Correcting the DC call constraint
The current constraint in TS 26.114 clause 6.2.10.1 states that a data channel SDP media description shall not be placed before the first SDP speech media description. This constraint is no longer applicable because 3GPP R19 SA2 has specified standalone data channel sessions that can establish data channels without MMTel media (e.g., audio, video, messaging).
The CR proposes to remove the restrictive placement constraint for data channel SDP media descriptions. Specifically:
Deleted Text:
- "A data channel SDP media description shall not be placed before the first SDP speech media description."
Modified Text:
The sentence describing data channel SDP media description inclusion is updated from:
- "One or more data channel SDP media descriptions formatted according to IETF RFC 8864 [172] may be contained alongside other SDP media descriptions such as e.g. speech, video, and text."
To:
- "One or more data channel SDP media descriptions formatted according to IETF RFC 8864 [172] may be added into the SDP independently, or to be added alongside other SDP media descriptions such as e.g. speech, video, and text."
This correction enables:
- Standalone data channel sessions without requiring MMTel media components
- Flexible SDP ordering where data channel media descriptions can appear in any position within the SDP
- Alignment with SA2 specifications for Rel-19 standalone data channel functionality
The following requirements remain intact:
- Support for data channel media remains optional for MTSI clients
- Media feature tag requirements (+sip.app-subtype with "webrtc-datachannel" value)
- g.3gpp.dc-mux media feature tag for bootstrap and application data channel multiplexing
- Protocol identifier and media format specifications (UDP/DTLS/SCTP and webrtc-datachannel)
- Bandwidth limit determination requirements per clause 6.2.5