WO2024171152A1 - Method and apparatus for service discovery during mobile device mobility - Google Patents

Abstract

According to an aspect, there is provided a method for execution by a first communication node of a target network. The method involves maintaining a local cache identifying services known to be available for a communication device in the target network. The method also involves, during a handover procedure for the communication device to the target from an initial network, receiving at least one service identifier from a second communication node. In accordance with an embodiment of the disclosure, the method involves, for each service identifier, signalling a service repository of the target network to discover a service corresponding to the service identifier only when that service is not identified in the local cache. In this manner, repeating discovery of services can be mitigated.

Description

METHOD AND APPARATUS FOR SERVICE DISCOVERY DURING MOBILE DEVICE MOBILITY

Related Application

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

Field of the Disclosure

[2] This disclosure relates to wireless communication systems, and more particularly to service discovery by communication nodes during mobile device mobility.

Background

[3] Referring first to Figure 1 , shown is a sequence drawing of a method for registration of a UE (User Equipment) with a network, in accordance with a known procedure. When a UE initially attaches to 5G NR (New Radio), the UE performs a registration procedure in NR. The registration procedure is self-explanatory with reference to steps 1 through 25 as depicted, and further details for steps 1 through 25 can be found in 3GPP TS 23.502 entitled “Procedures for the 5G System (5GS); Stage 2” version 18.1.0 uploaded 2022-12-21 (hereinafter “3GPP TS 23.502”).

[4] Some related procedures utilize one or more SUPIs (Subscription Permanent Identifiers) for NRF (Network Repository Function) discovery of services. An individual 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. An NF (Network Function) Group ID applies to all services of the NF.

[5] An AMF (Access and Mobility Management Function) can use a UE SUPI to do an NRF discovery for a UDM UECM (Unified Endpoint Configuration Management) service. The AMF can select one UDM from a UDM list returned by NRF, and the AMF can get a corresponding UDM Group ID that the UE SUPI belongs to from a udminfo (see table 1 below) of the selected UDM. The AMF uses the previously received UDM Group ID to find UDM_SDM from the local cache and NRF discovery for UDM_SDM is skipped. Next, the AMF uses the UE SUPI to do an NRF discovery for a PCF AM (Access Mobility) policy service. The AMF will select one PCF from a PCF list returned by NRF, and the AMF can get a corresponding PCF Group ID from pcfinfo (see Table 2 below) of the selected UDM.

[6] When the UE performs a PDU (Packet Data Unit) session establishment procedure in NR, the AMF can send an Nsmf_PDUSession_CreateSMContext Request with the UDM Group ID and the PCF Group ID to an SMF (Session Management Function). Alternatively, the AMF can send an Nsmf_PDUSession_CreateSMContext Request with the UDM Group ID and the PCF Group ID to an l-SMF (Intermediate Session Management Function), wherein the l-SMF in turn sends an Nsmf_PDUSession_Create Request with the UDM Group ID and the PCF Group ID to the SMF. Regardless, the SMF can then use the received UDM Group ID to do NRF discovery for the UDM UECM service, and use the received PCF Group ID to do NRF discovery for the PCF AM policy service.

[7] Unfortunately, repeating the NRF discovery for the UDM UECM service and repeating the NRF discovery for the PCF AM policy service can take some time, because such discovery involves signalling the NRF. More generally, repeating discovery of services within a communication system can take some time, because such discovery normally involves signalling a service repository. Tables 1 and 2 referenced above are produced below.

Table 1 : Definition of type Udminfo

Table 2: Definition of type Pcflnfo

Summary of the Disclosure

[8] According to an aspect, there is provided a method for execution by a first communication node of a target network. The method involves maintaining a local cache identifying services known to be available for a communication device in the target network.

The method also involves, during a handover procedure for the communication device to the target from an initial network, receiving at least one service identifier from a second communication node.

[9] The service identifiers can be used for service discovery. However, repeating discovery of services can take some time, because it normally involves signalling a remote repository. In accordance with an embodiment of the disclosure, the method involves, for each service identifier, signalling a service repository of the target network to discover a service corresponding to the service identifier when that service is not identified in the local cache, and skipping the signalling of the service repository when that service is identified in the local cache.

[10] In this manner, the repeating discovery of services can be mitigated. For instance, in some situations, the signaling with the service repository is skipped for a subset of the service identifiers. In other situations, the signaling with the service repository is skipped for all of the service identifiers. Note that this benefit can be enjoyed for a huge number of (e.g. millions of) UEs performing a mobility procedure (e.g. 4G mobility to 5G), which can bring good experience for UE mobility.

[11] 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, it is possible to skip discovery for UDM UECM (Unified Endpoint Configuration Management) service and/or skip discovery for PCF AM (Access Mobility) policy service. The skipping of such discovery may help to expedite processing for the handover procedure when the local cache allows for such skipping.

