Central Office Copper Connectivity Solutions The main distribution frame located at a central office terminates the cables leading to subscribers on the one side (line side), and cables leading to active equipment (such as DSLAMs and telephone switches) on the other (exchange side). Service is provided to a subscriber by manually wiring a twisted pair (called a jumper wire) between the subscriber line and the relevant DSL or POTS line circuit. It consists of MDF frame, cable terminal blocks, protector modules, central ground wire, column alarm unit (CAU), sliding type stepladder and insertion tools.