The term "circuit" denotes the direct transmission path between two exchanges, including the
associated terminating equipment in the exchanges. In transmission planning the circuit loss
includes the exchange loss.
In analogue exchanges this means that "half" the exchange loss at each end of the circuit is included
in the circuit loss. Therefore, the input of the circuit is in "the middle of" one exchange and the
output of the circuit is "in the middle of" the other exchange. The input and output points of a
circuit between analogue exchanges are not accessible points, but hypothetical points used for
transmission planning.