[SIPForum-discussion] Codec Prefrence Option (RTP Profile selectionin multiple Codec)
Herve Jourdain
herve.jourdain at mstarsemi.com
Wed May 21 02:20:41 UTC 2008
Hi,
Rtpmap is not mandatory for all codecs in the m line. Its only mandatory
for dynamic codecs. For the static ones, its encouraged to declare a
rtpmap, but its 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.
Its 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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://sipforum.org/pipermail/discussion/attachments/20080521/b5956ca1/attachment-0002.html>
More information about the discussion
mailing list