allocated in portions or slices for use by UE devices. Each network slice may provide particular capabilities or service to a UE. Different network slices and capabilities may be accessible via different AMFs. In addition, the same AMF may provide access to different capabilities or network slices.

When a UE registers with a public land mobile network (PLMN), during the registration procedure, the UE may communicate requested NSSAI information to the network indicating a type of network slice services requested by the UE. If the radio access node that receives the NSSAI information from the UE is capable of identifying an AMF that can provide the access to the requested network slice services, the radio access node forwards the registration request to the AMF, and the AMF provides access to the requested network slice services. However, in certain instances, the radio access node may not be capable of identifying an AMF that can provide access to the requested network slice services. One example of such a situation is when the requested NSSAI from the UE in a non-access stratum (NAS) registration request message is not a configured NSSAI for the PLMN, an allowed NSSAI for the PLMN and access type, or a default configured NSSAI. In such instances, the radio access node will route the NAS signaling to a default AMF.

When a UE context in the default AMF does not yet include an allowed NSSAI corresponding to the access type requested by or for the UE, the AMF queries the network slice selection function (NSSF) to identify an AMF that is capable of providing access to the requested network slice services. In another example, the network may decide to reallocate a UE to a different AMF than the AMF that initially receives an initial registration request.

According to 3GPP TS <NUM>, the network slice selection function provides two different services, referred to as NNSSF_NS selection service (hereinafter, "NS selection service") and NNSSF_NSSAI availability service (hereinafter, "NSSAI availability service"). NS selection service includes providing network slice information to a requestor. NSSAI availability service advises an NF consumer of the availability of subscribed NSSAIs (S-NSSAls) on a per-TA basis.

One problem with the existing 3GPP service architecture is that the NSSAI availability service and the NS selection service are decoupled. In other words, 3GPP TS <NUM> does not specify how to use the NSSAI availability service to optimize AMF selection in a manner that most efficiently allocates AMFs and network slice resources accessible via the AMFs.

For example, clause <NUM>. <NUM> of 3GPP TS <NUM> indicates that when multiple network slice instances in the UE's transfer area are able to serve a given subscribed NSSAI (S-NSSAI), based on the operator's configuration, the NSSF may select one of the network slice instances to serve the UE. A network slice instance is a set of NF instances and the required resources that form a deployed network slice. The AMF is the network node that provides access to the network slice instance. By leaving the selection of the network slice instance and corresponding AMF to the discretion of the network operator, 3GPP TS <NUM> does not define procedures for optimizing such selection. Thus, even though NSSAI availability information can be provided by the AMFs to the NSSF, 3GPP TS <NUM> does not specify how to use such information. In addition, other information, such as AMF loading, is not specified as being part of the NS selection process.

Accordingly, there exists a need for methods, systems, and computer readable media for providing for policy-based AMF selection based on NSSAI availability information obtained from an NSSAI availability service.

In <NPL>, system architecture for the <NUM> system is discussed.

In <NPL>, open topics of 5GS are discussed.

In <NPL>, network slice selection services are discussed.

A first aspect of the invention comprises a method for providing for policy-based access and mobility management function (AMF) selection using network slice selection assistance information (NSSAI) availability information obtained from an NSSAI availability service as set forth in claim <NUM>. The method comprises: by
a network slice selection function (NSSF) including at least one processor, obtaining, from an NSSAI availability service, NSSAI availability information regarding a plurality of AMFs. The method further includes receiving, from a first AMF, a network slice selection request specifying a network slice service requested by a user equipment (UE). The method further includes generating, based on the NSSAI availability information and the network slice service requested by the UE, a prioritized list including an identity of at least one AMF for supporting the network slice service. The method further includes communicating the prioritized list to the first AMF.

Obtaining the NSSAI availability information includes receiving hypertext transfer protocol (HTTP) messages from the AMFs, wherein each HTTP message indicates supported NSSAIs per transfer area (TA) for one of the AMFs.

Receiving a network slice selection request includes receiving a network slice selection request containing at least one NSSAI identifying a network slice service requested by the UE.

Generating the prioritized list includes prioritizing a second AMF that supports the requested network slice service over a third AMF that supports the requested network slice service and a greater number of network slice services in addition to the requested network slice service than the second AMF.