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

[13] 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 identifying services known to be available for a communication device in the target network, and service discovery circuitry coupled to the network interface and the computer readable medium.

[14] In accordance with an embodiment of the disclosure, the service discovery circuitry is configured to, during a handover procedure for the communication device to the target from an initial network, receive via the network interface at least one service identifier from a second communication node, and for each service identifier, signal via network interface a service repository of the target network to discover a service corresponding to the service identifier when that service is not identified in the local cache, and skip the signalling of the service repository when that service is identified in the local cache.

[15] Other aspects and features of the present disclosure will become apparent, to those ordinarily skilled in the art, upon review of the following description of the various embodiments of the disclosure. Brief Description of the Drawings

[16] Embodiments will now be described with reference to the attached drawings in which:

Figure 1 is a sequence drawing of a method for registration of a UE with a network, in accordance with a known procedure;

Figure 2 is a block diagram of a communication system having a pair of communication nodes for facilitating service discovery within the communication system;

Figure 3 is a flowchart of a method of service discovery by the communication system of Figure 2 that mitigates repeating of service discovery;

Figure 4 is a flowchart of another method of service discovery by a communication system that mitigates repeating of service discovery, in accordance with a first embodiment;

Figure 5 is a flowchart of another method of service discovery by a communication system that mitigates repeating of service discovery, in accordance with a second embodiment;

Figure 6A is a sequence drawing of a method for EPS to 5GS handover using an N26 interface, and Figure 6B is a sequence drawing of a method for PDU session creation;

Figure 7 is a schematic of an example cellular communications system in which some embodiments of the present disclosure may be implemented;

Figures 8A and 8B are block diagrams of a wireless communication system represented as a 5G network architecture in which some embodiments of the present disclosure may be implemented;

Figures 9 and 11 are block diagrams of a radio access node according to some embodiments of the present disclosure; Figure 10 is a block diagram that illustrates a virtualized embodiment of a radio access node according to some embodiments of the present disclosure;

Figures 12 and 13 are block diagrams of a wireless communication device; and

Figure 14 is a schematic of an example communication system according to some embodiments of the present disclosure.

Detailed Description of Embodiments

[17] It should be understood at the outset that although illustrative implementations of one or more embodiments of the present disclosure are provided below, the disclosed systems and/or methods may be implemented using any number of techniques. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents.

Introduction

[18] Referring first to Figure 2, shown is a block diagram of a communication system 100 having communication nodes 124 and 134 of a target network 102 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 which is engaging in a handover to the target network 102 from an initial network 101. Normally there would be numerous communication devices in the communication system 100, but they are not shown for simplicity. Also, the communication system 100 would normally have other components as well, but they are also not shown for simplicity.

[19] 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, for example an AMF (Access & Mobility Management Function) of a 5G core network. However, other implementations are possible and are within the scope of the 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 component discovery circuitry 126 coupled to the network interface 125 and the computer readable medium 129. In some implementations, the component discovery circuitry 126 includes a processor 127 that executes software, which can stem from a memory 128. However, other implementations are possible and are within the scope of this disclosure. The first communication node 124 can have additional components, but these are not shown for simplicity.

[20] 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, for example an SMF (Session Management Function) of a 5G core network. However, other implementations are possible and are within the scope of the 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 identifier conveying circuitry 136 coupled to the network interface 125. In some implementations, the identifier conveying circuitry 136 includes a processor 137 that executes software, which can stem from a memory 138. However, other implementations are possible and are within the scope of this disclosure. The second communication node 134 can have additional components, but these are not shown for simplicity.

[21] The component discovery circuitry 126 of the first communication node 124 and the identifier conveying circuitry 136 of the second communication node 134 operate to implement a method of service discovery by the communication system 100 that mitigates repeating of service discovery. Such operation will be described below with reference to Figure 3. Although the method of Figure 3 is described below with reference to the communication system 100 shown in Figure 2, it is to be understood that the method of Figure 3 is applicable to other communication systems. In general, the method of Figure 3 is applicable to any appropriately configured communication system.

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

[23] As noted above, the communication device 110 is engaging in a handover to the target network 102 from an initial network 101 . During such 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 identifiers can be used for service discovery. In the illustrated example, it is assumed that the service identifiers include a first service identifier and a second service identifier.

[24] As also noted above, repeating discovery of services can take some time, because it normally involves signalling the service repository 144. As described below, repeating discovery of services can be mitigated using the local cache.

[25] 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 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 for the first service (i.e. does not engage in signalling with the service repository 144).

[26] 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 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 for the second service (i.e. does not engage in signalling with the service repository 144). [27] Therefore, the repeating discovery of services can be mitigated. For instance, in some situations, the signaling with the service repository is skipped for a subset of the service identifiers. In other situations, the signaling with the service repository is skipped for all of the service identifiers. Note that this benefit can be enjoyed for a huge number of (e.g. millions of) UEs performing a mobility procedure (e.g. 4G mobility to 5G), which can bring good experience for UE mobility.

