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From: claris!netcom!onymouse@ames.arc.nasa.gov (John Debert)
Newsgroups: comp.dcom.telecom
Subject: Re: Coin Station Fraud Using External Ground
Message-ID: <6325@accuvax.nwu.edu>
Date: 12 Apr 90 08:02:20 GMT
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X-Telecom-Digest: Volume 10, Issue 250, Message 7 of 11


 From article <6056@accuvax.nwu.edu>, by kitty!larry@uunet.uu.net
(Larry Lippman): 

> >Most coin stations today are DTF (Dial Tone First) and no 
> longer resemble a ground-start line.  A DTF coin line behaves similar 
> to that of a loop-start line (it is actually more complex than that,
> but this will suffice for the purpose of this discussion); i.e., a 
> ground on a DTF coin line will not facilitate any fraud.

Grounding is still used on many coin phones to detect the presence of
coins. This in combination with a a sequence of idle tone pulses to ID
each coin dropped is used to validate a call. It is possible to fool
the phone into thinking that enough coins have been dropped through a
very simple procedure using one nickel. It is also possible to induce
the appropriate signals onto the line once ground has been
established, as was once demonstrated to me. Note, however, that this
does not work on COPT's or other "smart" coin sets. There are other
methods that apply to circumventing these.

jd
onymouse@netcom.UUCP