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From: mitel!spock!grayt@uunet.uu.net (Tom Gray)
Newsgroups: comp.dcom.telecom
Subject: Re: CPC / "Wink" Call Termination
Message-ID: <14455@accuvax.nwu.edu>
Date: 6 Nov 90 22:23:31 GMT
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In article <14261@accuvax.nwu.edu> DREUBEN@eagle.wesleyan.edu (Douglas
Scott Reuben) writes:

>I'm wondering if anyone here knows exactly (or not so exactly :-) )
>what the "wink", or I believe it is sometimes called "CPC" signal is.

>I'm referring to the process by which the Central Office switch can
>signal a end-user device (an answering machine, for example) that the
>calling party has hung up. i.e., someone calls my machine, hears the
>outgoing message, thinks it is really too long, and just hangs up. The
>machine "knows" that the caller has hung up even before it starts
>"listening" on the line to see if anyone is recording a message or
>not.

>I've heard from some sources that this is done with polarity reversal,
>and from others that there is just a drop in line current for a brief
>moment.  Is either (or both?) correct?

The problem described here occurs on loop start lines on which no
answer supervision is provided. A call is answerd by a machine The
answering machine needs an indication that the far end has
disconnected.  In the absence of answer supervision, how is this done?

Normally for non-answer supervision loops a service can be provided in
which the impedance of the loop is raised above 15K ohms for a short
period of time. This has the effect of lowering the loop current below
the off hook threshhold. Answering equipment can be designed to detect
the absence of loop current on a disconnect signal.  The usual means of
providing this service is to open the tip (A lead for non North
Americans) with a relay. in effect, the CO is providing the disconnect
signal normally provided on a ground start trunk on a loop start
service.

Naturally if answer supervision is provided on a loop. Far end
disconnect is indicated by an on hook signal. This is the reversal of
battery mentioned above (assuming that reverse battery signalling is
used).

The service described above (called Cut Off on Disconnect around here)
is the removal of loop current for a few hundred milliseconds. The
exact timimgs of this cut off will vary greatly depending on the type
of equipment installed.