What is Duplex in WCF?

Duplex in WCF allows clients and server to establish a communication pathway with each independently in which any of the entity can initiate a call to others. In order to establish communication between the source and destination duplex mode of communication would be used. If one entity is sending a message at the time another entity will receive the message. Moreover, in the duplex mode of communication, both source and destination will participate in the communication activity.