Topic: LAN access methods

At the heart of a LAN is an access method whereby network nodes share access to the transmission medium. The access method is also known as the MAC protocol (MAC: medium access control). There are essentially 2 access methods: CSMA and token passing. The patriarch of LANs, the Ethernet, uses CSMA with collision detection (CSMA/CD). The wireless LAN uses CSMA with collision avoidance (CSMA/CA). CSMA derived from the Aloha protocol, the 1st random access method developed for the Alohanet at the University of Hawaii (1971).

Robert Metcalf and his colleagues at Xerox PARC enhanced CSMA with CD and implemented CSMA/CD in their invention of Ethernet in the mid-1970’s. Ethernet was standardized in the early 80’s as IEEE 802.3.  In competitive effort, IBM invented the token passing method, and implemented it into its mighty Token Ring LAN, standardized as IEEE 802.5 in 1985. The access method determines the throughput and latency performance of a LAN. IBM’s Token Ring provably outperformed Ethernet, and thus was expected to dethrone Ethernet as the king of LANs. But Ethernet, for various reasons, has maintained its throne as the king of LANs to this day. And the Token Ring, for various reasons, has been left behind, sadly almost fading away into history.

Discussion: Research and comparatively analyze Ethernet’s CSMA/CD and Token Ring’s token passing.

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