Patent Publication Number: US-2022224760-A1

Title: Service based interface enabled home subscriber service selection

Description:
TECHNICAL FIELD 
     Embodiments described herein relate to methods and apparatus for obtaining and/or providing information relating to a Home Subscriber Server. 
     BACKGROUND 
     The IP Multimedia Subsystem or IP Multimedia Core Network Subsystem (IMS) is an architectural framework for delivering IP multimedia services. Historically, mobile phones have provided voice call services over a circuit-switched-style network, rather than strictly over an IP packet-switched network. Alternative methods of delivering voice (VoIP) or other multimedia services have become available on smartphones, but they have not become standardized across the industry. IMS is an architectural framework to provide such standardization. 
     A Network Repository Function (NRF) may be used by a Service Based Interface (SBI) capable IMS entity (for example, an Interrogating Call Session Control Function (I-CSCF), a Serving Call Session Control Function S-CSCF or an IMS Application Sever (AS)) to select the interface type to be used with a Home Subscriber Server (HSS) instance and to discover SBI capable HSS instances handling a particular subscriber. 
       FIG. 1  illustrates HSS instance and interface type discovery and selection via an NRF. 
     In step  101  an SBI capable HSS registers in the NRF using Nnrf_NFManagement_NFRegister_Request. In this example, different instances of HSS supporting different sets of user identification (e.g. pairs of IP Multimedia Private Identity 
     IMPI and IP Multimedia Public Identity IMPUs) are deployed in the Public Land Mobile Network (PLMN), the HSS may include in the NRF registration the IMPI/IMPU ranges and/or HSS Group ID it supports. 
     In this example, if HSS within the PLMN is enabled to support SBI interactions then the NRF will not keep any Network Function (NF) profile for SBI capable HSS instances. 
     In step  102 , the NRF registers the HSS instance in NRF and replies with a Nnrf_NFManagement_NFRegister_Response. 
     In step  103 , an SBI capable IMS entity may discover the SBI capable HSS instances available in the PLMN at any time using a Nnrf_NFDiscovery_Request. 
     In step  104 , the NRF provides the SBI capable IMS entity with the HSS instances registered in the PLMN. In some examples, different instances of HSS supporting different sets of IMPI/IMPUs are deployed in the PLMN, in which case the NRF may include the IMPI/IMPU ranges and/or HSS Group ID each available SBI capable HSS instance supports. 
     If no SBI capable HSS instance is available in the PLMN, then the NRF may reply to the SBI capable IMS entity with no information about available SBI capable HSS instances. 
     In step  105 , the SBI capable IMS entity stores the result of the NRF discovery. 
     The SBI capable IMS entity may request the NRF to be notified of updates in the SBI capable HSS instances registered in NRF by using a Nnrf_NFManagement_NFStatusSubscribe service operation. 
     In step  106 , the SBI capable IMS entity receives an IMS procedure related to a given IMS user (IMPI or IMPU depending on the procedure). 
     In step  107  the SBI capable IMS entity selects an HSS instance suitable for the IMS user. Towards that end, the SBI capable IMS entity checks in the list of available SBI capable HSS instances provided by the NRF in step  5 , if there is any SBI capable HSS instance available in the PLMN that can serve the IMS user. 
     If suitable SBI capable HSS instance(s) to serve the IMS user are found, the SBI capable IMS entity selects one and uses SBI IMS services to communicate with the selected SBI capable HSS instance. 
     The SBI capable IMS entity may have to execute an additional HSS discovery procedure e.g. if a previous HSS discovery procedure (steps  3 - 4 ) indicates that SBI capable HSS instances exists in the PLMN but they are deployed using different HSS Group IDs. This will be described in more detail with reference to  FIG. 2 . 
     In this case the SBI capable IMS entity sends a Nnrf_NFDiscovery_Request message to the NRF comprising the IMS user identity included in the IMS procedure. The NRF stores a mapping between HSS Group ID and IMS user identities to enable discovery of SBI capable HSS using the received user identity (IMPI/IMPU). 
     If no SBI capable HSS instance is found for the IMS user identity, the SBI capable IMS entity shall then attempt to communicate with the HSS using Diameter procedures. 
     In step  108 , the SBI capable IMS entity starts interaction with the selected HSS instance. 
     In the example described in step  107  in which multiple SBI capable HSS instances supporting different sets of IMPI/IMPUs are deployed in a PLMN, and the NRF provides the HSS group ID, to the SBI capable IMS entity, the SBI capable IMS entity needs to perform a second discovery with the NRF to locate the HSS instance corresponding to the registering IMPI/IMPU. To that effect, the SBI capable IMS entity sends the Nnrf_NFDiscovery_Request message to the NRF and includes the IMPI/IMPU pair received in the IMS procedure.  FIG. 2  illustrates this procedure in more detail. 
     In step  0   a  of  FIG. 2 , an SBI capable HSS registers in the NRF using Nnrf_NFManagement_NFRegister_Request, for example as in step  101  of  FIG. 1 . The HSS registers in this case one or more Group ID. 
