<div dir="ltr">I've heard that before when dialing a fax machine when sharing the primary voice line, it would do that kind of behavior to make sure the caller was actually a fax machine. <div><br></div><div>My guess is to save a voice caller's ears from getting the CNG tone whereas a fax machine would detect the line as answered and would start to send the tones causing the receiving fax machine to quit "ringing" and answer.</div><div><br></div><div>~Jared</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Jun 22, 2016 at 4:41 PM, David Knell <span dir="ltr"><<a href="mailto:david.knell@telng.com" target="_blank">david.knell@telng.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Best guess - it's fake ringback being generated by some auto fax/voice switch.<div><br></div><div>--Dave</div></div><div class="gmail_extra"><br><div class="gmail_quote"><div><div class="h5">On Wed, Jun 22, 2016 at 5:37 PM, Justin Grow <span dir="ltr"><<a href="mailto:jgrow@flowroute.com" target="_blank">jgrow@flowroute.com</a>></span> wrote:<br></div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div class="h5">
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<div>This is an interesting one. I'm running into issues with a fax application for a few numbers that are playing back a strange tone I have yet to identify. I originally thought it was FAS with international ringback, but it's occurring on a variety of numbers on various networks. The tone is playing immediately upon answer. Any help identifying what is causing this tone or what it is intended for is appreciated.</div><div><br></div><div>The numbers are all fax lines and do get the proper CED after this tone. I can't find any matching tone in the T.30 ITU-T rec. As best I can figure, it's 400Hz with a 0.03s period on/off cycle, played 1s on 2s off. Listen at the below link. Sorry for the compression; email me and I can send you the original wav recording. </div><div><br></div><div><a href="https://clyp.it/vcq010th" target="_blank">https://clyp.it/vcq010th</a></div><div><br></div><img align="left" width="0" height="0" style="border:0;width:0px;min-height:0px" src="https://app.mixmax.com/api/track/v2/oifmtMa69g0d9tu2k/i02bj5SZ0V3byd3bsZGQ39mcnpmI/IyZy9mLzB3blNWavZHQzB3blNWavZnI/gIzB3TlNWavZlI" alt="">
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<br></blockquote></div><span class="HOEnZb"><font color="#888888"><br><br clear="all"><div><br></div>-- <br><div data-smartmail="gmail_signature"><div dir="ltr"><pre cols="72"><font face="courier new, monospace">David Knell, Director, TelNG
T: <a href="tel:%2B44%201223%20797979" value="+441223797979" target="_blank">+44 1223 797979</a> / <a href="tel:%2B1%20970-315-4721" value="+19703154721" target="_blank">+1 970-315-4721</a>
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