A-D Conversion - Analog-to-digital conversion. A-D conversion is a process in which an analog signal is modified into a digital signal. A-D conversion takes place, for example, when an analog modem call reaches a digital modem.
ADSL (Asymmetric Digital Subscriber Line) - A modem technology for transmitting information at high speeds on existing copper phone lines to homes and businesses. It's so named because most of the channel sends information downstream to the user (at speeds ranging from 1.5 Mb/s to 9 Mb/s); the rest of the channel carries information upstream from the user (at speeds ranging from 16 kb/s to 640 kb/s.)
Attenuation - The reduction in the strength of a signal over distance, expressed in decibels per kilometer (dB/Km) or per 100 feet. Factors affecting attenuation are the frequency range of the signal, wire shielding, and type of cable. Unshielded twisted pair (UTP) cable suffers from the most attenuation, while fiber-optic cable has very little attenuation.

Backbone - The part of the communications network intended to carry the bulk of the traffic.
Bandwidth - The information-carrying capacity of a communications channel measured in bits-per-second for digital systems or in megaHertz for analog systems.
Binary - A numbering system that has two as its base: the digits 0 and 1. all data input into a computer consists of 0's and 1's, which are called binary digits or bits. By contrast, the universal numbering system is the decimal system, which has 10 as its base.
Binary Data - Data in the form of zeroes and ones.
Bit Rate - The number of bits that travel over a connection per second.
Bit Error Rate (BER) - A measure of transmission accuracy expressed as the ratio of bit errors received to bits sent. A common voice and data BER benchmark is 10-9 or one error in a billion.
Bit Error Rate Test - A test to determine the percentage of received bits in error compared to the total number of bits received. Usually expressed as a number to the power of 10.
Broadband - A communication network or channel capable of carrying large amounts of information.
Byte - 8 bits of data, also called an octet.

C Band - In electrical networks, a portion of the radio frequency spectrum. Communication satellites operate on C-band frequencies from 5.925 to 6.425 GHz for uplinks and 3.700 to 4.200 GHz for downlinks. In optical networks, a range of wavelengths between 1535nm and 1565nm.
Center Office (CO) - The building that houses the switching equipment to which are connected circuits of business and residence phones; also called Exchange.
Channelized T1/E1 - T1 or E1 service that is divided into individual 64 kbps channels (or channels that are multiples of 64 kbps such as a 256 kbps channel made from four 64 kbps channels), as opposed to unchannelized service, which uses the entire bandwidth of the T1 (1.544 Mbps) or E1 (2.048 Mbps). Channelized T1 or E1 lines can consist of switched lines with inband signaling or leased lines. Additionally, leased lines may be channelized, for example when a leased line runs from the central office to the corporate headquarters as a single T1 or E1 line, but then branches into channels to remote sites from the corporate headquarters. A line can have three types of channels:

• &Mac183; DSO - a 64-Kbps channel on a line using inband signaling. For information on inband signaling, see the entry for Inband signaling.
  
• &Mac183; B channel - 56-Kbps or 64-Kbps channel that carries user data on a line using signaling, see the entry for ISDN D-channel signaling.
  
• &Mac183; D channel - carries WAN synchronization information n a line using ISDN D-channel signaling. For information on ISDN D-channel signaling, see the entry for ISDN D-channel signaling.
  

Cladding - In fiber optics technology, the plastic or glass jacket that protects an optical fiber. It prevents loss of signal carried by the fiber by reflecting light back into the fiber's core.
Core - In fiber optics technology, the center of the glass that the light travels through.