RE: [AVT] How is SDP a=fmtp used for RFC 2198?

Colin,

One more related question below...

> -----Original Message-----
> From: Colin Perkins [mailto:csp@csperkins.org] 
> Sent: Friday, April 09, 2004 5:03 AM
> To: Mundra, Satish
> Cc: paulej@packetizer.com; Gunnar Hellstrom; Tim Melanchuk; 
> magnus.westerlund@ericsson.com; avt@ietf.org
> Subject: Re: [AVT] How is SDP a=fmtp used for RFC 2198?
> 
> 
> On 8 Apr 2004, at 22:32, Mundra, Satish wrote:
> > Does this mean that if one wants to provide redundancy for 
> different 
> > encoding methods on "m=" line, one can not do so using a single RED 
> > PT?
> 
> Correct. The "a=fmtp:" lines tell the sender how to encode particular 
> data.
> 
> > See example below where redundancy is desired for both 97 and 98.
> >
> > m=audio 5678 RTP/AVP 0 97 98 99 100
> > a=rtpmap:97 telephone-event/8000
> > a=rtpmap:98 t140/8000
> > a=rtpmap:99 red/8000
> > a=rtpmap:100 red/8000
> > a=fmtp:99 97/97/97/97/97
> > a=fmtp:100 98/98/98
> 
> Sending this much redundancy is excessive, but the example is 
> syntactically correct.
> 

Another question:
----------------- 

The redundancy header fields "F" and "Block PT" enable a receiver to decode
the RED packet,
the level of redundancy, the PTs used for primary/secondary (and tertiary
etc.).  

For e.g.,

m=audio 5678 RTP/AVP 0 97 98 99 
a=rtpmap:97 telephone-event/8000
a=rtpmap:98 t140/8000
a=rtpmap:99 red/8000
a=fmtp:99 97/98

Any comination of 97 or 98 as primary/secondary/tertiary as payload for RED
can be 
decoded using the redundancy header fields. The largest possible RED packet
size (maximum redundancy levels allowed) can not be determined from above. 

Is "estimating the additional bandwidth" the motivation for specifying the
maximum redundancy levels for each primary and hence separate RED PTs ?

Satish Mundra

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