ABSTRACT
Networks have become ubiquitous both at home and in the office, and various types of media have been
deployed to carry networking traffic. Much of the Internet is now carried over a fiber-optic backbone, and
most businesses use fiber-optic cables to provide high-speed connectivity on their corporate campuses.
Cable providers bring high-speed networking to many homes and businesses via coaxial cable. Local
exchange carriers (LECs) and competitive local exchange carriers (CLECs) bring high-speed networking to
many homes and businesses via twisted-pair cables, and numerous buildings are wired with twisted-pair
cables to support high-speed networking to user desktops. Wireless networks have been deployed to
provide network connectivity without the need for users to connect to any cables at all, although antennas
and pigtail cables (coaxial cables) can be used to great advantage in maximizing the value of a wireless
environment. These information highways and back roads lie within the physical layer of the seven-layer
OSI (Open Systems Interconnection) model. The physical layer of the OSI model comprises the cables,
standards, and devices over which data-link (layer 2 of the OSI model) encapsulation is performed.