     In step  0   b,  any SBI capable IMS entity (I-CSCF, AS, S-CSCF, etc.) may discover the SBI capable HSS instances, according to the procedure described above in steps  103  to  105 , including the Group ID available in the PLMN at any time using a nrf_NFDiscovery_Request. Each SBI capable IMS entity performing a discovery caches the result of the NRF discovery. 
     In step  1  of  FIG. 2 , after the wireless device has obtained IP connectivity, it may perform IMS registration. To do so, the wireless device sends the Register information flow to the Proxy Call Session Control Function (P-CSCF). 
     In step  2  of  FIG. 2 , the P-CSCF sends a Register information flow to the I-CSCF. 
     In step  3  of  FIG. 2 , the I-CSCF locates in its cache only HSS instance(s) with a Group ID and may need to do a second discovery to locate the HSS instance handling the registering UE IMPI/IMPU pair. The I-CSCF sends an Nnrf_NFDiscovery_Request to the NRF and includes the registering IMPI/IMPU. 
     In step  4  of  FIG. 2 , the NRF maps the IMPI/IMPU to the HSS Group ID. 
     In step  5  of  FIG. 2 , the NRF returns to the I-CSCF the HSS instance corresponding to the Group ID for the registering IMPI/IMPU as well as the Group ID. 
     In step  6  of  FIG. 2 , the I-CSCF queries the HSS instance to locate the S-CSCF allocated to the UE to fetch the context information for the registering IMPU/IMPI pair by sending a Nhss_ims_UECM_Get request to the UDM/HSS. 
     In step  7  of  FIG. 2 , the I-CSCF forwards the Register request to the S-CSCF. 
     In step  8  of  FIG. 2 , the S-CSCF has to locate the HSS instance for the registering wireless device. It performs the same steps  3 - 5  executed by the I-CSCF. The S-CSCF sends an Nnrf_NFDiscovery_Request to the NFR and includes the registering IMPI/IMPU. 
     In step  9  of  FIG. 2 , the NRF maps the IMPI/IMPU to the HSS Group ID. 
     in step  10  of  FIG. 2 , the NRF returns to the S-CSCF the HSS instance corresponding to the Group ID for the registering IMPI/IMPU. 
     In step  11  of  FIG. 2 , the S-CSCF fetches the registered IMPI/IMPU related subscriber information by sending to UDM/HSS Nhss_ims_SDM Get request and receiving the profile in the corresponding response. 
     In step  12  of  FIG. 2 , the S-CSCF sends the REGISTER Request to the AS in case of third-party registration. 
     In step  13  of  FIG. 2 , the AS has to locate the HSS instance for the registering UE. It performs the same store  3 - 5  executed by the I-CSCF. The AS sends an Nnrf_NFDiscovery_Request to the NFR and includes the registering IMPI/IMPU. 
     In step  14  of  FIG. 2 , the NRF maps the IMPI/IMPU to the HSS Group ID. 
     In step  15  of  FIG. 2 , the NRF returns to the AS the HSS instance corresponding to the Group ID for the registering IMPI/IMPU. 
     In step  16  of  FIG. 2 , the AS queries the HSS instance for the UE profile. 
     As can be seen from  FIG. 2 , multiple SBI capable IMS entities within a PLMN (I-CSCF, S-CSCF and IMS AS) repeat the same procedures to determine the type of interface to use to interact with HSS and to discover and select the SBI capable HSS instances applicable for a given IMS user (IMPI/IMPU) when SBA interactions can be used. 
     This represents a significant and unneglectable amount of signaling towards the NRF. Additionally, this will imply additional delays in the wireless device traffic procedures during registration and call procedures. 
     The NRF design is suited for off line traffic independent in most of the cases of UE procedures and this amount of signaling related to individual IMS user based discovery requests from SBI capable IMS entities may negatively impact the normal operation and performance of the NRF and NFs as the results of these IMS User based discovery requests cannot be cached in NF consumers for use with network procedures related to other IMS users. 
     SUMMARY 
     According to some embodiments there is provided a method in a first service based architecture, SBI, capable Internet Protocol Multimedia Subsystem, IMS, entity for providing information relating to a first Home Subscriber Service, HSS, instance. The method comprises receiving a user identification in a message; transmitting a request to a network repository function, NRF, wherein the request comprises the user identification; receiving an indication of a first HSS group identification from the NRF; and transmitting the indication of the first HSS group identification to a second SBI capable IMS entity. 
     According to some embodiments there is provided a method, in a second service based architecture, SBI, capable Internet Protocol Multimedia Subsystem, IMS, entity for providing information relating to a first Home Subscriber Service, HSS, instance. The method comprises receiving a message comprising a user identification and an indication of a first HSS group identification; and selecting a first HSS instance from a stored indication of a plurality of HSS instances, wherein the plurality of HSS instances are each associated with at least one HSS group identification, by selecting the first HSS instance having an associated HSS group identification that matches the first HSS group identification. 
