The Erlang loss formula is used to find the blocking probability of a M/M/c/c queue. The extended model takes account for the re-iteration probability.
To use this tool, click on the radio button to set the unknown, write your known parameters, then click on Run.
G. Zeng, “On the convergence of the Extended Erlang- model,” Mathematical and Computer Modelling, vol. 52, no. 1–2. Elsevier BV, pp. 128–133, Jul. 2010. doi: 10.1016/j.mcm.2010.01.022.