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Re: SDP DataChannels

From: Eric Rescorla <ekr@rtfm.com>
Date: Sat, 3 Aug 2013 08:11:32 +0200
Message-ID: <CABcZeBNHVvcmbaD0NiTr3Ohmq0Y4O9s=QXUXiENc1F1vwwCN1Q@mail.gmail.com>
To: "piranna@gmail.com" <piranna@gmail.com>
Cc: public-webrtc <public-webrtc@w3.org>
On Sat, Aug 3, 2013 at 1:29 AM, piranna@gmail.com <piranna@gmail.com> wrote:

> I've just been able to generate an offer only with DataChannels (seems
> the fact that audio m-lines where added on Chrome due a bug on the
> mediaConstraints, and that was the reason why SDP strings were so
> long) and I've been able to dump the generated SDP, being now more
> confident that SDP is not the best format at least for this use case
> (only DataChannels). Could be any body explain me why there are so
> much (almost) duplicated lines? What are the essential ones? What are
> just the essential bits of data required to create this DataChannels?
>

It's probably better to look at the SDP from Firefox because Chrome doesn't
currently implement the  data channel specification. Here is what the
Firefox
SDP looks like:

v=0
o=Mozilla-SIPUA-25.0a1 12613 0 IN IP4 0.0.0.0
s=SIP Call
t=0 0
a=ice-ufrag:9638f069
a=ice-pwd:90f72795622bd286d75dde68d9b7e02f
a=fingerprint:sha-256
7C:CE:6B:7A:D4:B0:2E:D7:0C:76:07:59:B5:9E:28:5C:14:6C:00:D7:E0:10:C6:CD:25:8B:4B:E8:1D:CC:FC:4F
m=application 51189 DTLS/SCTP 5000
c=IN IP4 89.246.150.136
a=fmtp:5000 protocol=webrtc-datachannel;streams=16
a=sendrecv
a=candidate:0 1 UDP 2113601791 10.0.1.158 53229 typ host
a=candidate:1 1 UDP 1694236671 89.246.150.136 51189 typ srflx raddr
10.0.1.158 rport 53229
a=candidate:0 2 UDP 2113601790 10.0.1.158 54571 typ host
a=candidate:1 2 UDP 1694236670 89.246.150.136 55176 typ srflx raddr
10.0.1.158 rport 54571
Received on Saturday, 3 August 2013 06:12:39 UTC

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