Method and apparatus for service discovery during mobile device mobility

Abstract

According to one aspect, there is provided a method for execution by a first communication node of a target network. The method includes maintaining a local cache identifying services known to be available for communication devices in a target network. The method further includes receiving at least one service identifier from the second communication node during a handover procedure of the communication device from the initial network to the target. According to one embodiment of the present disclosure, the method includes, for each service identifier, signaling a service repository of a target network to discover a service corresponding to the service identifier only when the service is not identified in a local cache. In this way, discovery of duplicate services can be mitigated.

Description

[0001] Related Applications

[0002] This application claims priority to PCT provisional patent application no. PCT / CN2023 / 076345, filed on February 16, 2023, the disclosure of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present disclosure relates to wireless communication systems, and more specifically, to service discovery of communication nodes during mobile device mobility. BACKGROUND

[0004] Reference is first made to Figure 1 , which shows a sequence diagram of a method for registering a UE (User Equipment) with a network according to known procedures. When a UE initially attaches to 5G NR (New Radio), the UE performs a registration procedure in NR. With reference to depicted steps 1 to 25, the registration procedure is self-explanatory, and further details of steps 1 to 25 can be found in 3GPP TS 23.502 version 18.1.0, entitled “Procedures for the 5G System (5GS); Stage 2”, published on 2022-12-21 (hereinafter “3GPP TS 23.502”).

[0005] Some related procedures utilize one or more SUPIs (Subscription Permanent Identifier) for NRF (Network Repository Function) discovery of services. A single SUPI belongs to one and only one UDM (Unified Data Management) group ID, AUSF (Authentication Server Function) group ID, UDR (Unified Data Repository) group ID, and / or PCF (Policy Control Function) group ID. However, multiple different SUPIs can belong to the same group ID. NF (Network Function) group IDs apply to all services of an NF.

[0006] An AMF (Access and Mobility Management Function) can use a UE SUPI for NRF discovery of a UDM UECM (Unified Endpoint Configuration Management) service. The AMF can select one UDM from a list of UDMs returned by the NRF, and the AMF can obtain a corresponding UDM group ID to which the UE SUPI belongs from a udminfo (see Table 1 below) of the selected UDM. The AMF uses the previously received UDM group ID to look up a UDM_SDM from a local cache, and skips NRF discovery of the UDM_SDM. Next, the AMF uses the UE SUPI for NRF discovery of a PCF AM (Access Mobility) policy service. The AMF will select one PCF from a list of PCFs returned by the NRF, and the AMF can obtain a corresponding PCF group ID from a pcfinfo (see Table 2 below) of the selected UDM.

[0007] When a UE performs a PDU (Packet Data Unit) session establishment procedure in NR, the AMF can send an Nsmf_PDUSession_CreateSMContext request to an SMF (Session Management Function) with the UDM group ID and the PCF group ID. Alternatively, the AMF can send an Nsmf_PDUSession_CreateSMContext request to an I-SMF (Intermediary Session Management Function) with the UDM group ID and the PCF group ID, where the I-SMF in turn sends an Nsmf_PDUSession_Create request to the SMF with the UDM group ID and the PCF group ID. In any case, the SMF can then use the received UDM group ID for NRF discovery of the UDM UECM service and the received PCF group ID for NRF discovery of the PCF AM policy service.

[0008] Unfortunately, the repeated NRF discovery of the UDM UECM service and the repeated NRF discovery of the PCF AM policy service can take some time, as such discovery involves signaling to the NRF. More generally, the repeated discovery of a service within a communication system can take some time, as such discovery typically involves signaling to a service repository. Tables 1 and 2 mentioned above are shown below.

[0009] Table 1: Definition of type UdmInfo

[0010]

[0011] Table 2: Definition of type PcfInfo

[0012] SUMMARY

[0013] According to one aspect, there is provided a method for execution by a first communication node of a target network. The method comprises maintaining a local cache identifying services known to be available for a communication device in the target network. The method further comprises receiving at least one service identifier from a second communication node during a handover procedure of the communication device from an initial network to the target.

[0014] The service identifier can be used for service discovery. However, the repeated discovery of a service can take some time, as it typically involves signaling to a remote repository. According to embodiments of the disclosure, the method comprises, for each service identifier, when the service corresponding to the service identifier is not identified in the local cache, signaling to a service repository of the target network to discover the service, and when the service is identified in the local cache, skipping signaling to said service repository.

[0015] In this way, the discovery of duplicate services can be mitigated. For example, in some cases, signaling to the service repository is skipped for a subset of service identifiers. In other cases, signaling to the service repository is skipped for all service identifiers. Note that this benefit can be enjoyed for a large number (e.g., millions) of UEs performing mobility procedures (e.g., 4G to 5G mobility), which can lead to a good experience for UE mobility.

[0016] In some implementations, the at least one service identifier includes a UDM (Unified Data Management) group ID and / or a PCF (Policy Control Function) group ID. Thus, discovery of a UDM UECM (Unified Endpoint Configuration Management) service and / or discovery of a PCF AM (Access Mobility) policy service can be skipped. Skipping such discovery can help speed up the processing of the handover procedure when the local cache allows such skipping.

[0017] According to another aspect, there is provided a non-transitory computer readable medium having statements and instructions recorded thereon, which, when executed by a processor of a first communication node, configure the processor to implement the method summarized above.

[0018] According to another aspect, there is provided a first communication node of a target network. The first communication node has: a network interface configured to communicate with other communication nodes; a computer readable medium configured to maintain a local cache that identifies services known to be available to communication devices in the target network; and a service discovery circuit coupled to the network interface and the computer readable medium.

[0019] According to embodiments of the disclosure, the service discovery circuit is configured to: during a handover procedure of a communication device from an initial network to a target, receive, via the network interface, at least one service identifier from a second communication node; and for each service identifier, when a service corresponding to the service identifier is not identified in the local cache, signal, via the network interface, to a service repository of the target network to discover the service, and when the service is identified in the local cache, skip signaling to the service repository.