According to yet another aspect of the subject matter described herein, prioritizing the second AMF over the third AMF includes computing a relevance R for the second and third AMFs, where R is equal to C/T, where C is equal to a number of common NSSAIs between NSSAIs requested by the UE and NSSAIs supported by the second or third AMF and T is equal to a total number of NSSAIs supported by the second or third AMF.

According to yet another aspect of the subject matter described herein, the method for providing for policy-based AMF selection includes obtaining load percentages of each of the AMFs.

According to yet another aspect of the subject matter described herein, obtaining the load percentages includes obtaining the load percentages from a network function repository function (NRF).

According to yet another aspect of the subject matter described herein, generating the prioritized list includes computing a weight W for the second and third AMFs, where the weight W is equal to R/L, L is the load percentage of the second or third AMFs.

According to yet another aspect of the subject matter described herein, communicating the prioritized list to the first AMF includes communicating a AMF identities of the second and third AMFs and the weights computed for the second and third AMFs to the first AMF.

According to yet another aspect of the subject matter described herein, communicating the prioritized list to the first AMF includes communicating AMF identities of the second and third AMFs in an order corresponding to the weights computed for the second and third AMFs.

A second aspect of the invention comprises a system for providing for policy-based access and mobility management function (AMF) selection using network slice selection assistance information (NSSAI) availability information obtained from an NSSAI availability as set in claim <NUM>. The system includes a network slice selection function (NSSF) including at least one processor. The system further includes an access and mobility management function (AMF) prioritizer implemented by the at least one processor for obtaining, using an NSSAI availability service, NSSAI availability information regarding a plurality of AMFs using, receiving, from a first AMF, a network slice selection request specifying a network slice service requested by a user equipment (UE), generating, based on the NSSAI availability information and the network slice service requested by the UE, a prioritized list including an identity of at least one AMF for supporting the network slice service, and communicating the prioritized list to the first AMF.

According to yet another aspect of the subject matter described herein, the AMF prioritizer is configured to obtain the NSSAI availability information by receiving hypertext transfer protocol (HTTP) messages from the AMFs, and each HTTP message indicates supported NSSAIs per transfer area (TA) for one of the AMFs.

According to yet another aspect of the subject matter described herein, the network slice selection request contains at least one NSSAI identifying a network slice service requested by the UE.

According to yet another aspect of the subject matter described herein, the AMF prioritizer is configured to generate the prioritized list by prioritizing a second AMF that provides the requested network slice service over a third AMF that supports the requested network slice service and a greater number of network slice services in addition to the requested network slice service than the second AMF.

According to yet another aspect of the subject matter described herein, the AMF prioritizer is configured to prioritize the second AMF over the third AMF by computing a relevance R for the second and third AMFs, where R=C/T, where C is equal to a number of common NSSAIs between NSSAIs requested by the UE and NSSAIs supported by the second or third AMF and T is equal to a total number of NSSAIs supported by the second or third AMF.

According to yet another aspect of the subject matter described herein, the AMF prioritizer is configured to obtain load percentages for the second and third AMFs and to compute weight values W for the second and third AMFs, where the weight value W for the second or third AMF is equal to R/L and L is the load percentage of the second or third AMF.

According to yet another aspect of the subject matter described herein, the AMF prioritizer is configured to obtain the load percentages from a network function repository function (NRF).

According to yet another aspect of the subject matter described herein, the prioritized list of AMFs includes AMF identities of the second and third AMFs and the weights computed for the second and third AMFs.

According to yet another aspect of the subject matter described herein, the prioritized list includes an ordered list of AMF identities of the second and third AMFs and an order of the AMF identities in the list corresponds to the weights computed for the second and third AMFs.

A third aspect of the invention comprises a non-transitory computer readable medium having stored thereon executable instructions that when executed by a processor of a computer in a network slice selection function, cause the network slice selection function to perform steps as set forth in claim <NUM>.

The steps include obtaining, from a network slice selection assistance information (NSSAI) availability service, NSSAI availability information regarding a plurality of AMFs using an NSSAI availability service. The steps further include receiving, from a first AMF, a network slice selection request specifying a network slice service requested by a user equipment (UE). The steps further include generating, based on the NSSAI availability information and the network slice service requested by the UE, a prioritized list including an identity of at least one AMF for supporting the network slice service. The steps further include communicating the prioritized list to the first AMF.

