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US 4,819,229 AGranted
Local area network priority control system
AssigneeUniversity of Strathclyde
InventorsDavid W. Pritty, Derek Masson
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AssigneeUniversity of Strathclyde
InventorsDavid W. Pritty, Derek Masson
Estimating the term…
A LAN priority control system is described which uses an interrupt priority control structure which suspends transmission of a packet from a lower priority node and allows a higher priority interrupting node, which desires to transmit a higher priority message, to obtain rapid access to the transmission medium and to transmit the message. The message is interrupted using a within packet interrupt which is taken to include any command which results in the transmission of a packet onto a common-medium being halted before the complete packet has been transmitted. In addition, the priority of nodes can be adjusted by a centralized network manager or by intelligent terminals distributed among the nodes, allowing priorities to be adjusted at nodes to correspond to the relative priorities of messages currently at these nodes rather than having a fixed allocation of priorities. In a token ring implementation, suspension of the message causes a busy token to be released which recirculates round the ring. A token is then freed to the interrupting node or nodes which claims the token and uses the token to transmit the higher priority message and, after transmission cycle of the message, the token is returned to its free state and its original node to complete transmission of the original message, in the absence of another active higher priority node. The within packet interrupt can be implemented in software or hardware and is suitable for use with token passing local area networks and especially a token passing ring.
A local area network interrupt node priority control system for use with a local area network having a plurality of nodes coupled to a shared transmission medium, each node being capable of receiving messages from external sources having different levels of priority, said local area network interrupt node priority control system comprising data carrying means for allocating access of each node to the shared transmission medium, said shared transmission medium incorporating a logically separate priority interrupt control channel coupled to each node of said plurality of nodes and in use, said data carrying means carrying a first message from a first node having a first level priority interrupt means for detecting when a second node has a higher priority message for transmission on said shared transmission medium, and for generating within packet interrupt signal to suspend transmission of said first message from said first node to release said data carrying means to said second node for transmitting said higher priority message, and means for eventually returning said data carrying means to said first node on completion of transmission of said higher priority message to complete transmission of said first message.
A method of permitting a higher priority message to be transmitted onto a shared transmission medium of a local area network, said local area network having a plurality of nodes coupled to said shared transmission medium and on which a lower priority message is currently being transmitted by data carrying means, said method comprising the steps of:
A local area network having a plurality of computer systems desiring access to a shared transmission medium for providing access of higher priority message to said shared transmission medium during transmission of lower priority messages, said local area network comprising a shared transmission medium, a plurality of nodes coupled to said shared transmission medium, each node consisting of a computer system coupled to the shared transmission medium via a transmission medium access unit, said shared transmission medium incorporating a logically separate priority control channel coupled to each node of said plurality of nodes said transmission medium access unit having monitoring means for monitoring priority of messages on said shared transmission and comparison means for comparing the priority of said transmitted messages with a priority of a message from its associated computer system desiring to be transmitted, interrupt generating means for generating a within packet interrupt for suspending the transmission of a message on said transmission medium having a lower priority, and said transmission medium access unit having priority control means for altering the priority of a data carrying signal to match the priority of said message to be transmitted, and for altering the priority of said data carrying means after transmission of said message of the original priority for completing transmission of said lower priority message.
Dependencies are inferred from the claim text.