[0020] Other aspects and features of the present disclosure will become apparent to those ordinarily skilled in the art upon reading the following description of various embodiments of the present disclosure in conjunction with the accompanying figures. BRIEF DESCRIPTION OF DRAWINGS

[0021] Embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:

[0022] Figure 1 is a sequence diagram of a method for registering a UE with a network according to known procedures;

[0023] Figure 2is a block diagram of a communication system with a pair of communication nodes for facilitating service discovery within the communication system;

[0024] Figure 3 is a method of service discovery by a communication system to mitigate duplication of service discovery according to a first embodiment; Figure 2 is a flowchart of a method of service discovery by a communication system to mitigate duplication of service discovery according to a second embodiment;

[0025] Figure 4 is a flowchart of another method of service discovery by a communication system to mitigate duplication of service discovery according to the first embodiment;

[0026] Figure 5 is a flowchart of another method of service discovery by a communication system to mitigate duplication of service discovery according to the second embodiment;

[0027] Figure 6A is a sequence diagram of a method for EPS to 5GS handover using N26 interface, Figure 6B is a sequence diagram of a method for PDU session creation;

[0028] Figure 7 is a schematic diagram of an example cellular communication system in which some embodiments of the disclosure can be implemented;

[0029] Figure 8A and Figure 8B is a block diagram of a wireless communication system represented as a 5G network architecture in which some embodiments of the disclosure can be implemented;

[0030] Figure 9 and Figure 11 is a block diagram of a radio access node according to some embodiments of the disclosure;

[0031] Figure 10 is a block diagram illustrating a virtualized embodiment of a radio access node according to some embodiments of the disclosure;

[0032] Figure 12 and Figure 13 is a block diagram of a wireless communication device; and

[0033] Figure 14 is a schematic diagram of an example communication system according to some embodiments of the disclosure. DETAILED DESCRIPTION

[0034] It should be understood that, although the following teachings provide illustrative implementations of one or more embodiments of the disclosure, any number of techniques can be used to implement the disclosed systems and / or methods. The disclosure should not be limited to the illustrative implementations, drawings, and techniques shown (including the exemplary designs and implementations shown and described herein), but can be modified in any manner within the scope of the appended claims and their equivalents.

[0035] Introduction

[0036] Referring first to Figure 2 , a block diagram of a communication system 100 having communication nodes 124 and 134 of a target network 102 is shown for facilitating service discovery within the target network 102. The communication nodes 124 and 134 include at least a first communication node 124 and a second communication node 134. The communication system 100 also has a service repository 144 and a communication device 110 that is in the process of a handover from an initial network 101 to the target network 102. Typically, there would be many communication devices in the communication system 100, but these are not shown for simplicity. Also, the communication system 100 typically has other components as well, but these are not shown for simplicity as well.

[0037] The first communication node 124 is configured to handle access and mobility management for communication devices, such as the communication device 110. In some implementations, the first communication node 124 is a component of a core network, such as an AMF (Access and Mobility Management Function) of a 5G core network. However, other implementations are possible and within the scope of the present disclosure. The first communication node 124 has a network interface 125 configured to communicate with other nodes of the communication system 100, a computer readable medium 129, and a component discovery circuit 126 coupled to the network interface 125 and the computer readable medium 129. In some implementations, the component discovery circuit 126 includes a processor 127 executing software that can be sourced from a memory 128. However, other implementations are possible and within the scope of the present disclosure. The first communication node 124 can have additional components, but these are not shown for simplicity.

[0038] The second communication node 134 is configured to handle communication sessions for communication devices, such as the communication device 110. In some implementations, the second communication node 134 is a component of a core network, such as an SMF (Session Management Function) of a 5G core network. However, other implementations are possible and within the scope of the present disclosure. The second communication node 134 has a network interface 135 configured to communicate with other nodes of the communication system 100, and also has an identifier transfer circuit 136 coupled to the network interface 125. In some implementations, the identifier transfer circuit 136 includes a processor 137 executing software that can be sourced from a memory 138. However, other implementations are possible and within the scope of the present disclosure. The second communication node 134 can have additional components, but these are not shown for simplicity.

[0039] The component discovery circuit 126 of the first communication node 124 and the identifier transfer circuit 136 of the second communication node 134 operate to implement a method of service discovery by the communication system 100 that mitigates duplicate service discovery. The method will be described below with reference to Figure 3 This operation is described with reference to the communication system 100 shown Figure 2 The method of the communication system 100 shown Figure 3 is described, but it will be appreciated that Figure 3 the method of the communication system 100 shown Figure 3 is described, but it will be appreciated that

[0040] At step 3-1, the first communication node 124 maintains a local cache that identifies services known to be available to the communication device 110 in the target network 102. The local cache can be stored, for example, in the computer-readable medium 129.

[0041] As noted above, the communication device 110 is undergoing a handover from the initial network 101 to the target network 102. During this handover, at step 3-2, the second communication node 134 sends at least one service identifier, and at step 3-3, the first communication node 124 receives the service identifier(s). The service identifier(s) can be used for service discovery. In the example shown, it is assumed that the service identifier includes a first service identifier and a second service identifier.

[0042] As also noted above, duplicate discovery of services can take some time because it typically involves signaling to the service repository 144. As described below, use of the local cache can mitigate duplicate discovery of services.

[0043] For the first service identifier, if at step 3-4, the local cache does not identify a first service corresponding to the first service identifier, then at step 3-5, the first communication node 124 signals to the service repository 144 to discover the first service. However, if at step 3-4, the local cache does identify the first service, then at step 3-6, the first communication node 124 skips discovery of the first service (i.e., does not participate in signaling to the service repository 144).

[0044] For the second service identifier, if at step 3-7, the local cache does not identify a second service corresponding to the second service identifier, then at step 3-8, the first communication node 124 signals to the service repository 144 to discover the second service. However, if at step 3-7, the local cache does identify the second service, then at step 3-9, the first communication node 124 skips discovery of the second service (i.e., does not participate in signaling to the service repository 144).

[0045] Accordingly, discovery of repeated services can be mitigated. For example, in some cases, signaling to a service repository is skipped for a subset of service identifiers. In other cases, signaling to a service repository is skipped for all service identifiers. Note that this can benefit a large number (e.g., millions) of UEs performing mobility procedures (e.g., 4G to 5G mobility), which can lead to a good experience for UE mobility.

[0046] There are many possibilities for the service identifier. In some implementations, the service identifier includes a UDM (Unified Data Management) group ID and / or a PCF (Policy Control Function) group ID. For such implementations, the service corresponding to the UDM group ID can be a UDM UE CM (Unified Endpoint Configuration Management) service or a UDM SDM (Subscription Data Management) service, and the service corresponding to the PCF group ID can be a PCF AM (Access Mobility) policy service. Accordingly, discovery of the UDM UE CM service and / or discovery of the PCF AM policy service can be skipped. This can help speed up processing of the handover procedure when local caching allows such skipping of discovery.

[0047] According to conventional approaches, when a UE moves to a NR (5G New Radio) network, the AMF (Access and Mobility Management Function) will still use the SUPI for NRF (Network Repository Function) discovery of the UDM UE CM service and the PCF AM policy service. Current 3GPP standards lack a function that enables the AMF to reuse the existing UDM / PCF group ID for this PDU session that can be obtained from the SMF (SMF obtains the NF group ID during the 4G PDN connection establishment procedure). Accordingly, embodiments of the present disclosure are a substantial improvement over conventional approaches.

[0048] In some aspects, the first communication node includes an AMF, the target network includes a NR network, the initial network includes a LTE (Long Term Evolution) network, and the service repository includes a NRF. Other implementations are also possible.