The subject matter described herein may be implemented in hardware, software, firmware, or any combination thereof. As such, the terms "function" "node" or "module" as used herein refer to hardware, which may also include software and/or firmware components, for implementing the feature being described. In one exemplary implementation, the subject matter described herein may be implemented using a computer readable medium having stored thereon computer executable instructions that when executed by the processor of a computer control the computer to perform steps. Exemplary computer readable media suitable for implementing the subject matter described herein include non-transitory computer-readable media, such as disk memory devices, chip memory devices, programmable logic devices, and application specific integrated circuits. In addition, a computer readable medium that implements the subject matter described herein may be located on a single device or computing platform or may be distributed across multiple devices or computing platforms.

<FIG> is a block diagram illustrating an exemplary <NUM> system network architecture. In <FIG>, the network includes NRF <NUM> and service communications proxy (SCP) <NUM>. As described above, NRF <NUM> may maintain profiles of available producer NF service instances and their supported services and allow consumer NFs or SCPs to subscribe to and be notified of the registration of new/updated producer NF service instances. SCP <NUM> may also support service discovery and selection of producer NFs. In addition, SCP <NUM> may perform load balancing of connections between consumer and producer NFs.

NRF <NUM> is a repository for NF profiles. In order to communicate with a producer NF, a consumer NF or an SCP must obtain the NF profile from NRF <NUM>. The NF profile is a JavaScript object notation (JSON) data structure defined in 3GPP TS <NUM>. The NF profile definition includes at least one of a fully qualified domain name (FQDN), an Internet protocol (IP) version <NUM> (IPv4) address or an IP version <NUM> (IPv6) address.

In <FIG>, any of the nodes (other than SCP <NUM> and NRF <NUM>) can be either consumer NFs or producer NFs, depending on whether they are requesting or providing services. In the illustrated example, the nodes include a policy control function (PCF) <NUM> that performs policy related operations in a network, a user data management (UDM) function <NUM> that manages user data, and an application function (AF) <NUM> that provides application services. The nodes illustrated in <FIG> further include a session management function (SMF) <NUM> that manages sessions between AMF <NUM> and PCF <NUM>. AMF <NUM> performs mobility and registration management operations similar to those performed by a mobility management entity (MME) in <NUM> networks. AMF <NUM> also serves as the access point for network slice services. AMF <NUM> may also perform AMF selection to select the serving AMF will provide access to the network slice services requested by a UE during registration.

An authentication server function (AUSF) <NUM> performs authentication services for user equipment (UEs), such as UE <NUM>, seeking access to the network.

A network slice selection function (NSSF) <NUM> provides the above-described NSSAI availability and NS selection services for devices seeking to access specific network capabilities. As will be described in further detail below, NSSF <NUM> may obtain AMF loading information from an NRF and NSSAI availability information from AMFs. NSSF <NUM> may store the AMF loading information and NSSAI availability information in an AMF selection database maintained by NSSF <NUM>. When NSSF <NUM> receives an NSSAI selection request from an AMF, NSSF <NUM> may utilize the stored AMF loading and NSSAI availability information to compute an AMF relevance score and a weight for each AMF capable of supporting the network slice services requested by a UE seeking access to network slice services. NSSF <NUM> may generate a prioritized list of AMFs capable of providing the requested services and the corresponding weights and communicate the list to the requesting AMF. The requesting AMF may then use the prioritized list of AMFs and the weights to select an AMF for providing access to the requested network slice services.

A network exposure function (NEF) <NUM> provides application programming interfaces (APIs) for application functions seeking to obtain information about Internet of things (IoT) devices and other UEs attached to the network. NEF <NUM> performs similar functions to the service capability exposure function (SCEF) in <NUM> networks.

A radio access network (RAN) <NUM> connects UE <NUM> to the network via a wireless link. Radio access network <NUM> may be accessed using a g-Node B (gNB) (not shown in <FIG>) or other wireless access point. A user plane function (UPF) <NUM> can support various proxy functionality for user plane services. One example of such proxy functionality is multipath transmission control protocol (MPTCP) proxy functionality. UPF <NUM> may also support performance measurement functionality, which may be used by UE <NUM> to obtain network performance measurements. Also illustrated in <FIG> is a data network (DN) <NUM> through which UEs access data network services, such as Internet services.