     According to some embodiments there is provided a first service based architecture, SBI, capable Internet Protocol Multimedia Subsystem, IMS, entity for providing information relating to a first Home Subscriber Service, HSS, instance. The first SBI capable IMS entity comprises processing circuitry configured to: receive a user identification in a message; transmit a request to a network repository function, NRF, wherein the request comprises the user identification; receive an indication of a first HSS group identification from the NRF; and transmit the indication of the first HSS group identification to a second SBI capable IMS entity. 
     According to some embodiments there is provided a second service based architecture, SBI, capable Internet Protocol Multimedia Subsystem, IMS, entity for providing information relating to a first Home Subscriber Service, HSS, instance. The second SBI capable IMS entity comprises processing circuitry configured to: receive a message comprising a user identification and an indication of a first HSS group identification; and select a first HSS instance from a stored indication of a plurality of HSS instances, wherein the plurality of HSS instances are each associated with at least one HSS group identification, by selecting the first HSS instance having an associated HSS group identification that matches the first HSS group identification. 
     According to some embodiments there is provided a method in a first service based architecture, SBI, capable Internet Protocol Multimedia Subsystem, IMS, entity for obtaining and providing Home Subscriber Service, HSS, information, the method comprising the steps of: transmitting a discovery request to a network repository function, NRF; receiving a response comprising HSS information from the NRF; and transmitting at least a portion of the HSS information to a second SBI capable IMS entity. 
     According to some embodiments there is provided a method, in a second service based architecture, SBI, capable Internet Protocol Multimedia Subsystem, IMS, entity for obtaining Home Subscriber Service, HSS, information, the method comprising:
         receiving a message comprising HSS information from a first SBI capable IMS entity, wherein the HSS information relates to a Public Land Mobile Network, PLMN.       

     According to some embodiments there is provided a first service based architecture, SBI, capable Internet Protocol Multimedia Subsystem, IMS, entity for obtaining and providing Home Subscriber Service, HSS, information, the first SBI capable IMS entity comprising processing circuitry configured to:
         transmit a discovery request to a network repository function, NRF;   receive a response comprising HSS information from the NRF; and   transmit at least a portion of the HSS information to a second SBI capable IMS entity.       

     According to some embodiments there is provided a second service based architecture, SBI, capable Internet Protocol Multimedia Subsystem, IMS, entity for obtaining Home Subscriber Service, HSS, information, the second SBI capable IMS entity comprising processing circuitry configured to:
         receive a message comprising HSS information from a first SBI capable IMS entity, wherein the HSS information relates to a Public Land Mobile Network, PLMN.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of examples of the present disclosure, and to show more clearly how the examples may be carried into effect, reference will now be made, by way of example only, to the following drawings in which: 
         FIG. 1  illustrates HSS instance and interface type discovery and selection via an NRF. 
         FIG. 2  illustrates that the same discovery procedure has to be repeated by every IMS capable node when a HSS Group ID is used by a HSS instance; 
         FIG. 3A  illustrates a complete procedure for the optimized call flow when HSS Group IDs are deployed by HSS instances according to some embodiments; 
         FIG. 3B  illustrates a method for obtaining and providing HSS information according to some embodiments. 
         FIG. 4  illustrates a method, in a first service based architecture, SBI, capable Internet Protocol Multimedia Subsystem, IMS, entity according to some embodiments; 
         FIG. 5A  illustrates a method, in a second service based architecture, SBI, capable Internet Protocol Multimedia Subsystem, IMS, entity according to some embodiments; 
         FIG. 5B  illustrates a further method, in a second service based architecture, SBI, capable Internet Protocol Multimedia Subsystem, IMS, entity according to some embodiments; 
         FIG. 6  illustrates a first service based architecture, SBI, capable Internet Protocol Multimedia Subsystem, IMS, entity according to some embodiments; 
         FIG. 7  illustrates a second service based architecture, SBI, capable Internet Protocol Multimedia Subsystem, IMS, entity according to some embodiments. 
     
    
    
     DESCRIPTION 
     The following sets forth specific details, such as particular embodiments for purposes of explanation and not limitation. It will be appreciated by one skilled in the art that other embodiments may be employed apart from these specific details. In some instances, detailed descriptions of well-known methods, nodes, interfaces, circuits, and devices are omitted so as to not obscure the description with unnecessary detail. Those skilled in the art will appreciate that the functions described may be implemented in one or more nodes using hardware circuitry (e.g., analog and/or discrete logic gates interconnected to perform a specialized function, ASICs, PLAs, etc.) and/or using software programs and data in conjunction with one or more digital microprocessors or general purpose computers that are specially adapted to carry out the processing disclosed herein, based on the execution of such programs. Nodes that communicate using the air interface also have suitable radio communications circuitry. Moreover, the technology can additionally be considered to be embodied entirely within any form of computer-readable memory, such as solid-state memory, magnetic disk, or optical disk containing an appropriate set of computer instructions that would cause a processor to carry out the techniques described herein. 
