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The Erlang B formula (or Erlang-B with a hyphen), also known as the Erlang loss formula, is a formula for the blocking probability that describes the probability of call losses for a group of identical parallel resources (telephone lines, circuits, traffic channels, or equivalent), sometimes referred to as an M/M/c/c queue. [5]
For example, one call-hour could be one call for an hour or two (possibly concurrent) calls for half an hour each. Call-seconds give a measure of the average number of concurrent calls. Offered load is defined as the traffic density per unit time, measured in erlangs. An erlang is defined as one call-hour per hour, or 3,600 call-seconds per hour.
In telecommunications networks, traffic intensity is a measure of the average occupancy of a server or resource during a specified period of time, normally a busy hour.It is measured in traffic units and defined as the ratio of the time during which a facility is cumulatively occupied to the time this facility is available for occupancy.
In telecommunications, busy-hour call attempts (BHCA) is a teletraffic engineering measurement used to evaluate and plan capacity for telephone networks. [1] BHCA is the number of telephone calls attempted at the sliding 60-minute period during which occurs the maximum total traffic load in a given 24-hour period (BHCA), and the higher the BHCA, the higher the stress on the network processors.
"Grade of Service" sometimes means a measure of inbound call center traffic to verify adherence to conditions to measure the success of customers served. On the other hand, the quality of service which a single circuit is designed or conditioned to provide, e.g. voice grade or program grade is called the quality of service.
The probability density function of the Erlang distribution is (;,) = ()!,,The parameter k is called the shape parameter, and the parameter is called the rate parameter.. An alternative, but equivalent, parametrization uses the scale parameter , which is the reciprocal of the rate parameter (i.e., = /):
The loss network was first studied by Erlang for a single telephone link. [2] Frank Kelly was awarded the Frederick W. Lanchester Prize [ 3 ] for his 1991 paper Loss Networks [ 4 ] [ 5 ] where he demonstrated the behaviour of loss networks can exhibit hysteresis .
In 1909, Agner Krarup Erlang, a Danish engineer who worked for the Copenhagen Telephone Exchange, published the first paper on what would now be called queueing theory. [9] [10] [11] He modeled the number of telephone calls arriving at an exchange by a Poisson process and solved the M/D/1 queue in 1917 and M/D/k queueing model in 1920. [12]