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A comment on I made 50k calls to explore the telephone network. Parent comment

Re:I made 50k calls to explore the telephone network by slumdev on Wednesday June 23, 2021 @09:17AM (#27604197)
A fax machine uses a modem of sorts, just with one specific protocol and purpose.

I can't find anything about how WarVOX differentiates modems from fax machines, but I wouldn't write them off right away.

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Re:I made 50k calls to explore the telephone network by hdmoore on Wednesday June 23, 2021 @07:41PM (#27612020)
It is based on peak frequency, you can visually see it here: https://speakerdeck.com/hdm/derbycon-2011-acoustic-intrusion...

IIRC (it has been a bit), there was a specific frequency only used by modem negotiation but not fax machines (3150?).

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