COLLISION DETECTION TECHNIQUE FOR AN OPTICAL PASSIVE STAR LOCAL AREA NETWORK USING CSMA/CD

摘要

A COLLISION DETECTION TECHNIQUE FOR AN OPTICALPASSIVE STAR LOCAL AREA NETWORK USING CSMA/CDAbstractThe present invention relates to a collision detection technique for anoptical Star LAN using CSMA/CD. The present technique is implemented bypreferably adding two or more fixed Hamming weight sequences, e.g., a fixedeven or odd number of 1's in each unique cyclic error correcting code word, tothe preamble section of each packet of information to be transmitted. Thesecollision detection sequences have a length which is beyond the vulnerable timeperiod of the CSMA/CD protocol (maximum round-trip propagation delay foreach packet) by at least one code word length in order to prevent anymisdetection, or false detection, of a collision. Each receiver in the listeningperiod, looks for a code pattern with a fixed Hamming weight. When codepatterns collide, the Hamming weight of the resulting code word in the collisionperiod will exceed the nominal sequence weight (will include more 1's than thefixed Hamming weight) and a sequence weight violation is detected. Suchdetection is used to stop the transceivers from transmitting over the LAN andrestart the network in order to avoid further collisions and network chaos.