Subject: [Sipping] comments on draft-kang-sipping-transc-scenario-00

From: Jonathan Rosenberg <[email-masked]>
Date: Sun, 06 Nov 2005 11:11:34 -0500

>  The transit party SHOULD provide all transcoding capability to the 
>    calling party and called party during call negotiation in call set up 
>    procedures[12-13]. This minimizes codec mismatch call setup failure 
>    due to a lack of codec negotiation information. 

what exactly is a "transit party", and what do you do in situations 
where there isn't a transit provider? I.e., two enterprises calling each 
other.

Also, I don't understand the references - 12/13 are to caller prefs. How 
is this relevant?

> A discriminator for codec characteristics SHOULD provide the 
>    information whether it will be transcoded or not. The discriminator 
>    prevents it from re-transcoding or transcoding-cycling occurring. 

what discriminator? Are you referring to an existing SDP attribute? Or 
proposing that a new one be developed?

> If T and B can not support a codec, T SHOULD reply to A with Not 
>    Acceptable:406 and Not transcoding supportable A at T after receiving 
>    Not Acceptable Here: 488 from B. 

I can't quite follow what you are proposing here. I think you are 
assuming that the offer sent by T to B contains all of the codecs 
supported by T, but none of those are compatible with B. Is that right?

406 seems the wrong response here. Also, your notation for indicating 
errors is hard to understand. Typeically the convention is response-code 
(reason), i.e., 406 (Not Acceptable). As such, I can't follow how you 
propose indicating "Not Acceptable:406 and Not transcoding supportable A 
at T". This seems like two error codes?

> T1 sends to T2 the codec a from A and the Tb from T1. T2 sends to T3 
>    the a from A, the Tb from T1, and the Tc from T2. T3 sends to B the a 
>    from A, the Tb from T1, the Tc from T2, and the Td from T3. 

You might want to explain how this can happen. Its not clear that it 
really can given the current transcoding models. It can if you have 
intermediaries which act as b2bua and force transcoding without it being 
requested.

Thanks,
Jonathan R.
-- 
Jonathan D. Rosenberg, Ph.D.                   600 Lanidex Plaza
Director, Service Provider VoIP Architecture   Parsippany, NJ 07054-2711
Cisco Systems
[email-masked]                              FAX:   (973) 952-5050
http://www.jdrosen.net                         PHONE: (973) 952-5000
http://www.cisco.com

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