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

Andrea Puddu androjoker at hotmail.com
Tue May 20 17:40:09 UTC 2008

Hello Rashid,

the second choice (100) is referred to telephone-event. It is not  a pure codec but it is a way  for the phone to say ("ok I support telephone event"). telephone events are used for example to send DTMF out-of-band.


Date: Tue, 20 May 2008 08:17:49 -0700
From: rshakil at covad.com
To: discussion at sipforum.org
Subject: [SIPForum-discussion] Codec Prefrence Option (RTP Profile selection	in 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

a=rtpmap:18 G729/8000

a=rtpmap:100 telephone-event/8000

a=fmtp:100 0-11



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