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List:       sip-implementors
Subject:    RE: [Sip-implementors] Codec negotiation questions (SDP)
From:       Jonathan Rosenberg <jdrosen () dynamicsoft ! com>
Date:       2001-04-27 9:06:24
Message-ID: B65B4F8437968F488A01A940B21982BF0128C070 () DYN-EXCH-001 ! dynamicsoft ! com
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> -----Original Message-----
> From: Takumi Ohba [mailto:ohba.takumi@lab.ntt.co.jp]
> Sent: Thursday, April 26, 2001 8:39 AM
> To: sip-implementors@cs.columbia.edu
> Subject: RE: [Sip-implementors] Codec negotiation questions (SDP)
> 
> 
> Hi,
> 
> I would like to add another question concerning codec negotiation.
> 
> At 4:22 PM -0400 01.4.25, Brett Tate wrote:
> > Note: the codecs in an SDP only signify the
> > listening codecs.  They are not used to
> > identify what you plan to send unless maybe
> > a oneway media session is being established.
> 
> If an SDP includes multiple codecs, the sender of the SDP 
> must be able to
> receive any RTP packets whichever codec in the SDP is used 
> during a call.
> In this case, the sender of the SDP must check the PT field 
> in each RTP
> packet and decide the way of decoding for each packet.
> 
> On the other hand, if one codec were selected during a call setup, the
> performance for the decoding wuold be greatly improved.
> 
> What is the merit of allowing multiple codecs for one RTP stream?
> Is there any positive reason why SIP does not negotiate 
> codecs to select
> only one for one RTP stream?

See:
http://www.cs.columbia.edu/~hgs/sip/faq/cache/103.html

---
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com

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