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

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