7 Packet Delivery Method
26.5173GPP5G Multicast-Broadcast User ServicesProtocols and FormatsRelease 17TS
7.1 General
The Packet Distribution Method reuses different delivery concepts from TS 26.346. Additional distribution methods may be defined in future.
7.2 Re-using MBMS Delivery Method as Packet Distribution Method
7.2.1 General
The Packet Distribution Method combines three different delivery methods of TS 26.346 [7] (namely the MBMS Streaming Delivery Method, Group Communication Delivery Method and Transparent Delivery Method) into a single distribution method, with a set of modifications.
For the Packet Distribution Method, the MBSTF may handle the ingested content on three different protocol layers according to the operating mode provisioned for the MBS Distribution Session:
– Proxy mode: The MBSTF handles UDP packet payloads and forwards UDP packet payloads from ingest into the MBS Distribution Session. The MBSTF may use different UDP ports for the MBS Distribution Session. The MBSTF re-uses the Proxy Mode of the Transparent Delivery Method as defined in clause 8B of [7].
– Forward-only mode: The MBS receives complete IP packets and forwards the ingested packets as MBS PDUs. The MBSTF re-uses the Group Communication Delivery Method as defined in clause 8A of [7] and the Forward-Only Mode of the Transparent Delivery Method as defined in clause 8B of [7].
7.2.3 Session Description
7.2.3.1 General
The Session Description metadata unit contains the needed information to activate the reception of a Packet Distribution Method. The Session Description metadata unit is formatted according to the Session Description Protocol [8]. The Session Description metadata unit for the Packet Distribution Method is based on the Session Description parameters as defined in clauses 8.3, 8A.3 and 8B.3 of TS 26.346 [7] with the following restrictions and extensions.
Restrictions:
– The Mode of MBMS bearer per media parameter (clauses 8.3.1.5 and 8B.3.2 of [7]) shall not be used.
– The QoE Metrics (as defined in clauses 8.3.2.1 and 8.4 of [7]) shall not be used.
– ROHC header compression (as defined in clauses 8A.4 and 8B.4 of [7]) shall not be used.
NOTE: ROHC is handled by RAN in 5MBS.
– The Alternative TMGI (clause 7.3.2.12 of [7]) shall not be used.
– The Start time and End time of the session (SDP t line) shall indicate a superset of the active times specified in the MBS Schedule Description metadata unit, if present. If there is no schedule specified, both values should be set to zero indicating undefined times.
Extensions:
– When the MBS User Service is of MBS Service Type Broadcast or when an MBS User Service of type Multicast uses a TMGI as its MBS Session ID, the MBS service type of MBS Session declaration attribute as defined in clause 6.2.2.2 shall be present in the Session Description.
7.2.3.2 SDP examples for Packet Distribution Method
Below is a full example of SDP description describing the media streams part of an MBS Packet Distribution session for RTP streaming:
Listing 7.2.3.2‑1: Session description for RTP streaming
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v=0 b=AS:77 a=mbs-mode:broadcast 123869108302929 a=source-filter: incl IN IP6 * 2001:210:1:2:240:96FF:FE25:8EC9 m=video 4002 RTP/AVP 96 b=TIAS:62000 b=RR:0 b=RS:600 a=maxprate:17 a=rtpmap:96 H264/90000 |
The following is a full example of SDP description for transparent streaming with two MPEG-2 Transport Streams:
Listing 7.2.3.2‑2: Session description for MPEG‑2 Transport Stream
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v=0 b=AS:8000000 a=mbs-mode:broadcast 123869108302929 a=source-filter: incl IN IP6 * 2001:210:1:2:240:96FF:FE25:8EC9 m=video 4002 UDP/RTP/AVP 96 b=TIAS:4000000 a=mms-framing-header:0 2 a=rtpmap:100 MP2T/90000 m=video 4002 RTP/AVP 98 b=TIAS:4000000 a=rtpmap:100 MP2T/90000 a=MBS-framing-trailer:0 2 |
Annex A (normative):
Syntax for Service Announcement