I am stuck in a problem that I cannot get out of. I am designing and developing a system that has to process one request at a time, put other requests into the queue and if the queue gets more than 5, return invalid statement to user. I tried many options but could not get the result that I am looking for. The brief new system design that I plan to implement now is shown below: 
My questions are:
- Is it possible to implement this kind of system design (calling one service contract from another)
- Is there any best approach to achieve this?
I just have to create a system that has a bottle neck into it. But if the queue is too long, return some invalid statements. I have already created service contract 2 and 3 where contract 2 handles multiple request and contract 3 handles one request at a time. The basic problem with this approach will be, if the queue get long enough, the users may face time execution error since there will be no response from the server.