5 Services offered by the SOR-AF

29.5503GPP5G SystemRelease 18Stage 3Steering of roaming application function servicesTS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

5.1 Introduction

The SOR-AF offers the following services to NF consumers (e.g. UDM) via the Nsoraf service based interface:

– Nsoraf_SteeringOfRoaming

Table 5.1-1 summarizes the corresponding APIs defined for this specification.

Table 5.1-1: APIs Description

Service Name	Clause	Description	OpenAPI Specification File	apiName	Annex
Nsoraf_SteeringOfRoaming	6.1	Nsoraf Steering Of Roaming Service	TS29550_Nsoraf_SOR.yaml	nsoraf-sor	A.2

5.2 Nsoraf_SteeringOfRoaming Service

5.2.1 Service Description

The Nsoraf_SteeringOfRoaming (Nsoraf_SOR) service provides Steering of Roaming services to NF consumers (e.g. UDM) to enable the retrieval of SoR information (i.e. the list of preferred PLMN/access technology combinations or an indication that no update to the list of preferred PLMN/access technology combinations is needed) to be conveyed to the UE, as specified in Annex C of 3GPP°TS°23.122 [14]. The latter specifies the 5GS control plane mechanism for Steering of Roaming that aims at allowing the HPLMN to update the "Operator Controlled PLMN Selector with Access Technology" list in the UE by providing and updating this list of preferred PLMN/access technology combinations.

5.2.2 Service Operations

5.2.2.1 Introduction

For the Nsoraf_SteeringOfRoaming service, the following service operations are defined:

– Get

– Info

5.2.2.2 Get

5.2.2.2.1 General

This service operation is used by a NF consumer (e.g. UDM) to retrieve SoR information.

The returned information can consist of either:

– a list of preferred PLMN/access technology combinations;

– a secured packet;

– neither of them.

NOTE: The secured packet contains the list of preferred PLMN/access technology combinations encapsulated with a security mechanism as described in 3GPP TS 31.115 [17].

The following procedures are supported using the "Get" service operation:

– SoR Information Retrieval

5.2.2.2.2 SoR Information Retrieval

Figure 5.2.2.2.2-1 depicts a scenario where a NF consumer (e.g. UDM) sends a request to the SOR-AF to retrieve the SoR information for a UE (see also clause C.2 in Annex C of 3GPP°TS°23.122°[14]).

The request contains the UE’s identity (/{supi}) and a set of query parameters (e.g. PLMN ID of the visited PLMN the UE is roaming in, or SNPN ID of the visited SNPN).

Figure 5.2.2.2.2-1: SoR Information Retrieval Procedure

1. The NF service consumer (e.g. UDM) sends a GET request to the resource representing the SoR information (sor-information), with query parameters indicating the PLMN ID or SNPN ID and other relevant information (e.g. Access type).

2a. On success, the SOR-AF responds with the HTTP status code "200 OK" with the message body containing the SoR information (i.e. list of preferred PLMN/access technology combinations, the SOR-CMCI, if any, and the "Store the SOR-CMCI in the ME" indicator, if any, or a secured packet by consuming Nspaf services as specified in 3GPP TS 29.544 [19]) for the concerned UE. The response also contains a Cache-Control HTTP header set to the value "no-cache" instructing the NF consumer (e.g. UDM) to not cache the received SoR information.

2b. If there is no valid SoR information for the UE (e.g. the resource does not exist, the SUPI is unknown to the SOR-AF), the SOR-AF responds with the HTTP status code "404 Not Found" including additional error information in the response body (within the "ProblemDetails" IE).

NOTE: An operator configurable timer shall be used by the NF Service Consumer (e.g. UDM) to control the acceptable time during which it shall wait for the GET response from the SOR-AF, as specified in clause C.2 of 3GPP°TS°23.122°[14] (step 3d of the procedure description). The default value and range of this timer is operator specific and shall take into account the importance of the related procedure (e.g. registration procedure).

On failure, the appropriate HTTP status code indicating the error shall be returned and appropriate additional error information should be returned in the GET response body.

5.2.2.3 Info

5.2.2.3.1 General

This service operation is used by a NF consumer (e.g. UDM) to provide the SOR-AF with the reception status of the acknowledgment on successful reception of SoR information by the UE, in case an acknowledgment was requested to the UE.

The following procedures are supported using the "Info" service operation:

– SoR Acknowledgment Reception Notification

5.2.2.3.2 SoR Acknowledgment Reception Notification

Figure 5.2.2.3.2-1 depicts a scenario where a NF consumer (e.g. UDM) sends an indication to the SOR-AF on the reception status of SoR information by the UE (see also clauses C.2 and C.3 in Annex C of 3GPP°TS°23.122°[14]).

The request contains the UE’s identity (/{supi}), the type of acknowledgment (/sor-information/sor-ack) and the indication (SorAckInfo).

Figure 5.2.2.3.2-1: SoR Acknowledgment Reception Notification procedure

1. The NF service consumer (e.g. UDM) sends a PUT request to the resource representing the SoR information acknowledgment (/{supi}/sor-information/sor-ack) with the SorAckInfo containing an indication on the reception status of SoR information by the UE, and "ME support of SOR-CMCI" if available.

2a. The SOR-AF responds with the HTTP status code "204 No Content".

2b. If there is an error (e.g. the SUPI is unknown to the SOR-AF), the SOR-AF shall respond with the HTTP status code "404 Not Found" including additional error information in the response body (within the "ProblemDetails" IE).

On failure, the appropriate HTTP status code indicating the error shall be returned and appropriate additional error information should be returned in the PUT response body.