[0049] In some implementations, the second communication node includes an SMF (Session Management Function). An example of this case (i.e., a first embodiment) is described below with reference to Figure 4 An example of this case (i.e., a first embodiment) is described below. In other implementations, the second communication node includes an MME (Mobile Management Entity). In such implementations, the MME can have obtained the service identifier from the SMF. An example of this case (i.e., a second embodiment) is described below with reference to Figure 5 An example of this case (i.e., a first embodiment) is described below. In other implementations, the second communication node includes an MME (Mobile Management Entity). In such implementations, the MME can have obtained the service identifier from the SMF. An example of this case (i.e., a second embodiment) is described below with reference to

[0050] According to another embodiment of the present disclosure, there is provided a non-transitory computer readable medium having recorded thereon statements and instructions which, when executed by a processor 127 of the first communication node 124, implement a method as described herein. The non-transitory computer readable medium can be the memory 128 of the first communication node 124 as shown in Figure 1

[0051] According to another embodiment of the present disclosure, there is provided a non-transitory computer readable medium having recorded thereon statements and instructions which, when executed by a processor 137 of the second communication node 134, implement a method as described herein. The non-transitory computer readable medium can be the memory 138 of the second communication node 134 as shown in Figure 1

[0052] Examples of the non-transitory computer readable medium include a memory, a SSD (Solid State Drive), a hard disk drive, a CD (Compact Disc), a DVD (Digital Video Disc), a BD (Blu-ray Disc), a memory stick, and the like. Other non-transitory computer readable media are also possible.

[0053] The illustrated examples described herein focus on software implementations. However, other implementations are possible and within the scope of the present invention. Note that other implementations can include additional or alternative hardware components, such as any suitably configured FPGA (Field Programmable Gate Array), ASIC (Application Specific Integrated Circuit), and / or microcontroller. Thus, the session update circuit 126 of the first communication node 124 and the session update circuit 136 of the second communication node 134 can alternatively be implemented with any suitable combination of hardware, software, and / or firmware.

[0054] Further example details are provided in the following sections. It should be understood that the following sections are very specific and are provided for example purposes only, such that other implementations are possible and within the scope of the present disclosure.

[0055] First embodiment

[0056] According to a first embodiment, the AMF receives the UDM / PCF group ID from the SMF during the Nsmf_PDUSession_CreateSMContext procedure when there is an LTE to NR handover. The SMF can send the UDM / PCF group ID to the AMF in the Nsmf_PDUSession_CreateSMContext response during the LTE to NR handover. After the LTE handover procedure is completed, the AMF performs the registration procedure.

[0057] ​​The AMF can use the received UDM Group ID for NRF discovery of UECM service, but if there is a local cache, it can skip the NRF discovery procedure for UDM UECM service. Also, the AMF uses the received PCF Group ID for NRF discovery of PCF AM Policy service, but if there is a local cache, it can skip the NRF discovery procedure.

[0058] Thus, depending on the local cache, two NRF discovery procedures (i.e. NRF discovery of UDM UECM service and NRF discovery of PCF AM Policy service) can be skipped to speed up the handling of the LTE to NR handover.

[0059] Reference is made below to Figure 4 Further details of the first embodiment are provided, Figure 4 is a flowchart of another method of service discovery by a communication system according to the first embodiment.

[0060] At step 4-1, after the UE has established a PDN connection in 4G, the UE initiates the LTE to NR handover by sending a handover indication to the E-UTRAN (Evolved UMTS (Universal Mobile Telecommunication System) Terrestrial Radio Access Network).

[0061] At step 4-2, the E-UTRAN sends a handover required to the MME.

[0062] At step 4-3, the MME sends a forward relocation request to the AMF.

[0063] At step 4-4, the AMF sends an Nsmf_PDUSession_CreateSMContext request (RAT Type: NR) to the SMF.

[0064] At step 4-5, the SMF performs a PFCP session modification procedure with the UPF.

[0065] At step 4-6, the SMF sends an Nsmf_PDUSession_CreateSMContext response (SmContextCreatedData\UDM Group ID, PCF Group ID) to the AMF. The UDM Group ID and the PCF Group ID are new attributes. Example details of the SmContextCreatedData are provided in Table 3 below.

[0066] Table 3: Definition of Type SmContextCreatedData

[0067]

[0068] At step 4-7, the AMF sends a Handover Request to the NG-RAN.

[0069] At step 4-8, the NG-RAN sends a Handover Request Ack to the AMF.

[0070] At step 4-9, the UE continues the LTE to NR handover procedure.

[0071] At step 4-10, after the UE completes the LTE to NR handover, the UE sends a Registration Request to the AMF.

[0072] At step 4-11, the AMF can use the received UDM Group ID to perform NRF discovery for UDM UECM service. However, if there is local cache, the NRF discovery procedure for UDM UECM can be skipped.

[0073] At step 4-12, the AMF performs Nudm_UECM_Registration Request / Response with the UDM.

[0074] At step 4-13, the AMF performs Nudm_SDM_GET procedure with the UDM to retrieve AccessAndMobilitySubscriptionData.

[0075] At step 4-14, the AMF performs Nudm_SDM_GET procedure with the UDM for smf-select-data.

[0076] At step 4-15, the AMF performs Nudm_SDM_Subscribe procedure with the UDM.

[0077] At step 4-16, the AMF can use the received PCF Group ID to perform NRF discovery for PCF AM Policy service. However, if there is local cache, the NRF discovery procedure can be skipped.

[0078] At step 4-17, the AMF performs Npcf_AMPolicyControl_Create procedure with the PCF.

[0079] At step 4-18, there is resource cleanup in EPC by the MME.

[0080] Note that if the UE performs LTE idle mobility to NR or Wifi mobility to NR, the first embodiment can not be applicable as the AMF registration procedure is completed before the interaction between the AMF and the SMF.

[0081] Second embodiment

[0082] According to the second embodiment, the AMF receives the UDM / PCF group ID from the MME during LTE mobility to 5G. During the LTE session establishment procedure, the SMF sends the UDM / PCF group ID to the MME if interworking with NR is supported. When the UE performs handover / idle mobility from 4G to 5G, the MME can transfer the UDM / PCF group ID to the AMF.

[0083] The AMF can use the received UDM group ID for NRF discovery of the UE CM service, but if there is a local cache, the NRF discovery procedure for the UDM UE CM service can be skipped. Also, the AMF can use the received PCF group ID for NRF discovery of the PCF AM policy service, but if there is a local cache, the NRF discovery procedure can be skipped.

[0084] Thus, two NRF discovery procedures (i.e., NRF discovery of the UDM UE CM service, and NRF discovery of the PCF AM policy service) can be skipped to speed up the PDU session LTE handover procedure to NR or the LTE idle mobility to NR processing.

[0085] Reference is made below to Figure 5 Further details of the second embodiment are provided, Figure 5 is a flowchart of another method of service discovery by a communication system according to the second embodiment.

[0086] At step 5-1, the UE establishes a PDN connection in 4G. The MME sends a create session request to the SMF.

