Method and apparatus for controlling latency and jitter in a local area network which uses a CSMA/CD protocol
First Claim
1. In a carrier-sense/collision-detect network, a method for transferring data over a communication channel between a first node and a second node whereby said first node ensures fairness of access and low bounded maximum access latency, comprising the steps of:
- forming the data into packets;
at said first node, detecting the state of a last action state variable;
if the last action variable indicates the last action performed by said first node was a receive action, transmitting a packet from said first node to said second node according to a last-action-equals-receive protocol such that said packet from said first node is given priority over a packet originating at said second node;
if the last action variable indicates the last action performed by said first node was a transmit action, transmitting a subsequently available packet from said first node to said second node according to a last-action-equals-transmit protocol such that transmissions from said first node are deferred if a packet from said second node is detected on said communication channel thereby giving priority to a packet originating at said second node; and
setting said last action state variable to conform to the last action performed by said first node on said channel.
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Accused Products
Abstract
An Ethernet network or other CSMA/CD network includes hub adaptors that are modified to provide a known bounded low maximum access latency. The modified adaptors maintain a state variable whose values indicates whether the last operation by the adaptor was a transmit or a receive. In the case where the last operation was a receive, the adaptor transmits a packet with a minimum or zero backoff and as an option with a reduced interpacket gap. In the case where the last operation was a transmit, the adaptor waits before transmitting a packet a period of time that allows the other node on the channel to transmit a packet if the other node has a packet to transmit.
31 Citations
14 Claims
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1. In a carrier-sense/collision-detect network, a method for transferring data over a communication channel between a first node and a second node whereby said first node ensures fairness of access and low bounded maximum access latency, comprising the steps of:
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forming the data into packets; at said first node, detecting the state of a last action state variable; if the last action variable indicates the last action performed by said first node was a receive action, transmitting a packet from said first node to said second node according to a last-action-equals-receive protocol such that said packet from said first node is given priority over a packet originating at said second node; if the last action variable indicates the last action performed by said first node was a transmit action, transmitting a subsequently available packet from said first node to said second node according to a last-action-equals-transmit protocol such that transmissions from said first node are deferred if a packet from said second node is detected on said communication channel thereby giving priority to a packet originating at said second node; and setting said last action state variable to conform to the last action performed by said first node on said channel. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. In a carrier-sense/collision-detect network, a method for transferring data over a communication channel between a first node and a second node ensuring fairness of access and low bounded maximum access latency, comprising the steps of:
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at said first node, detecting the state of a mode variable; if the mode variable indicates the first node is in a transmit mode, transmitting data from said first node to said second node according to a last-action-equals-receive protocol such that said data from said first node is given priority over data originating at said second node; if the mode variable indicates the first node is in a receive mode, transmitting data from said first node to said second node according to a last-action-equals-transmit protocol such that said first node defers data transmission when it detects data from said second node; and changing the value of mode variable from transmit to receive according to a predetermined timing schedule.
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12. A network for the exchange of digital data comprising;
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a first node having a plurality of first node adapters; a plurality of second nodes, each having a second node adaptor and each connected to a first node adaptor by a private communication channel, wherein each said first node adaptor comprises; means for receiving data from said first node for transmission on its connected communication channel to its connected second node; means for transmitting said data on said channel; means for detecting data on said channel from said second node; means for receiving said data from said channel; means for transferring said data to said first node; means for detecting collisions on said channel while said first node adapter is transmitting on said channel; state variable means for storing the state of the last action performed by said adaptor on said communications channel; and control means responsive to the state of said state variable means and said detecting means for controlling the transmitting of said data on said communications channel and the receiving of said packets from said channel. - View Dependent Claims (13)
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14. A method for enabling a plurality of 802.3 ethernet standard workstations to send and receive multi-media data and ensuring fairness of access and low bounded maximum access latency, comprising the steps of:
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connecting said standard 802.3 workstations to a multi-media enabled hub via a plurality of private point-to-point transmission channels; transmitting packet data between a first workstation and a second workstation by first transmitting a packet from said first workstation to said hub and then transmitting said packet from said hub to said second workstation; and using said hub to ensure low bounded access latency by said first node alternating its packet protocol such that said hub transmits a plurality of packets according to a protocol favoring said packets and then transmits a second plurality of packets according to a protocol such that said hub defers to any packets being sent by said workstations.
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Specification