Subject: RE: [SIP] comments on SDP section/bis-03

From: Jonathan Rosenberg <[email-masked]>
Date: Fri, 1 Jun 2001 03:10:12 -0400

> -----Original Message-----
> From: Shan Lu [mailto:[email-masked]]
> Sent: Thursday, May 31, 2001 1:45 PM
> To: [email-masked]
> Subject: [SIP] comments on SDP section/bis-03
> 
> 
> Hi,
> 
> 1. From Section B.3.1 (3rd paragraph):
> 
> "If the stream in the answer is marked as sendrecv, it MUST 
> contain at 
> least one codec the answerer is willing to both send and 
> receive with, 
> from amongst those listed in the offer. The stream MAY indicate 
> additional codes, not listed in the corresponding stream in 
> the offer, 
> that the answerer is willing to receive with."

Actually, the asymmetric case will not be that common based on the
interpretation of ordering as implying preferences. If A INVITEs B with
codecs 1,2 in that order, and B supports both, the answer has 1,2. Now,
according to the spec, A SHOULD send with codec 1, and B SHOULD send with
codec 1. The only trouble that would arise is if B returns, in the 200 OK,
codecs 2,1 in that order. THis leads to asymmetric operation. So, I am more
than willing to add the following piece of text instead:

"Although the answerer MAY list the codecs in their desired order of
preference, it is STRONGLY RECOMMENDED that unless there is a specific
reason, the answer list codecs in the same relative order they were present
in the offer. In other words, if a stream in the offer lists codecs 8, 22
and 48, in that order, and the answerer only supports codecs 8 and 48, it is
STRONGLY RECOMMENDED that, if the answer has no reason to change it, the
ordering of codecs in the answer be 8, 48, and not 48, 8. This helps ensure
that the same codec is used in both directions."

Now, this can't guarantee it, since one side may decide to change codecs
based on adaptation. 

The bit about packetization delay needs to be in there; I had forgotten to
mention it in -03 and will add it to -04. 

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

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---

From: Shan Lu <[email-masked]>
Date: Fri, 01 Jun 2001 12:07:36 -0400

The text looks good to me and will be helpful to eliminate some of the 
codec mismatch problems at Bakeoffs.

Regards,

Shan Lu

NexTone Communications