Service edge protection proxy (SEPP) <NUM> filters incoming traffic from another PLMN and performs topology hiding for traffic exiting the home PLMN. SEPP <NUM> may communicate with an SEPP in a foreign PLMN which manages security for the foreign PLMN. Thus, traffic between NFs in different PLMNs may traverse a minimum of two SEPP functions, one for the home PLMN and the other for the foreign PLMN.

As stated above, one problem with the existing 3GPP network architecture is that it does not provide for use of NSSAI availability or AMF loading information in the AMF selection process. For example, Table <NUM>. <NUM> (re-numbered as Table <NUM>) of 3GPP TS <NUM> is set forth below:.

In Table <NUM> above, the NSSF provides two distinct services. The first service provides network slice information to a requestor, and the second service provides for NSSAI availability information on a per TA basis. However, there is no link between these two services in 3GPP TS <NUM> or 3GPP TS <NUM> where the services are defined.

For example, as described above, when there are multiple AMFs that can provide access to the network slice services requested by a UE or when the network decides to reallocate a registration to an AMF other than the AMF that initially receives a registration message, the AMF may consult the NSSF to identify an AMF capable of providing the requested services. As per 3GPP TS <NUM>, a <NUM> UE can request up to <NUM>-NSSAIs as part of an initial registration procedure. The AMF selected for a UE should support all of the S-NSSAIs requested by the UE (See clause <NUM>. <NUM> of 3GPP TS <NUM>). The NSSAI is a collection of S-NSSAls. An NSSAI may be a configured NSSAI, a requested NSSAI or an allowed NSSAI. There can be at most eight S-NSSAIs in the allowed and requested NSSAIs sent in signaling messages between the UE and the network. The requested NSSAI signaled by the UE to the network allows the network to select the serving AMF, network slice(s) and network slice instance(s) for the UE, as specified in clause <NUM>. <NUM> of 3GPP TS <NUM>.

As stated above, AMF reallocation may occur due to network slice support. During a registration procedure in a PLMN, if the network decides that the UE should be served by a different AMF based on network slice aspects, then the AMF that first received the registration request redirects the registration request to another AMF via the RAN or via direct signaling between the initial AMF and the target AMF. If the target AMF(s) are returned from the NSSF and identified by a list of candidate AMF(s), the redirection message shall only be sent via the direct signaling between the initial AMF and the target AMF. If the redirection message is sent by the AMF via the RAN, the message includes information for selection of a new AMF to serve the UE.

For a UE that is already registered, the system supports a redirection initiated by the network of a UE from its serving AMF to a target AMF due to network slice considerations (e.g. the operator has changed the mapping between the network slice instances and their respective serving AMF(s)). Operator policy determines whether redirection between AMFs is allowed.

The subject matter described herein provides for using NSSAI availability information and AMF loading information to generate a prioritized list of AMFs capable of providing access to a requested network slice service and providing the prioritized list to an AMF to facilitate in selecting an optimal AMF to access the requested network slice services. The prioritized list of AMFs can be used to select the serving AMF in any of the instances described above when an AMF is required to select a serving AMF for a UE.

<FIG> is a network diagram illustrating services provided by the NSSF in more detail. In <FIG>, the NSSF is shown as a physical NSSF 116A and a virtual NSSF (V-NSSF) 116B. NSSFs 116A and 166B are in communication with AMF <NUM> and NRF <NUM>. NSSF 116A or 116B may register with NRF <NUM> to receive updates regarding NFs, such as AMF <NUM> when an AMF is added to the network and with the network slice or other services supported by AMF <NUM> change. NSSF 116A and 116B may also receive load information from NRF <NUM> for NFs (such as AMF <NUM>) to which NSSF 116A or 116B subscribe. In operation, NSSF 116A or 116B selects a network slice instance (NSI), determines allowed NSSAI information, and determines the AMF that will serve a UE. AMF <NUM> can retrieve the NRF, NSI ID, and target AMFs as part of a UE initial registration and packet data unit (PDU) session establishment procedure.

As stated above, two services provided by NSSF <NUM> are the NSSAI availability service and the NS selection service. The NS selection service is used by an NF service consumer (i.e., an AMF) to retrieve the information related to a network slice. The NS selection service also enables the NSSF to provide to the AMF the allowed NSSAI and the configured NSSAI for the serving PLMN. The NSSAI availability service enables updating with the NSSF of the S-NSSAI(s) that the NF service consumer (e.g., the AMF) supports on a per TA basis. The NSSAI availability service allows the AMF to subscribe to and be notified of any change in status, on a per TA basis, of the S-NSSAIs available per TA (unrestricted) and the restricted S-NSSAI(s) per PLMN in the TA of the serving PLMN of the UE.

