Re: [MMUSIC] [dispatch] FW: New Version Notification for draft-marcon-msrp-over-webrtc-data-channels-00.txt

Gavin Llewellyn <> Wed, 10 July 2013 11:50 UTC

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Date: Wed, 10 Jul 2013 12:50:51 +0100
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From: Gavin Llewellyn <>
To: "Ejzak, Richard P (Richard)" <>
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Subject: Re: [MMUSIC] [dispatch] FW: New Version Notification for draft-marcon-msrp-over-webrtc-data-channels-00.txt
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As a co-author of draft-pd-msrp-webrtc-00, I support this new draft for
establishment of MSRP sessions between WebRTC endpoints.  The SDP
enhancements allowing re-use of the SCTP association is very much along the
lines of what we had in mind for the next version of our draft, but we have
not had time to complete it.  We will likely be implementing this as a
feature in our WebRTC library in the near future, as the DataChannel
implementations in browsers mature (support SCTP, reliable delivery, binary
data, etc).

Having said that, it would have been appreciated if the authors had
contacted Peter and/or myself to discuss the existing draft and its
limitations - we would have been happy to receive feedback and work
together to find the best solution going forward.

I cannot see the value in introducing DataChannel gateways as a means to
communicate with traditional TCP-based MSRP endpoints.  I believe this is
better catered for by the WebSocket-based solution, as described in
which already has client and server implementations, and is currently
in-use in a production environment.  Given the (intentional) similarities
between the WebSocket and DataChannel APIs, it is not difficult for the
client application to support both transports.  I would like to see a clear
justification for this aspect of the draft.

One minor correction: the opening paragraph of section 5.2.3 appears to
reference the wrong SDP syntax for sub-protocol-specific attributes; I
believe it should reference the syntax for the new "wdcsa" attribute.

Gavin Llewellyn

Gavin Llewellyn
Principal Design Engineer
Crocodile RCS Ltd
GPG key: 0xF8F6FFF2

On 9 July 2013 20:32, Ejzak, Richard P (Richard) <> wrote:

> Please note our proposed alternative to draft-pd-msrp-webrtc-00 for how to
> use DataChannel transport for MSRP.  Our draft does not place restrictions
> on the number of MSRP sessions that can be established within an SCTP
> association and describes alternatives for using a gateway to interconnect
> to existing MSRP endpoints.  The SDP extensions described are applicable to
> other potential DataChannel sub-protocols such as T.140, BFCP, T.38, etc.
> Richard
> -----Original Message-----
> From: []
> Sent: Monday, July 08, 2013 6:31 PM
> To: Ejzak, Richard P (Richard); MARCON, JEROME (JEROME)
> Subject: New Version Notification for
> draft-marcon-msrp-over-webrtc-data-channels-00.txt
> A new version of I-D, draft-marcon-msrp-over-webrtc-data-channels-00.txt
> has been successfully submitted by Jerome Marcon and posted to the IETF
> repository.
> Filename:        draft-marcon-msrp-over-webrtc-data-channels
> Revision:        00
> Title:           MSRP over WebRTC data channels
> Creation date:   2013-07-09
> Group:           Individual Submission
> Number of pages: 12
> URL:
> Status:
> Htmlized:
> Abstract:
>    The Real-Time Communication in WEB-browsers (RTCWeb) working group is
>    charged to provide protocols to support direct interactive rich
>    communication using audio, video, and data between two peers' web-
>    browsers.  For the support of data communication, the RTCWeb working
>    group has in particular defined the concept of bi-directional data
>    channels over SCTP, where each data channel might be used to
>    transport other protocols, called sub-protocols.  This document
>    specifies how the Message Session Relay Protocol (MSRP) can be
>    instantiated as a WebRTC data channel sub-protocol, using the SDP
>    offer/exchange to negotiate out-of-band the sub-protocol specific
>    parameters.  Two network configurations are documented: a WebRTC end-
>    to-end configuration (connecting two MSRP over data channel
>    endpoints), and a gateway configuration (connecting an MSRP over data
>    channel endpoint with an MSRP over TCP endpoint).
> The IETF Secretariat
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