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From: dbb@aicchi.chi.aic.com (Ben Burch)
Newsgroups: comp.dcom.telecom
Subject: Re: Detecting the End of an Incoming Call
Message-ID: <16173@accuvax.nwu.edu>
Date: 18 Jan 91 15:01:08 GMT
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X-Telecom-Digest: Volume 11, Issue 47, Message 5 of 12


In the US (and I imagine that the UK is similar since we can exchange
hardware) many (not all) COs return a "disconnect pulse" when a call
terminates.  The width of this pulse varies from 100 ms to 500 ms
depending on the type of switch you are connected to.  The pulse is
simply a loss of loop current.  You can often tell if this happens
with a lighted dial phone.  If the light blinks after a caller hangs
up, then you get the pulses.  In the hardware I've worked on, we use
an opto and a couple of diodes to detect both ringing and loop
current.


Ben Burch
dbb@aicchi.chi.aic.com