Poisson determines the number of trunks when traffic in Erlang is given, or traffic in Erlang when the number of trunks is given. In both cases, the Poisson loss probability must be known. The Poisson distributions is based on the following assumptions:

  • Calls are served in random order
  • There are an infinite number of sources
  • Blocked calls are held
  • Holding time is exponential or constant