[SIPForum-discussion] What does 101 represents in media format list?

[AnilKumar Yadagiri]

To refer whats in "m" line, refer the "a" attribute as well. From RFC 4566:

*a=rtpmap:<payload type> <encoding name>/<clock rate> [/<encoding parameters>]

**

*         This attribute maps from an RTP payload type number (as used in
         an "m=" line) to an encoding name denoting the payload format
         to be used.  It also provides information on the clock rate and
         encoding parameters.  It is a media-level attribute that is not
         dependent on charset.

         Although an RTP profile may make static assignments of payload
         type numbers to payload formats, it is more common for that
         assignment to be done dynamically using "a=rtpmap:" attributes.
         As an example of a static payload type, consider u-law PCM
         coded single-channel audio sampled at 8 kHz.  This is
         completely defined in the RTP Audio/Video profile as payload
         type 0, so there is no need for an "a=rtpmap:" attribute, and
         the media for such a stream sent to UDP port 49232 can be
         specified as:

            m=audio 49232 RTP/AVP 0

         An example of a dynamic payload type is 16-bit linear encoded
         stereo audio sampled at 16 kHz.  If we wish to use the dynamic
         RTP/AVP payload type 98 for this stream, additional information
         is required to decode it:

            *m=audio 49232 RTP/AVP 98
            a=rtpmap:98 L16/16000/2*

         Up to one rtpmap attribute can be defined for each media format
         specified.  Thus, we might have the following:

            m=audio 49230 RTP/AVP 96 97 98
            a=rtpmap:96 L8/8000
            a=rtpmap:97 L16/8000
           * a=rtpmap:98 L16/11025/2*


*

**m=<media> <port>/<number of ports> <proto> <fmt> ...*


<fmt> is a media format description.  The fourth and any subsequent
      sub-fields describe the format of the media.  The interpretation
      of the media format depends on the value of the <proto> sub-field.

      If the <proto> sub-field is "RTP/AVP" or "RTP/SAVP" the <fmt>
      sub-fields contain RTP payload type numbers.  When a list of
      payload type numbers is given, this implies that all of these
      payload formats MAY be used in the session, but the first of these
      formats SHOULD be used as the default format for the session.  For
      dynamic payload type assignments the "a=rtpmap:" attribute (see
      Section 6 <http://tools.ietf.org/html/rfc4566#section-6>) SHOULD
be used to map from an RTP payload type number
      to a media encoding name that identifies the payload format.  The
      "a=fmtp:"  attribute MAY be used to specify format parameters (see
      Section 6 <http://tools.ietf.org/html/rfc4566#section-6>).


So, in your case, 101 would be having a sampling definition/RTPMAP in the
"a" line.

On Fri, Mar 29, 2013 at 4:25 AM, Deepa Mhaisane <deepa at gslab.com> wrote:

>  Hi All,
>
> Can anyone please explain what does codec 101 represent in media of SDP.
> e.g m=audio 25008 RTP/AVP 0* **101 *13
>
> Regards
> Deepa M
> GS Lab.
>
>
>
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