[rtcweb] *MUST* DCEP?

Paul Kyzivat <pkyzivat@alum.mit.edu> Tue, 04 March 2014 11:05 UTC

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Date: Tue, 04 Mar 2014 11:03:04 +0000
From: Paul Kyzivat <pkyzivat@alum.mit.edu>
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Subject: [rtcweb] *MUST* DCEP?
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(I think this was open issue #8)

You closed discussion on this, saying that this should be specified in 
some rtcweb "system" document. IIUC, then I disagree.

This is important to others besides rtcweb. We want to use this 
mechanism, both with and without components that are implementing 
rtcweb. Certainly for non-browsers.

This ultimately comes down to what I can expect after having negotiated 
(in SDP) the establishment of an SCTP association. When doing so, I use 
a=sctpmap to negotiate the how the association will be used. If I intend 
to use data channels and DCEP then I want an assurance that the other 
end does too. (That is the purpose of the SDP negotiation.)

AFAIK, current when I specify 'a=sctpmap:webrtc-datachannel' (or 
'a=sctp-datachannel' depending on where I look), that means the other 
side supports data channels *and* guarantees support for DCEP. There is 
no means to indicate support for data channels *without* DCEP.

I don't see any urgent need to have data channels without DCEP, as long 
as *use* of DCEP is optional.

IMO things would be less confusing if the two documents were merged into 
one, that defines the *Data Channel Protocol* (that runs over SCTP). 
This protocol runs over pairs of SCTP streams, has a small number of 
messages (open, ack, string-payload, binary-payload, close), and encodes 
them in SCTP using SCTP messages with particular payloads and SCTP 
stream reset. The open and ack messages would be optional.