3GPP TS <NUM> allows the NSSF to obtain NSSAI availability information from AMFs but does not specify the use of NSSAI availability information for AMF selection. The subject matter described herein includes using NSSAI availability information obtained through the NSSAI availability service to determine weights for the candidate AMFs, the providing of the weights to the requesting AMF, and the utilization of the weights by the requesting AMF to select an AMF to serve a session involving a UE, such as an IoT device.

<FIG> is a message flow diagram illustrating NS selection service performed without NSSAI availability information. Referring to <FIG>, in line <NUM>, an AMF <NUM>, which may be a default AMF to which an initial registration of a UE is routed or an AMF that decides for network slice reasons that the initial registration should be routed to a different AMF, sends a hypertext transfer protocol (HTTP) GET message to NSSF <NUM>. The HTTP GET message specifies a list of requested NSSAIs, a list of subscribed NSSAIs, a transfer area identifier (TAI), a PLMN identifier, and a network function identifier, which identifies AMF <NUM>. Based on the requested and subscribed NSSAIs, the PLMN ID, the TA ID, and the identity of the requesting AMF, NSSF <NUM> determines the network slice identifiers (NSIs) and the target AMFs which provide access to the services identified by the NSIs, and, in line <NUM>, sends an NF discovery request to NRF <NUM>. The NF discovery request specifies the set of target AMFs which provide access to the requested network slice services.

In line <NUM>, NRF <NUM> responds with the list of AMFs which belong to the target AMF set identified in the request in line <NUM>. In line <NUM>, NSSF <NUM> sends a response to the requesting AMF with the candidate AMF list. AMF <NUM> then selects one of the AMFs to provide access to the requested network slice service. It should be noted that NSSAI availability information obtained from the NSSAI availability service is not used in the AMF selection process in <FIG>.

<FIG> is a message flow diagram illustrating NSSF <NUM> receiving NSSAI availability information via the NSSAI availability service. Referring to <FIG>, in line <NUM>, NSSF <NUM> receives an HTTP PUT/PATCH message from AMF1 <NUM>. The HTTP PUT/PATCH message contains supported NSSAIs per TA. In the illustrated example, the supported NSSAIs are embedded battery (eMBBATT) and massive IoT (mIOT). The mIOT NSSAI may be requested by or on behalf of a large number of IoT devices requesting the same service from the network. The eMBBATT NSSAI may be requested by a UE, such as an IoT device, with an embedded battery. The parameter 0x2345 is the identifier for the TA. Another example of an NSSAI that may be specified is ultra-reliable low latency communications (URLLC). URLLC can be used for industrial automation and remote-control applications requiring low latency, ultra-reliable communications. Yet another NSSAI that may be specified is enhanced mobile broadband (emBB) for mobile broadband services, such as streaming video.

According to the subject matter described herein, NSSF <NUM> may store and utilize the NSSAI availability information to provide a list of AMFs to a querying AMF that is utilizing the NF selection service illustrated in <FIG>. Thus, after line <NUM>, NSSF <NUM> stores an identifier for AMF1 <NUM> along with the supported NSSAIs per TA for AMF <NUM>, and this data may be used to respond to an NS selection query. In line <NUM> of the message flow diagram, NSSF <NUM> responds to AMF1 <NUM> with an authorized NSSAI availability data message acknowledging receipt of the NSSAI availability information.

In line <NUM> of the message flow diagram, AMF2 <NUM> sends an HTTP PUT information to NSSF <NUM> identifying mIOT service for the transfer area identified by the identifier 0x2345. In response to the HTTP PUT message, NSSF <NUM> stores an identifier for AMF2 <NUM>, the TA ID, and the NSSAIs. Table <NUM> shown below illustrates an example of NSSAI availability information that may be stored by NSSF <NUM> after the call flow illustrated in <FIG>.