[28] There are many possibilities for the service identifiers. In some implementations, the service identifiers include 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 UECM (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. Thus, it is possible to skip discovery for UDM UECM service and/or skip discovery for PCF AM policy service. The skipping of such discovery may help to expedite processing for the handover procedure when the local cache allows for such skipping.

[29] According to conventional approaches, when a UE moves to an NR (5G New Radio) network, an AMF (Access and Mobility Management Function) would still use SUPI to do NRF (Network Repository Function) discovery for UDM UECM service and PCF AM policy service. Current 3GPP standards lack the function to enable the AMF to reuse existing UDM/PCF Group ID for this PDU session that can be got from SMF (SMF gets NF Group ID during 4G PDN connection establishment procedure). Thus, embodiments of the disclosure are a substantial improvement over the conventional approaches.

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

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

[32] According to another embodiment of the disclosure, there is provided a non- transitory computer readable medium having recorded thereon statements and instructions that, when executed by the 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 shown in Figure 1 , or some other non- transitory computer readable medium.

[33] According to another embodiment of the disclosure, there is provided a non- transitory computer readable medium having recorded thereon statements and instructions that, when executed by the 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 shown in Figure 1 , or some other non-transitory computer readable medium.

[34] Examples of a non-transitory computer readable medium include memory, an 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, etc. Other non-transitory computer readable mediums are also possible.

[35] The illustrated examples described herein focus on software implementations. However, other implementations are possible and are within the scope of this disclosure. It is noted that other implementations can include additional or alternative hardware components, such as any appropriately configured FPGA (Field-Programmable Gate Array), ASIC (Application-Specific Integrated Circuit), and/or microcontroller, for example. Thus, the session update circuitry 126 of the first communication node 124 and the session update circuitry 136 of the second communication node 134 can instead be implemented with any suitable combination of hardware, software and/or firmware. [36] Further example details are provided in the following sections. It is to be understood that the following sections are very specific and are provided merely for exemplary purposes, such that other implementations are possible and within the scope of the disclosure.

First Embodiment

[37] According to a first embodiment, an AMF receives a UDM/PCF Group ID from an SMF during a Nsmf_PDUSession_CreateSMContext procedure when there is an LTE handover to NR. During the LTE handover to NR, the SMF can send UDM/PCF Group IDs to the AMF in an Nsmf_PDUSession_CreateSMContext Response. Later after the LTE handover procedure is finished, the AMF performs registration procedure.

[38] The AMF can use the received UDM Group ID to do NRF discovery for UECM service, but the NRF discovery procedure for UDM UECM service can be skipped if there is local cache. Furthermore, the AMF uses the received PCF Group ID to do NRF discovery for PCF AM policy service, but this NRF discovery procedure can be skipped if there is local cache.

[39] Therefore, it is possible to skip two NRF discovery produces (i.e. NRF discovery for UDM UECM service, and NRF discovery for PCF AM policy service) to expedite processing for the LTE handover to NR, depending on the local cache.

[40] Further details of the first embodiment are provided below with reference to Figure 4, which is a flowchart of another method of service discovery by a communication system according to the first embodiment.

[41] At step 4-1 , after the UE has established a PDN Connection in 4G, the UE initiates an LTE handover to NR by sending a Handover Indication to the E-UTRAN (Evolved UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access Network).

[42] At step 4-2, the E-UTRAN sends a Handover Required to the MME. [43] At step 4-3, the MME sends a Forward Relocation Request to the AMF.

[44] At step 4-4, the AMF sends a Nsmf_PDUSession_CreateSMContext Request (RAT TYPE: NR) to the SMF.

[45] At step 4-5, the SMF performs an PFCP Session Modification procedure with the UPF.

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

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

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

[49] At step 4-9, the UE continues the procedure of LTE handover to NR. [50] At step 4-10, after the UE finishes the LTE handover to NR, the UE sends a Registration Request to the AMF.

[51] At step 4-11 , the AMF can use the received UDM Group ID to do NRF Discovery for UDM UECM services. However, the NRF discovery procedures for UDM UECM can be skipped if there is local cache.

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

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

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

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

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

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

[58] At step 4-18, there is Resource Cleanup in EPC by the MME.

[59] Note that, if the UE performs LTE Idle mobility to NR, or Wifi mobility to NR, the first embodiment might not be applicable because the AMF registration procedure is done before the interaction between the AMF and the SMF.

Second Embodiment.

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

[61] The AMF can use the received UDM Group ID to do NRF Discovery for UECM service, but the NRF discovery procedure for UDM UECM service can be skipped if there is local cache. Furthermore, the AMF can use the received PCF Group ID to do NRF discovery for PCF AM policy service, but this NRF discovery procedure can be skipped if there is local cache.