[0087] At step 5-2, since the SMF has set up the UDM and PCF connections and obtained the UDM / PCF group ID, the SMF sends a create session response to the MME with new attributes UDM group ID and PCF group ID. Example details of the create session response are provided in Table 4 below.

[0088] Table 4: Information elements in create session response

[0089]

[0090] At step 5-3, the UE sends a handover indication to the E-UTRAN.

[0091] At step 5-4, the E-UTRAN sends a handover required to the MME.

[0092] At step 5-5, the MME sends a forward relocation request to the AMF with new attributes UDM group ID and PCF group ID. Example details of the forward relocation request are provided in Table 5 below.

[0093] Table 5: MME / SGSN / AMF UE EPS PDN connections within the Forward Relocating Request

[0094]

[0095] At step 5-6, the AMF sends Nsmf_PDUSession_CreateSMContext request (RAT Type: NR) to the SMF.

[0096] At step 5-7, the SMF performs PFCP Session Modification procedure with the UPF.

[0097] At step 5-8, the SMF sends Nsmf_PDUSession_CreateSMContext response to the AMF. Example details of the Context Response are provided in Table 6 below.

[0098] Table 6: MME / SGSN / AMF UE EPS PDN connections within the Context Response

[0099]

[0100] At step 5-9, the AMF sends Handover Request to the NG-RAN.

[0101] At step 5-10, the NG-RAN sends Handover Request Ack to the AMF.

[0102] At step 5-11, the UE continues the procedure for LTE to NR handover.

[0103] At step 5-12, after the UE completes the LTE to NR handover, the UE sends Registration Request to the AMF.

[0104] At step 5-13, the AMF uses the received UDM Group ID to perform NRF discovery for UECM service, but if there is local cache, it can skip the NRF discovery procedure for UDM UECM service.

[0105] At step 5-14, the AMF performs Nudm_UECM_Registration Request / Response with the UDM.

[0106] At step 5-15, the AMF performs Nudm_SDM_GET procedure with the UDM for retrieving AccessAndMobilitySubscriptionData.

[0107] At step 5-16, the AMF performs Nudm_SDM_GET procedure with the UDM for smf-select-data.

[0108] At step 5-17, the AMF performs the Nudm_SDM_Subscribe procedure with the UDM.

[0109] At step 5-18, the AMF uses the received PCF Group ID to perform NRF discovery towards the PCF AM Policy service, but this NRF discovery procedure can be skipped if there is a local cache.

[0110] At step 5-19, the AMF performs the Npcf AMPolicyControl Create procedure with the PCF.

[0111] At step 5-20, there is resource cleanup in the EPC by the MME.

[0112] Note that the second embodiment can not be applicable to Wifi access since the 3GPP standard has not yet defined the interface between epdg and AMF.

[0113] Further details

[0114] Further details are provided. It should be understood that these details are very specific and are for exemplary purposes only. The further details provide a non-limiting example of how certain aspects disclosed herein can be implemented within the framework of a particular standard (e.g., 3GPP TS 29.502, entitled “5G System; Session Management Service; Stage 3,” version 18.1.0, uploaded on 2022-12-16, hereinafter “3GPP TS 29.502”). These changes are merely intended to illustrate how certain aspects disclosed herein can be implemented in a particular standard. However, the aspects disclosed herein can also be implemented in other suitable manners in the particular standard and other specifications or standards.

[0115] For all other UE SUPIs that belong to the UDM / PCF Group ID, the SMF does not need to perform the external NRF discovery procedure towards the NRF for the individual UE SUPI, the SMF uses the UDM / PCF Group ID (instead of the individual UE SUPI) to find the appropriate UDM / PCF from the local NRF cache. This will save two NRF discovery procedures (NRF discovery for the UDM UECM, NRF discovery for the PCF) in the SMF for all UE SUPIs that belong to the UDM / PCF Group ID to speed up the PDU session establishment procedure.

[0116] When a UE initially attaches in 4G EPC using 3GPP or non-3GPP access, since there is no NF Group Id input from MME / ePDG, the combined PWG-C / SMF configured to store PDU session information in UDM using N10 can use the SUPI for NRF discovery towards UDM and PCF, and select a UDM / PCF from the returned list of UDM / PCF from NRF discovery, the SMF can obtain the corresponding UDM / PCF Group ID from the udminfo / pcfinfo of the selected UDM / PCF.

[0117] When a UE initially attaches in 4G, the SMF can obtain the UDM Group ID and PCF Group ID. When the UE performs a 4G to 5G mobility, the AMF can obtain the UDM Group ID and PCF Group ID obtained during the 4G establishment procedure from the SMF or MME, and use the UDM Group ID and PCF Group ID to skip NRF discovery if there is local cache. This improvement enables to skip two NRF discovery procedures (NRF discovery towards UDM UECM, NRF discovery towards PCF AM policy) to speed up the 4G to 5G mobility procedure.

[0118] The NF Group Id can be used to facilitate NF selection for SUPIs belonging to the same NF Group, where the NF consumer has stored the NF profile of the NF with the same NF Group Id through previous NF selection signaling.

[0119] PCF Group ID This refers to one or more PCF instances managing a specific set of SUPIs. A PCF Group comprises one or more PCF sets.

[0120] UDM Group ID This refers to one or more UDM instances managing a specific set of SUPIs. A UDM Group comprises one or more UDM sets.

[0121] As specified in 3GPP TS 23.501:

[0122] The AMF can infer the UDM Group ID to which the SUPI of the UE belongs based on the result of the UDM discovery procedure with the NRF. The AMF provides the UDM Group ID to which the SUPI belongs to other UDM NF consumers as described in TS 23.502.

[0123] Therefore, other UDM NF consumers can use the UDM Group Id to which the SUPI belongs to facilitate UDM selection for this SUPI, considering that the NF profile of candidate UDMs with the same UDM Group Id can be available in cache, therefore, skipping network signaling towards NRF for service discovery.

[0124] However, when the UE initially attaches to the network via 4G access, only the combined PGW-C / SMF can have the UDM Group Id information after performing the UDM selection. In this scenario, it would be beneficial to populate the UDM Group Id from the SMF back to the AMF during the 4G to 5G handover procedure, where the signaling interaction between the SMF and the AMF happens before the signaling procedure between the AMF and the UDM, so that with the UDM Group Id, the AMF can skip the signaling towards the NRF, instead, the AMF can select the UDM from its local cache.

[0125] Similarly, the SMF can populate the PCF Group Id (for session management policy control) to the AMF to facilitate the AMF to select the AM / UE policy PCF.

[0126] It is proposed to include two new attributes "udmGroupId" and "pcfGroupId" in the data types SmContextCreatedData and PduSessionCreatedData. Otherwise, there can be additional signaling from the target AMF towards the NRF to select the UDM / PCF.

