In WCF there are the following 3 types of Message Exchange Pattern:
This is the default Message Exchange Pattern. In this pattern the client sends a request to the server and it waits for the response until the server does not stop processing.
2. One way
This mode is used when we don't want to show any type of error to the client because when we use the Message Exchange Pattern then it doesn't give any message to the client. We can set these patterns using IsOneWay = true in the service, the exception will be thrown if IsOneWay = true is declared in the output parameter, reference parameter or return value.
The duplex pattern implements both of the OneWay and Request/Response message patterns. The client and the service both initiate this pattern. This pattern is more complex than other patterns because the additional communication is added.