Sessions cannot be used in basichttpbindin g, can anyone please tell me the reason for the same

Thanks in advance

WCF throttling behavior gives us the facility to manage the max concurrent instances, what I want to do is control the instances created by the client were wcf services are consumed. for e.g:- if client calls a method hosted on wcf service and the execution is going to take long hours I want to restrict the calls upto 5 instances. My question is can we control the max instances manually where in if 6th call is made it should return the exception...