Telephone Calls as a Birth Process---I

• Consider example given on previous page.

• Consider every second.

  of receiving one call:

  essentially no probability of receiving >1 call.

• Thus, each second can be described by variable which has Poisson distribution with parameter .

• The number of calls in time t seconds is which from additivity is also Poisson with parameter .

• So

  

  is probability of receiving k calls in t seconds.