Typical inputs and outputs:
Power: In a Central Office it is likely to be -48V, it can be 250V ac with a dc output of 48V.
Lan: Ethernet LAN port for connection to the outside world.
MMI Port: Required for a laptop connection to do initial configuration & unit set up.
Ground: All test measurements are relative to Earth so a good ground is essential.
Switch Bus: Will operate TAM or TASM modules to automate access to the line under test.
Status LED: A view of the unit status, flashing, on, off etc
Inputs: A number of 2 wire or 4 wire input ports.
You can see all the inputs / outputs identified in the diagram above on the real product below.
A single Test Head is unlikely to have more than eight Test Bus ports and can only test any one at a time. A very large central office may require more test ports to stop congestion and tests being queued. A simple solution is to daisy chain multiple Test Heads together allowing more test to be run simultaneously. The service provider fits algorythms into the controling software to us ethe next free Test Head on the correct Test Bus.