A unit used to measure communications traffic. Note 1: A call-second is equivalent to 1 call 1 second long. Note 2: One user making two 75-second calls is equivalent to two users each making one 75-second call. Each case produces 150 call-seconds of traffic. Note 3: The CCS, equivalent to 100 call-seconds, is often used. Note 4: 3600 call-seconds = 36 CCS = 1 call-hour. Note 5: 3600 call-seconds per hour = 36 CCS per hour = 1 call-hour per hour = 1 erlang = 1 traffic unit.