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[webrtc-pc] currentRemoteDescription.sdp -- does it need to match the last SDP set via setRemoteDescription?

From: Philipp Hancke via GitHub <sysbot+gh@w3.org>
Date: Mon, 07 Nov 2016 11:56:47 +0000
To: public-webrtc@w3.org
Message-ID: <issues.opened-187693412-1478519805-sysbot+gh@w3.org>
fippo has just created a new issue for 
https://github.com/w3c/webrtc-pc:

== currentRemoteDescription.sdp -- does it need to match the last SDP 
set via setRemoteDescription? ==
When doing the following:
```
var pc = new RTCPeerConnection();
pc.setRemoteDescription({ type: 'offer', sdp: "v=0\no=- 
6276735615230473072 2 IN IP4 127.0.0.1\ns=-\nt=0 0\na=group:BUNDLE 
audio\na=msid-semantic: WMS 
*\na=ice-ufrag:nGx0Ag==\na=ice-pwd:MEA9YrgtlxtSZ3/M69h/oc3Svvs2KA==\na=setup:actpass\na=fingerprint:sha-256
 
05:EC:AE:05:A1:EF:7F:13:8A:7D:E3:C6:05:67:E3:CE:8D:16:6B:7A:78:92:58:F9:18:FC:FB:84:4A:5D:3C:F6\nm=audio
 9 UDP/TLS/RTP/SAVPF 111\nc=IN IP4 0.0.0.0\na=rtcp:9 IN IP4 
0.0.0.0\na=mid:audio\na=extmap:3 
http://www.webrtc.org/experiments/rtp-hdrext/abs-send-time\na=maxptime:60\na=recvonly\na=rtcp-mux\na=rtpmap:111
 opus/48000/2\na=fmtp:111 minptime=10;useinbandfec=1\n" })
```
I get the following pc.remoteDescription.sdp from Chrome:
```
v=0
o=- 6276735615230473072 2 IN IP4 127.0.0.1
s=-
t=0 0
a=group:BUNDLE audio
a=msid-semantic: WMS
m=audio 9 UDP/TLS/RTP/SAVPF 111
c=IN IP4 0.0.0.0
a=rtcp:9 IN IP4 0.0.0.0
a=ice-ufrag:nGx0Ag==
a=ice-pwd:MEA9YrgtlxtSZ3/M69h/oc3Svvs2KA==
a=fingerprint:sha-256 
05:EC:AE:05:A1:EF:7F:13:8A:7D:E3:C6:05:67:E3:CE:8D:16:6B:7A:78:92:58:F9:18:FC:FB:84:4A:5D:3C:F6
a=setup:actpass
a=mid:audio
a=extmap:3 http://www.webrtc.org/experiments/rtp-hdrext/abs-send-time
a=recvonly
a=rtcp-mux
a=rtpmap:111 opus/48000/2
a=fmtp:111 minptime=10;useinbandfec=1
a=maxptime:60
```
i.e. Chrome moved ufrag, pwd and fingerprint.

[the 
spec](http://w3c.github.io/webrtc-pc/#dom-rtcpeerconnection-currentremotedescription)
describes the currentRemoteDescription as 
```represents the last remote RTCSessionDescription [...] plus any 
remote candidates that have been supplied via addIceCandidate() since 
the offer or answer was created.```

Does that mean that the sdp attribute must be exactly the same 
(ignoring candidates) or are modifications like pulling the 
fingerprints and ice-ufrags from the session level down to the m-lines
 allowed? Chromes behaviour is somewhat useful since it allows 
inspecting its internal state and what parts of the SDP were actually 
consumed. But it might not be spec-compliant.

Please view or discuss this issue at 
https://github.com/w3c/webrtc-pc/issues/921 using your GitHub account
Received on Monday, 7 November 2016 11:56:53 UTC

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