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)
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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
