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ETHERNET TECHNOLOGY

Part 1: Frames, Collisions, and 10 Mbps LANs

by James Antonakos

Start ý Ethernet Frame Format ý The Interframe Gap ý Collision Or No Collision ý Detecting Errors ý Random Waiting Period ý 10-Mbps Ethernet ý 10BaseFý Errors In Ethernet LANS ý More To Come ý Sources and PDF

DETECTING ERRORS

Figure 6 shows a simplified circuit for detecting a collision by comparing the transmitted and received bit streams with each other. In other words, the Ethernet transceiver listens to itself as it is transmitting. If a zero signal was transmitted, the receiver should see a zero. The same is true for a one signal. If the signals do not match, it is most likely because of a collision or some other network malfunction. As indicated in Figure 6, an exclusive-OR gate is used to identify when the transmitted and received bit streams are different. The delay is required on the transmitter input of the exclusive-OR gate to compensate for the time required by the transmitter and receiver circuits.

The jam sequence generated by stations detecting a collision is a 32-bit pattern designed to propagate the collision throughout the network. The contents of the jam pattern may not represent a valid FCS for the current frame.

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