High performance channels for data processing systems

Buffers 54,58 are provided in two elements 52,56 between which data is to be transferred wherein both buffers are managed solely by the originator of the data transfer. Only one transfer is required to transmit a message, and a second transfer acknowledges the completion of the function because message delivery to the receiver is guaranteed under the implemented protocol. When a request is sent, a message timer is started at the sender. When the normal response for the request is received, the timer is reset; however, if the duration of the message operation exceeds the timeout value, a message-timeout procedure is initiated. When the cancel command is issued, a second timer is set. If this timer is exceeded, subsequent cancel commands can be issued. If subsequent cancel commands are issued, a cancel complete command must be sent and responded to. Since the commands must be executed in the sequence in which they are received, a response to the cancel complete command ensures that there are no other cancel operation commands remaining in the receiver, allowing subsequent operations to start without danger of being cancelled.