[62] Therefore, it is possible to skip two NRF discovery produces (i.e. NRF discovery for UDM UECM service, and NRF discovery for PCF AM policy service) to expedite processing for the PDU session LTE handover to NR procedure or LTE Idle Mobility to NR.

[63] Further details of the second embodiment are provided below with reference to Figure 5, which is a flowchart of another method of service discovery by a communication system according to the second embodiment.

[64] At step 5-1 , the UE establishes a PDN Connection in 4G. The MME sends a Create Session Request to the SMF.

[65] At step 5-2, since the SMF already setup UDM and PCF connections and gets 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 below in Table 4.

Table 4: Information Elements in a Create Session Response

[66] At step 5-3, the UE sends a Handover Indication to the E-UTRAN.

[67] At step 5-4, the E-UTRAN sends a Handover Required to the MME.

[68] 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 below in Table 5.

Table 5: MME/SGSN/AMF UE EPS PDN Connections within Forward Relocation Request

[69] At step 5-6, the AMF sends a Nsmf_PDUSession_CreateSMContext Request (RAT TYPE: NR) to the SMF.

[70] At step 5-7, the SMF performs a PFCP Session Modification procedure with the UPF. [71] At step 5-8. The SMF sends a Nsmf_PDUSession_CreateSMContext Response to the AMF. Example details of the Context Response are provided below in Table 6.

Table 6: MME/SGSN/AMF UE EPS PDN Connections within Context Response

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

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

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

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

[76] At step 5-13, the AMF uses the received UDM Group ID to do NRF discovery for UECM services, but the NRF discovery procedure for UDM UECM service can be skipped if there is local cache.

[77] At step 5-14, the AMF performs a Nudm_UECM_Registration Request/Response with the UDM. [78] At step 5-15, the AMF performs a Nudm_SDM_GET procedure for retrieving AccessAndMobilitySubscriptionData with the UDM.

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

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

[81] At step 5-18, the AMF uses the received PCF Group ID to do an NRF discovery for PCF AM policy service, but this NRF discovery procedures can be skipped if there is local cache.

[82] At step 5-19, the AMF performs a Npcf_AMPolicyControl_Create procedure with the PCF.

[83] At step 5-20, there is a Resource Cleanup in EPC by MME.

[84] Note that, since 3GPP standard has not defined the interface between epdg and AMF, the second embodiment might not be applicable for Wifi access.

Further Details

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

[86] For all the other UE SUPI that belongs to the UDM/PCF Group ID, the SMF need not do external NRF discovery procedures towards NRF for the individual UE SUPI, the SMF uses UDM /PCF Group ID (instead of the individual UE SUPI) to find the proper UDM/PCF from the local NRF cache. For all UE SUPI that belongs to the UDM/PCF Group ID, this will save two NRF discovery produces in SMF (NRF discovers for UDM UECM, NRF discovery for PCF) to speed up the PDU session establishment procedure.

[87] When one UE initially attaches in 4G EPC either using 3GPP or non-3GPP access, since no NF Group Id input from MME/ePDG, a combined PWG-C/SMF that it is configured to use N10 to store PDU Session info in UDM, can use SUPI to do NRF discovery for UDM and PCF, and selects the UDM/PCF from the returned UDM/PCF list of NRF discovery, the SMF can get the corresponding UDM/PCF Group ID from the udminfo/pcfinfo of selected UDM/PCF.

[88] When the UE initially attaches in 4G, the SMF can get the UDM Group ID and PCF Group ID. When the UE performs mobility from 4G to 5G, the AMF can get the UDM Group ID and PCF Group ID from the SMF or MME which are got during 4G establishment procedure, and use the UDM Group ID and PCF Group ID to skip NRF discovery if there is local cache. The improvement can skip two NRF discovery produces (NRF discovers for UDM UECM, NRF discovery for PCF AM policy) to fast 4G mobility to 5G procedure.

[89] The NF Group Id may be used to facilitate NF selection for a SUPI pertain to the same NF group where the NF consumer has already stored NF profiles for the NFs with the same NF Group Id through previous NF selection signalling.

This refers to one or more PCF instances managing a specific set of SUPIs.

A PCF Group consists of one or multiple PCF Sets.

This refers to one or more UDM instances managing a specific set of

SUPIs. An UDM Group consists of one or multiple UDM Sets.

[90] As specified in 3GPP TS 23.501 :

The AMF can infer the UDM Group ID the UE's SUPI belongs to, based on the results of UDM discovery procedures with NRF. The AMF provides the UDM Group ID the SUPI belongs to other UDM NF consumers as described in TS 23.502. [91] So that other UDM NF consumer can use the UDM Group Id to which the SUPI pertains to facilitate UDM selection for this SUPI, considering the NF profile of candidate UDMs with the same UDM Group Id are likely available in the cache, thus, to skip the network signalling towards the NRF for service discovery.

