I was wondering if anybody knows how to bypass a PABX for caller-ID
information, so the internally connected handsets having the feature of
showing caller-ID actually show it...
Most PABX do not transfer this caller-ID information to the internal lines
Could it be done using some passive filter system ?
Or does it need optical insulation and active parts ?
Did anybody here already try to bypass it ?
Has anybody have any information on the signal level and "frequency" of
caller -ID ?
(I do know it's sent *before* the actual ringing signal, but that's about
Most current PBX do transfer caller ID to their extensions, as long as the
analog trunk interface cards are of Caller ID supporting type. Some older
(Key systems) can also be upgraded to support caller ID by updating their
processor card (and trunk card(s) where needed). You cannot actually
bypass the processor board of the PBX to make the Caller ID ride to the
extension for several reasons:
#1 the phone sets should have internal feature to show Caller ID, and not
just the display. Only analog phones would qualify, not the PBX feature
#2 the processor actually stores the Caller ID info, and then transfers it
to the feature phones using its own, proprietary protocol. This protocol
is pretty heavily guarded by the manufacturers (because it lets them sell
more feature phones), and it is not the same as the Caller ID you'd get
from the PSTN to your regular house phone.
#3 it is the processor that decides which extension the call will go to,
so how do you know beforehand which extension is going to receive the
If you get lucky, and you have a key system (not a PBX), and your trunk
cards are supporting Caller ID, you may try to use a separate caller ID
device to see if it actually gets through or, alternatively, hook the
caller ID device directly to the incoming lines, especially if your
extension is only picking up one line.
Dmitri Abaimov, RCDD
- well, it's an analog pabx, call it an internal central passing calls from
outside line to multiple internal phones
- depending on who picks up first gets the call
- more as one internal phone supports caller-ID
- the actual switching in the pabx is done using ordinary relays
(might be interesting : type pabx is Profoon CX28 see