Content for  TS 26.501  Word version:  18.6.0

Figure 4.9.1-1 below depicts an architecture for downlink 5G Media Streaming via MBS as defined in TS 26.502 that combines the functions and reference points of the 5GMS System with those of the MBS System. In the simple case, the 5GMSd AF is deployed in a Trusted DN together with the MBS System according to the collaboration model in clause A.3 of TS 26.502 and Nmbsf service operations on the MBSF are invoked by the 5GMSd AF directly at reference point Nmb10. In other deployments, as for example shown in clauses A.4 and A.5 of TS 26.502, the 5GMS System may be external to the MBS System. In this case, the service operations on the MBSF are instead invoked on the NEF at reference point N33, and the NEF then communicates with the MBSF at reference point Nmb5.

This arrangement allows 5GMS-based downlink media streaming to be deployed as an MBS-Aware Application on top of the MBS System as defined in TS 26.502. In this case:

1. The 5GMSd AF configures the delivery of 5GMSd content to an MBS Client in the UE by provisioning an MBS User Service as defined in clause 4.5.1 of TS 26.502. In order to additionally deliver this content over one or more MBS Distribution Session, the 5GMSd AF invokes control plane procedures on the MBSF as specified in clause 7.2 of TS 26.502 and, as a result, content is ingested by the MBSTF from the 5GMSd AS using the pull-based object ingest procedures at reference point Nmb8 specified in clause 6.1 of TS 26.502.
2. The 5GMSd Client acts as MBS-Aware Application (as defined in TS 26.502) for the MBS Client. Thus, the MBS Client is controlled by the 5GMSd Client via the MBS-6 API.
3. The MBSTF Client receives media and other objects from the MBSTF according to the Object Distribution Method specified in clause 6.1 of TS 26.502. If Object Repair as specified in clause 4.2.6 of TS 26.502 is available in the MBS System, the MBS Client uses the unicast repair delivery procedures to recover damaged objects received from the MBSTF by interacting at reference point MBS-4-UC.
4. The Media Server subfunction of the MBSTF Client provides a media server interface and shall expose the content received (and possibly repaired) by the MBS Client to the Media Player in the 5GMSd Client via reference point MBS-7 using interactions equivalent to those defined at reference point M4d.
5. The Media Player sends requests according to the signalled object availability times in the manifest. In case a media object transmitted via an MBS Distribution Session is not received by the MBS Client by the object availability times, or if it cannot be repaired in time for consumption by the 5GMSd Client, the Media Server in the MBS Client returns either an error or else a partial object in response to the Media Player's request for the media object. In this case, the Media Player may instead attempt to retrieve the media object, or ranges of it, from the 5GMSd AS at reference point M4d, if available. The object shall be available for download from the 5GMSd AS for a well-defined time period.

The usage of existing reference points to support these scenarios is documented in the following clauses. Procedures for 5GMS via MBS are defined in clause 5.12.