[SIPForum-discussion] Codec Prefrence Option (RTP Profile selectionin multiple Codec)

[Donald Lee]

Very clear, thanks.

On Wed, May 21, 2008 at 10:20 AM, Herve Jourdain <
herve.jourdain at mstarsemi.com> wrote:

>  Hi,
>
>
>
> Rtpmap is not mandatory for all codecs in the m line. It's only mandatory
> for dynamic codecs. For the static ones, it's encouraged to declare a
> rtpmap, but it's not mandatory.
>
> So it does it for G.729, but not for G.711 µLaw, which is the codec
> identified as "0" in your m line.
>
> It's possible to do so, even if declaring it also as a rtpmap is strongly
> encouraged by the RTP RFCs.
>
> Static codecs are described in the RTP/AVP RFC, and so should be supported
> by all VoIP SW even without rtpmap.
>
>
>
> As for the precedence, it comes from the order in the m line, regardless of
> rtpmap being present or not. Rtpmap just describes the codec by its MIME
> type, and links it to a Payload Type used to transport it, no more no less.
>
>
>
> Regards,
>
>
>
> Herve
>
>
>  ------------------------------
>
> *From:* discussion-bounces at sipforum.org [mailto:
> discussion-bounces at sipforum.org] *On Behalf Of *Shakil, Rashid
> *Sent:* mardi 20 mai 2008 17:18
> *To:* discussion at sipforum.org
> *Subject:* [SIPForum-discussion] Codec Prefrence Option (RTP Profile
> selectionin multiple Codec)
>
>
>
>
>
> Hello,
>
>
>
> Quick question I was analyzing the SDP which my softswtich is sending in
> response to an INVITE for an inbound call I received from my SIP peer. I
> noticed that I can see two codec choices in media description (m=) line but
> the rtpmap attribute of the SDP just showing one. Can any one tell what does
> it means and which one has precedence if I have media description and rtpmap
> present in an SDP?
>
>
>
> c=IN IP4 5.5.5.2
>
> t=0 0
>
> *m=audio 21092 RTP/AVP 18 0 100*
>
> *a=rtpmap:18 G729/8000*
>
> a=rtpmap:100 telephone-event/8000
>
> a=fmtp:100 0-11
>
>
>
>
>
> _______________________________________________
> This is the SIP Forum discussion mailing list
> TO UNSUBSCRIBE, or edit your delivery options, please visit
> http://sipforum.org/mailman/listinfo/discussion
> Post to the list at discussion at sipforum.org
>
>


-- 
BR
Donald
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://sipforum.org/pipermail/discussion/attachments/20080522/1328bcd7/attachment-0002.html>