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

[93] Similarly the SMF may populate PCF Group Id (for Session Management Policy Control) to the AMF, to facilitate the AMF to select a AM/UE Policy PCF.

[94] It is proposed to include two new attributes "udmGroupId" and “pcfGroupId” in the data types SmContextCreatedData and PduSessionCreatedData. Otherwise, there may be extra signalling towards NRF from the target AMF to select a UDM/PCF

EPS to 5GS Handover Preparation using N26 interface

[95] The NF Service Consumer (e.g. AMF) shall request the SMF to handover a UE EPS PDN connection to 5GS using N26 interface, as shown in Figure 6A.

[96] 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:

- UE EPS PDN connection, including the EPS bearer contexts, representing the individual SM context resource to be created;

- hoState attribute set to PREPARING (see clause 5.2.2.3.4.1 of

3GPP TS 29.502);

- the indication of whether direct or indirect DL data forwarding applies; - targetld identifying the target RAN Node ID and TAI based on the Target ID IE received in the Forward Relocation Request message from the source MME.

NOTE 1 : The Target ID IE can be set to the Target NG-RAN Node ID containing a Global RAN Node ID and selected TAI with 3-octets length, or the Target eNB ID containing a Global eNB ID and selected TAI with 2-octets length; for the latter case, the NF Service Consumer, i.e. the AMF needs determine a value for the Target NG-RAN Node ID and TAI with 3-octets length based on the local configuration to be provided to the SMF.

[97] At step 6A-2a, upon receipt of such a request, if a corresponding PDU session is found based on the EPS bearer contexts (after invoking a Create service operation towards the H-SMF, for a Home Routed PDU session) and it is possible to proceed with handing over the PDN connection to 5GS, the SMF shall return a 201 Created response including the following information:

- hoState attribute set to PREPARING and N2 SM information to request the target 5G-AN to assign resources to the PDU session, as specified in step 2 of Figure

5.2.2.3.4.2-1 of 3GPP TS 29.502; if the SMF was indicated in step 1 that direct data forwarding is applicable, the SMF shall include an indication that a direct forwarding path is available in the N2 SM information;

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

- S-NSSAI assigned to the PDU session; in home routed roaming case, the S- NSSAI for home PLMN shall be returned;

- allocatedEbiList, containing the EBI(s) allocated to the PDU session.

- udmGroupId, containing the identity of the UDM group serving the UE, to facilitate the UDM selection at the target AMF.

- pcfGroupId, containing the identity of the PCF group for Session Management Policy for the PDU session, to facilitate the PCF selection at the target AMF. The "Location" header shall be present in the POST response and shall contain the URI of the created SM context resource.

The NF Service Consumer (e.g. AMF) shall store the association of the PDU Session ID and the SMF ID, and store the allocated EBI(s) associated to the PDU Session ID.

NOTE 2: The behaviour specified in this step also applies if the POST request collides with an existing SM context, i.e. if the POST request includes the same SUPI, or PEI for an emergency registered UE without a UICC or without an authenticated SUPI, and the default EPS bearer ID received in the UE EPS PDN connection is the same as in the existing SM context.

[98] Step 6A-2b is the same as step 2b of Figure 5.2.2.7.1 -1 of 3GPP TS 29.502with the following additions. Steps 3 and 4 of Figure 5.2.2.3.8.2-1 of 3GPP TS 29.502 are skipped in this case.

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".

When receiving a 4xx/5xx response from the SMF, the NF service consumer (e.g. the AMF) shall regard the hoState of the SM Context to be NONE.

EPS to 5GS Handover Preparation

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

[100] Step 6B-1 of Figure 6B is the same as step 1 of Figure 5.2.2.7.1-1 of 3GPP TS 29.502, with the following modifications.

The POST request shall contain:

- the list of EPS Bearer Ids received from the MME; - the PGW S8-C F-TEID received from the MME;

- the hoPreparationlndication IE set to "true", to indicate that a handover preparation is in progress and the PGW-C/SMF shall not switch the DL user plane of the PDU session yet.

[101] Step 6B-2a is the same as step 2 of Figure 5.2.2.7.1-1 of 3GPP TS 29.502, with the following modifications.

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

- PDU Session ID corresponding to the EPS PDN connection;

- other PDU session parameters, such as PDU Session Type, Session AMBR, QoS flows information.

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

- pcfGroupId, containing the identity of the PCF group for Session Management Policy for the PDU session, to facilitate the PCF selection at the target AMF. The V/I-SMF shall forward this IE in the SmContextCreatedData to the target AMF.

The SMF shall not switch the DL user plane of the PDU session, if the hoPreparationlndication IE was set to "true" in the request.

NOTE: The behaviour specified in this step also applies if the POST request collides with an existing PDU session context, i.e. if the POST request includes the same SUPI, or PEI for an emergency registered UE without a UICC or without an authenticated SUPI, and the received EPS bearer ID is the same as in the existing PDU session context. [102] Step 6B-2b is the same as step 2b of Figure 5.2.2.7.1-1 of 3GPP TS 29.502, with the following additions.

