EP0132645A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Method and apparatus for facilitating collision detection
Assignee: International Business Machines Corp
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Filing: 1984-07-05
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Granted: —
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Expires: 2004-07-05
Abstract
Abstract In multiple access bit-serial baseband data communication systems, transceiver stations "listen" for collisions while their transmitters are actively signalling on a common bus. Any station detecting collision it aborts its transmission and reschedules the same. In order to avoid erroneous collision detection the presently disclosed stations are made sensitive to collisions only while transmitting a particular binary level and insensitive at other times. When transmitting at the particular level, the station's driver is conditioned to present high impedance to the bus, so as not to interfere with reception of signals sent by other stations. Transitions to this high impedance state are delayed by a short increment of time, relative to corresponding transitions in the bit signals at the driver input, for allowing active/quick removal of charges accumulated at the local bus connection site during the previous bit transfer period. If all but one detect collision, those detecting collision will defer and the station not detecting collision will continue its transmission.
Inventors
- 👤 Yuan Chang
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-02 18:42
CPC Classifications
H; H04; H04L; H04L12/00; H04L12/28; H04L12/40; H04L12/407; H04L12/413; H04L12/4135
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
262 words
An apparatus for facilitating collision detection in a multiple access data communication system, in which plural transceiver stations may simultaneously begin to transmit baseband signals on a bus , monitor the bus for collision, and abort and deferrably reschedule transmissions upon detecting collision, said apparatus being characterized in that it comprises : three-state driver circuit means in the transmitting section of a said station's transceiver for passing information bit signals from the station to the bus; means for conditioning said driver circuit means to distinct first, second and third states to effect transfers of information bit signals from the station to the bus; said conditioning means actively setting said driver circuit means steadily to said first state for actively transferring a signal at a first amplitude level to said bus, said signal having a first logical bit significance; said conditioning means setting said driver circuit means transiently to said second state to actively transfer to said bus a second signal level, different from said first level, when initiating transmission from the station of bit information having second logical significance opposite to said first logical significance, after prior transmission of bit information having said first logical significance; said bus charging to and remaining at said second level when no other station driver is simultaneously operating in said first state; and said conditioning means setting said driver circuit means to said third state for the remaining transmission of said bit information having said second logical significance; said driver circuit presenting a high impedance effectively isolating it from said bus while in said third state.
Claim 2
Independent Claim
262 words
An apparatus for facilitating collision detection in a multiple access data communication system, in which plural transceiver stations may simultaneously begin to transmit baseband signals on a bus , monitor the bus for collision, and abort and deferrably reschedule transmissions upon detecting collision, said apparatus being characterized in that it comprises : three-state driver circuit means in the transmitting section of a said station's transceiver for passing information bit signals from the station to the bus; means for conditioning said driver circuit means to distinct first, second and third states to effect transfers of information bit signals from the station to the bus; said conditioning means actively setting said driver circuit means steadily to said first state for actively transferring a signal at a first amplitude level to said bus, said signal having a first logical bit significance; said conditioning means setting said driver circuit means transiently to said second state to actively transfer to said bus a second signal level, different from said first level, when initiating transmission from the station of bit information having second logical significance opposite to said first logical significance, after prior transmission of bit information having said first logical significance; said bus charging to and remaining at said second level when no other station driver is simultaneously operating in said first state; and said conditioning means setting said driver circuit means to said third state for the remaining transmission of said bit information having said second logical significance; said driver circuit presenting a high impedance effectively isolating it from said bus while in said third state.
Claim 3
Dependent Claim
149 words
Apparatus in accordance with claim 1, characterized in that it comprises : bit sampling means in the receiver section of said station transceiver for receivably sampling the signal level on the bus at a predetermined time within each interval allotted for transmitting a bit signal from the respective station to the bus; the time of said level sampling always trailing times at which the respective driver means is conditioned to said second state by a predetermined time increment allowing for active steeling of said bus to said second level; means for storing information bit functions sampled by said bit sampling means; means associated with said storing means for determining from the information stored therein if a collision has occurred on said bus, and means responsive to said collision determining means for controlling the transmitting section of the station to continue or discontinue a transmission operation conditional on said determination.
Claim 4
Dependent Claim
62 words
Apparatus in accordance with claim 2 characterized in that said stations comprise user devices linked via transceivers with said bus for exchanging byte information with said bus, each user device containing a general purpose digital computer which is programmably adapted to act as said collision determining means in addition to its primary task responsibilities concerned with processing data within said user device.
Claim 5
Independent Claim
229 words
A method of facilitating collision detection by contending transceivers in a multiple access data communication system, in which plural transceivers having tapped connections to a common bus may simultaneously attempt to transmit packets of digital information in a bit-serial baseband form, each packet comprising multiple bit signals representing logical 1 and 0 digital information, said method being characterized in that it comprises, at each site of connection between a transceiver and the bus : isolating the transmitting section of the transceiver from the bus during intervals locally allotted to transfers of signal levels to the bus representing one particular logical information bit value; actively coupling the same section to the bus during intervals allotted to transfers of the opposite logical bit signal level to the bus; receivably sampling the bit signal level on said bus at approximately the midpoint in time of each interval locally allotted to transferring a bit from the transceiver to the bus; and timing transitions of said transmitting section from the actively coupled state to the isolated state to occur later than corresponding transitions in the logical bit information presented to the input of the transmitting section but earlier than the next time allotted for receivably sampling the bus level, whereby charge conditions accumulated at said connection site ban be actively removed through the transmitting section before that section is placed in said isolated state.
Claim 6
Independent Claim
229 words
A method of facilitating collision detection by contending transceivers in a multiple access data communication system, in which plural transceivers having tapped connections to a common bus may simultaneously attempt to transmit packets of digital information in a bit-serial baseband form, each packet comprising multiple bit signals representing logical 1 and 0 digital information, said method being characterized in that it comprises, at each site of connection between a transceiver and the bus : isolating the transmitting section of the transceiver from the bus during intervals locally allotted to transfers of signal levels to the bus representing one particular logical information bit value; actively coupling the same section to the bus during intervals allotted to transfers of the opposite logical bit signal level to the bus; receivably sampling the bit signal level on said bus at approximately the midpoint in time of each interval locally allotted to transferring a bit from the transceiver to the bus; and timing transitions of said transmitting section from the actively coupled state to the isolated state to occur later than corresponding transitions in the logical bit information presented to the input of the transmitting section but earlier than the next time allotted for receivably sampling the bus level, whereby charge conditions accumulated at said connection site ban be actively removed through the transmitting section before that section is placed in said isolated state.
Claim 7
Dependent Claim
188 words
A method of facilitating collision detection in accordance with Claim 4, in a system in which each transceiver interfaces between the bus and a user device which contains a general purpose digital computer, characterized in that it comprises at each said connection site : transmitting said information signals in a bit-serial baseband asynchronous form in which each group of bit signals forming a byte is preceded by a pair of stop and start signals whose transition provides a time reference for reception of the respective bit group at other transceiver connection sites; tailoring times allotted to said stop signals to specific operating characteristics of the computer in the respective user device; storing bit level samples acquired in said receivably sampling step to accumulate samples acquired during transfer of an outgoing byte; transferring said stored samples to said respective computer during the stop signalling interval immediately following the transfer of said outgoing byte; and during the same stop interval, comparing said transferred samples to byte information previously stored in said computer and determining thereby if a collision occurred on said bus during the previous interval of outgoing byte transfer.
References Cited (Backward Citations)
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