Erlang B
Calculates traffic in loss systems. If a request is not served when it is offered to the resource then it is lost. These systems can be considered as non-queued. This model assumes the blocked traffic is immediately cleared.
Erlang B formula
:Eb(0, t) = 1 \\,
:Eb(r,t) = { {t Eb(r-1,t)} \\over {r+t Eb(r-1,t)} } \\,
where:
Eb is the probability of blocking
r is the number of resources.
t is the number of Erlang offered
Extended Erlang B
This formula is essentially Erlang B, but assumes that a certain percentage of the system, when blocked will immediately represent themselves to the system. This formula can account for this retry percentage.