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

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 ?  
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

Satish Mundra

> -----Original Message-----
> From: Colin Perkins [mailto:csp@csperkins.org] 
> Sent: Monday, April 05, 2004 8:33 AM
> To: Tim Melanchuk
> Cc: magnus.westerlund@ericsson.com; avt@ietf.org; 
> paulej@packetizer.com; Gunnar Hellstrom
> Subject: Re: [AVT] How is SDP a=fmtp used for RFC 2198?
> 
> 
> On 2 Apr 2004, at 19:45, Tim Melanchuk wrote:
> > to clarify with respect to using rfc2198 redundancy with rfc2833 
> > telephone events, the sdp for the example on page 10 of 
> rfc2833, which 
> > shows 3 events in one packet, would have had:
> >
> > a=rtpmap:96 red/8000
> > a=rtpmap:97 telephone-event/8000
> > a=fmtp:96 97/97/97
> >
> > as well, at most 3 telephone-events could occur in one 
> packet. is this 
> > interpretation correct?
> 
> Yes, according to Section 5 of RFC 2198:
> 
>     To receive a redundant stream, this is all that is 
> required.  However
>     to send a redundant stream, the sender needs to know 
> which codecs are
>     recommended for the primary and secondary (and tertiary, etc)
>     encodings.  This information is specific to the redundancy format,
>     and is specified using an additional attribute "fmtp" 
> which conveys
>     format-specific information.  A session directory does 
> not parse the
>     values specified in an fmtp attribute but merely hands it to the
>     media tool unchanged.  For redundancy, we define the format
>     parameters to be a slash "/" separated list of RTP payload types.
> 
> Colin
> 
> 
> _______________________________________________
> Audio/Video Transport Working Group
> avt@ietf.org
> https://www1.ietf.org/mailman/listinfo/avt
> 

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