[Standards] UPDATED: XEP-0301 (In-Band Real Time Text)

Gunnar Hellström gunnar.hellstrom at omnitor.se
Mon Jul 9 14:30:43 UTC 2012


On 2012-07-09 13:31, Edward Tie wrote:
> 8.3 Textphones and TTYs in the PSTN (Informational)
> Real-time text is also implemented in the PSTN, through various text 
> telephone modulation protocols specified in ITU-T V.18 *or V.22 or 300 
> baud ASCII or DTMF.*  It is possible to implement gateways between 
> audio and XEP-0301 based real-time text in IP networks and textphones 
> (called TTY in North America)  based on V.18*or V.22 or *any of its 
> Annexes in the PSTN. When designing such gateways, the limitations in 
> speed, transmission direction, character sets and media simultaneity 
> valid for these textphone protocols must be taken into consideration 
> as well as the user need to be able to at least alternate between 
> audio and real-time text during the call.

Edward,
We shall not try to tell the whole story about PSTN text telephony (and 
TTY) in this XMPP document.
I rather want to follow Peter's advice to reduce it.

XEP-0301 has its important role as improvement of user experience of 
XMPP text messaging. Details on interoperability should be specified 
elsewhere.  I suggest a very brief paragraph to be kept about legacy 
textphone interoperability. (coming soon)

---------------------------------------------------------------------------------------------------------
Anyway, for your info,
ITU-T V.18 has one annex for each of the legacy textphone protocols: 
Baudot (=TTY), V.21, DTMF, V.23(Minitel and even Prestel), Bell 
103("ASCII"), and even for V.18 itself. You wanted to add V.22 to the 
list. I know it is in use in The Netherlands, but The Netherlands never 
wanted it to be included in V.18. So, V.22 is not standardized anywhere 
as a textphone transport, and as I understand it, all Dutch V.22 
textphones can also do automatic switching to DTMF based text telephony.
Therefore mentioning "V.18 or its annexes" could be as far as we go 
here. ( if at all...)

Gunnar




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