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Content for  TS 26.502  Word version:  18.1.0

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6 MBS User Services distribution methods  6.1 Object Distribution Method  6.2 Packet Distribution Method 
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6  MBS User Services distribution methods  p. 54

6.1  Object Distribution Method  p. 54

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-shot object 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 object delivery, including updates of objects.
  • 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.
The operating modes for the Object Distribution Method are summarised in Table 6.1-1 below.
Distribution method Operating mode Description
OBJECTOBJECT_SINGLEEach object ingested by the MBSTF is distributed once.
Either pull-based and push-based object acquisition methods may be provisioned in combination with this operating mode.
When the pull-based object acquisition method is provisioned, the MBS Distribution Session parameters (see Table 4.5.6-2) shall cite a set of one or more object URLs as Object acquisition identifiers. When the push-based object acquisition method is provisioned, the set of Object acquisition identifiers shall be empty.
OBJECT_COLLECTIONA set of objects described by a manifest (see NOTE) is ingested by the MBSTF and distributed once.
Either pull-based and push-based object acquisition methods may be provisioned in combination with this operating mode.
When the push-based object acquisition method is provisioned, the object manifest (only) shall be pushed to the MBSTF; the objects referenced by the object manifest shall be pulled.
The MBS Distribution Session parameters (see Table 4.5.6-2) shall cite a single object manifest URL in Object acquisition identifiers.
OBJECT_CAROUSELA 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.
Either pull-based and push-based object acquisition methods may be provisioned in combination with this operating mode.
When the push-based object acquisition method is provisioned, the object manifest (only) shall be pushed to the MBSTF; the objects referenced by the object manifest shall be pulled.
The MBS Distribution Session parameters (see Table 4.5.6-2) shall cite a single object manifest URL in Object acquisition identifiers.
OBJECT_STREAMINGA sequence of objects is ingested by the MBSTF and streamed in real time, for example according to a schedule described in an Application Service Entry Point document (e.g. DASH MPD).
Either pull-based and push-based object acquisition methods may be provisioned in combination with this operating mode.
For both object acquisition methods, the MBS Distribution Session parameters (see Table 4.5.6-2) shall cite a single Application Service Entry Point URL of each type in Object acquisition identifiers (see NOTE 2). As a consequence, the referenced Application Service Entry Point document(s) shall be included in the MBS User Service Announcement Channel as ancillary objects.
All Application Service Entry Points referenced by an MBS Distribution Session shall be for equivalent presentations, i.e., comprising common object streams according to compatible presentation timelines.
NOTE:
OBJECT_COLLECTION operating mode is a special case of OBJECT_CAROUSEL operating mode in which the objects described by the manifest are distributed only once. The baseline parameters of the object manifest are defined in clause 4.5.10.
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 schedules packet transmission to the MBS Client.
Object repair functionality may be utilized to repair object fragments that are 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 using the procedure defined in clause 5.6. This procedure may be invoked during an ongoing MBS User Services Session or after an MBS User Services Session has finished.
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6.2  Packet Distribution Method  p. 56

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.
Distribution method Operating mode Description
PACKETPACKET_FORWARD_ONLYThe payloads of IP packets ingested by the MBSTF are forwarded to the MB-UPF in new IP packets (Layer 3 proxying).
PACKET_PROXYThe 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.
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