AT&T 7300 series, 7500 series manual Transmission Types, Analog Transmission, Digital Transmission

Models: 7400 series 2500 series 7200 series 7500 series 7300 series 7100 series

1 348
Download 348 pages 35.19 Kb
Page 23
Image 23

TRANSMISSION TYPES

_______________________________________________________________________________________

_

Both analog and digital transmission can be used to carry information across telephone lines and data links.

ANALOG TRANSMISSION

Analog transmission carries information as continuously varying electrical waves. Variables like the wave amplitude, phase, and frequency impart the information contained in the signal.

Analog transmission can carry both voice and data.

Voice: Since voice originates as analog sound waves, analog voice terminals can transmit it over analog facilities without any conversion.

VOICE

(SOUND WAVES)

VOICE TERMINAL

ANALOG

SIGNAL

Data: The discrete binary pulses that are generated by digital terminal equipment cannot be carried across analog lines. However, they can be used to vary (modulate) a carrier signal, which analog facilities can carry. At the destination, the variation in the signal is mapped to the original binary pulses (demodulated), and the original pulses are regenerated. Modems perform this modulation/demodulation function.

The analog facilities over which voice and modulated data are carried are sometimes called voice-grade lines. Hence, the name voice-grade data has been used for data carried over analog facilities.

DATA (BINARY

VOLTAGE PULSES)

MODEM

ANALOG (CARRIER

SIGNAL FREQUENCY)

DIGITAL TRANSMISSION

Digital transmission carries information as discrete pulses transmitted at different voltage levels (for example, +3 volts/3 volts). Each pulse represents a binary bit (for example, a +3-volt pulse might represent a binary 1, while a 3-volt pulse might represent a binary 0). The bits are grouped into 8-bit units called bytes that convey the information. Like analog transmission, digital transmission can carry both voice and data.

1-3

Page 23
Image 23
AT&T 7300 series, 7500 series, 7100 series, 2500 series manual Transmission Types, Analog Transmission, Digital Transmission