[Standards] RTT, take 2

Gunnar Hellström gunnar.hellstrom at omnitor.se
Thu Jun 23 16:29:16 UTC 2011


Hi,
I saw a challenge to say something in the discussion on
Re: http://xmpp.org/extensions/inbox/realtimetext.html

-----Extract from Peter and Mark's discussion------------

Section 7.1 talks about interoperability with RFC 4103 and T.140. How
>
>     does an XMPP entity negotiate an RTT session with a SIP entity? (I'm
>     wondering if we need a Jingle application type for RTT...)
>
>
> The RFC4103 people are covering that.  I've published a SUPPLEMENT 
> document on realjabber.org <http://realjabber.org> that briefly 
> touches upon this; and will be expanded.  Gunnar Helstrom of Omnitor, 
> is the go-to guy for this.
>
-------

Yes, a way to express capabilities of both kinds of RTT transport and 
negotiate their use is needed.

There are many foreseeable situations where this is desired.

I hoped the SIXPAC action in IETF to take the lead and define a 
framework for one kind of interoperability situation - when two SIP 
entities need to negotiate between use of RFC 4103 declared as m=text 
and payload types red and t140 in sdp, versus a XMPP-RTT session 
declared in some yet undefined SIP headers. But SIXPAC activity is low, 
so we need to check the need for this and work on it separately.

Another situation is a straightforward gateway between SIP sessions with 
RFC 4103 based RTT, and XMPP with XMPP-RTT, where the session initiator 
of course want to get a confirmation if the intended RTT stream was 
successfully established in the far leg of the session.

The gateway case may be needed for the important emergency service case. 
RFC 5012 and draft-ietf-ecrit-phonebcp have only a firm description of 
use of SIP with RFC 4103 for RTT in emergency calls. XMPP is only 
vaguely mentioned, and naturally not XMPP-RTT because of its young age.
Future users of XMPP-RTT may expect to be able to contact emergency 
services using their RTT enabled communication, so it must be considered 
if it is to be arranged through a gateway or natively in the emergency 
service interface.

And, yes, a Jingle application type for Real-Time text will be a good 
step to enable some of these interoperability situations in a smooth way.

I think we need, as Mark says, work in parallell on this topic and see 
if it will influence the XMPP-RTT spec.

I have also a small editorial note on the spec.
In section 7.2, there is this paragraph:

"It is noted there is also another real-time text standard (RFC 4103, 
RFC 5194), used for SIP messaging and real-time text. In the situation 
where an implementor needs to decide which real-time text standard to 
use, it is generally recommended to use the real-time text extension of 
the specific instant messaging standard in use for that particular 
conversation."

I see a mixup of messaging, and real-time here.
I suggest rewording to:

"It is noted there is also another real-time text standard (RFC 4103, 
RFC 5194), used for SIP *sessions* with real-time text. In the situation 
where an implementor needs to decide which real-time text standard to 
use, it is generally recommended to use the real-time text 
*specification* of the specific *session control* standard in use for 
that particular *session*."


/Gunnar










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