2 cissp ® Official Study Guide Eighth Edition

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Chapter 11 
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Secure Network Architecture and Securing Network Components
Fiber Distributed Data Interface (FDDI)
Fiber Distributed Data Interface (FDDI)
is a high-speed token-passing technology that 
employs two rings with traffic flowing in opposite directions. FDDI is often used as a back-
bone for large enterprise networks. Its dual-ring design allows for self-healing by removing 
the failed segment from the loop and creating a single loop out of the remaining inner and 
outer ring portions. FDDI is expensive but was often used in campus environments before 
Fast Ethernet and Gigabit Ethernet were developed. A less-expensive, distance-limited, 
and slower version known as Copper Distributed Data Interface (CDDI) uses twisted-pair 
cables. CDDI is also more vulnerable to interference and eavesdropping.
Subtechnologies
Most networks comprise numerous technologies rather than a single technology. For exam-
ple, 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 digi-
tal 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.
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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 communica-
tion occurs by variances in the constant signal.
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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 interfer-
ence 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.

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Cabling, Wireless, Topology, Communications, and Transmission Media Technology