1 -Request/reply 2-one way 3 duplex

There are three types of message exchange pattern in WCF: 1. One-Way, 2. Request-Reply, 3. Duplex .Request-Reply is the Default one. In One Way message exchange pattern , WCF does not need to send reply back to client application and client application does not wait for the reply even. In Request-Reply, Client application sends message to Service application and waits for the reponse from the service application. In Duplex communication, client application or service application can start the communication and expect notification/ acknowledgement from their counter part.

1 -Request/reply (Default ) 2-one way 3 duplex (For Call back operations)

There are 3 types of message exchange patterns are available in WCF: (01.) Request/Reply: In the request-reply pattern, a client application sends a message to a WCF service and then waits for a reply. You will use this pattern most often. (02.) One Way: In the one-way message exchange pattern, the client application sends a message to a WCF service but the service does not send a reply message to the client. You can use this pattern when the client does not need to wait for a reply from the service. (03.) Duplex/Callback: In the duplex pattern, both the client and the service can initiate communication. You can use this pattern when you want the service to send a notification or alert to the client after the client has called the service.

Please once go through following link: https://msdn.microsoft.com/en-us/library/ff395349.aspx

https://kiranpatils.wordpress.com/2011/10/16/wcf-behavioral-contracts-and-message-exchange-patterns/

Request-Reply, One way & Duplex.[OperationContract(IsOneWay = false)]-->Oneway [OperationContract(IsOneWay = true)]-->Req-rephttp://www.codeproject.com/Articles/566543/WCF-Message-Exchange-Patterns-MEPs

http://www.codeproject.com/Articles/566543/WCF-Message-Exchange-Patterns-MEPs

service contract data contract message contract fault contract