Re: [dcp] Issues with adoption of DCCP for RTP applications

"Andrei Gurtov" <gurtov@cs.helsinki.fi> Tue, 18 June 2002 08:01 UTC

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From: Andrei Gurtov <gurtov@cs.helsinki.fi>
To: dcp@ietf.org
References: <3.0.32.20020614081346.00e1d9f0@mail.real.com>
Subject: Re: [dcp] Issues with adoption of DCCP for RTP applications
Date: Tue, 18 Jun 2002 10:59:35 +0300
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I agree that issues of running RTP over DCCP need to be resolved. If DCCP is
to gain wide acceptance it should allow applications to utilize numerious
payload profiles built around RTP. Additionally, there are nice RTP
extensions like SR-RTP providing messaging (application data unit)
transport, selective reliability and timeliness. I think integration of DCCP
with RTP should be included explicitly into the requirements draft.

Andrei


----- Original Message -----
From: "Damon Lanphear" <damonlan@real.com>
To: <dcp@ietf.org>
Sent: Friday, June 14, 2002 6:13 PM
Subject: [dcp] Issues with adoption of DCCP for RTP applications


> A potential issue for the adoption of DCCP for RTP applications is the
> redundant use of data in the two protocol layers.  Both DCCP and RTP place
> a sequence number in the data packet header, and both DCCP and RTP employ
a
> receiver report mechanism.  The receiver report mechanism, in the RTP
case,
> can be extended to transmit the same data as would be placed in a
> DCCP-style feedback packet.
> It is important to be clear about how the "redundant" data is actually
> used by both DCCP and RTP.  Both DCCP and RTP use sequence numbers to
> detect packet loss.  For RTP applications, sequence numbers may be used to
> establish frame ordering, to perform ARQ in a time sensitive way, and to
> compute loss metrics that have relevance to the overlying application.
RTP
> must therefore make the sequence number known to the overlying application
> in order to support such features, whereas DCCP does not.  Simply stated,
> the problem domains of DCCP and RTP are sufficiently different that the
> redundancy of the sequence number datum may be justifiable.
> The same principle is applicable to the issue of redundant information in
> receiver reports.  In both DCCP and RTP the form of receiver reports is
> reasonably flexible.  There is a clear separation between RTP and DCCP of
> the application's concerns and the concerns of a congestion control
> mechanism, respectively.  This seperation assists in maintaining the
> respective protocols appropriateness for a variety of applications.
> What are the group's thoughts on these issues?  Are they seemingly moot
> as my current line of thinking implies, or ought we work to reconcille
such
> redundancies?
>
> damon
>
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