What is the Request Reply contract in WCF services ?

Answer:

It is the default contract of a WCF service.
In this contract, client will be able to send request to the server and waits to get a response from the server. this is known as ReceiveTimeout.
If client doesn't gets any response untill that ReceiveTimeout, he will get TimeOutExecption instead.
After getting the response, it starts executing the remaining thing.