2 cissp ® Official Study Guide Eighth Edition

Transmission Media
The type of connectivity media employed in a network is important to the network’s 
design, layout, and capabilities. Without the right cabling or 
transmission media
, a network 
may not be able to span your entire enterprise, or it may not support the necessary traffic 
volume. In fact, the most common causes of network failure (in other words, violations of 
availability) are cable failures or misconfigurations. It is important for you to understand 
that different types of network devices and technologies are used with different types of 
cabling. Each cable type has unique useful lengths, throughput rates, and connectivity 
requirements.
Coaxial Cable
Coaxial cable
, also called 
coax
, was a popular networking cable type used throughout the 
1970s and 1980s. In the early 1990s, its use quickly declined because of the popularity and 
capabilities of twisted-pair wiring (explained in more detail later). In the 2000s, you are 
unlikely to encounter coax being used as a network cable but may still see some use of it as 
an audio/visual connection cable (such as with some cable television equipment or satellite 
dish equipment, although the final connection from the service equipment to your television 
is most likely HDMI today).
Coaxial cable has a center core of copper wire surrounded by a layer of insulation, 
which is in turn surrounded by a conductive braided shielding and encased in a final insula-
tion sheath.
The center copper core and the braided shielding layer act as two independent conduc-
tors, thus allowing two-way communications over a coaxial cable. The design of coaxial 

---

Cabling, Wireless, Topology, Communications, and Transmission Media Technology 
497
cable makes it fairly resistant to 
electromagnetic interference (EMI) 
and makes it able to 
support high bandwidths (in comparison to other technologies of the time period), and it 
offers longer usable lengths than twisted-pair. It ultimately failed to retain its place as the 
popular networking cable technology because of twisted-pair’s much lower cost and ease 
of installation. Coaxial cable requires the use of segment terminators, whereas twisted-
pair cabling does not. Coaxial cable is bulkier and has a larger minimum arc radius than 
twisted-pair. (The arc radius is the maximum distance the cable can be bent before dam-
aging the internal conductors.) Additionally, with the widespread deployment of switched 
networks, the issues of cable distance became moot because of the implementation of hier-
archical wiring patterns.
There are two main types of coaxial cable: thinnet and thicknet. 
Thinnet
, also known 
as 
10Base2
, was commonly used to connect systems to backbone trunks of thicknet 
cabling. Thinnet can span distances of 185 meters and provide throughput up to 10 Mbps. 
Thicknet
, also known as 
10Base5
, can span 500 meters and provide throughput up to 
10 Mbps (megabits per second).
The most common problems with coax cable are or were as follows:
■
Bending the coax cable past its maximum arc radius and thus breaking the center 
conductor
■
Deploying the coax cable in a length greater than its maximum recommended length 
(which is 185 meters for 10Base2 or 500 meters for 10Base5)
■
Not properly terminating the ends of the coax cable with a 50 ohm resistor
■
Not grounding at least one end of a terminated coax cable