Figure 1. Protocols Used to Transmit a Stream

When a node is ready to transmit a stream, it prepares a control record to initiate the stream. A request initiate (R I) RCB with a value of X‘90’ indicates that a request has been made to initiate a stream. The receiving node receives the request and prepares a control record to indicate whether or not it can receive the stream. If the node can receive the stream, the receiving node responds by preparing an RCB with a value of X'A0'. If the stream is unwilling or unable to receive the new stream, it sends a receiver cancel (R C) RCB with a value of X'B0'

The sending node cannot send any transmission buffers until the proper control records are exchanged. The sender may only send a transmission buffer after the receiver has responded with a permission to initiate a stream (RCB X'A0'). Only one job may be sent for each request to initiate a stream, unless the multi-job stream option is in effect. If the receiving node receives a request to initiate a stream that is already active, the receiving node should return an R C record (RCB X‘B0’).