A Fiber Distributed Data Interface (FDDI) network provides
high-speed connections for various types of networks. FDDI was
designed for use with computers that required speeds greater
than the 10 Mbps available from Ethernet or the 4 Mbps available
from existing token ring architectures. An FDDI network can
support several low-capacity LANs that require a high-speed
backbone.
An FDDI network consists of two similar streams of data flowing
in opposite directions around two rings. One ring is called the
primary ring and the other is called the secondary ring. If
there is a problem with the primary ring, such as a ring failure
or a cable break, the ring reconfigures itself by transferring
data to the secondary ring, which continues transmitting.
Access Method
The access method used in an FDDI network is token passing. A
computer on an FDDI network can transmit as many packets as it
can produce within a predetermined time before releasing the
token. As soon as a computer has finished transmitting or after
a predetermined transmittal time is up, the computer releases
the token.
Because a computer releases the token when it finishes
transmitting, several packets can circulate on the ring at the
same time. This method of token passing is more efficient than
that on a standard token ring network, which allows only one
frame at a time to circulate. This method of token passing also
provides greater data throughput at the same transmission rate.
Transfer Speed
The transfer speed in an FDDI network is between 155 and 622
Mbps.