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".

Type: SmContextCreatedData

Table 7: Definition of type SmContextCreatedData

Type: PduSessionCreatedData

Table 8: Definition of type PduSessionCreatedData

Example Communications System

[103] Figure 7 illustrates one example of a cellular communications system 500 in which embodiments of the present disclosure may be implemented. In the embodiments described herein, the cellular communications system 500 is a 5GS (5G system) including a NG-RAN (Next Generation RAN) and a 5GC (5G Core). In this example, the RAN includes base stations 102-1 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 may also include a number 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 (such as pico or femto base stations) or RRHs (Remote Radio Heads), or the like. Notably, while not illustrated, one or more of the small cells 508-1 through 508-4 may alternatively be provided by the 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 the 5GC. The base stations 502 (and optionally the low power nodes 506) are connected to the core network 510.

[104] The base stations 502 and the low power nodes 506 provide service to 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 oftentimes UEs, but the present disclosure is not limited thereto.

[105] Referring now to Figure 8A, shown is a block diagram of a wireless communication system represented as a 5G network architecture composed of core NFs (Network Functions), where interaction between any two NFs is represented by a point-to- point reference point/interface. Figure 8A can be viewed as one particular implementation of the system 500 of Figure 7.

[106] Seen from the access side the 5G network architecture shown in Figure 8A includes a plurality of UEs 613 connected to either a RAN 607 or an (Access Network) as well as an AMF 600. Typically, the R(AN) 607 comprises base stations, e.g. such as eNBs or gNBs or similar. Seen from the core network side, the 5GC NFs shown in Figure 8A include a NSSF 602, an AUSF 604, a UDM 606, the AMF 600, a SMF 608, a PCF 610, and an AF (Application Function) 612.

[107] Reference point representations of the 5G network architecture are used to develop detailed call flows in the normative standardization. The N1 reference point is defined to carry signaling between the UE 613 and AMF 600. The reference points for connecting between the AN 607 and AMF 600 and between the AN 607 and UPF 614 are defined as N2 and N3, respectively. There is a reference point, N11 , between the AMF 600 and SMF 608, which implies that the SMF 608 is at least partly controlled by the AMF 600. N4 is used by the SMF 608 and UPF 614 so that the UPF 614 can be set using the control signal generated by the SMF 608, and the UPF 614 can report its state to the SMF 608. N9 is the reference point for the connection between different UPFs 614, and N14 is the reference point connecting between different AMFs 600, respectively. N15 and N7 are defined since the PCF 610 applies policy to the AMF 600 and SMF 608, respectively. N12 is utilized 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 utilized for the AMF 600 and SMF 608.

[108] The 5GC network aims at separating UP and CP. The UP carries user traffic while the CP carries signaling in the network. In Figure 8A, the UPF 614 is in the UP and all other NFs, i.e., the AMF 600, SMF 608, PCF 610, AF 612, NSSF 602, AUSF 604, and UDM 606, are in the CP. Separating the UP and CP guarantees each plane resource to be scaled independently. It also allows UPFs to be deployed separately from CP functions in a distributed fashion. In this architecture, UPFs may be deployed very close to UEs to shorten the RTT (Round Trip Time) between UEs and data network for some applications involving low latency.

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

[110] Each NF interacts with another NF directly. It is possible to use intermediate functions to route messages from one NF to another NF. In the CP, a set of interactions between two NFs is defined as service so that its reuse is possible. This service enables support for modularity. The UP supports interactions such as forwarding operations between different UPFs.

[111] Referring now to Figure 8B, shown is a block diagram of a 5G network architecture using service-based interfaces between the 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 service(s) etc. that a NF provides to other authorized NFs can be exposed to the authorized NFs through the service-based interface. In Figure 8B, the service based interfaces are indicated by the letter “N” followed by the name of the NF, e.g. Namf for the service based interface of the AMF 600 and Nsmf for the service based interface of the SMF 608, etc. The NEF 603 and the NRF 601 in Figure 8B are not shown in Figure 8A discussed above. However, it should be clarified that all NFs depicted in Figure 8A can interact with the NEF 603 and the NRF 601 of Figure 8B as necessary, though not explicitly indicated in Figure 8A.

[112] Some properties of the NFs shown in Figures 8A and 8B may be described in the following manner. The AMF 600 provides UE-based authentication, authorization, mobility management, etc. A UE 613 even using multiple access technologies is basically connected to a single AMF 600 because the AMF 600 is independent of the access technologies. The SMF 608 is responsible for session management and allocates IP (Internet Protocol) addresses to UEs. It also selects and controls the UPF 614 for data transfer. If a UE 613 has multiple sessions, different SMFs 608 may be allocated to each session to manage them individually and possibly provide different functionalities per session. The AF 612 provides information on the packet flow to the PCF 610 responsible for policy control in order to support QoS. Based on the information, the PCF 610 determines policies about mobility and session management to make the AMF 600 and SMF 608 operate properly. The AUSF 604 supports authentication function for UEs or similar and thus stores data for authentication of UEs or similar 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 and similar.