In Table <NUM>, it can be seen that NSSF <NUM> stores an AMF identifier, corresponding TA identifiers, and NSSAIs for each TA ID. In the illustrated example, the AMF identifiers are AMF1 and AMF2 identifying AMF1 <NUM> and AMF2 <NUM> illustrated in <FIG>. The TA identifiers are 0x2345 for both AMF1 and AMF2. It is understood that a given AMF may support multiple TAs, and, in such case, multiple TA IDs may be stored in an AMF selection database maintained by NSSF <NUM>. The third column in Table <NUM> are the NSSAIs for each TA and each AMF. In the illustrated example, the NSSAIs for AMF1 and TA 0x2345 are eMBBATT and mIOT. The NSSAI for AMF2 <NUM>, TA ID 0x2345 is mIOT, indicating that AMF2 <NUM> and TA ID 0x2345 provides access to mIOT service.

Once the NSSAI availability information, such as that illustrated in Table <NUM>, is stored by NSSF <NUM>, NSSF <NUM> may utilize the NSSAI availability information to respond to NS selection requests. <FIG> is a message flow diagram illustrating the use of NSSAI availability information to respond to NS selection requests. Referring to <FIG>, in line <NUM> of the message flow diagram, AMF1 <NUM> sends an HTTP PUT/PATCH message to NSSF <NUM>. The HTTP PUT/PATCH message contains supported NSSAIs per TA. In the illustrated example, the supported NSSAIs are eMBBATT and mIOT. The TA is identified by the number 0x2345. NSSF <NUM> receives the HTTP PUT/PATCH message and stores the supported NSSAIs per TA as illustrated in Table <NUM>. In line <NUM> of the message flow diagram, NSSF <NUM> responds to the HTTP PUT/PATCH message with an authorized NSSAI availability data message.

In line <NUM> of the message flow diagram, AMF2 <NUM> sends an HTTP PUT message to NSSF <NUM> containing the NSSAI availability data mIOT for the TA 0x2345. NSSF <NUM> receives the HTTP PUT message and stores the NSSAI availability data in its local AMF selection database. In line <NUM>, NSSF <NUM> responds to AMF2 <NUM> with an authorized NSSAI availability data response message.

In line <NUM> of the message flow diagram, AMF1 <NUM> sends an NS selection GET request message to NSSF <NUM>. The NS selection GET request message specifies the requested NSSAI, which in the illustrated example is mIOT and the TA ID 0x2345. NSSF <NUM> receives the NS selection GET request message and executes a most relevant AMF selection algorithm to generate a prioritized list of AMFs capable of providing access to the requested network slice service or services. In one example, the most relevant AMF selection algorithm may utilize at least the following two factors to compute relative AMF priorities:.

The first factor is the load of the AMF, which, in one example, is a measure of the current processing load of the AMF. The load of the AMF may be obtained from the NRF in the discovery response message in a message flow similar to that illustrated in <FIG>. The second factor is the relevance of the AMF, which can be determined using the list of S-NSSAIs supported by the AMF. In one example, a weight W is computed for each AMF which is present in the NRF discovery response. The higher the weight, the higher the AMF is prioritized the response to the NSSAI selection GET request. The weight W may be computed using the following formula:.

The AMF relevance is defined as the ratio of the lowest number of S-NSSAIs required to serve slices selected to the total number of S-NSSAI supported by the AMF. The AMF relevance is calculated using the following formula:<MAT>.

Using the example illustrated in <FIG>, there is one requested NSSAI, mIOT, in the NS selection GET request in line <NUM>. Both AMF1 and AMF2 have one NSSAI in common with the requested NSSAI, mIOT. Accordingly, the value of C in the relevance equation is equal to <NUM> for both AMF1 <NUM> and AMF2 <NUM>. The total number of NSSAIs supported by AMF1 <NUM> is <NUM> (eMBBATT and mIOT). The total number of NSSAIs supported by AMF2 <NUM> is <NUM> (mIOT). Accordingly, the relevance score for AMF1 <NUM> is calculated as follows: <MAT>.

The relevance score for AMF2 <NUM> can be calculated using the following expression: <MAT>.

If the loadings of AMF1 <NUM> and AMF2 <NUM> are equal, for example, <NUM>%, the weight for AMF1 <NUM> may be calculated as follows: <MAT>.

The weight for AMF2 <NUM> determined using the following expression: <MAT>.

Returning to the message flow in <FIG>, in line <NUM>, NSSF <NUM> returns AMF2 <NUM> as the response candidate AMF because the most relevant selection algorithm resulted in AMF2 <NUM> as the AMF having the highest weight value. In alternate implementation, NSSF <NUM> may return a prioritized list of AMFs that are capable of providing the requested service along with the corresponding weights. For example, in <FIG>, the list would include the identity of AMF1 <NUM> with a weight of <NUM> and AMF2 <NUM> with a weight of <NUM>.

