Answer to “Limitations”:
_Some_ limitations to the Erlang B law are the implied assumptions that are made by deciding that calls follow a poisson distribution.
Some examples that highlight the limitations could be:
– if your grade of service is affected by some other parameters (e.g. interference), the GoS that you will use in the formula is only the GoS due to channels availability. The real GoS that you will experience should be bigger.
– people who try to call several time if they cannot seize some TCH. You should now fall under some “extended Erlang B law”.
– some “event” happens at a precise time (e.g. end of the final match of the football world cup): in the country that wins, a lot of people will try to give calls at the same time.