The parameter that holds the data to be streamed must be the only parameter in the method. To stream data, the OperationContract for the service must satisfy two requirements:
To enable streaming, define the OperationContract appropriately and enable streaming at the transport level. Streaming mode is also useful when the message is too large to be entirely buffered. The streaming mode is useful when the information that is passed is lengthy and can be processed serially. In streaming transfer mode, the receiver can begin to process the message before it is completely delivered. In the default buffered-transfer mode, a message must be completely delivered before a receiver can read it. Windows Communication Foundation (WCF) can send messages using either buffered or streamed transfers.