Look at the back there is a white line in carrier A that is marked TDM, most likely there is a terminator installed right now, that is where you're cable should go.
The terminator should then be installed in the B carrier.
PS in the B carrier there is a jumper somewhere in the bottom right that tells the carrier if it is a B, C or D carrier Please let me know if the information that was provided is helpfull.
Edwin Plat
A.K.A. Europe