3, pp. 567 568). In the earlier Aloha network, terminals equipped with packet radios shared a multiaccess radio channel, and a random access procedure was used for allocation. In the Aloha network, each terminal made independent decisions as to when to transmit. If two terminals decide to transmit at the same time, a "collision" occurred, and each terminal then was required to wait for a random interval before attempting to retransmit. This procedure eliminated the need for a central control; however, efficiency decreased, as use increased.
This earlier procedure was modified when Xerox developed Ethernet. When an Ethernet station decides to transmit, "a carrier sensing mechanism is first used" (Chorafas, 1989, p. 237). In a transmission from another station is in progress, the sensing station must wait until the network is free; otherwise, the station may commence transmission at once.
The stations in an internal LAN are connected to the network by coaxial cable. Another difference between the LAN concept and the earlier Aloha network is that the waiting time for each station in the network waiting to transmit is varied as a means of insuring that collisions will not occur. These waiting times increas
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