It can be seen from the example described with respect to <FIG> that the AMF relevance determination algorithm results in preferentially assigning AMFs that provide the smallest set of matching network slice services to UE sessions. For example, in <FIG>, both AMF1 <NUM> and AMF2 <NUM> support the requested mIOT service. However, AMF1 <NUM> also supports eMBBATT service. As a result, if the UE session were assigned to AMF1, a UE that needed access to AMF1 <NUM> for its emBBATT service may be prevented from accessing the resources of AMF1 <NUM>. Because AMF2 <NUM> only provides mIOT service, it is more efficient to assign a UE requesting mIOT service to AMF2 <NUM>, assuming that the loading of AMF1 <NUM> and AMF2 <NUM> is the same.

<FIG> illustrates another example of providing for NSSAI availability-based AMF selection where the loading of AMFs is considered in the AMF selection process. Referring to <FIG>, in line <NUM>, AMF1 <NUM> sends a HTTP PUT/PATCH message to NSSF <NUM> indicating the network slice capabilities of AMF1 <NUM>. In the illustrated example, AMF1 <NUM> supports mIOT service for transfer areas 0x2345. In line <NUM>, NSSF <NUM> responds to the HTTP PUT/PATCH message.

In line <NUM>, AMF2 <NUM> sends an HTTP PUT message to NSSF <NUM> indicating that AMF2 <NUM> provides mIOT service for transfer areas U0x2345. In line <NUM>, NSSF <NUM> responds to the HTTP PUT message from AMF2 <NUM>. Thus, after line <NUM>, NSSF <NUM> stores supported NSSAI availability information for AMF1 <NUM> and AMF2 <NUM> for transfer area 0x2345.

In line <NUM> of the message flow diagram, NSSF <NUM> receives an NS selection request from AMF1 <NUM> requesting mIOT service for a UE. In response to the NS selection GET request message, NSSF <NUM> computes the relevance and waits for AMF1 <NUM> and AMF2 <NUM>. Using the formulas above, the relevance score for AMF1 <NUM> is calculated as follows: <MAT>.

The relevance score for AMF2 <NUM> is calculated using the following expression: <MAT>.

Thus, the relevance scores of AMF1 <NUM> and AMF2 <NUM> are equal. In this example it is assumed that AMF1 is <NUM>% loaded and AMF2 is <NUM>% loaded. Accordingly, the weight for AMF1 <NUM> is calculated as follows: <MAT>.

The weight for AMF2 <NUM> is determined as follows: <MAT>.

Thus, in this example, AMF1 <NUM> has a higher weight than AMF2 <NUM>. Accordingly, in line <NUM>, NSSF <NUM> returns a list including AMF1 <NUM> and AMF2 <NUM> with AMF1 <NUM> being preferred due to its higher weight.

<FIG> is a block diagram illustrating an exemplary NSSF capable of performing NSSAI relevance determination and facilitating AMF selection using NSSAI availability information. Referring to <FIG>, NSSF <NUM> includes at least one processor <NUM> and a memory <NUM>. An AMF prioritizer <NUM> may be executable by processor <NUM> and reside in memory <NUM>. AMF prioritizer <NUM> obtains NSSAI availability information using the NSSAI availability procedure described above. AMF prioritizer <NUM> may also obtain AMF loading information by communicating with the NRF. AMF prioritizer <NUM> may store the NSSAI availability information and the AMF loading information in an AMF selection database <NUM>. Using Table <NUM> above as an example, the AMF selection database <NUM> may include the NSSAI availability information on a per TA basis as illustrated in Table <NUM>. In addition, AMF loading information may be added as a third column or field to each database entry.

AMF prioritizer <NUM> may receive NS selection GET request messages from AMFs, identify requested NSSAI information in the request messages, and use the NSSAI availability and AMF loading information stored in AMF selection database <NUM> to determine a relevance and a weight for each AMF capable of providing the requested network slice service. AMF prioritizer <NUM> may return a prioritized list of one or more AMFs capable of providing access to the requested network slice services. The receiving AMF may use the prioritized list to select an AMF and forward the registration request for the user session to the selected AMF.