[113] An NF may be implemented either as a network element on a dedicated hardware, as a software instance running on a dedicated hardware, or as a virtualized function instantiated on an appropriate platform, e.g., a cloud infrastructure.

[114] Figure 9 is 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 may be, for example, a base station 102 or 106 or a network node that implements all or part of the functionality of the base station 102 or gNB described herein. As illustrated, the radio access node 700 includes a control system 702 that 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 may include one or more radio units 710 that each includes one or more transmitters 712 and one or more receivers 714 coupled to one or more antennas 716. The radio units 710 may be referred to 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 potentially the antenna(s) 716 are integrated together with the control system 702. The one or more processors 704 operate to provide one or more functions of a radio access node 700 as described herein. In some embodiments, the function(s) are implemented in software that is stored, e.g., in the memory 706 and executed by the one or more processors 704.

[115] Figure 10 is a schematic block diagram that illustrates a virtualized embodiment of the radio access node 700 according to some embodiments of the present disclosure. This discussion is equally applicable to other types of network nodes. Further, other types of network nodes may have similar virtualized architectures. Again, optional features are represented by dashed boxes.

[116] As used herein, a “virtualized” radio access node is an implementation of the radio access node 700 in which at least a portion 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 may include the control system 702 and/or the one or more radio units 710, as described above. The control system 702 may 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 the radio unit(s) 710 are connected to the processing node(s) 800 via the network 802. Each processing node 800 includes one or more processors 804 (e.g., CPUs, ASICs, FPGAs, and/or the like), memory 806, and a network interface 808.

[117] In this example, functions 810 of the radio access node 700 described herein are implemented at the one or more processing nodes 800 or distributed across the one or more processing nodes 800 and the control system 802 and/or the radio unit(s) 810 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 by one of ordinary skill in the art, 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 may not be included, in which case the radio unit(s) 810 communicates directly with the processing node(s) 800 via an appropriate network interface(s).

[118] 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 radio access node 700 or a node (e.g., a processing node 800) implementing one or more of the functions 810 of the radio access node 700 in a virtual environment according to any of the embodiments described herein is provided. In some embodiments, a carrier comprising the aforementioned computer program product is provided. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium such as memory).

[119] Figure 11 is a schematic block diagram of the 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 may be implemented at one of the processing nodes 700 or distributed across multiple processing nodes 700 and/or distributed across the processing node(s) 700 and the control system 702.

[120] Figure 12 is a schematic block diagram of a wireless communication device 900 according to some embodiments of the present disclosure. As illustrated, the wireless communication device 900 includes one or more processors 902 (e.g., CPUs, ASICs, FPGAs, and/or the like), 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 includes 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 on of ordinary skill in the art. The processors 902 are also referred to herein as processing circuitry. The transceivers 906 are also referred to herein as radio circuitry. In some embodiments, the functionality of the wireless communication device 900 described above may be fully or partially implemented in software that is, e.g., stored in the memory 904 and executed by the processor(s) 902. Note that the wireless communication device 900 may include additional components not illustrated in Figure 12 such as, e.g., one or more user interface components (e.g., an input/output interface including a display, buttons, a touch screen, a microphone, a speaker(s), and/or the like and/or any other components for allowing input of information into the wireless communication device 900 and/or allowing output of information from the wireless communication device 900), a power supply (e.g., a battery and associated power circuitry), etc.

[121] In some embodiments, a computer program including instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of the wireless communication device 900 according to any of the embodiments described herein is provided. In some embodiments, a carrier comprising the aforementioned computer program product is provided. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium such as memory). [122] Figure 13 is a schematic block diagram of the 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.

[123] Each station 1106A, 1106B, 1106C is connectable to the core network 1104 over a wired or wireless connection 1110. A first UE 1112 located in coverage area 1108C is configured to wirelessly connect to, or be paged by, the corresponding base station 1106C. A second UE 1114 in coverage area 1108A is wirelessly connectable 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 a sole UE is in the coverage area or where a sole UE is connecting to the corresponding base station 1106.

[124] The telecommunication network 1100 is itself connected to a host computer 1116, which may be embodied in the hardware and/or software of a standalone server, a cloud-implemented server, a distributed server, or as processing resources in a server farm. The host computer 1116 may be under the ownership or control of a service provider, or may be operated by the service provider or on behalf of the service provider. Connections 1118 and 1120 between the telecommunication network 1100 and the host computer 1116 may extend directly from the core network 1104 to the host computer 1116 or may go via an optional intermediate network 1122. The intermediate network 1122 may be one of, or a combination of more than one of, a public, private, or hosted network; the intermediate network 1122, if any, may be a backbone network or the Internet; in particular, the intermediate network 1122 may comprise two or more sub-networks (not shown).

