Subject: Re: [AVT] Address/port to which separate FEC stream is directed

From: Rajesh Kumar <[email-masked]>
Date: Fri, 01 Feb 2002 12:01:57 -0800

I agree with the justification for the requirement. However, it is 
necessary to mandate that the separate FEC stream constitute a separate 
session with its unique port? It it possible to work around the timestamp 
problem, and use share the session (IP address and RTP port) with the media 
packets. There are applications in which the port number range exhaustion 
is a problem.

So my question is: Can separate media/FEC sessions be interpreted as a 
"required option" (i.e. something which must be supported if the other side 
asks for it) and not as a hard-and-fast requirement in all cases? I am 
hoping that such leeway is permitted by rfc2733.

Rajesh

At 11:20 PM 1/31/2002 -0500, you wrote:

>Rajesh Kumar wrote:
> >
> > Jonathan, Henning
> >
> > rfc2733 seems to mandate that a separate FEC stream, when produced, must
> > be
> > sent to a different port or IP address. Isn't is possible to send the
> > FEC
> > packets to the same port/address as the media packets? Even if this is
> > do,  you cannot omit the parameters <port>, <network type>,  <address
> > type>
> > and <connection address>, right?
>
>Well, my recollection is fuzzy here, but I recall that we decided that a
>separate RTP session was better. One reason that I remember was rtp
>header compression/rohc, since the timestamp predictors would be wrong
>every time a FEC packet was emitted. I suspect there are other reasons
>too, but that is the one I remember.
>
>Anyway, rfc2733 does explicitly say that the FEC stream is sent as a
>separate RTP session. Its in section 3:
>
>  The FEC packets are not sent in the same RTP stream as the media
>    packets. They can be sent as a separate stream, or as a secondary
>    codec in the redundant codec payload format [5].
>
>-Jonathan R.
>
>--
>Jonathan D. Rosenberg, Ph.D.            72 Eagle Rock Avenue
>Chief Scientist                         First Floor
>dynamicsoft                             East Hanover, NJ 07936
>[email-masked]                 FAX: (973) 952-5050
>http://www.jdrosen.net                  PH:  (973) 952-5000
>http://www.dynamicsoft.com

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From: Colin Perkins <[email-masked]>
Date: Fri, 01 Feb 2002 15:29:21 -0500

You can use RFC 2198 redundancy to piggyback the FEC onto the original
packets.

Colin