Subject: Re: [MMUSIC] How big can SDP get

From: Randell Jesup <[email-masked]>
Date: Mon, 26 Jun 2006 12:11:48 -0400

Magnus Westerlund <[email-masked]> writes:
>One thing is obvious. It is easy to make a large SDP file. Attached is a
>10744 bytes large SDP.
>
>The SDP contains some errors as I have no interest of specifying unique
>ports for all ICE flows for example. However it should be possible to
>understand.
>
>The session is intended to be a offer from a transcoding gateway to a
>session receiver of a presentation session with a text chat session. So
>there is one video showing the presenter, protected by a separate FEC
>stream (ULP). There is a second video with retransmission for the document
>cam. There is one  audio stream protected by a second stream of FEC. Then
>there is a text session for chatting and a subtitle session. Add ICE, ANAT,
>SRTP with security description and few other small extension and you broke
>the 10k barrier.

And if we add something to allow for secure-or-non-secure connections (see
draft-andreasen-mmusic-sdp-capability-negotiation-00.txt) or grouping
(RFC-whatever) or mime multipart, SIP-level overhead (auth lines), etc and
you might be able to double or possibly triple that without adding more
codecs or streams.  Admittedly, it's a pretty nasty/odd variant you give,
but then again that's the point.

Good idea using H264 in all possible packetization modes, though the H264
stuff could be expanded quite a bit more with more optional parameters,
especially if there are variant payloads for different profiles (different
parameter sets for example).  And you didn't even both to offer "normal"
audio codecs like PCMU/A, 729, etc (and include the rtpmaps for all of
them), nor RFC2833 payloads.

I wonder if there's a way to mix TCP and UDP in SIP to get (some of) the
advantages of both.  This was/is a common trick in realtime IP stuff such
as online games (the first example I know of it was in 'netrek' back in
circa 1992-ish, before the web).  Or maybe to use TFRC-style congestion
avoidance in a reliable datagram service.  RDP (RFC's 908/1151) doesn't
seem to use a TCP-friendly congestion control from a quick look.

-- 
Randell Jesup, Worldgate (developers of the Ojo videophone), ex-Amiga OS team
[email-masked]
"The fetters imposed on liberty at home have ever been forged out of the weapons
provided for defence against real, pretended, or imaginary dangers from abroad."
		- James Madison, 4th US president (1751-1836)

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---

From: "Mark Handley" <[email-masked]>
Date: Mon, 26 Jun 2006 17:36:24 +0100

On 5/17/06, Magnus Westerlund <[email-masked]> wrote:
> Hi,

Although it still fits in a single 1500-byte UDP packet if you gzip it :-)

 - Mark