     Hardware implementation may include or encompass, without limitation, digital signal processor (DSP) hardware, a reduced instruction set processor, hardware (e.g., digital or analog) circuitry including but not limited to application specific integrated circuit(s) (ASIC) and/or field programmable gate array(s) (FPGA(s)), and (where appropriate) state machines capable of performing such functions. 
     In terms of computer implementation, a computer is generally understood to comprise one or more processors, one or more processing modules or one or more controllers, and the terms computer, processor, processing module and controller may be employed interchangeably. When provided by a computer, processor, or controller, the functions may be provided by a single dedicated computer or processor or controller, by a single shared computer or processor or controller, or by a plurality of individual computers or processors or controllers, some of which may be shared or distributed. Moreover, the term “processor” or “controller” also refers to other hardware capable of performing such functions and/or executing software, such as the example hardware recited above. 
       FIG. 2  illustrates that the same discovery procedure has to be repeated by every IMS capable node when a HSS Group ID is used by a HSS instance, and no HSS instance is located in the cache of the IMS capable node for the registering IMPI/IMPU. This is inefficient and can be optimized to avoid the repetitive procedures by all these IMS capable nodes. 
     In embodiments described herein, the actual discovery procedure to locate the HSS instance corresponding to a Group ID is only performed once. The Group ID may then passed on, for example in the SIP signaling, to all IMS nodes in the SIP signaling path. These IMS nodes will examine their own caches to locate the HSS instance corresponding to the received Group ID, since they had already executed the discovery procedure to fetch the HSS information from NRF and cached the result. Hence they can avoid performing a second query with the NRF using the IMPI/IMPU. 
     The improvement/optimization in the interface type and SBI capable HSS selection processes executed by SBI capable IMS entities (e.g. I-CSCF, S-CSCF and IMS AS) described herein allows for a significant reduction in NRF traffic in scenarios where SBI Capable HSS instances are deployed in the PLMN and/or when segments of SBI capable HSSs managing different sets of users within the HPLMN are deployed and the HSS segmentation is not realized using IMPI/IMPU ranges. 
     Additionally, by avoiding the NRF interaction during the execution of related wireless device traffic procedures, the latency in these procedures will not suffer any unnecessary delays. 
     Furthermore, SBI capable IMS entities may optimize the storage of HSS discovery procedures as IMS user based HSS discovery requests will be avoided or at least minimized to an extent, and all or most NRF discovery results may then be cached and used for HSS selection in the context of multiple SUPIs. 
       FIG. 3A  illustrates complete procedure for the optimized call flow when Group IDs are deployed by HSS instances. 
     In step  0   a  of  FIG. 3A , an SBI capable HSS instance registers in NRF using Nnrf_NFManagement_NFRegister_Request. The HSS instance registers in this case a Group ID. 
     In step  0   b,  any SBI capable IMS entity (I-CSCF, AS, S-CSCF, etc.) may discover the SBI capable HSS instances, including the Group ID available in the PLMN at any time using a Nnrf_NFDiscovery_Request. Each SBI capable IMS entity doing a discovery caches the result of the NRF discovery. For example, each SI capable IMS entity may receive, from the NRF, an indication of a plurality of HSS instances each associated with at least one HSS group identification; and may store the indication of the plurality of HSS instances and the associated at least one HSS group identification. 
     In step  1  of  FIG. 3A , after the UE has obtained IP connectivity, it may perform IMS registration. To do so, the UE sends the Register information flow to the P-CSCF. The Register information flow is used as an example and other SIP messages may be used for example SIP INVITE. Any message comprising the user identification may be suitable. 
     In step  2  of  FIG. 3A , The P-CSCF may send the Register information flow to the I-CSCF. 
     In step  3  of  FIG. 3A , The I-CSCF locates in its cache only HSS instance(s) with a Group ID and needs to do a second discovery to locate the HSS instance handling the registering UE. The I-CSCF sends an Nnrf_NFDiscovery_Request to the NFR and includes the user identification IMPI/IMPU. The I-CSCF therefore transmits a request to a network repository function, NRF, wherein the request comprises the user identification. 
     In step  4  of  FIG. 3A , the NRF maps the user identification (IMPI/IMPU) to the HSS Group ID. 
     In step  5  of  FIG. 3A , the NRF returns to the I-CSCF the first HSS instance corresponding to the Group ID for the registering IMPI/IMPU, as well as the Group ID. 
     The I-CSCF therefore receives an indication of a first HSS group identification from the NRF. The I-CSCF may also receive an indication of a type of interface to be used with the first HSS instance from the NRF in this step. 
     In step  6  of  FIG. 3A , The I-CSCF queries the first HSS instance to locate S-CSCF allocated to the UE, or provide information for the I-SCSF to select an S-CSCF, to fetch the context information for the registering IMPU/IMPI pair by sending an Nhss_ims_UECM_Get request to the UDM/HSS instance. 
