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<div class="nine-pg" dir="auto">One thing to be careful of Is proprietary modems with VoIP.</div>
<div class="nine-pg" dir="auto">Here in Italy we have a lottery Company that removed modem negotiation (setting fixed speeds and removing preamble etc.) This created havoc with MoIP so we had to fix the profile manually on their services and not rely on
renegotiation for detection.</div>
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<div class="nine-pg" dir="auto">Brian Turnbow</div>
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<div style="border:none; padding:3.0pt 0cm 0cm 0cm" dir="auto"><span style="font-size:11.0pt;font-family:Calibri, Arial, Helvetica, sans-serif"><b>Da:</b> Jay Hennigan via VoiceOps <voiceops@voiceops.org><br>
<b>Inviato:</b> martedì 21 settembre 2021 20:09<br>
<b>A:</b> Shawn L; VoiceOps<br>
<b>Oggetto:</b> Re: [VoiceOps] Porting a TTY Line<br>
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<div class="nine-pg" dir="auto" style="null">On 9/21/21 10:42, Shawn L via VoiceOps wrote:<br>
> Does anyone have any familiarity with TTY lines?<br>
> <br>
> A customer has asked us to port one, but I have no idea what, if <br>
> anything is required on the back end. From the limited information I <br>
> can find, it looks like a standard POTS line, but with a TTY terminal on <br>
> both ends. But there's also the mention of an operator who acts like a <br>
> go-between for communication. I'd like to know more about how it <br>
> operates and what we have to provide / if we can provide it before going <br>
> forward.</div>
<div class="nine-pg" dir="auto" style="null">To the best of my knowledge it's a POTS line. The terminal uses a modem
<br>
to communicate. Early devices were acoustically coupled, half-duplex and <br>
used refurbished Teletype machines. The Teletypes were big and noisy, <br>
but the noisy part isn't really a factor in this application. There are <br>
smaller portable units these days. Nothing special about the line itself <br>
from a technical standpoint but there may be discounted billing rates in <br>
some jurisdictions as well as possible directory listing flags that it's <br>
TTY.</div>
<div class="nine-pg" dir="auto" style="null">Modem encoding is FSK, slow and forgiving enough that it should work
<br>
over a VoIP connection with G.711 codecs without issue. Some are <br>
half-duplex meaning that only one side sends at a time. Typically <br>
hand-over is done with "GA" at the end of a message, like "over" in a <br>
two-way radio setup. Then the other party turns their modem to transmit <br>
and starts typing.</div>
<div class="nine-pg" dir="auto" style="null">The go-between operator is reached by dialing special service code 711,
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and 711 should recognize both regular speech (inbound call voice->TTY) <br>
and modem (outbound call TTY -> speech). The operator basically reads <br>
the text to the hearing party and types the message to the <br>
hearing-impaired party.</div>
<div class="nine-pg" dir="auto" style="null">Some good info and history in the book, "A Phone of Our Own"<br>
http://gupress.gallaudet.edu/POOO.html</div>
<div class="nine-pg" dir="auto" style="null">-- <br>
Jay Hennigan - jay@west.net<br>
Network Engineering - CCIE #7880<br>
503 897-8550 - WB6RDV<br>
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