What is the Messaging Pattern? Which Messaging Pattern WCF supports?

Messaging patterns describes how client and server should exchange the message. There is a protocol between client and server for sending and receiving the message. These are also called Message Exchange Pattern. 
WCF supports following 3 types of Message Exchange Patterns:
1. request - reply (default message exchange pattern) 
2. OneWay (Simplex / datagram) 
3. Duplex(CallBack)