     In step  7  of  FIG. 3A , the I-CSCF forwards the Register request (or other SIP message) to the S-CSCF, and includes in this case the first HSS Group ID. For example, the I-CSCF may include the first HSS Group ID of the SBI capable HSS instances associated with the IMS user in an &lt;HSS Group ID&gt; header field in SIP REGISTER and/or INVITE messages. In general therefore, the I-CSCF may transmit a Session Initiation Protocol, SIP, message to the second SBI capable IMS entity, wherein the SIP message comprises a first header field comprising the indication of the first HSS group identification. 
     Furthermore, the I-CSCF may also include a type of interface to be used with first HSS instance and/or the first HSS Group ID of the SBI capable HSS instances associated with the IMS user in a &lt;HSS interface type&gt; and &lt;HSS Group ID&gt; header fields respectively in SIP 3 rd  Party REGISTER and INVITE messages (or other suitable SIP message). In other words, the SIP message may further comprise a second header field comprising an indication of a type of interface to be used with the first HSS instance. 
     In step  8  of  FIG. 3A , the S-CSCF locates the first HSS instance for the registering wireless device. In this case, the S-CSCF examines its cache from the discovery request performed in step  0   b  to locate the first HSS instance that maps to the received first HSS Group ID. In other words, the S-CSCF selects a first HSS instance from a stored indication of a plurality of HSS instances, wherein the plurality of HSS instances are each associated with at least one HSS group identification, by selecting the first HSS instance having an associated HSS group identification that matches the first HSS group identification received in step  7 . 
     In step  9  of  FIG. 3A , the S-CSCF fetches the registered IMPI/IMPU related subscriber information by sending to the UDM/HSS instance an Nhss_ims_SDM Get request and receiving the subscriber information profile in the corresponding response. 
     In step  10  of  FIG. 3A , the S-CSCF stores the Group ID in the user context. 
     In step  11  of  FIG. 3A , the S-CSCF sends the REGISTER Request (or any other suitable SIP message) to the AS in case of third-party registration (or other procedure) and includes the first HSS Group ID in this case. For example, as previously, the S-CSCF may transmit the first HSS Group ID in a first header field of the SIP message. Furthermore, the S-CSCF may also include a second header field comprising an indication of the type of interface to use with the first HSS instance. This indication of the type of interface may have been received from the I-CSC in the message transmitted in Step  7  of  FIG. 3A . 
     In step  12  of  FIG. 3A , the AS locates the first HSS instance for the registering wireless device. In this case, the AS examines its cache from the discovery request performed in step  0   b  to locate the first HSS instance that maps to the received first HSS Group ID. In other words, the AS selects a first HSS instance from a stored indication of a plurality of HSS instances, wherein the plurality of HSS instances are each associated with at least one HSS group identification, by selecting the first HSS instance having an associated HSS group identification that matches the first HSS group identification received in step  11 . 
     In step  13  of  FIG. 3A , the AS queries the first HSS instance for the wireless device profile. 
     In step  14  of  FIG. 3A , the IMS AS stores the first HSS Group ID in the user context. 
     The S-CSCF and IMS AS may store the information regarding the type of interface to be used with first HSS instance and/or the HSS Group ID of the SBI capable HSS instances associated with the IMS user for future use. 
     In further aspects of embodiments, an SBI capable IMS entity may transmit an NRF discovery request (Nnrf_NFDiscovery Request Q) at any time to the NRF. This is shown in  FIG. 3B , in which the discovery request is sent in step  1 , before the IMS procedure begins (in step  3 ). In response to the NRF discovery request, the NRF may transmit to the SBI capable IMS entity a response (in step  2  of  FIG. 3B , Nnrf_NFDiscovery_Request Response (HSS Instance)). The discovery request may be triggered by any suitable trigger, implementation dependent. As an example of this, in some aspects of embodiments the discovery request may by triggered by the power up of the SBI capable IMS entity. 
     As discussed above, the discovery request may be sent before an IMS procedure; alternatively, the discovery request and response may be performed after the IMS procedure. The discovery request and response after the IMS procedure are shown by steps  4  and  5  respectively in  FIG. 3B . 
     The response to the discovery request may comprise HSS information related to the PLMN. In situations where no SBI capable HSS instance or HSS Group ID is available in the PLMN, the HSS information provided may comprise an indication that no SBI capable HSS instance or HSS Group ID is available in the PLMN. The indication that that no SBI capable HSS instance or HSS Group ID is available in the PLMN may be, for example, an empty discovery result from the NRF, or an explicit instruction from the NRF to use an alternative system such as Diameter. 
     Alternatively, the HSS information may comprise indicators of one or more HSS instances and/or HSS Group IDs registered in the PLMN, in particular, the response may comprise an indication of a plurality of HSS instances each associated with at least one HSS Group ID (which may also be provided). 
