Collision avoiding system and protocol for a multiple access digital communications system
First Claim
1. A method for controlling digital signals in a communications system, said system including a communications loop, a plurality of stations, at least two of said stations being respectively coupled to a first and a second signal path of said loop, said method including the steps of writing a first packet signal on said first path and reading a second packet signal from said second path and characterized in that said method further comprising the steps ofreading a third packet signal from said first path andavoiding a collision on said communications loop in response to said third packet.
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Accused Products
Abstract
With the advent of digital communications, it is common to transfer packets of information among a plurality of stations, e.g., digital computers. In order to control the transfer of the packets, various protocols have been introduced. However, the efficiency related to known multiples access digital communications system protocols tends to decrease as the digital signal rate increases. To overcome such problems, the instant communications system and protocol contemplate a communications loop having first and second oppositely directed signal paths. At least two stations are coupled to both the first and the second signal paths. A station includes an arrangement for writing a first signal on the first path and an arrangement for reading a second signal from the second path. In addition, the station includes an arrangement for reading a third signal from the first path. The third signal is coupled from the first path to the station by an arrangement which electrically precedes the arrangement for writing the first signal on the first path. If the station has a packet to transmit, it can overwrite a busy control field of the third signal packet on the first path. Having read the third signal on the first path, a logical interpretation may be made within the station as to whether the first path is busy or not busy. If the first path is not busy, the packet may be written on the first path by overwriting the third signal thereon. If the first path is busy, the station may overwrite a request control field of the third signal for indicating that the station was unable to transmit the packet. The packets flow around the loop and are monitored on the second path. Eventually all packets will be transmitted and the request control field may be detected at the receive side of a head station for indicating the event that all packets have been transmitted, in which event a new cycle may be started by initializing each station on the loop and by permitting each station to transmit.
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Citations
25 Claims
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1. A method for controlling digital signals in a communications system, said system including a communications loop, a plurality of stations, at least two of said stations being respectively coupled to a first and a second signal path of said loop, said method including the steps of writing a first packet signal on said first path and reading a second packet signal from said second path and characterized in that said method further comprising the steps of
reading a third packet signal from said first path and avoiding a collision on said communications loop in response to said third packet.
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8. A communications system comprising a communications loop, said loop including a first and a second signal path, said signal paths being oppositely directed, a plurality of stations, each of at least two of said stations being coupled to both said first and said second signal paths, a station including means for writing a first packet signal on said first path and means for reading a second packet signal from said second path and characterized in that said system further comprises:
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means for reading a third packet signal from said first path, means for said first path reading means to be coupled to said first path in a manner electrically preceding said first path writing means, and means responsive to said first, second and third packet signals for avoiding collisions on said communications loop. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16)
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17. Station apparatus for controlling digital signals, said station adapted to be coupled to a communications loop, said loop including a first and a second signal path, said signal paths being oppositely directed, said station including means for writing a first packet signal on said first path and means for reading a second packet signal from said second path and characterized in that said station further comprises:
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means for reading a third packet signal from said first path, means for said first path reading means to be coupled to said first path in a manner electrically preceding said first path writing means, and means responsive to said first, second and third packet signals for avoiding collisions on said communications loop. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25)
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Specification