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

"MARCON, JEROME (JEROME)" <jerome.marcon@alcatel-lucent.com> Wed, 06 March 2013 10:40 UTC

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From: "MARCON, JEROME (JEROME)" <jerome.marcon@alcatel-lucent.com>
To: Randell Jesup <randell-ietf@jesup.org>, "rtcweb@ietf.org" <rtcweb@ietf.org>
Thread-Topic: [rtcweb] I-D Action: draft-ietf-rtcweb-data-channel-04.txt
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Date: Wed, 6 Mar 2013 10:40:08 +0000
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Subject: Re: [rtcweb] I-D Action: draft-ietf-rtcweb-data-channel-04.txt
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Randell,

Thanks, some other comments inline. Please answer (again) to question 4, I have other pending questions related to this matter.

Jerome

> -----Message d'origine-----
> De : rtcweb-bounces@ietf.org [mailto:rtcweb-bounces@ietf.org] 
> De la part de Randell Jesup
> Envoyé : mardi 5 mars 2013 11:18
> À : rtcweb@ietf.org
> Objet : Re: [rtcweb] I-D Action: draft-ietf-rtcweb-data-channel-04.txt
> 
> 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).
> 
OK, that should be in the text.

> > 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.
> 
I am following Michael's clarifications on this.

> > 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).
> 
OK, so you said In Boston. At least the text should say when the offer should signal (or the answerer should interpret) that the list of data channels is no longer valid. How to signal this is I understand in the scope of MMUSIC which hopefully will find a cleaner way that just repeating some now invalid information. 

> > 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.
> 
> 

That does not answer to my question, so I reformulate: some time after the initial SDP Opening Handshake, can the DATA_CHANNEL_OPEN message create in-band a data channel with a 'subprotocol' not negotiated by the initial SDP Opening Handshake ?

> 
> --
> Randell Jesup
> randell-ietf@jesup.org
> 
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