Request A Request message is used to request data from a receiver or to request an action to be performed by a receiver. A Request message always results in an associated response message that can contain either the requested data or indicate the result of an action. A Request message can optionally contain a payload. For any given Request message type, there can be only one associated receiver. The receiver handles the request and issues a response message. From a developer perspective, a Request message can be thought as being a method call.
Response A Response message is the result of a single Request message. A Response message can optionally contain a payload. From a developer perspective, a Response message can be thought as the return value of a method. The value can be of a specific type or not (void).