[0127] EPS to 5GS handover preparation using N26 interface

[0128] The NF service consumer (e.g. AMF) shall use the N26 interface to request the SMF to handover the UE EPS PDN connection to 5GS, as shown in Figure 6A .

[0129] At step 6A-1, the NF service consumer shall send a POST request, as specified in clause 5.2.2.2.1 of 3GPP TS 29.502, with the following additional information:

[0130] - UE EPS PDN connection, which includes the EPS bearer context, representing the individual SM context resources to be created;

[0131] - hoState attribute, which is set to PREPARING (see clause 5.2.2.3.4.1 of 3GPP TS 29.502);

[0132] - an indication of whether direct DL data forwarding or indirect DL data forwarding is applicable;

[0133] - targetId, which identifies the target RAN node ID and TAI based on the target ID IE received in the Forward Relocation Request message from the source MME.

[0134] NOTE 1: The Target ID IE can be set to contain the Target NG-RAN node ID with Global RAN node ID of 3 octets length and the selected TAI, or the Target eNB ID with Global eNB ID of 2 octets length and the selected TAI; for the latter case, the NF service consumer (i.e. AMF) needs to determine the value of the Target NG-RAN node ID with 3 octets length and TAI based on the local configuration to be provided to the SMF.

[0135] At step 6A-2a, upon reception of such a request, if the corresponding PDU session is found based on the EPS bearer context (for a home routed PDU session, after the Create service operation has been invoked towards the H-SMF) and it is possible to continue the PDN connection handover to 5GS, the SMF shall return a 201 Created response including the following information:

[0136] - the hoState attribute set to PREPARING, and the N2 SM information requesting the target 5G-AN to allocate resources to the PDU session as specified in step 2 of clause Figure 5 2.2.3.4.2-1 of 3GPP TS 29.502; if the SMF has been indicated in step 1 that direct data forwarding applies, the SMF shall include in the N2 SM information an indication that direct forwarding path is available;

[0137] - the PDU Session ID corresponding to the default EPS bearer ID of the EPS PDN connection;

[0138] - the S-NSSAI allocated to the PDU session; in case of home routed roaming, the S-NSSAI for the home PLMN shall be returned;

[0139] - the allocatedEbiList containing the EBI(s) allocated to the PDU session.

[0140] - the udmGroupId containing the identity of the UDM group serving E to facilitate UDM selection at the target AMF.

[0141] - the pcfGroupId containing the identity of the PCF group for the session management policy of the PDU session to facilitate PCF selection at the target AMF.

[0142] The "Location" header shall be present in the POST response and shall contain the URI of the created SM context resource.

[0143] The NF service consumer (e.g. AMF) shall store the association of PDU Session ID with SMF ID and store the allocated EBI(s) associated with the PDU Session ID.

[0144] NOTE 2: The behaviour specified in this step also applies if the POST request conflicts with an existing SM context, i.e. if the POST request includes the same SUPI or PEI for a UE with no UICC or no authenticated SUPI for emergency registration and the default EPS Bearer ID received in the UE EPS PDN connection is the same as in the existing SM context.

[0145] Step 6A-2b is the same as step 2b of clause Figure 5 2.2.7.1-1 of 3GPP TS 29.502, but with the following additions. In this case, steps 3 and 4 of clause Figure 5 2.2.3.8.2-1 of 3GPP TS 29.502 are skipped.

[0146] If the SMF determines that seamless session continuity from EPS to 5GS is not supported for the PDU Session, the SMF shall set the "cause" attribute in the ProblemDetails structure to "NO_EPS_5GS_CONTINUITY".

[0147] When receiving a 4xx / 5xx response from the SMF, the NF service consumer (e.g. AMF) shall consider the hoState of the SM context as NONE.

[0148] EPS to 5GS handover preparation

[0149] The requirements specified in clause 5.2.2.7.1 of 3GPP TS 29.502 shall apply, but with the following modifications.

[0150] Figure 6B Step 6B-1 is the same as step 1 of clause Figure 5 2.2.7.1-1 of 3GPP TS 29.502, but with the following modifications.

[0151] The POST request shall contain:

[0152] - a list of EPS Bearer Ids received from the MME;

[0153] - PGW S8-C F-TEID received from the MME;

[0154] - the hoPreparationIndication IE is set to "TRUE" to indicate that handover preparation is in progress and the PGW-C / SMF should not handover the DL user plane of the PDU session yet.

[0155] Step 6B-2a is the same as step 2 of 3GPP TS 29.502 Figure 5 .2.2.7.1-1, but with the following modification.

[0156] If the SMF finds the corresponding PDU session based on the EPS Bearer Id and PGW S8-C F-TEID received in the request and if it can continue the procedure, the SMF shall return a 201 Created response including the following information:

[0157] - the PDU session ID corresponding to the EPS PDN connection.

[0158] - other PDU session parameters, e.g. PDU session type, session AMBR, QoS flow information.

[0159] - the udmGroupId containing the identity of the UDM group serving the UE to facilitate UDM selection at the target AMF. The V / I-SMF shall forward this IE to the target AMF in the SmContextCreatedData.

[0160] - the pcfGroupId containing the identity of the PCF group for session management policies for the PDU session to facilitate PCF selection at the target AMF. The V / I-SMF shall forward this IE to the target AMF in the SmContextCreatedData.

[0161] If the hoPreparationIndication IE is set to "TRUE" in the request, the SMF shall not handover the DL user plane of the PDU session.

[0162] NOTE: The behaviour specified in this step also applies if the POST request conflicts with an existing PDU session context, i.e. if the POST request includes the same SUPI or PEI for an emergency registered UE without UICC or without authentication and the received EPS Bearer Id is the same as in the existing PDU session context.

[0163] Step 6B-2b is the same as step 2b of 3GPP TS 29.502 Figure 5 .2.2.7.1-1, but with the following addition.

[0164] If the H-SMF determines that seamless session continuity from EPS to 5GS is not supported for the PDU session, the H-SMF shall set the "cause" attribute in the ProblemDetails structure to "NO_EPS_5GS_CONTINUITY".

