Page 828 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

Network Topologies

The physical layout and organization of computers and networking
devices is known as the network topology. The logical topology is the
grouping of networked systems into trusted collectives. The physical
topology is not always the same as the logical topology. There are four
basic topologies of the physical layout of a network: ring, bus, star, and

mesh.

Ring Topology A ring topology connects each system as points on a
circle (see Figure 11.9). The connection medium acts as a
unidirectional transmission loop. Only one system can transmit data
at a time. Traffic management is performed by a token. A token is a
digital hall pass that travels around the ring until a system grabs it. A
system in possession of the token can transmit data. Data and the

token are transmitted to a specific destination. As the data travels
around the loop, each system checks to see whether it is the intended
recipient of the data. If not, it passes the token on. If so, it reads the
data. Once the data is received, the token is released and returns to
traveling around the loop until another system grabs it. If any one
segment of the loop is broken, all communication around the loop
ceases. Some implementations of ring topologies employ a fault

tolerance mechanism, such as dual loops running in opposite
directions, to prevent single points of failure.