Subject: [AVT] Use of RFC 2793(bis) between gateways

From: Tom Taylor <[email-masked]>
Date: Wed, 09 Feb 2005 16:44:05 -0500

I'm currently updating draft-ietf-avt-rfc2833bisdata along the lines I've 
indicated earlier, and in particular rewriting the V.18 section.  I have added 
words encouraging the use of RFC 2793(bis) between gateways when possible.  Having 
said that, however, I can see the need for another RFC providing advice on how to 
do it.  I have two particular issues:

1) How does such a session start up?  Does either gateway act as a proxy for the 
far-end terminal?  Do both of them?  Do they each try to appear to the terminal at 
their end as if they were a similar terminal?  As a result, do they modify any 
V.8- or similarly-signalled capabilities they receive from the remote end?

This question would have to be worked through using various terminal types and 
startup sequences.

2) I see the possibility that a gateway knows how to convert V.21 signals, for 
example, into RFC 2793(bis) payload, but doesn't understand V.23.  How does it 
signal which modems it understands?

On a peripherally related topic, I'm adding a generic voice-band data indicator 
event to draft-ietf-avt-rfc2833bisdata to allow for the case where the sending 
gateway recognizes that it is receiving modem-like tone sequences but doesn't 
recognize the particular modem involved.

Tom Taylor

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
https://www1.ietf.org/mailman/listinfo/avt

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From: "Gunnar Hellstrom" <[email-masked]>
Date: Thu, 10 Feb 2005 00:07:30 +0100

Tom,
the issues you bring up are covered in various ways in ITU-T H.248.2, V.152 and draft
V.151.

My view:

It is of very little interest to convey detailed information about achieved modes of
operation in both gateways. The looser coupling the better.

One gateway may negotiate with an EDT, the other with a Baudot textphone, and both have
one audio channel and one rfc2793bis text channel in between them to convey the media.
There is no need in that case to tell details about achieved modes for setting up the
call.

The signaling could be with sdp, setting up the channels.

V.18 supporting all textphone modes is simple. Introducing signalling about modes seems to
introduce more complexity.

However, in the ITU protocols there are ways to signal capabilities and achieved modes.

Gunnar
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>-----Original Message-----
>From: [email-masked] [mailto:[email-masked]]On Behalf Of Tom
>Taylor
>Sent: Wednesday, February 09, 2005 10:44 PM
>To: [email-masked]
>Subject: [AVT] Use of RFC 2793(bis) between gateways
>
>