Erlang's Lost Call Assumptions
To calculate the Grade of Service of a specified group of circuits or routes, Agner Krarup Erlang used a set of assumptions that relied on the network losing calls when all circuits in a group were busy. These assumptions are:
- All traffic through the network is pure-chance traffic, i.e. all call arrivals and terminations are independent random events
- There is statistical equilibrium, i.e., the average number of calls does not change
- Full availability of the network, i.e., every outlet from a switch is accessible from every inlet
- Any call that encounters congestion is immediately lost.
From these assumptions Erlang developed the Erlang-B formula which describes the probability of congestion in a circuit group. The probability of congestion gives the Grade of Service experienced.
Read more about this topic: Grade Of Service
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