     If the discovery request is sent without including a user ID (where the user ID may be an IMPI or IMPU), then the discovery request may be referred to as a generic discovery request and the response from the NRF may include information on any available HSS instances and/or HSS Group IDs registered in the PLMN. The generic discovery request may be based on a PLMN ID. Each HSS NF profile may include the information about supported HSS Group ID. Different HSS instances may support different HSS Group IDs. By contrast, if the discovery request includes a user ID, the response from the NRF may include information relating only to the HSS instances and/or HSS Group IDs registered in the PLMN that may handle the specific user associated with the user ID. 
     When the SBI capable IMS entity has received the response from the NRF, the HSS information may be stored at the first SBI capable IMS entity. This is shown in step  6  of  FIG. 3B . Although step  6  is shown in  FIG. 3B  as occurring after the start of the IMS procedure (in step  3 ), the storage may take place at any time after the discovery request response has been received by the SBI capable IMS entity. 
     The IMS procedure (see step  3 ) may be an SIP procedure related to a specific user having a specific user ID which, as discussed above, may be an IMPI or IMPU, or another form of user ID. When the IMS procedure begins, the SBI capable IMS entity may send a further discovery request to the NRF, the further discovery request including the user ID (see step  7  of  FIG. 3B ). The NRF may then submit a group ID map query including the user ID to the UDR (see step  8 ), and may obtain from the UDR one or more given HSS group ID for one or more groups handling the user associated with the user ID (see step  9 ). The given HSS group ID (or IDs) is then mapped by the NRF to the corresponding HSS instance for the HSS Group ID, and the corresponding NF profiles of these HSS instances may then be sent in the response from the NRF to the SBI capable IMS entity (see step  10 ). The SBI capable IMS entity may then store this information, that is, the HSS group ID may be stored in association with the specific user ID. 
     As discussed above, the SBI capable IMS entity may transmit HSS information to one or more further SBI capable IMS entities (for example, entities in an SIP signalling path). All of the HSS information obtained from the NRF may be transmitted to further SBI capable IMS entities, for example, where the HSS information is an indication no SBI capable HSS instance or HSS Group ID is available in the PLMN, this indication may be transmitted. Where no SBI capable HSS instance or HSS Group ID is available in the PLMN, the IMS entity may transmit an instruction to the further IMS entity to use an alternate system, for example, an indication that Diameter should be used by the further IMS entity. The instruction may be sent, for example in a header. Alternatively, a portion of the HSS information received by the SBI capable IMS entity may be transmitted to further SBI capable IMS entities. The HSS information may comprise an HSS Group ID serving a specific user. In some aspects of embodiments, a Session Initiation Protocol, SIP, message may be transmitted to a further SBI capable IMS entity, wherein the SIP message comprises a first header field comprising a given HSS Group ID related to a given HSS instance that is serving the IMS user, wherein the given HSS Group ID is obtained from the HSS information. 
     The further SBI capable IMS entity that receives a message comprising HSS information from the first SBI capable IMS may then store the HSS information, and may use the contents of the message to minimise further NRF queries. Where the HSS information is an indication that no SBI capable HSS instance or HSS Group ID is available in the PLMN, the further SBI capable IMS entity may use this information to avoid transmitting NRF discovery requests (which would return negative results indicating no SBI capable HSS instance or HSS Group ID is available), and may instead attempt to communicate with the HSS using Diameter procedures as discussed above. Alternatively, the HSS information may comprise a given HSS Group ID that is related to a given HSS instance, wherein the given HSS instance is serving an IMS user connected to the first SBI capable IMS entity. 
     Where the HSS information comprises a given HSS Group ID, the further SBI capable IMS entity may select a first HSS instance from a stored indication of a plurality of HSS instances, wherein the plurality of HSS instances are each associated with at least one HSS Group ID, by selecting a particular HSS instance having an associated HSS group ID that matches the given HSS Group ID indicated in the HSS information. This step may be performed by the further SBI capable IMS entity where that entity has obtained and stored an indication of a plurality of HSS instances each associated with at least one SS Group ID, either by sending a request to the NRF and receiving a response as set out above in the context of the first SBI capable IMS entity, or from another source. 
     Where the HSS information comprises a given HSS Group ID but the further SBI capable IMS entity has not obtained an indication of a plurality of HSS instances each associated with at least one HSS Group ID, the further SBI capable IMS entity may then transmit a discovery request to a network repository function, NRF, the discovery request comprising the given HSS Group ID, and receive a response comprising HSS information related to the given HSS Group ID from the NRF. The further SBI capable IMS entity may then store the HSS information related to the given HSS Group ID. 
     In the above aspects of embodiments, the first SBI capable IMS entity may comprise, for example, an Interrogating Call Session Control Function (I-CSCF) or a Serving Call Session Control Function (S-CSCF). The further SBI capable IMS entity may comprise, for example, a Serving Call Session Control Function (S-CSCF) or an IMS Application Server (IMS AS). 
       FIG. 4  illustrates a method, in a first service based architecture, SBI, capable Internet Protocol Multimedia Subsystem, IMS, entity for providing information relating to a first Home Subscriber Service, HSS, instance. The method may be performed by an I-CSCF or an S-CSCF. 
