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.
