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

On 9 Apr 2004, at 19:17, Mundra, Satish wrote:
...
> 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 ?

No, the receiver can decode the data without this information. The 
"a=fmtp:" lines tell the sender what is required for the session. See 
RFC 2198 section 5.

-- 
Colin Perkins
http://csperkins.org/

_______________________________________________
Audio/Video Transport Working Group
avt@ietf.org
https://www1.ietf.org/mailman/listinfo/avt