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    <blockquote cite="mid:4FFAADB6.6010608@xs4all.nl" type="cite">
      <blockquote
cite="mid:CAA79oDkR0fsSwtHP27yhswdmncgmVpNYodi6RjTswpuByBgS+A@mail.gmail.com"
        type="cite">
        <div class="gmail_quote">
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            <div>One sentence will be added to satisfy this.</div>
            <div><a moz-do-not-send="true"
href="http://xmpp.org/extensions/xep-0301.html#interoperability_considerations">http://xmpp.org/extensions/xep-0301.html#interoperability_considerations</a> </div>
            <div>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)</div>
            <div><br>
            </div>
            <div>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).</div>
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      </blockquote>
      <br>
      it's now a clear history :-) <br>
      <br>
    </blockquote>
    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.<br>
    <br>
    But, since we already have that interoperability chapter, it can be
    extended with a sentence.<br>
    <br>
    I suggest this addition:<br>
    <br>
    8.3 Textphones and TTYs in the PSTN (Informational)<br>
    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. <br>
    <br>
    Gunnar<br>
    <br>
    <blockquote cite="mid:4FFAADB6.6010608@xs4all.nl" type="cite"> <br>
      <br>
      <blockquote
cite="mid:CAA79oDkR0fsSwtHP27yhswdmncgmVpNYodi6RjTswpuByBgS+A@mail.gmail.com"
        type="cite">
        <div class="gmail_quote">
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            <div><br class="Apple-interchange-newline">
            </div>
          </div>
          <div> </div>
          <blockquote class="gmail_quote" style="margin:0 0 0
            .8ex;border-left:1px #ccc solid;padding-left:1ex">
            <div bgcolor="#FFFFFF" text="#000000">
              <h2><span>Protocols</span></h2>
              <p>There are many different textphone standards.</p>
              <h3> <span>Baudot code</span></h3>
              <p>The original standard used by TTYs is the <a
                  moz-do-not-send="true"
                  href="http://en.wikipedia.org/wiki/Baudot_code"
                  title="Baudot code" target="_blank">Baudot code</a>
                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.</p>
              <h3> <span>Turbo Code</span></h3>
              <p>In addition to regular Baudot, the <a
                  moz-do-not-send="true"
href="http://en.wikipedia.org/w/index.php?title=UltraTec&action=edit&redlink=1"
                  title="UltraTec (page does not exist)" target="_blank">UltraTec</a>
                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 <a moz-do-not-send="true"
                  href="http://en.wikipedia.org/wiki/ASCII"
                  title="ASCII" target="_blank">ASCII</a> compliance,
                and full-duplex capability. However, Turbo Code is
                proprietary, and UltraTec only gives its specifications
                to parties who are willing to license it.</p>
              <h3> <span>Other legacy protocols</span></h3>
              <p>Other protocols used for text telephony are European
                Deaf Telephone (EDT) and <a moz-do-not-send="true"
                  href="http://en.wikipedia.org/wiki/Dual-tone_multi-frequency_signaling"
                  title="Dual-tone multi-frequency signaling"
                  target="_blank">Dual-tone multi-frequency signaling</a>
                (DTMF).</p>
              <p>The ITU V series recommendations are a collection of
                early modem standards approved by the <a
                  moz-do-not-send="true"
                  href="http://en.wikipedia.org/wiki/ITU" title="ITU"
                  target="_blank">ITU</a> in 1988.</p>
              <ul>
                <li><a moz-do-not-send="true"
                    href="http://en.wikipedia.org/wiki/ITU_V.21"
                    title="ITU V.21" target="_blank">ITU V.21</a> <a
                    moz-do-not-send="true" rel="nofollow"
href="http://www.itu.int/rec/T-REC-V.21/recommendation.asp?lang=en&parent=T-REC-V.21-198811-I"
                    target="_blank">[1]</a> specifies 300 bits per
                  second duplex mode.</li>
                <li><a moz-do-not-send="true"
                    href="http://en.wikipedia.org/wiki/ITU_V.23"
                    title="ITU V.23" target="_blank">ITU V.23</a> <a
                    moz-do-not-send="true" rel="nofollow"
href="http://www.itu.int/rec/T-REC-V/recommendation.asp?lang=en&parent=T-REC-V.23"
                    target="_blank">[2]</a> specifies <a
                    moz-do-not-send="true"
                    href="http://en.wikipedia.org/wiki/Audio_frequency-shift_keying"
                    title="Audio frequency-shift keying" target="_blank">audio


                    frequency-shift keying</a> modulation to encode and
                  transfer data at 600/1200 bits per second.</li>
              </ul>
              <h3> <span>V.18</span></h3>
              <p>In 1994 the <a moz-do-not-send="true"
href="http://en.wikipedia.org/wiki/International_Telecommunication_Union"
                  title="International Telecommunication Union"
                  target="_blank">ITU</a> approved the <a
                  moz-do-not-send="true"
href="http://en.wikipedia.org/w/index.php?title=ITU_V.18&action=edit&redlink=1"
                  title="ITU V.18 (page does not exist)" target="_blank">V.18</a>
                standard <a moz-do-not-send="true" rel="nofollow"
                  href="http://www.itu.int/rec/T-REC-V.18/en"
                  target="_blank">[3]</a>. 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 <a moz-do-not-send="true"
                  href="http://en.wikipedia.org/wiki/ASCII"
                  title="ASCII" target="_blank">ASCII</a> full- or
                half-duplex modulation method.</p>
              <p>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.</p>
              <p>In the UK, a virtual V.18 network, called TextDirect,
                exists as part of the <a moz-do-not-send="true"
                  href="http://en.wikipedia.org/wiki/Public_Switched_Telephone_Network"
                  title="Public Switched Telephone Network"
                  target="_blank">Public Switched Telephone Network</a>,
                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.</p>
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