[Standards] UPDATED: XEP-0301 (In-Band Real Time Text)
famtie at xs4all.nl
Mon Jul 9 10:08:54 UTC 2012
Op 09/07/2012 11:40, Mark Rejhon schreef:
> On Mon, Jul 9, 2012 at 2:09 AM, Edward Tie <famtie at xs4all.nl
> <mailto:famtie at 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.
> 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,
it's now a clear history :-)
> 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
> 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
> 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> 
> specifies 300 bits per second duplex mode.
> * ITU V.23 <http://en.wikipedia.org/wiki/ITU_V.23> 
> specifies audio frequency-shift keying
> modulation to encode and transfer data at 600/1200 bits per
> In 1994 the ITU
> approved the V.18
> standard  <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
> 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.
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