RE: (PMOD) Caller ID: Is it ever wrong?

Bruce Farnham (Bruce.Farnham@twtelecom.com)
Wed, 22 Sep 1999 10:12:10 -0600

In addition to Jay,s comments I would like to add that caller ID can also be
changed at the originating
customers telephone company central office.
This is usually arranged by the originating customer with the specific
telco. I have seen
where errors in setting this up has resulted in the wrong number being
delivered to the
terminating end of the call.

Bruce Farnham\
Time Warner Telecom
Switching Technical Support

-----Original Message-----
From: Jay Hennigan [mailto:jay@west.net]
Sent: Tuesday, September 21, 1999 11:28 PM
To: Brad Martin
Cc: Jose de Leon; portmaster-modems@livingston.com
Subject: Re: (PMOD) Caller ID: Is it ever wrong?

On Wed, 22 Sep 1999, Brad Martin wrote:

> Well, I've seen where normal caller ID is wrong. It happens when someone
> dials in from a PBX, as in a hotel or office complex. When I call home
> from the local college, it shows some random trunk line phone number.
> That's probably what's happening to you.

It isn't really wrong in such cases. The number displayed is the one on
which the call originated. It may not be a number that correlates to the
extension behind the PBX, but it is indeed an outbound trunk on it.

Typically, a PBX will have direct-in trunks, where the last few digits
of the phone number don't correspond to a given physical trunk. When
you call someone on one of these "direct lines", your call goes over
a random trunk in the pool to the PBX, which then extracts the called
number (by any of a number of means, D-channel PRI signalling, DTMF,
etc.) and rings the extension mapped to these last digits.

For outbound calls, the PBX just grabs a random outbound trunk that
has no one-to-one correspondence to the extension. In some cases, it
may not even be a dialable number, but a "fictitious" number like
181-0987 or the like which will show up as "out of area" or "unavailable".

This can be trouble with calls to 9-1-1 where a PBX covers a wide area,
especially if it has a VoIP connection to a remote office several hundred
miles away.

99 times out of 100, an "out of area" on caller-ID is a telemarketer. 

-- 
--        Jay Hennigan     jay@west.net    805-884-6323          --  
WestNet:  Internet service to Santa Barbara, Ventura and the world.




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