Re: [rtcweb] *MUST* DCEP?

"Makaraju, Maridi Raju (Raju)" <> Tue, 04 March 2014 12:08 UTC

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From: "Makaraju, Maridi Raju (Raju)" <>
To: Ted Hardie <>, Paul Kyzivat <>
Thread-Topic: [rtcweb] *MUST* DCEP?
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Date: Tue, 04 Mar 2014 12:08:18 +0000
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Subject: Re: [rtcweb] *MUST* DCEP?
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While a=sctpmap assumes use of DCEP, indication of external negotiation (instead of DCEP) also requires subprotocol and it's parameters to be conveyed. This has to be done per data channel stream.
Are you looking at more than what is documented in [I-D.ejzak-mmusic-data-channel-sdpneg]?
Or are you looking for an indication of this (for all streams) directly in a=sctpmap?

How about item 3 of the following proposal?


From: rtcweb [] On Behalf Of Ted Hardie
Sent: Tuesday, March 04, 2014 5:17 AM
To: Paul Kyzivat
Subject: Re: [rtcweb] *MUST* DCEP?

On Tue, Mar 4, 2014 at 11:03 AM, Paul Kyzivat <<>> wrote:

(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.

Help me understand why it wouldn't then be in their systems documents?


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.