On Sat, 19 Jun 2004, Fred Cisin wrote:
> and put in the bullshit about inmates as part of the
> DANGER! DANGER! hook.
Trust me, inmates have attempted this and other scams and have gotten away
with them on plenty of occasions. But that would've been years ago when
inmate phone systems weren't as secure and locked down as they are now.
> You know far more about phone systems than I do.
> But is there ANY system that will initiate 3-way-calling
> just by pressing 9 during a conversation?
Technically it's possible, but I don't know of any phone system that works
like that. At any rate, that's what the flash hook is for. I'm pretty
sure the hoax calls for flash hook and then dialing a nine. So the
entire hoax is based on the assumption that you're calling an office with
a PBX installed (or even Centrex phone lines, which are lines provided by
the local telco that have PBX type features).
> Wouldn't there have to be some sort of hook-flash or line button? What
> would prevent the CALLER from DTMF control of the system?
I think the hoax implies a flash hook or something, even though it's not
explicitly stated. However, you should know that it is possible to
discern remote touch tones from locally generated touch tones. There are
a number of methods. On many digital phone systems, the keypresses on the
number pad are transmitted as digital codes over either a separate wire
pair or out of band signal. So in theory, you could program the number
keys to be active during a conversation. Also, it is possible to filter
out remote DTMF in a way. You can do that by dB levels. I know that one
phone system I work with has very poor DTMF detection on incoming trunks,
so that trying to set up a DISA (Direct Inward System Access, i.e.
programming a trunk on the phone system that you can dial in to, enter an
access code, then dial back out of or access other features of the PBX) is
useless because it cannot detect DTMF from a remote telco CO, but it can
if you are calling through the local CO. It has to do with dB levels and
poor design. Another phone system I've worked with (Siemens Saturn) did
not have this problem. Anyway, this is just to illustrate that it is
technically feasible, though not entirely desirable.
> But that doesn't stop the resurfacing of the WARNING!s
> that tell you that inmates or other lowlifes are going
> to cheat you out of THOUSANDS of dollars.
Well, they are :) Inmates have nothing to do all day. They've got a
phone in their cell and they're going to use it.
--
Sellam Ismail Vintage Computer Festival
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Received on Sat Jun 19 2004 - 22:12:41 BST