Subject: [Sip] Reg draft-ietf-avt-rtp-mime-05.txt

From: Sharma Kanchinadham <[email-masked]>
Date: Tue, 27 Nov 2001 08:54:51 -0600

Hi,

I have some comments/observations on draft-ietf-avt-rtp-mime-05.txt. Please
provide your inputs/opinion.

The link to the draft is:
http://search.ietf.org/internet-drafts/draft-ietf-avt-rtp-mime-05.txt

1. The parameter "annexb" is not always applicable. For example in G.711 the
Silence Suppression is Appendix II. Hence there needs to be more values such
as "appendix_II" and "cisco_vad".

2. The second item is currently if the "annexb" parameter is ommitted then
it is assumed that Silence Suppression is supported (basically it is treated
as if it is "yes"). This would create backward compatibility problems when
interworking with platforms that do not want to do the development. Is it
possible to reverse this ?

Thanks ,
Sharma Kanchinadham
Worldcom

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---

From: Colin Perkins <[email-masked]>
Date: Tue, 27 Nov 2001 10:19:21 -0500

>http://search.ietf.org/internet-drafts/draft-ietf-avt-rtp-mime-05.txt

You should really ask this question on the AVT group's mailing list
<[email-masked]>, since it doesn't relate to SIP.

>as "appendix_II" and "cisco_vad".

The annexb parameter is defined only for G.729. It cannot be applied to
other payload formats.

>possible to reverse this ?

There is no backwards compatibility issue, since this parameter is only
valid for G729, and was introduced at the same time as that payload format. 

Colin

---

From: Sharma Kanchinadham <[email-masked]>
Date: Tue, 27 Nov 2001 10:12:24 -0600

Hi ,

Thanks for the info on the AVT working group.

Regarding item 1 what i am trying to say is that:

There needs to be a new MIME subtype of G.711 as shown below:

MIME media type name: audio
MIME subtype name: G711
Required parameters: None
Optional parameters:

               appendix_II: indicates that appendix_II, silence suppression
                             is used.

Also there can be 2 types of Silence Suppression with G.729 i.e. G.729
annexb, or some kind of a proprietary silence suppression for example: G.729
with Cisco VAD. Hence it is suggested that there be a 'cisco_vad' or
'unspecified_vad' as another optional parameter under G.729.

The below mentioned draft is being considered as a basis for Silence
Suppression negotiation. In this connection, the second point assumes
significance. Assume a SIP client that is not conformant to this Internet
Draft. Hence it would not pass the 'annexb' parameter etc. However the draft
assumes that if 'annexb' is not passed it supports 'annexb'. Hence the far
end might start sending Silence Suppression packets and the SIP client may
not handle the SS packets properly. Thats what i mean by saying that it
causes backward compatibility problems.

Please see if you agree.

Thanks ,
Sharma Kanchinadham
Worldcom

============================================================================

-----Original Message-----
From: Colin Perkins [mailto:[email-masked]]
Sent: Tuesday, November 27, 2001 9:19 AM
To: [email-masked]
Cc: [email-masked]
Subject: Re: [Sip] Reg draft-ietf-avt-rtp-mime-05.txt

Colin