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

Gunnar Hellström gunnar.hellstrom at omnitor.se
Mon Jul 9 11:12:44 UTC 2012

>> 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 :-)
I agree with Mark. XEP-0301 is a protocol specification for XMPP, mainly 
on the transport level, and should not be loaded with too much info on 
other possibly related areas.

But, since we already have that interoperability chapter, it can be 
extended with a sentence.

I suggest this addition:

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.  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 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.


>>         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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