Overview

Signaling, Digital Voice, Analog to Digital Conversion, Pulse Code Modulation (PCM), SNA and SDLC and Signaling System 7 (SS7)

The term bit is a contraction of binary digit, the smallest unit of digital information-either a zero or a one-a signal for either on or off. The major computer codes use either seven plus a parity bit for error control (ASCII) or eight (EBCDIC) bits to represent one letter, number or symbol.

Each data digit is called a bit. A string of bits, usually eight or 16, that a computer can address as an individual group is called a byte. (A four-bit byte is a nibble.)

The slowest digital transmission speeds are measured in bits per second (bps). Faster communications run at kbps (kilobits per second) or thousands of bits per second, Mbps (megabits per second) or millions of bits per second and Gbps (gigabits per second) or billions of bits per second.

Digital Voice: Analog to Digital Conversion

Every wire acts as an antenna. Copper wires pick up signals from electrical radiation sources that exist almost everywhere. Fluorescent lights, motor starters, photocopiers and ring voltage bleeding over from close copper pairs can cause interference with a signal.

Analog signals fade with distance and must be amplified periodically. (Analog signal amplifiers are spaced at intervals of 18,000-meters.) The noise that is always present on copper circuits is amplified right along with the signal. Eventually the volume of the noise exceeds the signal volume and conversation becomes difficult or impossible to...