Fiber optics are made from glass. Unlike copper links, which transmit messages in the form of electrical impulses, fiber optics transmit messages in the form of light and at the speed of light. Information transmitted over a fiber optic cable can be sent more cheaply, efficiently and purely than the same information sent over a copper cable. Nonphysical links include microwaves and radio waves. Radio waves are used to transmit messages from stations to portable devices, such as cellular telephones, pagers and modem-equipped laptop computers.
Trunks connect switches to switches.
A line can be a loop, with a switch at one end but not at the other, or, in the case of a private line, it can be a link with no switching equipment at either end. The basic building blocks of any telecommunications network. Links are transmission media through which messages travel. Nonphysical links include microwaves and radio waves. A link can be either a loop or a trunk.