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

Shakil, Rashid rshakil at covad.com
Thu May 22 05:00:36 UTC 2008

Yes very comprehensive and detailed response..Thanks 


-----Original Message-----
From: Donald Lee [mailto:baolovebao at gmail.com] 
Sent: Wednesday, May 21, 2008 10:53 PM
To: Herve Jourdain
Cc: Shakil, Rashid; discussion at sipforum.org
Subject: Re: [SIPForum-discussion] Codec Prefrence Option (RTP Profile selectionin multiple Codec)


Very clear, thanks.

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



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.







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)





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

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


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://sipforum.org/pipermail/discussion/attachments/20080521/a0a72ab9/attachment-0002.html>

More information about the discussion mailing list