Appendix C: Glossary

A

Abend

A contraction of the words abnormal end used to describe a computer crash in the mainframe world.

Absorption

A form of optical attenuation in which optical energy is converted into an alternative form, often heat. Often caused by impurities in the fiber, hydroxyl absorption is the best-known form.

Acceptance angle

The critical angle within which incident light is totally internally reflected inside the core of an optical fiber.

Access

The set of technologies used to reach the network by a user.

Active video

That part of the video signal that is visible.

Add-Drop Multiplexer (ADM)

A device used in SONET and SDH systems that has the capability to add and remove signal components without having to demultiplex the entire transmitted transmission stream, a significant advantage over legacy multiplexing systems such as DS-3.

Advanced Mobile Phone Service (AMPS)

The modern analog cellular network.

Aerial plant

Transmission equipment (including media, amplifiers, splice cases, and so on) that is suspended in the air between poles.

Alternate mark inversion

The encoding scheme used in T-1. Every other one is inverted in polarity from the one that preceded or follows it.

American Standards Code for Information Interchange (ASCII)

A 7-bit data encoding scheme.

Amplifier

A device that increases the transmitted power of a signal. Amplifiers are typically spaced at carefully selected intervals along a transmission span.

Amplitude modulation

The process of causing an electromagnetic wave to carry information by changing or modulating the amplitude or loudness of the wave.

Analog