Collision detection technique for an optical passive star local

Details Collision detection technique for an optical passive star local Collision detection technique for an optical passive star local

1986-07-24

1987-10-20

Olms, Douglas W.

Multiplex communications

Wide area network

Packet switching

370 94, 3408255, 371 57, H04J 302, G06F 1100

Patent

active

047019093

ABSTRACT:
The present invention relates to a collision detection technique for an optical Star LAN using CSMA/CD. The present technique is implemented by preferably adding two or more fixed Hamming weight sequences, e.g., a fixed even or odd number of 1's in each unique cyclic error correcting code word, to the preamble section of each packet of information to be transmitted. These collision detection sequences have a length which is beyond the vulnerable time period of the CSMA/CD protocol (maximum round-trip propagation delay for each packet) by at least one code word length in order to prevent any misdetection, or false detection, of a collision. Each receiver in the listening period, looks for a code pattern with a fixed Hamming weight. When code patterns collide, the Hamming weight of the resulting code word in the collision period will exceed the nominal sequence weight (will include more 1's than the fixed Hamming weight) and a sequence weight violation is detected. Such detection is used to stop the transceivers from transmitting over the LAN and restart the network in order to avoid further collisions and network chaos.

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