     In step  400 , the method comprises transmitting a discovery request to a network repository function, NRF. As explained above with reference to  FIG. 3B , this step may be performed before step  401 , wherein the discovery request is a generic discovery request that does not contain a user ID. Alternatively or additionally, a request comprising the user ID may be transmitted as discussed below with reference to step  402 . In some aspects of embodiments, step  400  may be omitted. 
     In step  401 , the method comprises receiving a user identification in a message. The message may comprise any suitable SIP protocol message, for example SIP REGISTER or SIP INVITE. The user identification may comprise an IP Multimedia Private Identity (IMPI) and/or an IP Multimedia Public Identity (IMPUs). In examples where the first SBI capable IMS entity comprises an I-CSCF the message may be received from a P-CSCF. In examples where the first SBI capable IMS entity comprises an S-CSCF the message may be received from an I-CSCF. 
     In step  402 , the method comprisestransmitting a request to a network repository function, NRF, wherein the request comprises the user identification. 
     In step  403 , the method comprises receiving an indication of a first HSS group identification from the NRF. 
     In step  404 , the method comprises transmitting the indication of the first HSS group identification to a second SBI capable IMS entity. In examples where the first SBI capable IMS entity comprises an I-CSCF, the second SBI capable IMS entity may comprise an S-CSCF. In examples where the first SBI capable IMS entity comprises an S-CSCF, the second SBI capable IMS entity may comprise an IMS AS. 
     The indication may be transmitted as part of an SIP message. For example, the indication may be included in a header field in the forwarding of the message received in step  401  to the second SBI capable IMS entity. 
       FIG. 5A  illustrates a method, in a second service based architecture, SBI, capable Internet Protocol Multimedia Subsystem, IMS, entity for providing information relating to a first Home Subscriber Service, HSS, instance. In some examples, the second SBI capable IMS entity comprises an S-CSCF. In some examples, the second SBI capable IMS entity comprises an IMS AS. 
     In step  501  the method comprises receiving a message comprising a user identification and an indication of a first HSS group identification. The message may comprise any suitable SIP message, for example SIP REGISTER or SIP INVITE. In examples where the second SBI capable IMS entity comprises an S-CSCF, the message may be received from an I-CSCF. In examples where the second SBI capable IMS entity comprises an IMS AS, the message may be received from an S-CSCF. 
     The indication of the first HSS group identification may be indicated in a first header field of the message. 
     In step  502 , the method comprises selecting a first HSS instance from a stored indication of a plurality of HSS instances, wherein the plurality of HSS instances are each associated with at least one HSS group identification, by selecting the first HSS instance having an associated HSS group identification that matches the first HSS group identification. 
       FIG. 5B  illustrates a further method in a second service based architecture, SBI, capable Internet Protocol Multimedia Subsystem, IMS, entity for obtaining Home Subscriber Service, HSS, information. In some examples, the second SBI capable IMS entity comprises an S-CSCF. In some examples, the second SBI capable IMS entity comprises an IMS AS. 
     In step  503 , the method comprises receiving a message comprising HSS information from a first SBI capable IMS entity, wherein the HSS information relates to a Public Land Mobile Network, PLMN. 
     The HSS information may comprises a given HSS Group ID that is related to a given HSS instance, wherein the given HSS instance is serving an IMS user connected to the first SBI capable IMS entity. In this case, the method may further comprise selecting a first HSS instance from a stored indication of a plurality of HSS instances, wherein the plurality of HSS instances are each associated with at least one HSS Group ID, by selecting the first HSS instance having an associated HSS group ID that matches the given HSS Group ID indicated in the HSS information. Alternatively, the HSS information may be an indication that no SBI capable HSS instance or HSS Group ID is available in the PLMN. In this case, the method may further comprise selecting Diameter procedures to communicate with the HSS. 
       FIG. 6  is a schematic diagram of a first SBI capable IMS entity  600 . 
     The first SBI capable IMS entity  600  comprising processing circuitry (or logic)  602 . The processing circuitry  602  controls the operation of the first SBI capable IMS entity  600  and can implement the method described above with respect to  FIG. 4  or the I-SCSF in  FIG. 3A , for example. The processing circuitry  602  of the first SBI capable IMS entity  600  can also implement the method as shown in  FIG. 3B . The first SBI capable IMS entity  600  may also comprise an S-CSCF. The processing circuitry  602  can comprise one or more processors, processing units, multi-core processors or modules that are configured or programmed to control the first SBI capable IMS entity  600  in the manner described herein. In particular implementations, the processing circuitry  602  can comprise a plurality of software and/or hardware modules that are each configured to perform, or are for performing, individual or multiple steps of the method described herein in relation to the first SBI capable IMS entity  600 . 
