Op 09/07/2012 16:30, Gunnar Hellström schreef:
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.
yes. it's true
So, V.22 is not standardized anywhere as a textphone transport, and as
I understand it,
Only Dutch next generation textphone (HGT teksttelefoon) supports V.22
(1200) and V.22bis. It called TDD.
See dutch summery:
http://home.planet.nl/~hgtgm000/Downloads/TT_appendix_A_en_B.pdf
all Dutch V.22 textphones can also do automatic switching to DTMF
based text telephony.
Yes. Dutch old generation textphones (Goedhart visicom and PTT
teksttelefoon) supports only DTMF.
