is the main planning target for the network capacity. The capacity peaks are momentary and therefore define a blocking probability, which is the accepted level for unsuccessful call attempts due to lack of resources. This parameter has already been defined by the customer at the beginning of the planning process. The amount of traffic is expressed in Erlangs, which is the magnitude of telecommunications traffic. An Erlang describes the amount of traffic in one hour. The definition for Erlang is the following: (number of calls in hour) (average call length) Erlang = (2.49) as an example of an Erlang calculation, 25 users make a phone call for each an average of three minutes in an hour. How much traffic are the users creating in Erlangs? Traffic in (2.50) A quite normal dimensioning value for traffic per user is 15-30 mErl during the network busy hour, which means 54-108 S call times. This value varies a lot depending on the user, but one average value is needed in the network dimensioning phase. The value of traffic per user can be said to be linked to the culture. In detailed capacity planning different user profiles can be used to simulate different types of usages. The capacity can be calculated using Erlang formulas, where the B formula is for the case without queuing and the C formula for the case which takes queuing into account. The Erlang formulas are presented below. The Erlang formula B calculates the call blocking probability PB for traffic T with the amount of channels C. The traffic is given in Erlangs. The amount of traffic to be served with an accepted blocking probability level is T' = T/(1 - B). According to this formula the blocked calls are terminated without queuing: (2.51) The Erlang C formula calculates the probability for queuing, i.e. the probability that the user has to wait to be served. The calculation parameters traffic T and number of traffic channels C are the same as for the Erlang B formula: T°C/[C!(C - T)] (2.52) Tables and automatic calculators based on Erlang formulas can be fou