Multiple access data communication system

Details Multiple access data communication system Multiple access data communication system

1983-07-28

1985-09-03

Olms, Douglas W.

Multiplex communications

Wide area network

Packet switching

370 94, H04J 302, H04J 300, H04J 600

Patent

active

045396779

ABSTRACT:
In this data communication system, stations linked to a single line bus exchange information in a bit-serial asynchronous format in which transitions between stop and start signals mark beginnings of information bytes. The stations use a modified CSMA/CD protocol (carrier sense multiple access with collision detection) to obtain sending access to the bus. During information transfers, durations of stop signals are less than a predetermined limiting time length, but long enough to allow general purpose processing equipment at a station to participate directly in the real time process of information reception, thereby avoiding the need for having complex and costly adapting equipment interface between the bus and such processing equipment. When any transmission concludes, the bus remains at the stop signalling level. By conditioning detection of bus availability on timeouts conducted while the bus is in this condition, stations then ready to transmit avoid interfering with on-going transmissions. After timing out, any station may begin transmitting. At this same time, all stations monitor the bus receptively. If a station not currently sending detects a start-stop transition, its processor is interrupted and directly examines the following information byte signals. If a sending station detects a transition, its processor acts to sense for bus collision by comparing the byte last transmitted with the byte last received from the bus. If collision is detected, the sending process is aborted and the timeout process for detecting bus availability is repeated. If collision is not detected, the sending process continues.

REFERENCES:
patent: 3752932 (1973-08-01), Frisone
patent: 4210777 (1980-07-01), Bowerman et al.
patent: 4412326 (1983-10-01), Limb
patent: 4445193 (1984-04-01), Mueller et al.

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