[asterisk-users] T1 Wire Level Tapping

[Leo Ann Boon]

Shane Spencer wrote:
> I am trying to do a wire level tap on T1 equipment using digum
> equipment.  So far most call monitoring hardware for call centers try
> to stay on the analog side requiring a lot of rewiring.  I have
> already posted to the list about T1 "bridging" using DAC's support in
> the zaptel drivers.  I still don't know if I can spy on channel
> information since I don't have any digium hardware on me until the
> project begins.
>
There are a number of systems using ISDN digital taps. The proper way 
requires a high impedance bridge - you don't want to load the line that 
you're tapping.

> Anybody found a method of spying on a D-Channel and all voice channels
> using standard T1 equipment?  I am making a rough assumption that if I
> can trick the zaptel drivers into operating without anything
> responding to a TX signal then I can do the following:
You can directly bridge the 2 ports and extract what you need as you 
bridge - see pridump.c in libpri. You don't even need asterisk, just the 
zaptel and libpri. The only problem with this approach, is that the 
bridge becomes a point of failure. Your box down, your PRI goes down as 
well.
>
> S-T1 = T1 to Spy On
> T1-1 = Digium T1 card #1
> T1-2 = Digium T1 card #2
>
> Map S-T1(RX) to T1-1(RX) and S-T1(TX) to T1-2(RX) and decode the
> D-Channel where appropriate, should I be able to spy on the RX/TX
> channels enough to make a recording including CID information?  This
> would help in situations where the monitoring system needs to be
> replaced or taken down without bothering in-progress calls.
This is technically correct, but I don't know how well it works. Eicon 
recommends a similar technique to do monitoring with their Eicon Server 
cards. For the BRI, it's done this way. But for the PRI card, they 
actually suggest using a custom cable. Eicon cards have a special Hi-Z 
monitoring mode to support this application.
http://www.eicon.com/worldwide/solutions/How_To_Call_Tapping_and_Monitoring_with_Diva_Server

FYI, Voicetronix has a Hi-Z version of their OpenPRI card that work with 
an open-sourced voice logging application available from their site.

Leo