Re: [rtcweb] I-D Action: draft-ietf-rtcweb-data-channel-04.txt

Randell Jesup <> Tue, 05 March 2013 10:18 UTC

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Date: Tue, 05 Mar 2013 05:17:46 -0500
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Subject: Re: [rtcweb] I-D Action: draft-ietf-rtcweb-data-channel-04.txt
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On 3/4/2013 9:36 AM, MARCON, JEROME (JEROME) wrote:
> Randell,
> Thanks for this update. There are some points not (yet) explained in the text:
> 1. Following the SDP opening handshake, are the data channels implicitly opened, or does the offerer send one DATA_CHANNEL_OPEN message per new data channel ?

One Open per new channel which can be followed immediately with data.  
If the application has some out-of-band way to know about the channels 
expected (see the text), it could indicate so (effectively allowing 
application-mediated negotiation with no Open messages in-band - not 
that I generally would suggest this for normal uses).

> 2. "channel is available to send as soon as the DATA_CHANNEL_OPEN has been sent". And the SACK received I guess ?

No SACK required I believe.  As far as SCTP is concerned, Open messages 
are just data on the stream.

> 3. Assuming an endpoint creating a new offer (e.g. to reflect a change in media streams) while an SCTP association is already established. In this case, what does the SCTP association m-line contain: the unchanged list of data channels contained in the initial offer (which created the SCTP association), or the list of data channels currently opened, or .. ?

Just the listing for the association that was in the original offer 
(though this would be the SCTP SDP MMUSIC draft's issue).

> 4. What happens if the SDP Opening Handshake agreed on some data channels using the 'chat' subprotocol, and later on an endpoint creates in-band a new channel with 'file transfer' subprotocol ?

When you create a channel, it sends Open on an unused Stream.

Randell Jesup