EP0632620A2
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EP
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Backoff time evaluation method for ethernet
Assignee: Cabletron Systems Inc
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Filing: 1994-06-28
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Granted: —
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Expires: 2014-06-28
Abstract
Abstract A technique for modifying the IEEE 802.3 standard for selecting backoff times in a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) network, in the event that a collision is sensed by a node that has captured the network communication channel. If there is a small number of active nodes on the network, one node may capture the channel and the standard backoff algorithm makes it increasingly unlikely for another node to transmit. The new technique provides for less aggressive, i.e. longer, backoff times before at least the first retransmission attempt made by a node that has captured the channel. Three specific examples of the technique are disclosed. Even though the invention represents a departure from the standard CSMA/CD backoff algorithm, the overall average backoff times provided by the invention can be selected to be consistent with the average times provided by the standard. Moreover, nodes using the invention interoperate successfully with nodes that do not.
Inventors
- 👤 Henry Sho-Che Yang
- 👤 Kadangode K. Ramakrishnan
- 👤 William R. Hawe
- 👤 Anthony G Lauck
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-02 07:00
CPC Classifications
H; H04; H04L; H04L12/00; H04L12/28; H04L12/40; H04L12/407; H04L12/413
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
167 words
For use in a node of a network employing a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol for channel access wherein there is a plurality of nodes, and wherein a plurality of data packets is transmitted through a network channel, a method for improving fairness of access, comprising the steps of: sensing when a predetermined node has captured the channel by successfully transmitting a first data packet and beginning a second packet transmission without relinquishing the channel to another node; after sensing capture of the channel, sensing a collision between a second packet transmission and a transmission by another node; and after sensing a collision, selecting a backoff time to wait before attempting retransmission, wherein the backoff time before at least a first retransmission attempt is selected to be actually or potentially longer than a back off time that would be selected if the node had not captured the channel; whereby a node that has not captured the channel is given an opportunity to transmit.
Claim 2
Dependent Claim
54 words
A method as defined in claim 1, wherein: the step of selecting a backoff time includes selecting a first retransmission attempt backoff time and a second retransmission attempt backoff time with an overall average value no less than the average backoff time for first and second retransmission attempts when there is no channel capture.
Claim 3
Dependent Claim
97 words
A method as defined in claim 1, wherein the step of selecting a backoff time includes: selecting a first backoff time of approximately two slot times, to be used prior to a first attempt to retransmit, where a slot time is approximately equal to at least the round trip signal propagation time for the full length of the channel; selecting a second backoff time of zero, to be used prior to a second attempt to retransmit; and selecting third and subsequent backoff times in accordance with a standard approach used when no channel capture has been detected.
Claim 4
Dependent Claim
114 words
A method as defined in claim 1, wherein the step of selecting a backoff time includes: selecting a first backoff time that is a random number of slot times between zero and three, to be used prior to a first attempt to retransmit, where a slot time is approximately equal to at least the round trip signal propagation time for the full length of the channel; selecting a second backoff time that is a random number of slot times between zero and one, to be used prior to a second attempt to retransmit; and selecting third and subsequent backoff times in accordance with a standard approach used when no channel capture has been detected.
Claim 5
Dependent Claim
79 words
A method as defined in claim 1, wherein the step of selecting a backoff time includes: selecting a first backoff time of four slot times, to be used prior to a first attempt to retransmit, where a slot time is approximately equal to at least the round trip signal propagation time for the full length of the channel; and selecting second and subsequent backoff times in accordance with a standard approach used when no channel capture has been detected.
Claim 6
Dependent Claim
47 words
A method as defined in claim 1, wherein the step of sensing when this node has captured the channel includes: sensing when this node has begun to transmit a packet subsequent to the successful transmission of a prior packet, without detecting any intervening transmission by another node.
Claim 7
Dependent Claim
44 words
A method as defined in claim 1, wherein the step of sensing when this node has captured the channel includes: sensing when this node has begun to transmit a packet after a standard interpacket gap interval following the successful transmission of a prior packet.
Claim 8
Dependent Claim
191 words
For use in a node of a network employing a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol for channel access wherein there is a plurality of nodes, and wherein a plurality of data packets is transmitted through a network channel, apparatus for improving fairness of access, comprising: means for sensing when a predetermined node has captured the channel by successfully transmitting a first data packet and beginning a second data packet transmission without relinquishing the channel to another node; means operative after sensing capture of the channel, for sensing a collision between a second packet transmission and a transmission by another node; and means operative after sensing a collision, for selecting a backoff time to wait before attempting retransmission, wherein the backoff time before at least the first retransmission attempt is selected to be actually or potentially longer than a back off time that would be selected if the node had not captured the channel; whereby a node that has not captured the channel is given an opportunity to transmit, because of an actually or potentially larger back off time selected by the node that has captured the channel.
Claim 9
Dependent Claim
67 words
Apparatus as defined in claim 8, wherein: the means for selecting a backoff time includes means for selecting a first retransmission attempt backoff time and means for selecting a second retransmission attempt backoff time, wherein the first and second retransmission attempt backoff times have an overall average value no less than the average backoff time for first and second retransmission attempts when there is no channel capture.
Claim 10
Dependent Claim
102 words
Apparatus as defined in claim 8, wherein the means for selecting a backoff time includes: means for selecting a first backoff time of approximately two slot times, to be used prior to a first attempt to retransmit, where a slot time is approximately equal to at least the round trip signal propagation time for the full length of the channel; means for selecting a second backoff time of zero, to be used prior to a second attempt to retransmit; and means for selecting third and subsequent backoff times in accordance with a standard approach used when no channel capture has been detected.
Claim 11
Dependent Claim
119 words
Apparatus as defined in claim 8, wherein the means for selecting a backoff time includes: means for selecting a first backoff time that is a random number of slot times between zero and three, to be used prior to a first attempt to retransmit, where a slot time is approximately equal to at least the round trip signal propagation time for the full length of the channel; means for selecting a second backoff time that is a random number of slot times between zero and one, to be used prior to a second attempt to retransmit; and means for selecting third and subsequent backoff times in accordance with a standard approach used when no channel capture has been detected.
Claim 12
Dependent Claim
82 words
Apparatus as defined in claim 8, wherein the means for selecting a backoff time includes: means for selecting a first backoff time of four slot times, to be used prior to a first attempt to retransmit, where a slot time is approximately equal to at least the round trip signal propagation time for the full length of the channel; and means for selecting second and subsequent backoff times in accordance with a standard approach used when no channel capture has been detected.
Claim 13
Dependent Claim
50 words
Apparatus as defined in claim 1, wherein the means for sensing when said predetermined node has captured the channel includes: means for sensing when said predetermined node has begun to transmit a packet subsequent to the successful transmission of a prior packet, without detecting any intervening transmission by another node.
Claim 14
Dependent Claim
47 words
Apparatus as defined in claim 1, wherein the means for sensing when said predetermined node has captured the channel includes: means for sensing when said predetermined node has begun to transmit a packet after a standard interpacket gap interval following the successful transmission of a prior packet.
References Cited (Backward Citations)
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