Call duration explained

In telecommunications, the term call duration has the following meanings:

1. In telephone systems, the time between (a) the instant a circuit, i.e., off-hook condition at each end, is established between the call originator and the call receiver and (b) the instant the call originator or the call receiver terminates the call.
2. In data transmission, the duration of the information transfer phase of an information transfer transaction.

Source: from Federal Standard 1037C