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

Mark Rejhon markybox at gmail.com
Mon Jul 9 09:40:12 UTC 2012

On Mon, Jul 9, 2012 at 2:09 AM, Edward Tie <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

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).

> 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.
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