## CR Summary: TR 26.502 CR 0051 – MBS User Service Announcement Parameter Alignment (Rel-19, Cat A)

**Source:** BBC | **WI:** 5MBUSA | **Affected spec:** TS 26.502 (stage 2); mirrors changes in TS 26.580/26.581

### Problem
During 5G-MAG reference implementation of MBS User Services, multiple gaps and ambiguities were found between stage 2 (TS 26.502) and stage 3 (TS 26.517) definitions for User Service Announcement parameters.

### Changes Made

- **Conformance profiles** (table 4.5.6-1 & 4.5.8-1): Added as a new parameter (0..*) assigned by the MBS Application Provider, referencing clause 12 profiles. Impacts Nmb10/Nmb5 (CT3).

- **Transport security protection** (table 4.5.6-1): Clarified that this flag is set by the MBS Application Provider *or* the MBSF (in the special case of the User Service Announcement Channel). Impacts Nmb10/Nmb5 and Nmb2.

- **Object acquisition identifiers** (table 4.5.6-2): Added optional MIME content type per identifier; made mandatory when the identifier is an Application Service Entry Point locator. Impacts Nmb10/Nmb5 and Nmb2.

- **Object repair back-off parameters** (tables 4.5.6-2 & 4.5.8-2): Defined new parameters (0..2) for in-session and post-session repair scheduling (offset time + random time period). Clarified that Object Repair is enabled by the MBSF, not provisioned by the MBS Application Provider (clause 4.2.6 updated accordingly). No CT impact.

- **New reference point MBS-1** (clauses 4.3.2, 4.4.1, 5.2, 5.4): Formally defined as the interface by which the MBS Application Provider retrieves User Service Announcement bundles from the MBSF for private re-advertisement via MBS-8. Impacts Nmb10/Nmb5.

- **User Service advertisement notification** (clause 4.6.2, table 4.6.2-1 & clause 5.4): Clarified that the full User Service Announcement exposed in the "User Service advertisement" event notification is the **User Service Announcement bundle**, and that the notification includes a URL for the MBS Application Provider to retrieve it via MBS-1. Terminology updated from "composite" to "full" where appropriate.

### Consequence if Not Approved
Stage 2/stage 3 misalignment for MBS User Services remains, blocking correct implementation.