In telecommunications, a call-second is a unit used to measure communications traffic density, equivalent to one call with a duration of one second.
In a communication network, a trunk (link) can carry numerous concurrent calls by means of multiplexing.
Hence a particular number of call-seconds can be carried in infinitely many ways as calls are established and cleared over time.
Offered load is defined as the traffic density per unit time, measured in erlangs.
Hence, if one CCS is measured over a one-hour period, the offered load is 1/36 erlangs.