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The Impact of Switching on Traditional Layer 2 LAN
Protocols
The development of LAN switches has, to a certain extent, reinvented
networking—particularly Ethernet networking. Before LAN switching,
FDDI, CDDI, and ATM were considered the backbone technologies.
Each offered 100Mbps or higher dedicated transfer rates, and by
using routers and bridges, Ethernet and Token Rings could be scaled
to efficient sizes and interconnected through the backbone. It was
believed by many that Fast Ethernet would be a viable contender
against these protocols, particularly because Fast Ethernet uses the
identical MTU size of standard Ethernet, and that protocol accounts for
the majority of installed LAN infrastructures. However, the different
protocol variations, shared bandwidth format, and limited distance
and expansion options deterred its usage initially as a backbone
technology.
Token Technologies RIP
Although there is a substantial installation base of Token Ring
in production, its long-term viability is questionable. Token
Ring's cost, complexity, additional configuration requirements,
and lack of built-in support on any computer platform have, in
a sense, made it a legacy protocol. This is also becoming the
case with FDDI, where cost and waning hardware support over
time will relegate it to legacy status.
Oddly enough, their demise was brought about largely from
the evolution of bridging to switching, even though both
protocols were commonly used with bridging. Although they,
like Ethernet, benefited from the performance gains made
possible by switching, subsequent switching technology
enhancements did not translate into the FDDI and Token Ring
protocols as well as they did for Ethernet. For example, full
duplex support, which was invented for the efficient use of Fast
Ethernet and Gigabit Ethernet for backbone applications, was
only available with certain FDDI implementations and provided
little performance enhancements for Token Ring.
This is not to say that they will disappear tomorrow. IBM still
touts Token Ring as a cutting edge networking solution. FDDI