What are the different types of distributing frames used in exchanges?

The various distribution frames used in exchange are demonstrated in figure. Every subscriber in a telephone network is linked generally to the nearest switching office through means of a dedicated pair of wires. Subscriber loop considers to this pair of wires. This is unwisely to run physically independent pairs from all subscriber premises to the exchange. This is far easier to lay cables having a number of pairs of wires for several geographical locations and run individual pairs as needed by the subscriber premises.

FIG - Cable Hierarchy For Subscriber Loops.

Here MDF = main distribution frame;

MF = main feeder;

FP = feeder point;

BF = branch feeder;

DW = drop wires;

DP = distribution point;

DC = distribution cable

Usually four levels of cabling are used as demonstrated in figure. At the subscriber end, the drop wires are acquired to a distribution point. The drop wires are the single pairs which run in the subscriber premises. On the distribution point, the drop wires are linked to wire pairs in the distribution cables. Several distribution cables from nearby geographical locations are terminated on a feeder point; here they are connected to branch feeder cables that, in turn, are linked to the main feeder cable. This main feeder cables carry a larger number of wire pairs, classically 100-2000, than the distribution cables that carry usually 10-500 pairs. The feeder cables are finished on a main distribution frame (MDF) at the exchange. The subscriber cable pairs emanating by the exchange are also terminated at the main distribution frame.