[0165] Type: SmContextCreatedData

[0166] Table 7: Definition of type SmContextCreatedData

[0167]

[0168] Type: PduSessionCreatedData

[0169] Table 8: Definition of type PduSessionCreatedData

[0170]

[0171] Example communication system

[0172] Figure 7One example of a cellular communications system 500 in which embodiments of the present disclosure can be implemented is shown. In the embodiments described herein, the cellular communications system 500 is a 5GS (5G System) that includes an NG-RAN (Next Generation RAN) and a 5GC (5G Core). In this example, the RAN includes base stations 502-1 and 502-2, which in the 5GS include NR base stations (gNBs) and optionally next generation eNBs (ng-eNBs) (e.g., LTE RAN nodes connected to the 5GC), controlling corresponding (macro) cells 504-1 and 504-2. The base stations 502-1 and 502-2 are generally referred to herein collectively as base stations 502 and individually as base station 502. Likewise, the (macro) cells 504-1 and 504-2 are generally referred to herein collectively as (macro) cells 504 and individually as (macro) cell 504. The RAN can also include a plurality of low power nodes 506-1 through 506-4 controlling corresponding small cells 508-1 through 508-4. The low power nodes 506-1 through 506-4 can be small base stations (e.g., pico or femto base stations) or RRHs (Remote Radio Heads) or the like. Notably, while not shown, one or more of the small cells 508-1 through 508-4 can alternatively be provided by base stations 502. The low power nodes 506-1 through 506-4 are generally referred to herein collectively as low power nodes 506 and individually as low power node 506. Likewise, the small cells 508-1 through 508-4 are generally referred to herein collectively as small cells 508 and individually as small cell 508. The cellular communications system 500 also includes a core network 510, which in the 5G System (5GS) is referred to as a 5GC. The base stations 502 (and optionally the low power nodes 506) are connected to the core network 510.

[0173] The base stations 502 and the low power nodes 506 serve wireless communication devices 512-1 through 512-5 in the corresponding cells 504 and 508. The wireless communication devices 512-1 through 512-5 are generally referred to herein collectively as wireless communication devices 512 and individually as wireless communication device 512. In the following description, the wireless communication devices 512 are typically UEs, but the present disclosure is not limited thereto.

[0174] Reference is now made to Figure 8A , which shows a block diagram of a wireless communication system represented as a 5G network architecture including core NFs (Network Functions), where interactions between any two NFs are represented by point-to-point reference points / interfaces. Figure 8A The system 500 can be considered as Figure 7 one particular implementation of the system 500.

[0175] From an access side, Figure 8AThe 5G network architecture shown in FIG. 6 includes a plurality of UEs 613 connected to a RAN 607 or AN (Access Network) and an AMF 600. Generally, the (R)AN 607 includes a base station, e.g., an eNB or gNB, etc. From the core network side, the AMF 600 is connected to the RAN 607 via an N2 reference point. The AMF 600 is also connected to the UDM 606 via an N13 reference point. The AMF 600 is connected to the SMF 608 via an N11 reference point. The AMF 600 is connected to the PCF 610 via an N15 reference point. The AMF 600 is connected to the AUSF 604 via an N31 reference point. The AMF 600 is connected to the NSSF 602 via an N7 reference point. The AMF 600 is connected to the UDM 606 via an N8 reference point. The AMF 600 is connected to the 5G-EIR (not shown) via an N10 reference point. Figure 8A The 5GC NFs shown in FIG. 6 include the NSSF 602, the AUSF 604, the UDM 606, the AMF 600, the SMF 608, the PCF 610, and the AF (Application Function) 612.

[0176] The reference points of the 5G network architecture represent the interfaces used to develop detailed call flows in the specification standardization. The N1 reference point is defined as carrying the signaling between the UE 613 and the AMF 600. The reference points used to connect between the AN 607 and the AMF 600 and between the AN 607 and the UPF 614 are defined as N2 and N3, respectively. There is a reference point N11 between the AMF 600 and the SMF 608, which means that the SMF 608 is at least partially controlled by the AMF 600. The N4 is used by the SMF 608 and the UPF 614 so that the UPF 614 can be set using control signals generated by the SMF 608, and the UPF 614 can report its status to the SMF 608. N9 is the reference point for the connection between different UPFs 614, while N14 is the reference point for the connection between different AMFs 600. N15 and N7 are defined because the PCF 610 applies policies to the AMF 600 and the SMF 608, respectively. N12 is used for the AMF 600 to perform authentication of the UE 613. N8 and N10 are defined because the subscription data of the UE 613 is used for the AMF 600 and the SMF 608.

[0177] The purpose of the 5GC network is to separate the UP and CP. The UP carries user traffic, while the CP carries signaling in the network. In Figure 8A In FIG. 6, the UPF 614 is in the UP, and all other NFs (i.e., the AMF 600, the SMF 608, the PCF 610, the AF 612, the NSSF 602, the AUSF 604, and the UDM 606) are in the CP. Separating the UP and CP guarantees that each plane resource is scaled independently. It also allows the UPF to be deployed in a distributed manner separately from the CP functions. In this architecture, for certain applications involving low latency, the UPF can be deployed very close to the UE to shorten the RTT (Round-Trip Time) between the UE and the data network.

[0178] The core 5G network architecture includes modularized functions. For example, the AMF 600 and the SMF 608 are independent functions in the CP. The separate AMF 600 and SMF 608 allow independent evolution and scaling. Other CP functions, such as the PCF 610 and the AUSF 604, can be separated as shown. Figure 8A The modularized function design enables the 5GC network to flexibly support various services.

[0179] Each NF interacts directly with another NF. An intermediary function can be used to route a message from one NF to another NF. In the CP, a set of interactions between two NFs is defined as a service to make reuse of the service possible. The service enables support of modularity. The UP supports interactions such as forwarding operations between different UPFs.

[0180] Reference is now made to Figure 8B , which shows a block diagram of a 5G network architecture using service-based interfaces between NFs in the CP instead of the point-to-point reference points / interfaces used in the 5G network architecture of Figure 8A However, the NFs described above with reference to Figure 8B correspond to the NFs shown in Figure 8A The (one or more services) that an NF provides to other authorized NFs can be exposed to authorized NFs through the service-based interfaces. In Figure 8B The service-based interfaces are indicated by the letter “N” followed by the name of the NF, for example, Namf for the service-based interfaces of the AMF 600, Nsmf for the service-based interfaces of the SMF 608, and so on. Figure 8B The NEF 603 and the NRF 601 in Figure 8A are not shown in the above-described Figure 8A However, it should be clarified that all the NFs depicted in Figure 8B can interact with the NEF 603 and the NRF 601 of Figure 8A if needed, although not explicitly indicated in

[0181] Figure 8A and 8BSome of the characteristics of the NFs shown in the middle can be described as follows. The AMF 600 provides authentication, authorization, mobility management, etc. based on the UE. The UE 613 is basically connected to a single AMF 600 even if multiple access technologies are used, because the AMF 600 is independent of the access technology. The SMF 608 is responsible for session management, and allocates an IP (Internet Protocol) address to the UE. It also selects and controls the UPF 614 for data transfer. If the UE 613 has multiple sessions, different SMFs 608 can be assigned to each session to manage the sessions individually, and different functions can be provided per session. The AF 612 provides information on packet flow to the PCF 610 responsible for policy control in order to support QoS. Based on this information, the PCF 610 determines policies regarding mobility and session management so that the AMF 600 and the SMF 608 operate correctly. The AUSF 604 supports authentication functions for the UE, etc., and thus stores data for authentication of the UE, etc., while the UDM 606 stores subscription data of the UE 613. The DN (Data Network) (not part of the 5GC network) provides Internet access or operator services, etc.

