v151 · webrtc · sdp
SDP & SCTP Inspector
Generate a real SDP offer with createOffer() and read the lines that set up the SCTP-over-DTLS data-channel transport. SNAP adds one new media attribute — a=sctp-init — carrying the SCTP INIT parameters. This tool highlights the SCTP lines and probes the live offer for that exact attribute, reporting present or absent honestly.
offer SDP
Press “Generate real offer SDP” to create a live RTCPeerConnection offer and inspect its SCTP lines.
SCTP negotiation
what SNAP adds
WebRTC data channels are signalled in SDP with a media section like m=application <port> UDP/DTLS/SCTP webrtc-datachannel, plus a=sctp-port and a=max-message-size. SNAP defines a new media-level attribute on that same section:
m=application 9 UDP/DTLS/SCTP webrtc-datachannel
a=sctp-port:5000
a=max-message-size:262144
a=setup:actpass
a=fingerprint:sha-256 …
a=sctp-init:AQAAHols3R0AUAAA/////+B5ZR3AAAAEgAgABoLA ← SNAP: base64 SCTP INIT paramsThe proposal defines a=sctp-init as a base64-encoded SCTP INIT chunk. A supporting offerer includes its value; a supporting answerer validates that value and returns its own. If both values are negotiated, the expired -00 draft says the endpoints should consider the SCTP association established once DTLS finishes, skipping the separate SCTP handshake. Chrome's implementation is an origin trial (runtime feature WebRtcSctpSnap, experimental; register for the trial or launch with --enable-blink-features=WebRtcSctpSnap). This inspector proves only what the generated offer contains. If the attribute is absent, the offer provides no SNAP evidence; it does not expose SCTP association state or the packets later sent over DTLS.
see also
- Open-Latency Lab — measure a broader local open interval that includes SNAP-adjacent work.
- Reliable vs Unreliable Streams — inspect per-channel reliability controls that SNAP does not negotiate.