NK,
By default RTP goes on an even port and RTCP goes on the following odd
port. IIRC (I'm not looking this up) if the declared port is odd you are
still supposed to round it down to the previous even one for the RTP and
use the odd one for the RTCP.
But then look at RFC 3605. It defines a=rtcp:<port>. With that, you can
put the RTCP on a port independent of where the RTP goes. In that case
the odd port in the m-line should be honored for the RTP.
Unfortunately, in general if you use a=rtcp in an offer you have no
guarantee that the answerer will support this extension.
Thanks,
Paul
On 1/10/14 11:07 AM, NK wrote:
> Dear All,
>
> Can you please help me on one issue, where one of client is complaining
> that they need RTP even port in SDP not the ODD. Which is Fax Call.
>
> Although I checked the RFC 2327 & 4566 for SDP. In RFC 2327 its clearly
> mentioned that we should use even port for RTP compliance, whereas in RFC
> 4566 Its not clearing that is it MANDATORY or not.
>
> Can you please help me on this.
>
>>From RFC2327
>
>
>
> m=<media> <port> <transport> <fmt list>
>
>
>
> A session description may contain a number of media descriptions. Each
> media description starts with an "m=" field, and is terminated by either
> the next "m=" field or by the end of the session description.A media field
> also has several sub-fields:
>
> o The first sub-field is the media type. Currently defined media
> are "audio",
> "video", "application", "data" and "control", though this list may be
> extended as new communication modalities emerge (e.g.,telepresense).The
> difference between "application" and "data" is that the former is a media
> flow such as whiteboard information, and
>
> the latter is bulk-data transfer such as multicasting of program executables
> which will not typically be displayed to the user. "control" is used to
> specify an additional conference control channel for the session.
>
> o The second sub-field is the transport port to which the media stream
> will be sent. The meaning of the transport port depends on the network
> being used as specified in the relevant "c" field and on the transport
> protocol defined in the third sub-field. Other ports used by the media
> application (such as the RTCP port, see
>
> [2]) should be derived algorithmically from the base media port.
>
>
> *Note: For transports based on UDP, the value should be in the range 1024
> to 65535 inclusive. For RTP compliance it should be an even number.*
>
>
> *Regards,*
>
> *Nitin Kapoor*
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