     Briefly, the processing circuitry  602  of the first SBI capable IMS entity  600  may be configured to: receive a user identification in a message; transmit a request to a network repository function, NRF, wherein the request comprises the user identification; receive an indication of a first HSS group identification from the NRF; and transmit the indication of the first HSS group identification to a second SBI capable IMS entity. The processing circuitry  602  may additionally or alternatively be configured to: transmit a discovery request to a network repository function, NRF; receive a response comprising HSS information from the NRF; and transmit at least a portion of the HSS information to a second SBI capable IMS entity. 
     In some embodiments, the first SBI capable IMS entity  600  may optionally comprise a communications interface  604 . The communications interface  604  of the first SBI capable IMS entity  600  can be for use in communicating with other nodes, such as other virtual nodes. For example, the communications interface  604  of the first SBI capable IMS entity  600  can be configured to transmit to and/or receive from other nodes requests, resources, information, data, signals, or similar. The processing circuitry  602  of the first SBI capable IMS entity  600  may be configured to control the communications interface  604  of the first SBI capable IMS entity  600  to transmit to and/or receive from other nodes requests, resources, information, data, signals, or similar. 
     Optionally, the first SBI capable IMS entity  600  may comprise a memory  606 . In some embodiments, the memory  606  of the first SBI capable IMS entity  600  can be configured to store program code that can be executed by the processing circuitry  602  of the first SBI capable IMS entity  600  to perform the method described herein in relation to the first SBI capable IMS entity  600 . Alternatively or in addition, the memory  606  of the first SBI capable IMS entity  600 , can be configured to store any requests, resources, information, data, signals, or similar that are described herein. The processing circuitry  602  of the first SBI capable IMS entity  600  may be configured to control the memory  606  of the first SBI capable IMS entity  600  to store any requests, resources, information, data, signals, or similar that are described herein. 
       FIG. 7  is a schematic diagram of a second SBI capable IMS entity  700 . 
     The second SBI capable IMS entity  700  comprising processing circuitry (or logic)  702 . The processing circuitry  702  controls the operation of the second SBI capable IMS entity  700  and can implement the method described above with respect to  FIG. 5A or 5B  or the S-SCSF or IMS AS in  FIG. 3A , for example. The processing circuitry  702  of the second SBI capable IMS entity  700  can also implement the method as shown in  FIG. 3B . The processing circuitry  702  can comprise one or more processors, processing units, multi-core processors or modules that are configured or programmed to control the second SBI capable IMS entity  700  in the manner described herein. In particular implementations, the processing circuitry  702  can comprise a plurality of software and/or hardware modules that are each configured to perform, or are for performing, individual or multiple steps of the method described herein in relation to the second SBI capable IMS entity  700 . 
     Briefly, the processing circuitry  702  of the second SBI capable IMS entity  700  may be configured to: receive a message comprising a user identification and an indication of a first HSS group identification; and select a first HSS instance from a stored indication of a plurality of HSS instances, wherein the plurality of HSS instances are each associated with at least one HSS group identification, by selecting the first HSS instance having an associated HSS group identification that matches the first HSS group identification. The processing circuitry  702  may additionally or alternatively be configured to receive a message comprising HSS information from a first SBI capable IMS entity, wherein the HSS information relates to a Public Land Mobile Network, PLMN. 
     In some embodiments, the second SBI capable IMS entity  700  may optionally comprise a communications interface  704 . The communications interface  704  of the second SBI capable IMS entity  700  can be for use in communicating with other nodes, such as other virtual nodes. For example, the communications interface  704  of the second SBI capable IMS entity  700  can be configured to transmit to and/or receive from other nodes requests, resources, information, data, signals, or similar. The processing circuitry  702  of the second SBI capable IMS entity  700  may be configured to control the communications interface  704  of the second SBI capable IMS entity  700  to transmit to and/or receive from other nodes requests, resources, information, data, signals, or similar. 
     Optionally, the second SBI capable IMS entity  700  may comprise a memory  706 . In some embodiments, the memory  706  of the second SBI capable IMS entity  700  can be configured to store program code that can be executed by the processing circuitry  702  of the second SBI capable IMS entity  700  to perform the method described herein in relation to the second SBI capable IMS entity  700 . Alternatively or in addition, the memory  706  of the second SBI capable IMS entity  700 , can be configured to store any requests, resources, information, data, signals, or similar that are described herein. The processing circuitry  702  of the second SBI capable IMS entity  700  may be configured to control the memory  706  of the second SBI capable IMS entity  700  to store any requests, resources, information, data, signals, or similar that are described herein. 
     Any appropriate steps, methods, features, functions, or benefits disclosed herein may be performed through one or more functional units or modules of one or more virtual apparatuses. Each virtual apparatus may comprise a number of these functional units. These functional units may be implemented via processing circuitry, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include digital signal processors (DSPs), special-purpose digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as read-only memory (ROM), random-access memory (RAM), cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory includes program instructions for executing one or more telecommunications and/or data communications protocols as well as instructions for carrying out one or more of the techniques described herein. In some implementations, the processing circuitry may be used to cause the respective functional unit to perform corresponding functions according one or more embodiments of the present disclosure.