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Examining Campus LAN Technologies 83
can use the switch to directly attach large numbers of clients or servers, thereby replacing
concentrators. The Cisco Catalyst 3900 and 5000 are examples of Token Ring switches
commonly deployed in many networks.
FDDI
Fiber Distributed Data Interface (FDDI) is a high-speed backbone for mission-critical and
high-traffic networks. It can transport data at a rate of 100 Mbps and can support up to 500
stations on a single network. FDDI was designed to run through fiber cables, but it can also run
on copper as Copper Distributed Data Interface (CDDI) using electrical signals. Figure 3-4
shows an FDDI network.
Figure 3-4
FDDI Network
FDDI is highly reliable because FDDI networks consist of two counter-rotating rings. A
secondary ring provides an alternative data path in case a fault occurs on the primary ring. FDDI
stations incorporate this secondary ring into the data path to route traffic around the fault.
FDDI has seen its best days. It is being phased out in upgrade installations in favor of ATM and
Gigabit Ethernet.
ATM Switches
ATM is a high-speed packet-switching technique that uses short fixed-length packets called
cells. Fixed-length cells simplify the design of an ATM switch at the high switching speeds
involved. Campus design that requires the capacity to handle multiservice traffic can take
advantage of ATM switching. ATM switches can support all classes of traffic at high speeds.
WAN
Primary
Secondary
Concentrator
FDDI
87200333.book Page 83 Wednesday, August 22, 2001 2:18 PM