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.
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. ~Jared On Wed, Jun 22, 2016 at 4:41 PM, David Knell <[email protected]> wrote: > Best guess - it's fake ringback being generated by some auto fax/voice > switch. > > --Dave > > On Wed, Jun 22, 2016 at 5:37 PM, Justin Grow <[email protected]> wrote: > >> 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. >> >> 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. >> >> https://clyp.it/vcq010th >> >> >> _______________________________________________ >> VoiceOps mailing list >> [email protected] >> https://puck.nether.net/mailman/listinfo/voiceops >> >> > > > -- > > David Knell, Director, TelNG > T: +44 1223 797979 / +1 970-315-4721 > W: http://www.telng.com > H: http://www.daveknell.com > > > _______________________________________________ > VoiceOps mailing list > [email protected] > https://puck.nether.net/mailman/listinfo/voiceops > >
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