Op 09/07/2012 11:40, Mark Rejhon schreef:
On Mon, Jul 9, 2012 at 2:09 AM, Edward Tie <fam...@xs4all.nl
<mailto:fam...@xs4all.nl>> wrote:
Hi Mark,
I want to add on history of textphone and XMPP to old
telephones that uses older protocols:
Hello Edward,
Good history -- however, this is already beyond scope of XEP-0301.
Anybody can create an XEP-0301 gateway that converts to almost
anything (including any of the protocols you mention).
One sentence will be added to satisfy this.
http://xmpp.org/extensions/xep-0301.html#interoperability_considerations
To just simply mention that "...a gateway can be built as a part of a
complete solution (i.e. with optional audio, such as to support Voice
Carry Over) to support any legacy protocols used by TTY and textphones
using various protocols including Baudot, 300 baud ASCII, DTMF, ITU-T
V.18, ITU-T V.22, and other text transmission protocols". (wording
will be refined upon consultation within R3TF including Gregg
Vanderheiden who helps out in this area)
There was a lot of debate within our group (i.e. Gregg Vanderheiden)
about the careful choice of wording, because we need to be sensitive
about the "complete solution" (such as worldwide interoperability, the
ability to use voice, accessibility to people who don't have Internet,
etc).
it's now a clear history :-)
Protocols
There are many different textphone standards.
Baudot code
The original standard used by TTYs is the Baudot code
<http://en.wikipedia.org/wiki/Baudot_code> implemented
asynchronously at either 45.5 or 50 baud, 1 start bit, 5 data
bits, and 1.5 stop bits. Baudot is a common protocol in the US.
Turbo Code
In addition to regular Baudot, the UltraTec
<http://en.wikipedia.org/w/index.php?title=UltraTec&action=edit&redlink=1>
company implements another protocol known as Enhanced TTY, which
it calls "Turbo Code," in its products. Turbo Code has some
advantages over Baudot protocols, such as a higher data rate, full
ASCII <http://en.wikipedia.org/wiki/ASCII> compliance, and
full-duplex capability. However, Turbo Code is proprietary, and
UltraTec only gives its specifications to parties who are willing
to license it.
Other legacy protocols
Other protocols used for text telephony are European Deaf
Telephone (EDT) and Dual-tone multi-frequency signaling
<http://en.wikipedia.org/wiki/Dual-tone_multi-frequency_signaling>
(DTMF).
The ITU V series recommendations are a collection of early modem
standards approved by the ITU <http://en.wikipedia.org/wiki/ITU>
in 1988.
* ITU V.21 <http://en.wikipedia.org/wiki/ITU_V.21> [1]
<http://www.itu.int/rec/T-REC-V.21/recommendation.asp?lang=en&parent=T-REC-V.21-198811-I>
specifies 300 bits per second duplex mode.
* ITU V.23 <http://en.wikipedia.org/wiki/ITU_V.23> [2]
<http://www.itu.int/rec/T-REC-V/recommendation.asp?lang=en&parent=T-REC-V.23>
specifies audio frequency-shift keying
<http://en.wikipedia.org/wiki/Audio_frequency-shift_keying>
modulation to encode and transfer data at 600/1200 bits per
second.
V.18
In 1994 the ITU
<http://en.wikipedia.org/wiki/International_Telecommunication_Union>
approved the V.18
<http://en.wikipedia.org/w/index.php?title=ITU_V.18&action=edit&redlink=1>
standard [3] <http://www.itu.int/rec/T-REC-V.18/en>. V.18 is a
dual standard. It is both an umbrella protocol that allows
recognition and interoperability of some of the most commonly used
textphone protocols, as well as offering a native V.18 mode, which
is an ASCII <http://en.wikipedia.org/wiki/ASCII> full- or
half-duplex modulation method.
Computers can, with appropriate software and modem, emulate a V.18
TTY. Some voice modems, coupled with appropriate software, can now
be converted to TTY modems by using a software-based decoder for
TTY tones. Same can be done with such software using a computer's
sound card, when coupled to the telephone line.
In the UK, a virtual V.18 network, called TextDirect, exists as
part of the Public Switched Telephone Network
<http://en.wikipedia.org/wiki/Public_Switched_Telephone_Network>,
thereby offering interoperability between textphones using
different protocols. The platform also offers additional
functionality like call progress and status information in text
and automatic invocation of a relay service for speech-to-text calls.
