Page 842 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

Most networks comprise numerous technologies rather than a single
technology. For example, Ethernet is not just a single technology but a

superset of subtechnologies that support its common and expected
activity and behavior. Ethernet includes the technologies of digital
communications, synchronous communications, and baseband
communications, and it supports broadcast, multicast, and unicast
communications and Carrier-Sense Multiple Access with Collision
Detection (CSMA/CD). Many of the LAN technologies, such as
Ethernet, Token Ring, and FDDI, may include many of the

subtechnologies described in the following sections.

Analog and Digital

One subtechnology common to many forms of network
communications is the mechanism used to actually transmit signals
over a physical medium, such as a cable. There are two types: analog
and digital.

Analog communications occur with a continuous signal that varies

in frequency, amplitude, phase, voltage, and so on. The variances
in the continuous signal produce a wave shape (as opposed to the
square shape of a digital signal). The actual communication occurs
by variances in the constant signal.

Digital communications occur through the use of a discontinuous
electrical signal and a state change or on-off pulses.

Digital signals are more reliable than analog signals over long
distances or when interference is present. This is because of a digital

signal’s definitive information storage method employing direct
current voltage where voltage on represents a value of 1 and voltage off
represents a value of 0. These on-off pulses create a stream of binary
data. Analog signals become altered and corrupted because of
attenuation over long distances and interference. Since an analog
signal can have an infinite number of variations used for signal

encoding as opposed to digital’s two states, unwanted alterations to
the signal make extraction of the data more difficult as the degradation
increases.

Synchronous and Asynchronous