Here we discuss the Messaging system in WCF. There are three types of applications in WCF For sending and receiving messages:

1) Clients.

2) Services

3) Intermediaries

Now we discuss the role of these applications one by one:

Clients: It initiates communication by sending message. It sends a message to a service and waits for a response. The Service receives the message and sends a response.

Services: A service is a program that receives messages and performs predefined actions according to the contents of the message. A service can handle more than one clients.

Intermediaries: It plays a role like a firewall in between the Client and the Service. It can prevent unwanted messages from getting in, it can routing messages just like a gateway or many other actions done by it. Both the Client and the Service has no idea about the existence of the intermediary.