[Standards] Comments on XEP-0301 -- Section 1 - TTY

Gunnar Hellström gunnar.hellstrom at omnitor.se
Thu Aug 23 19:52:51 UTC 2012


On 2012-08-23 18:31, Peter Saint-Andre wrote:
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> On 8/23/12 10:22 AM, Matthew Miller wrote:
>
>> I do realize this might seem pointless to some, but I really do
>> want to understand where this technology is coming from.
> Matt, it's basically a matter of the history of computing at this
> point. Unfortunately, these days (when XML is considered old) few
> people care about such ancient technologies.
>
> The best historical reference I've found is a pamphlet published by
> the Teletype Corporation in 1963 (Editors: R. A. Nelson; K. M. Lovitt,
> Editor; October 1963; Teletype Corporation, 5555 West Touhy Avenue,
> Skokie, Illinois). I found a scanned-in copy here:
>
> http://www.rtty.com/TTYSTORY/ttsindex.htm
>
> Or did you want something more modern?
>
> Peter
>
Yes, that reference was the pre-history.
In the 1960-s deaf engineers in USA got surplus teletypewriters and 
designed an FSK modem for them so they could be used for limited 
real-time text communication over PSTN. I think the original 
Teletypewriters used DC transmission, unsuitable for the PSTN, and 
needed that upgrade. Later, purpose-built terminals were created, using 
the same transmission technology, having the modem built-in. They 
continued to use the name TTY, but are quite different from the original 
Teletypewriter TTY. That is why we should not just refer to 
Teletypewriter in this use of the term TTY.

People in Europe thought that the idea was good, but took various 
standard modems in use for the same purpose, and created text 
telephones, sadly with different uninteroperable modems in different 
countries during the 70s and 80s. The mistake in created fragmented 
islands of uninteroperable groups was discovered, and an effort was done 
to harmonize with an automoding modem protocol, called ITU-T V.18.
But the regulatory or market forces were too weak, so V.18 became common 
only in UK.  Other countries continued to use their national variants.

If you really think it is important to have a technical reference 
describing the protocols for TTY and the other text telephone types, we 
can have a look at three documents that might be suitable:

ITU-T Recommendation V.18, Automoding procedures for DCEs working in the 
text telephone mode.
http://www.itu.int/rec/T-REC-V.18-200011-I with amendment 
http://www.itu.int/rec/T-REC-V.18-200211-I!Amd1 
<http://www.itu.int/rec/T-REC-V.18-200211-I%21Amd1>
The annexes describe the different modem based protocols for the 
different text telephone standards, ( Including TTY, that is called 
5-bit in this reference.

ETSI EG 102 230 Duplex Universal Speech and Text
http://www.etsi.org/deliver/etsi_eg/202300_202399/202320/01.02.01_60/eg_202320v010201p.pdf
Where Annex A.2 contains a brief description of the current textphone 
systems.

IETF RFC 5194 Framework for Real-Time Text over IP Using the Session 
Initiation Protocol (SIP)
http://www.rfc-editor.org/rfc/rfc5194.txt
where section 6.2.5.1. PSTN Interworking contains a very brief 
introduction to the textphone protocols.


/Gunnar












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