Method and apparatus for predicting and controlling data transmission in a CSMA/CD LAN

摘要

A repeater in a LAN maintains a count of collisions and retransmission attempts for each node coupled to the repeater since that node's last successful packet transmission. The count is used to prioritize which of the nodes involved in a subsequent collision will be allowed to continue transmitting. The time at which data packets from the nodes arrive at the repeater will vary according to the propagation delay attributed to the varying lengths of the communication medium between each of the nodes and the repeater. For the repeater to arbitrate among the nodes that begin transmitting, it is useful to receive the data packets from each node at the same time. The repeater automatically equalizes the transmission delay. The repeater buffers the data packet received from each node until sufficient time has elapsed to begin receiving a data packet from each node that is attempting to transmit a data packet during the current arbitration interval. For each node, the repeater maintains a slot time counter. The backoff time following a collision is measured in increments of slot time, so using the slot time counter for a node allows the repeater to predict when it will receive a data packet from a node that is currently backed off. When a node has an opportunity to attempt transmitting a data packet at each slot time, the repeater determines if that node is going to attempt to transmit a data packet before deciding which node will be allowed to transmit a data packet.