[125] The communication system of Figure 14 as a whole enables connectivity between the connected UEs 1112, 1114 and the host computer 1116. The connectivity may 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 via 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 may be transparent in the sense that the participating communication devices through which the OTT connection 1124 passes are unaware of routing of uplink and downlink communications. For example, the base station 1106 may not or need not be informed about the past routing of an incoming downlink communication with data originating from the host computer 1116 to be forwarded (e.g., handed over) to a connected UE 1112. Similarly, the base station 1106 need not be aware of the future routing of an outgoing uplink communication originating from the UE 1112 towards the host computer 1116.

[126] 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 DSPs (Digital Signal Processor), 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 ROM (Read Only Memory), RAM (Random Access Memory), 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.

[127] While processes in the figures may show a particular order of operations performed by certain embodiments of the present disclosure, it should be understood that such order is exemplary (e.g., alternative embodiments may perform the operations in a different order, combine certain operations, overlap certain operations, etc.). [128] Numerous modifications and variations of the present disclosure are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practised otherwise than as specifically described herein.

Claims

We Claim:

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 for a communication device in the target network; during a handover procedure for the communication device to the target from an initial network, receiving at least one service identifier from a second communication node; and for each service identifier, signalling a service repository of the target network to discover a service corresponding to the service identifier when that service is not identified in the local cache, and skipping the signalling of the service repository when that service is identified in the local cache.

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

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

4. The method of any one of claims 1 to 3, wherein the at least one service identifier comprises a UDM (Unified Data Management) Group ID and/or a PCF (Policy Control Function) Group ID.

5. 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 UECM (Unified Endpoint Configuration Management) service or a UDM SDM (Subscription Data Management) service, and wherein skipping the signaling of the service repository comprises skipping discovery for the UDM UECM service or the UDM SDM service.

6. 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 AM (Access and Mobility) policy service, and wherein skipping the signaling of the service repository comprises skipping discovery for the PCF AM service.

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 UECM (Unified Endpoint Configuration Management) service or a UDM SDM (Subscription Data Management) service, and wherein skipping the signaling of the service repository comprises skipping discovery for 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 AM (Access and Mobility) policy service, and wherein skipping the signaling of the service repository comprises skipping discovery for the PCF AM service.

8. The method of any one of claims 1 to 7, wherein the first communication node comprises an AMF (Access and Mobility Management Function), the target network comprises an NR (5G New Radio) network, the initial network comprises an LTE (Long- Term Evolution) network, and the service repository comprises an NRF (Network Repository Function).

9. The method of claim 8, wherein the second communication node comprises an SMF (Session Management Function).

10. The method of claim 8 or claim 9, wherein the second communication node comprises an MME (Mobile Management Entity).

11. A non-transitory computer readable medium having recorded thereon statements and instructions 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 for a communication device in the target network; during a handover procedure for the communication device to the target from an initial network, receive at least one service identifier from a second communication node; and for each service identifier, signal a service repository of the target network to discover a service corresponding to the service identifier when that service is not identified in the local cache, and skip the signaling of the service repository when that service is identified in the local cache.

12. The non-transitory computer readable medium of claim 11 , wherein the statements and instructions, when executed by the processor of the first communication node, configure 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 for a communication device in the target network; and service discovery circuitry coupled to the network interface and the computer readable medium, wherein the service discovery circuitry is configured to: during a handover procedure for the communication device to the target from an initial network, receive via the network interface at least one service identifier from a second communication node; and for each service identifier, signal via network interface a service repository of the target network to discover a service corresponding to the service identifier when that service is not identified in the local cache, and skip the signalling of the service repository when that service is identified in the local cache.

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

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

16. The first communication node of any one of claims 13 to 15, wherein the at least one service identifier comprises a UDM (Unified Data Management) Group ID and/or a PCF (Policy Control Function) 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 UECM (Unified Endpoint Configuration Management) service or a UDM SDM (Subscription Data Management) service, and wherein the first communication node skips the signaling of the service repository by skipping discovery for 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 AM (Access and Mobility) policy service, and wherein the first communication node skips the signaling of the service repository by skipping discovery for 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 UECM (Unified Endpoint Configuration Management) service or a UDM SDM (Subscription Data Management) service, and wherein the first communication node skips the signaling of the service repository by skipping discovery for 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 AM (Access and Mobility) policy service, and wherein the first communication node skips the signaling of the service repository by skipping discovery for the PCF AM service.

20. The first communication node of any one of claims 13 to 19, wherein the first communication node comprises an AMF (Access and Mobility Management Function), the target network comprises an NR (5G New Radio) network, the initial network comprises an LTE (Long-Term Evolution) network, and the service repository comprises an NRF (Network Repository Function).