The measurement of how many telephone calls or connections (sometimes called traffic intensity) a communications system can make. The measurement is concerned with delays in obtaining a service or lost calls where a connection cannot be made. Traffic intensity is a dimensionless number relating to the congestion or occupancy of a system, line, or network link. It is measured in erlangs (symbol: E): when a system, line, or link is being fully used for one hour it is said to have a traffic intensity of one erlang of traffic. Centum call second (CCS), or hundred call second, is another method used to measure traffic intensity, most common in the US: one CCS is one thirty-sixth of an erlang.