<FIG> is a flow chart illustrating an exemplary process for providing for policy-based AMF selection using NSSAI availability information. The steps illustrated in <FIG> may be performed at a network slice selection function including at least one processor. Referring to <FIG>, in step <NUM>, NSSF <NUM> obtains NSSAI availability information regarding a plurality of AMFs using an NSSAI availability service. For example, NSSF <NUM> may receive NSSAI availability information from AMFs through HTTP PUT/PATCH messages specifying supported NSSAIs per transfer area.

In step <NUM>, the process includes obtaining AMF loading information. NSSF <NUM> may obtain AMF loading information from NRF <NUM> by sending an NF discovery request to NRF <NUM>, where the NF discovery request identifies the AMFs for which NSSF <NUM> desires to obtain AMF loading information. NRF <NUM> may respond to the NF discovery request with a list of AMF identities and corresponding loading information. In one example, the AMF loading information may indicate a percentage of processing capacity of the AMF that is currently being used.

In step <NUM>, the process includes receiving a network slice selection request message specifying a network slice service requested by user equipment. For example, NSSF <NUM> may receive an NS selection GET request message identifying one or more requested NSSAIs and corresponding transfer area.

In step <NUM>, the process includes generating, based on the NSSAI availability information, the AMF loading information, and the network slice service requested by the UE, a prioritized list including at least one AMF for supporting the network slice service. For example, NSSF <NUM> may identify, based on the NSSAIs in the NS selection request and the supported NSSAIs obtained from the NSSAI availability service, a list of AMFs capable of providing the requested NS service(s). In the example described above, the priorities are based on the ratio of the number of requested network slice services provided by the AMF to the total number of services provided by the AMF and the relative loading of the AMFs. In one further example, the prioritized list may include only the AMF with the highest relative priority.

In step <NUM>, the prioritized list is provided to the requesting AMF. In one example, NSSF <NUM> may send a list and corresponding weights to the requesting AMF, where the weights are computed from the relevances and the load percentages of the AMFs computing using the formulas described above. In another example, NSSF <NUM> may send a list of AMF identities, where the order of the AMFs in the list indicates their relative priorities.

In step <NUM>, the list is used to select an AMF for handling the user session. For example, the requesting AMF may receive the prioritized list of AMFs and select the AMF with the highest weight (assigned based on relevance and loading) in the list to provide access to the requested network slice service.

The subject matter described herein allows the NSSF to use NSSAI availability information to select and prioritize a candidate AMF list. Using NSSAI availability information to select and prioritize a candidate AMF list, especially where AMF relevance is considered as a prioritization criterion, makes it more likely that a UE session will be forwarded to an AMF that is most specialized to provide the network slice service requested by the UE rather than to a generic AMF that supports a larger set of network slice services. The subject matter described herein makes traffic segregation based on quality of service (QoS) possible by prioritizing candidate AMFs based on their supporting S-NSSAI information. The subject matter described herein reduces the likelihood of overloading AMFs that support a larger set of S-NSSAIs by preferentially selecting AMFs with smaller sets of S-NSSAIs that match the NSSAIs requested by a UE.

Claim 1:
A method for providing for policy-based access and mobility management function, AMF, selection using network slice selection assistance information, NSSAI, availability information obtained from an NSSAI availability service, the method comprising:
by a network slice selection function, NSSF, (<NUM>) including at least one processor:
obtaining (<NUM>), using an NSSAI availability service, NSSAI availability information regarding a plurality of AMFs, wherein obtaining the NSSAI availability information includes receiving hypertext transfer protocol, HTTP, messages from the AMFs, wherein each HTTP message indicates supported NSSAIs per transfer area, TA, for one of the AMFs;
receiving (<NUM>), from a first AMF (<NUM>), a network slice selection request specifying a network slice service requested by a user equipment, UE (<NUM>), wherein receiving the network selection request includes receiving a network slice selection request including at least one NSSAI identifying a network slice service requested by the UE;
generating (<NUM>), based on the NSSAI availability information and the network slice service requested by the UE, a prioritized list including an identity of at least one AMF for supporting the network slice service; and
communicating (<NUM>) the prioritized list to the first AMF;
wherein generating the prioritized list includes prioritizing a second AMF that supports the requested network slice service over a third AMF that supports the requested network slice service and a greater number of network slice services in addition to the requested network slice service than the second AMF.