6 MBS User Services distribution methods

26.5023GPP5G Multicast-Broadcast User Service ArchitectureRelease 17TS

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

6.1 Object Distribution Method

The Object Distribution Method is used to deliver binary objects to the MBS Client over an MBS Session that have been received from the MBS Application Provider over reference point Nmb8.

The following Use Cases are supported:

– Single file delivery.

– Delivering a root object and its dependent objects as a collection, e.g. a web page and all the assets needed to render it.

– Object carouselling for file delivery, including updates of files.

– Real-time object streaming, for example for regular-latency or low-latency streaming delivery. In the latter case, the objects distributed may be CMAF segments as defined by the 5G Media Streaming DASH Interoperability Point specified in clause 7.3.11 of TS 26.247 [10].

The operating modes for the Object Distribution Method are summarised in table 6.1‑1 below.

Table 6.1‑1: Summary of operating modes for Object Distribution Method

Distribution method	Operating mode	Description
OBJECT	OBJECT_SINGLE	Each object ingested by the MBSTF is distributed once.
	OBJECT_COLLECTION	A set of objects described by a manifest (see NOTE) is ingested by the MBSTF and distributed once.
	OBJECT_CAROUSEL	A set of one or more objects described by a manifest (see NOTE) is ingested by the MBSTF and distributed according to a repetition pattern specified in the manifest. Any change to an object during the course of the MBS Distribution Session is reflected in the distribution at the next available opportunity.
	OBJECT_STREAMING	A sequence of objects is ingested by the MBSTF and streamed in real time, for example according to a schedule described in a presentation manifest (e.g. DASH MPD).
NOTE: The manifest format is specified in TS 26.517 [13].

Based on the configuration received from the MBSF via reference point Nmb2, the objects are ingested by the MBSTF from the MBS Application Provider via the pull-based or push-based object ingest method. As defined in clause 4, the MBSTF segments the objects into appropriate payloads, adds the FEC redundancy and schedule packet transmission to the MBS Client.

NOTE: Pull-based object ingest may occur once at the start of each active period of the associated MBS User Data Ingest Session, or the pulled objects may be revalidated (and possibly re-ingested) periodically, for example once per rotation of an object carousel.

File repair functionality may be utilized to repair object fragments transmitted by the MBSTF using the Object Distribution Method but lost or corrupted in transit. In such cases, the MBS Client may request the missing object fragments from the MBS AS. File repair may be done during an ongoing MBS User Services Session or after an MBS User Services Session.

6.2 Packet Distribution Method

The Packet Distribution Method is used to deliver packet streams to the MBS Client over an MBS Session that have been received from the MBS Application Provider over reference point Nmb8. This distribution method is particularly useful for multicast and broadcast of IP-based services for which the content delivery protocols are defined outside the scope of the MBS specification.

The MBSTF receives packet streams from the MBS Application Provider, typically in the form of UDP/IP packets, and sends them to the configured MBS Session. Optionally, packet sequence numbering and/or FEC redundancy may be added by the MBSTF.

The Packet Distribution Session may be operated in one of two different modes:

– In Forward-only mode, the transport protocol on top of IP is opaque to the MBS System, as described in clause B.3.1. The User Service Announcement may be handled by the MBS Application Provider via external means at reference point MBS-8.

– In Proxy mode, the UDP packet payload of the UDP streams is opaque to the MBS Session, as described in clause B.3.2. An MBS Client is expected to make the UDP Payloads available directly to the MBS-Aware Application, without further knowledge of the content carried.

The operating modes for the Packet Distribution Method are summarised in table 6.2‑1 below.

Table 6.2‑1: Summary of operating modes for Packet Distribution Method

Distribution method	Operating mode	Description
PACKET	PACKET_FORWARD_ONLY	The payloads of IP packets ingested by the MBSTF are forwarded to the MB-UPF in new IP packets (Layer 3 proxying).
	PACKET_PROXY	The payloads of UDP packets ingested by the MBSTF are forwarded to the MB-UPF in new UDP packets (Layer 4 proxying).
NOTE 1: RTP packets formatted according to RFC 3550 [8] can be distributed using either of the above operating modes. NOTE 2: The MBSTF is not required to inspect or otherwise act on the payload of ingested UDP packets.