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

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

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From: "MARCON, JEROME (JEROME)" <jerome.marcon@alcatel-lucent.com>
To: Michael Tuexen <Michael.Tuexen@lurchi.franken.de>, "rtcweb@ietf.org" <rtcweb@ietf.org>, Randell Jesup <randell-ietf@jesup.org>
Thread-Topic: [rtcweb] I-D Action: draft-ietf-rtcweb-data-channel-04.txt
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Date: Wed, 6 Mar 2013 10:05:31 +0000
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Subject: Re: [rtcweb] I-D Action: draft-ietf-rtcweb-data-channel-04.txt
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Thanks Michael, I still have a question/comment inline.

> -----Message d'origine-----
> De : Michael Tuexen [mailto:Michael.Tuexen@lurchi.franken.de] 
> Envoyé : lundi 4 mars 2013 19:47
> À : MARCON, JEROME (JEROME)
> Cc : rtcweb@ietf.org; Randell Jesup
> Objet : Re: [rtcweb] I-D Action: draft-ietf-rtcweb-data-channel-04.txt
> 
> On Mar 4, 2013, at 3:36 PM, 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 ?
> > 
> > 2. "channel is available to send as soon as the 
> DATA_CHANNEL_OPEN has been sent". And the SACK received I guess ?
> The SACK is an SCTP level ack. So you only know that the SCTP 
> stack of the peer has received it, so you don't know if the 
> application has received it or even processed it. So if you 
> want some sort of ack, you need an application level ack. 
> This was done in the 3 way handshake stuff which was in the 
> older version.
> 
> In this version, the sender sends an DATA_CHANNEL_OPEN as the 
> first message and the receiver has to buffer user messages 
> until the DATA_CHANNEL_OPEN message has been received in case 
> of reordering in the network and using unordered delivery for 
> user messages.
> 
> Best regards
> Michael

OK thanks. I am not sure to get your last point about order of delivery. You seem to refer to the SCTP endpoint behaviors (section 6.6) that unordered messages a) could bypass the in-order messages in the outbound transmission queue and b) must be delivered before in-order messages on the receiver side.

But then the DATA_CHANNEL_OPEN message should be sent 'unordered'. Otherwise this situation could occur: the sender app sends DATA_CHANNEL_OPEN 'in-order' and then immediately many 'unordered' messages. Those messages would all bypass the transmission of the DATA_CHANNEL_OPEN message.

> > 
> > 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 .. ?
> > 
> > 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 ?
> > 
> > Jerome
> > 
> >> -----Message d'origine-----
> >> De : rtcweb-bounces@ietf.org 
> [mailto:rtcweb-bounces@ietf.org] De la 
> >> part de internet-drafts@ietf.org Envoyé : lundi 25 février 
> 2013 23:40 
> >> À : i-d-announce@ietf.org Cc : rtcweb@ietf.org Objet : 
> [rtcweb] I-D 
> >> Action: draft-ietf-rtcweb-data-channel-04.txt
> >> 
> >> 
> >> A New Internet-Draft is available from the on-line 
> >> Internet-Drafts directories.
> >> This draft is a work item of the Real-Time Communication in 
> >> WEB-browsers Working Group of the IETF.
> >> 
> >> 	Title           : RTCWeb Data Channels
> >> 	Author(s)       : Randell Jesup
> >>                          Salvatore Loreto
> >>                          Michael Tuexen
> >> 	Filename        : draft-ietf-rtcweb-data-channel-04.txt
> >> 	Pages           : 13
> >> 	Date            : 2013-02-25
> >> 
> >> Abstract:
> >>   The Web Real-Time Communication (WebRTC) working group is 
> >> charged to
> >>   provide protocol support for direct interactive rich 
> communication
> >>   using audio, video, and data between two peers' 
> web-browsers.  This
> >>   document specifies the non-media data transport aspects of 
> >> the WebRTC
> >>   framework.  It provides an architectural overview of how 
> the Stream
> >>   Control Transmission Protocol (SCTP) is used in the WebRTC 
> >> context as
> >>   a generic transport service allowing Web Browser to 
> >> exchange generic
> >>   data from peer to peer.
> >> 
> >> 
> >> The IETF datatracker status page for this draft is:
> >> https://datatracker.ietf.org/doc/draft-ietf-rtcweb-data-channel
> >> 
> >> There's also a htmlized version available at:
> >> http://tools.ietf.org/html/draft-ietf-rtcweb-data-channel-04
> >> 
> >> A diff from the previous version is available at:
> >> http://www.ietf.org/rfcdiff?url2=draft-ietf-rtcweb-data-channel-04
> >> 
> >> 
> >> Internet-Drafts are also available by anonymous FTP at:
> >> ftp://ftp.ietf.org/internet-drafts/
> >> 
> >> _______________________________________________
> >> rtcweb mailing list
> >> rtcweb@ietf.org
> >> https://www.ietf.org/mailman/listinfo/rtcweb
> >> 
> > _______________________________________________
> > rtcweb mailing list
> > rtcweb@ietf.org
> > https://www.ietf.org/mailman/listinfo/rtcweb
> > 
> 
>