NOTE All standards are available from the IEEE website at www.ieee.org/getieee802
Other LAN Technologies: Token Bus, Token Ring, and FDDI
In addition to Ethernet, other LAN technologies were also developed during the 1980s.
Three of them??”Token Bus, Token Ring, and Fiber Distributed Data Interface (FDDI)??”
were notably prominent. They have even been standardized as IEEE 802.4 for Token
Bus and IEEE 802.5 for Token Ring, whereas FDDI was standardized by the American
National Standards Institute (ANSI), as the X3T9.5.
The discussion of these technologies in any detail is outside the scope of this book,
but briefly, all these technologies employ a special control frame called a token. Only the
workstation on the LAN that possess the token (and there is only one token per LAN)
can transmit. Because there is only a single token and hence only one token holder,
collisions are not possible.
Each of these LAN technologies was developed for different reasons and has its benefits
and shortcomings. Token Bus was primarily driven by General Motors and others
that were interested in factory automation and wanted a reliable, efficient, predictable,
and high-throughput system at heavy loads that aligned well with their assembly lines.
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