To answer your earlier question- raw signalling theory- Any digital signal requires clocking.
Let's say you (an electronic device) receive a signal- ...10011101110110100011011111010001...
8 of those digits together mean something to you. You can make sense of that if you know where to start, but the digits just keep coming. A clocking signal gives you that starting point. Usually a system will take it's clocking from the LEC (Primary, in Nortel speak.) In your case, one of the systems you're connecting, usually the first cabinet, will have to be set to Master (generating the signal), and the other to Primary.