[0182] The NFs can be implemented as network elements on dedicated hardware, software instances running on dedicated hardware, or virtualized functions instantiated on an appropriate platform (e.g., cloud infrastructure).

[0183] Figure 9is a schematic block diagram of a radio access node 700 according to some embodiments of the present disclosure. Optional features are represented by dashed boxes. The radio access node 700 can be, for example, a base station 102 or 106 or a network node that implements all or part of the functionality of a base station 102 or gNB described herein. As illustrated, the radio access node 700 includes a control system 702, which includes one or more processors 704 (e.g., CPUs (central processing units), ASICs (application-specific integrated circuits), FPGAs (field-programmable gate arrays), and / or the like), memory 706, and a network interface 708. The one or more processors 704 are also referred to herein as processing circuitry. In addition, the radio access node 700 can include one or more radio units 710 that each include one or more transmitters 712 and one or more receivers 714 coupled to one or more antennas 716. The radio units 710 can be referred to as, or be part of, radio interface circuitry. In some embodiments, the radio unit(s) 710 is external to the control system 702 and connected to the control system 702 via, e.g., a wired connection (e.g., an optical cable). However, in some other embodiments, the radio unit(s) 710 and possibly the antenna(s) 716 are integrated with the control system 702. The one or more processors 704 operate to provide one or more functions of the radio access node 700 as described herein. In some embodiments, the function(s) are implemented in software that is stored, e.g., in memory 706 and executed by the one or more processors 704.

[0184] Figure 10 is a schematic block diagram illustrating a virtualized embodiment of a radio access node 700 according to some embodiments of the present disclosure. The discussion above applies similarly to other types of network nodes. Further, other types of network nodes can have similar virtualized architectures. Again, optional features are represented by dashed boxes.

[0185] As used herein, a “virtualized” radio access node is an implementation of the radio access node 700 in which at least part of the functionality of the radio access node 700 is implemented as a virtual component(s) (e.g., via a virtual machine(s) executing on a physical processing node(s) in a network(s)). As illustrated, in this example, the radio access node 700 can include a control system 702 and / or one or more radio units 710, as described above. The control system 702 can be connected to the radio unit(s) 710 via, for example, an optical cable or the like. The radio access node 700 includes one or more processing nodes 800 coupled to or included as part of a network(s) 802. If present, the control system 702 or radio unit(s) 710 are connected to the processing node(s) 800 via the network(s) 802. Each processing node 800 includes one or more processors 804 (e.g., CPUs, ASICs, FPGAs, or the like), memory 806, and a network interface 808.

[0186] In this example, the functions 810 of the radio access node 700 described herein are implemented at the processing node(s) 800 or distributed among the control system 802 and / or radio unit(s) 810 and the one or more processing nodes 800 in any desired manner. In some particular embodiments, some or all of the functions 810 of the radio access node 700 described herein are implemented as virtual components executed by one or more virtual machines implemented in a virtual environment(s) hosted by the processing node(s) 800. As will be appreciated, additional signaling or communication between the processing node(s) 800 and the control system 802 is used in order to carry out at least some of the desired functions 810. Notably, in some embodiments, the control system 802 can not be included, in which case the radio unit(s) 810 communicate directly with the processing node(s) 800 via an appropriate network interface(s).

[0187] In some embodiments, a computer program including instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of a radio access node 700 according to any of the embodiments described herein or a node (e.g., processing node 800) implementing one or more of the functions 810 of a radio access node 700 in a virtual environment is provided. In some embodiments, a carrier containing the computer program

[0188] Figure 11 is a schematic block diagram of a radio access node 700 according to some other embodiments of the present disclosure. The radio access node 700 includes one or more modules 800, each of which is implemented in software. The module(s) 800 provide the functionality of the radio access node 700 described herein. This discussion is equally applicable to the processing node 700 of Figure 10 , where the modules 800 can be implemented at one of the processing nodes 700, or distributed across multiple processing nodes 700 and / or distributed across the processing node(s) 700 and the control system 702.

[0189] Figure 12 is a schematic block diagram of a wireless communication device 900 according to some embodiments of the present disclosure. As shown, the wireless communication device 900 includes one or more processors 902 (e.g., CPUs, ASICs, FPGAs, etc.), memory 904, and one or more transceivers 906 each including one or more transmitters 908 and one or more receivers 910 coupled to one or more antennas 912. The transceiver(s) 906 include radio-front end circuitry connected to the antenna(s) 912 that is configured to condition signals communicated between the antenna(s) 912 and the processor(s) 902, as will be appreciated by one of ordinary skill in the art. The processor(s) 902 are also referred to herein as processing circuitry. The transceiver(s) 906 are also referred to herein as radio circuitry. In some embodiments, the functionality of the wireless communication device 900 described above can be fully or partially implemented in software that is, for example, stored in the memory 904 and executed by the processor(s) 902. Note that the wireless communication device 900 can include additional components not Figure 12 indicated in FIG. 9, such as, for example, one or more user interface components (e.g., input / output interfaces including displays, buttons, touch-screens, microphones, speaker(s), etc., and / or any other components for allowing input of information into and / or output of information from the wireless communication device 900), a power supply (e.g., a battery and associated power circuitry), etc.

[0190] In some embodiments, a computer program including instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of a wireless communication device 900 according to any of the embodiments described herein is provided. In some embodiments, a carrier containing the computer program

[0191] Figure 13is a schematic block diagram of a wireless communication device 900 according to some other embodiments of the present disclosure. The wireless communication device 900 includes one or more modules 1000, each of which is implemented in software. The module(s) 1000 provide the functionality of the wireless communication device 900 described herein.

[0192] Each of the stations 1106A, 1106B, 1106C can be connected to the core network 1104 through wired or wireless connection 1110. A first UE 1112 located in the coverage area 1108C is configured to connect wirelessly to, or be paged by, the corresponding base station 1106C. A second UE 1114 in the coverage area 1108A can wirelessly connect to the corresponding base station 1106A. While a plurality of UEs 1112, 1114 are illustrated in this example, the disclosed embodiments are equally applicable to a situation where only a single UE is in a coverage area or is connecting to the corresponding base station 1106.

[0193] The telecommunication network 1100 is itself connected to a host computer 1116, which can be implemented in hardware and / or software and can represent all or a portion of one or more publishing, application service provider (ASP) or Internet service provider (ISP) systems, or a server farm. It will be appreciated that host computer 1116 can also include server(s) associated with a cloud computing, distributed computing, or other remote computing paradigm. The connection 1118, 1120 between the telecommunication network 1100 and the host computer 1116 can pass through one or more intermediate networks, such as the Internet, which can itself be a collection of interconnected public and / or private networks, rather than a single discrete network.

