Network collision detection and avoidance apparatus

• US 4,745,600 A
• Filed: 04/14/1986
• Issued: 05/17/1988
• Est. Priority Date: 07/09/1985
• Status: Expired due to Term

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Codex Corporation
• Inventors: Smith, Robert L. Jr., Herman, Alexander
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): KUNTZ, CURTIS A
• Application Number:
  US06/851,253
• Time in Patent Office: 764 Days
• Field of Search: 340/825.5, 370/85, 370/60, 370/94, 370/95, 370/110.1, 370/89, 455/16, 455/33, 455/38
• US Class Current: 370/445
• CPC Class Codes: H04L 12/40163 by assigning priority to messages according to a message field
• CPC Class Codes: H04L 12/4135 using bit-wise arbitration

Abstract

A technique for regulating the transmission of messages initiated simultaneously by a plurality of nodes of a network, in which clock intervals are established for the network, a sequence of digital values is included in each message and is transmitted to the medium at the rate of one digital value per clock interval, the sequences included in messages that are initiated at the same time by more than one node are transmitted in the same sequence of clock intervals, the presence on the medium of a selected digital value during any clock interval in which a node is transmitting a different digital value within the sequence of a message is detected, and the transmission of the message is interrupted by the node upon such detection, without corrupting another node'"'"'s transmission.

Claims

1. In a synchronous digital data communications network having a multiplicity of nodes each having a transmitter and a receiver for connection to a medium, means for regulating the transmission of messages initiated simultaneously by a plurality of nodes, said means for regulating comprising

clock means for determining clock intervals for said network,

coding means connected to be responsive to said clock means for including in each message a sequence of digital values and for transmitting to said medium each said sequence at a rate of one digital value per clock interval as determined by said clock means,

timing means for causing each said sequence included in each one of a plurality of said messages initiated simultaneously by a plurality of said nodes to be transmitted in the same clock intervals,

monitoring means connected to be responsive to said medium for detecting the presence on said medium of a selected digital value during any said clock interval in which a node is transmitting a different digital value within said sequence included in a said message, and

collision control means connected to be responsive to said monitoring means for interrupting transmission of said message by said node upon such detection by said monitoring means.

2. The network of claim 1, wherein said coding means codes said different digital value into an energy-free clock interval and codes said selected digital value into an energy-containing clock interval, and said monitoring means causes the receiver of each said node to listen for energy on said medium during each clock interval in which said node is transmitting no energy during transmission of a said sequence.

3. The network of claim 1 wherein said messages comprise a series of digital values where said digital values are transmitted at a rate of one digital value per clock interval.

4. The network of claim 1, wherein said sequence is unique to the node initiating the transmission of each said message.

5. The network of claim 4, wherein said sequence comprises a source address of said initiating node.

6. The network of claim 1, wherein said digital values are binary values.

7. The network of claim 6, wherein said coding means further comprises means for converting said binary values into a format wherein one binary level is represented by a pulse during a said clock interval, said pulse comprising a transition of a carrier signal level from low to high and then from high to low during some part of said clock interval, and the other binary level is represented by said carrier signal level remaining low during an entire clock interval.

8. The network of claim 7, wherein said coding means further comprises means for transmitting said pulse as a burst of RF energy, and means for disabling the transmitter of said transceiver during said clock intervals when said carrier signal level remains low.

9. The network of claim 1, wherein said clock means comprises means in each said node for deriving said clock intervals from messages received from said network, except when said node is attempting to transmit.

10. The network of claim 1 wherein said sequence of digital values included in each said message are indicative of a predetermined relative priority of said message.

11. The network of claim 10 wherein at least a portion of said sequence is unique to said node and represents a predetermined relative priority of messages sent by said node.

12. The network of claim 10 wherein said messages fall into a plurality of categories having different priorities, and said sequence comprises two portions, one portion being unique to said node, the second portion not being unique to said node, said second portion being indicative of the priority category of said message.

13. The network of claim 12 wherein said second portion comprises one segment indicative of said priority category, and a second segment indicative of subpriorities of said messages within at least one of said priority categories.

14. The network of claim 13 wherein said subpriorities are dynamically allocated.

18. The network of claim 1 wherein said digital value present on said medium during said clock interval is part of one of said messages transmitted by another said node and said other node is permitted to continue transmitting said message after said collision control means interrupts transmission by said first node.

19. The network of claim 1 wherein said node whose transmission is interrupted is able to receive the entirety of the message with which its own interrupted transmission had collided.

20. The network of claim 1 wherein each said node has an address within said network, and said digital values included in said message correspond to said address.

21. The network of claim 20 wherein each said address is unique within said network.

15. A method for regulating the transmission of messages initiated simultaneously by a plurality of nodes in a synchronous digital data communications network that includes a multiplicity of nodes each having a transmitter and a receiver for connection to a medium, comprising the steps of

establishing clock intervals for said network,

including in each message a sequence of digital values and transmitting to said medium each sequence at a rate of one digital value per clock interval,

causing sequences included in a plurality of messages initiated simultaneously by a plurality of nodes to be transmitted in the same sequence of clock intervals,

detecting the presence on said medium of a selected digital value any clock interval in which a node is transmitting a different value within said sequence of a message, and

interrupting transmission of said message by said node upon said detection.

16. The method of claim 15 wherein

said step of including comprises coding said different digital value into an energy-free clock interval, and said selected digital value into an energy containing clock interval, and

said step of detecting includes causing the receiver of each of said node to listen for energy on said medium during each clock interval in which said node is transmitted no energy during transmission of a said sequence.

17. The method of claim 15 wherein said step of including comprises causing said sequence of digital values to be indicative of a predetermined relative priority of said message.