There are three modes of communication in WCF :
One-Way : In the One-Way operation mode, the client will send a request to the server and does not care whether it is success or failure of service execution. There is no return from the server side, it is one-way communication.
Request-Reply : When as client makes a request to the WCF service and client will wait to get a response from service (till receiveTimeout). After getting the response it will start executing the rest of the statement.
Callback : It is the service to call the client. In which, service will act as client and client will act as service.