[0194] Figure 14The communication system as a whole enables connectivity between the connected UEs 1112, 1114 and the host computer 1116. The connectivity can be described as an OTT (over-the-top) connection 1124. The host computer 1116 and the connected UEs 1112, 1114 are configured to communicate data and / or signaling over the OTT connection 1124 using the access network 1102, the core network 1104, any intermediate network 1122, and possible further infrastructure (not shown) as intermediaries. The OTT connection 1124 can be transparent in the sense that the participating communication devices through which the OTT connection 1124 passes are unaware of the application, the session, and / or the data that the OTT connection 1124 communicates. For example, an incoming downlink communication from the host computer 1116, with data originating from a web server, can be switched and / or routed by

[0195] Any appropriate steps, methods, features, functions, or benefits expressly mentioned in this disclosure can be performed by one or more virtual means. Each virtual means can comprise a number of these functional units. These functional units can be implemented by processing circuitry, which can include one or more microprocessors or microcontrollers, as well as other digital hardware, including Digital Signal Processors (DSPs), special-purpose computer chips, etc. The processing circuitry can be configured to execute program code stored in memory, which can 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. The program code stored in memory includes program instructions for executing one or more telecommunication and / or data communication protocols and program instructions for implementing one or more of the techniques described herein. In some embodiments, the processing circuitry can be used to cause the respective functional units to perform corresponding functions according to one or more embodiments of the present disclosure.

[0196] While the processes in the figures can show a particular order of operations, it is understood that the order of operations can be changed as alternatives (e.g., the order of operations can be reversed, particular operations can be performed concurrently, etc.).

[0197] Many modifications and variations of this disclosure can be made in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the disclosure can be practiced otherwise than as specifically described.

Claims

1. A method for execution by a first communication node of a target network, comprising: maintaining a local cache identifying services known to be available to a communication device in the target network; receiving at least one service identifier from a second communication node during a handover procedure of the communication device from an initial network to the target; and for each service identifier, signaling a service repository of the target network to discover a service corresponding to the service identifier when the service is not identified in the local cache, and skipping signaling the service repository when the service is identified in the local cache. signaling the service repository is skipped for a subset of the service identifiers.

2. The method of claim 1, wherein, signaling the service repository is skipped for all of the service identifiers.

3. The method of claim 1, wherein, the at least one service identifier comprises a unified data management (UDM) group ID and / or a policy control function (PCF) group ID.

4. The method of any one of claims 1 to 3, wherein, the at least one service identifier comprises the UDM group ID, and wherein the service corresponding to the UDM group ID is a UDM unified endpoint configuration management (UECM) service or a UDM subscription data management (SDM) service, and wherein skipping signaling the service repository comprises skipping discovery of the UDM UECM service or the UDM SDM service.

5. The method of claim 4, wherein, the at least one service identifier comprises the PCF group ID, and wherein the service corresponding to the PCF group ID is a PCF access and mobility (AM) policy service, and wherein skipping signaling the service repository comprises skipping discovery of the PCF AM service.

6. The method of claim 4, wherein, 7. The method of claim 4, wherein: the at least one service identifier comprises the UDM group ID, and wherein the service corresponding to the UDM group ID is a UDM unified endpoint configuration management (UECM) service or a UDM subscription data management (SDM) service, and wherein skipping signaling the service repository comprises skipping discovery of the UDM UECM service or the UDM SDM service; and the at least one service identifier comprises the PCF group ID, and wherein the service corresponding to the PCF group ID is a PCF access and mobility (AM) policy service, and wherein skipping signaling the service repository comprises skipping discovery of the PCF AM service. the first communication node comprises an access and mobility management function (AMF), the target network comprises a 5G new radio (NR) network, the initial network comprises a long term evolution (LTE) network, and the service repository comprises a network repository function (NRF).

8. The method of any one of claims 1 to 7, wherein, the second communication node comprises a session management function (SMF).

9. The method of claim 8, wherein, the second communication node comprises a mobility management entity (MME).

10. The method of claim 8 or 9, wherein, 11. A non-transitory computer-readable medium having statements and instructions recorded thereon that, when executed by a processor of a first communication node, configure the first communication node to: maintain a local cache identifying services known to be available to a communication device in the target network; ​ receiving, from a second communication node, at least one service identifier during a handover procedure of a communication device from an initial network to the target; and for each service identifier, signaling a service repository of the target network to discover a service corresponding to the service identifier when the service is not identified in the local cache, and skipping signaling the service repository when the service is identified in the local cache.

12. The non-transitory computer-readable medium of claim 11, wherein, The statements and instructions configure the first communication node, when executed by the processor of the first communication node, to implement the method of any one of claims 2 to 10.

13. A first communication node of a target network, comprising: a network interface configured to communicate with other communication nodes; a computer readable medium configured to maintain a local cache identifying services known to be available to communication devices in the target network; and a service discovery circuit coupled to the network interface and the computer readable medium, wherein the service discovery circuit is configured to: receive, from a second communication node via the network interface, at least one service identifier during a handover procedure of a communication device from an initial network to the target; and for each service identifier, signal a service repository of the target network via the network interface to discover a service corresponding to the service identifier when the service is not identified in the local cache, and skip signaling the service repository when the service is identified in the local cache.

14. The first communication node of claim 13, wherein, The service discovery circuit is configured to skip signaling the service repository for a subset of the service identifiers.

15. The first communication node of claim 13, wherein, The service discovery circuit is configured to skip signaling the service repository for all of the service identifiers.

16. The first communication node according to any of claims 13 to 15, wherein, The at least one service identifier comprises a Unified Data Management, UDM, group ID and / or a Policy Control Function, PCF, group ID.

17. The first communication node of claim 16, wherein, The at least one service identifier comprises the UDM group ID, and wherein the service corresponding to the UDM group ID is a UDM Unified Endpoint Configuration Management, UECM, service or a UDM Subscription Data Management, SDM, service, and wherein the first communication node skips signaling the service repository by skipping discovery of the UDM UECM service or the UDM SDM service.

18. The first communication node of claim 16, wherein, The at least one service identifier comprises the PCF group ID, and wherein the service corresponding to the PCF group ID is a PCF Access and Mobility, AM, policy service, and wherein the first communication node skips signaling the service repository by skipping discovery of the PCF AM service.

19. The first communication node of claim 16, wherein: the at least one service identifier comprises the UDM group ID, and wherein the service corresponding to the UDM group ID is a UDM unified endpoint configuration management, UECM, service or a UDM subscription data management, SDM, service, and wherein the first communication node skips signaling to the service repository by skipping discovery of the UDM UECM service or the UDM SDM service; and the at least one service identifier comprises the PCF group ID, and wherein the service corresponding to the PCF group ID is a PCF access and mobility, AM, policy service, and wherein the first communication node skips signaling to the service repository by skipping discovery of the PCF AM service.

20. The first communication node according to any of claims 13-19, wherein, the first communication node comprises an access and mobility management function, AMF, the target network comprises a 5G new radio, NR, network, the initial network comprises a long term evolution, LTE, network, and the service repository comprises a network repository function, NRF.

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