# CR Summary: TR 26.502 CR 0050 – MBS User Service Announcement Parameter Alignment (Rel-18)

**Source:** BBC | **Work Item:** 5MBUSA | **Category:** A (mirror to earlier release) | **Affected spec:** TS 26.502 v18.5.0

## Purpose
Addresses gaps and ambiguities found during 5G-MAG reference implementation of MBS User Services, where stage 3 (TS 26.517) was correct but stage 2 (TS 26.502) lacked corresponding definitions or was unclear.

## Key Changes

- **Conformance profiles** (Change #1): Added as a new parameter (cardinality 0..*) in the MBS Distribution Session entity (Table 4.5.6-1), assigned by the MBS Application Provider. Also added to MBS Distribution Session Announcement (Table 4.5.8-1).

- **Transport security protection** (Change #2): Clarified in Table 4.5.6-1 that this flag is assigned by either the MBS Application Provider *or the MBSF* (the latter for the User Service Announcement Channel special case). Assigner column updated accordingly.

- **Object acquisition identifiers – MIME type** (Change #3): Clarified in Table 4.5.6-2 that each identifier *may* be accompanied by a content type, and that this content type *shall* be present when the identifier is an Application Service Entry Point locator. Reflected in Table 4.5.8-2 (Application Service Entry Point locators always paired with MIME type).

- **Object repair back-off parameters** (Change #4): Added as a new parameter (0..1, assigned by MBSF) in both Table 4.5.6-2 and Table 4.5.8-2. Clarified throughout (clauses 4.2.6, 4.5.6, 4.5.8) that Object Repair is *enabled by the MBSF* (not provisioned by the MBS Application Provider). Object repair base URL description updated to use "enabled" instead of "provisioned."

- **New reference point MBS-1** (Change #5): Formally defined in clause 4.4.1 as the interface for the MBS Application Provider to retrieve User Service Announcement bundles from the MBSF for private advertisement via MBS-8. Referenced in clauses 4.3.2, 5.2, and 5.4.

- **User Service Announcement bundle clarification** (Change #6): Clause 5.4 (procedure C) updated to clarify that the full User Service Announcement exposed via the *User Service advertisement* notification and retrievable at MBS-1 is the **User Service Announcement bundle** (replacing "composite").

## Impact
- Affects reference points Nmb10/Nmb5 (TS 29.580, CT3) and Nmb2 (TS 29.581, CT4) for changes #1–#3 and #5–#6.
- Changes #4 (back-off parameters) have no CT impact.
- Related specs: TS 26.580, TS 26.581.
- **If not approved:** Stage 2/stage 3 misalignment persists for MBS User Services implementation.