Data Communications and Computer Networks Ch 2

Unicode

A character encoding technique that can represent all the languages on the planet.

Self-Clocking

A characteristic of a signal in which the signal changes at a regular pattern, which allows the receiver to stay synchronized with the signal's incoming bit stream.

Bipolar-AMI

A digital encoding technique with no DC-component; logic 9s are denoted by zero voltage, and logic 1s are denoted by alernating positive and negative voltages.

Digital Data

Entities that are represented by discrete waveforms, rather than continuous waveforms. Between a minimum value X and a maximum value Y, the discrete waveform takes on only a finite number of values.

Data

Entities that convey meaning within a computer or computer system.

Quantization Levels

The divisions of the y-axis that are used in pulse code modulation.

Signals

The electric or electromagnetic encoding of data. Signals are used to transmit data.

Digital Signals

The electric or eletromagnetic encoding of data that is represented by discrete waveforms rather than continuous waveforms. Between a minimum value X and a maximum value Y, the discrete waveform takes on only a finite number of values.

Quantization Error

The error that is introduced during digitization. Also known as quantization noise.

Amplification

The gain of the signal strength (power) of an analog signal.

Amplitude

The height of the wave, above or below a given reference point.

Period

The length, or time interval of one cycle.

Quantization Noise

The noise that occurs during digitization.

Intermodulation Distortion

The noise that occurs when the frequencies of two or more signals mix together and create new frequencies.

Slope Overload Noise

The noise that results during analog-to-digital conversion when the analog waveform rises or drops too quickly and the hardware tracking it is not able to keep up with the change.

Bits Per Second (bps)

The number of bits that are transmitted across a medium in a given second.

Baud Rate

The number of signal elements or signal level changes per second.

Frequency

The number of times a signal makes a complete cycle within a given time frame.

Phase

The position of the waveform relative to given moment of time or relative to time zero.

Digitization

The process of converting an analog signal or data into digital data.

Modulation

The process of converting digital data into an analog signal.

Spectrum

The range of frequencies that a signal spans from minimum to maximum.

Sampling Rate

The rate at which an analog input is sampled in order to convert it to a digital stream of 1's and 0's.

Hertz (Hz)

Cycles per second, or frequency.

American Standard Code for Information Interchange (ASCII)

A 7-bit code that is used to represent all the printable characters on a keyboard plus many non-printable control characters.

Codec

A device that accepts analog data and converts it into digital signals. This process is also known as digitization.

Manchester Code

A digital encoding scheme that ensures that each bit has a signal change in the middle of the bit and thus solves the synchronization problem.

4B/5B

A digital encoding scheme that takes 4 bits of data, converts the 4 bits in to a unique 5-bit sequence, and encodes the 5 bits using NRZI.

Non-return to Zero inverted (NRZI) Code

A digital encoding technique that assigns a binary 1 or a binary 0 by the voltage change or lack of voltage change at the beginning of the bit.

Non-return to Zero-Level (NRZ-L) Code

A digital encoding technique that assigns a binary 1 or binary 0 to a low or high voltage level.

Differential Manchester Code

A digital encoding technique that transmits a binary 0 when there is a voltage change at the beginning of the bit frame, and transmits a binary 1 when there is no voltage change at the begininng of the bit frame. This technique ensures that there is always a voltage transition in the middle of the bit frame.

Delta Modulation

A method of converting analog data to a digital signal in which the incoming analog signal is tracked and a binary 1 or 0 is transmitted when the analog signal rises or falls.

Frequency Shift Keying

A modulation technique for encoding digital data using various frequencies of an analog signal.

Phase Shift Keying

A modulation technique for encoding digital data using various phases of an analog signal.

Amplitude Shift Keying

A modulation technique for endcoding digital data using various amplitude levels of an analog signal.

Quadrature Phase Shift Keying

A modulation technique that incorporates four different phase angles, each of which represents 2 bits.

Quadrature Amplitude Modulation

A modulation technique that incorporates multiple phase angles with multiple amplitude levels to produce numerous combinations, creating a bps that is greather than the baud rate.

Decibel (dB)

A relative measure of signal loss or gain that is used to measure the strength of a signal.

Shift Keying

A technique in which digital data is converted to an analog signal for transmission over a telephone line.

Shannon's Theorem

A theorem that demonstrates that the data rate of a signal is proportional to the frequency of the signal and its power level, and inversely proportional to the singal's noise level.

Nyquist's Theorem

A theorem that states that the data transfer rate of a signal is a function of the frequency of the signal and the number of signal levels.

Extended Binary Coded Decimal Interchange Code (EBCDIC)

An 8-bit code allowing 256 possible combinations of textual symbols (2 to the 8th power = 256).

Pulse Code Modulation (PCM)

An encoding technique that converts analog data to a digital signal. Also known as digitization.

Analog Data

Data that is represented by continuous waveforms, which can be at an infinite number of points between some given minimum and maximum.

Analog Signal

Signals that are represented by continuous waveforms, which can be at an infinite number of points between some given minimum and maximum.

Bandwidth

The absolute value of the difference between the lowest and highest frequencies.

Effective Bandwidth

The bandwidth of a signal after noise and other factors such as environmental conditions have been applied.

Attenuation

The continuous loss of strength (power) that a signal experiences as it travels through a medium.

Data Code

The set of all textual character or symbols and their corresponding binary patterns.

Data Rate

The speed at which data is transmitted between two devices; often refered to in bits per second (bps).

Pulse Amplitude Modulation (PAM)

Tracking an analog waveform and converting it to pulses that represent the wave's height above or below a threshold; part of pulse code modulation.

Noise

Unwanted electrical or electromagnetic energy that degrades the quality of signals and data.