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2.5 Local Network Technology     continued...

Physically the first ethernet systems were thick, shielded coaxial cables up to 1 kilometer long. Workstations and other machines that wished to connect to the network could tap into the ether at arbitrary locations provided they were separated by a few meters. With cables of this length, there are situations where two nodes can transmit at the same time and interfere with each other. If two nodes at opposite ends of the ether see the network idle and decide to begin transmitting, it will take a few microseconds for the signals to reach the other end of the ether, so two nodes can begin transmitting only to discover a few microseconds later that another message was in the ether. To overcome this problem, each node continually monitors the network as it is transmitting, and if it ever sees its own transmission become garbled it will stop, assuming the problem was caused by another node that began transmitting at the same time. These thick-cable ethernet systems had a bandwidth of 10 million bits per second (Mbps).