Chapter 3

Question 1

Modem

Answer 1

At the senders computer, translates the computers digital data into analog data that can be transmitted through the voice communication circuits. A second modem at the receivers end translates the analog transmission back into digital data for use by the receivers computer

Question 2

Codec

Answer 2

Translates analog voice data into digital form for transmission over digital computer circuits

Question 3

5 key benefits of digital transmission over analog transmission

Answer 3

• digital transmission produces fewer errors, easier to detect and correct errors
• digital transmission permits higher maximum transmission rates
• digital transmission is more efficient
• digital transmissions is more secure because it is easier to encrypt
• integrating voice, video, and data on the same circuit is far simpler with digital transmission

Question 4

Simplex transmission

Answer 4

Data flows in one direction (TV, radio’s)

Question 5

Half-duplex transmission

Answer 5

Data flows both directions, but only one at a time

Question 6

Full duplex transmission

Answer 6

Data flows simultaneously in both directions

Question 7

Multiplexing

Answer 7

Divide a high-speed circuit into several slower (logical) circuits

Question 8

Frequency division multiplexing (FDM)

Answer 8

Dividing the circuit “horizontally” so that many signals can travel a single communication circuit simultaneously

Question 9

Time division multiplexing (TDM)

Answer 9

Shares a communication circuit among two or more computers by having them take turns, dividing the circuit vertically

Question 10

Statistical time division multiplexing (STDM)

Answer 10

Allows more terminals or computers to be connected to a circuit than does FDM or TDM.

Selection of transmission for the multiplexed circuit is based on a statistical analysis of the usage requirements of the circuits to be multiplexed.

Question 11

Wavelength division multiplexing (WDM)

Answer 11

A version of FDM used in fiber-optic cables

Question 12

Digital Subscriber Line (DSL)

Answer 12

Allows for simultaneous transmission of voice (phone calls), data going to the internet (upstream data), and data coming to your house from the internet (downstream data)

Question 13

Inverse multiplexing

Answer 13

Combines many low-speed circuits into one high-speed circuit

Question 14

Guided media

Answer 14

Transmission flows along physical medium

Question 15

Wireless (radiates) media

Answer 15

Transmission flows through the air

Question 16

Coax cable

Answer 16

Has a single copper core, plus outer insulation, shielding, and inner insulation

• less prone to interference
  characteristics:

Price - inexpensive (but more costly than TP)
Distance- up to 2km (1.2mi)
Use- cable tv/internet

Question 17

Twisted Pair cable

Answer 17

Insulated pair of wires bundled together

Characteristics:

Price- inexpensive
Distance- typically up to 100m
Use- telephones/LAN

Question 18

Fiber optic cable

Answer 18

• Data transmitted using light from lasers or LEDs
• Resistant to interference or corrosion
• extremely fast data rates

Characteristics:

Price- expensive
Distance- 500m-100km
Use- trunk line/backbone, long distance circuits, undersea cables

Question 19

Radio transmission

Answer 19

Wireless transmission of electrical waves through air

Characteristics:

Distance- depends on frequency and power
Use- wireless LANs, cellular and cordless phones, baby monitors

Question 20

Microwave transmission

Answer 20

• High-frequency radio communication
• requires line of sight which may require large antennas and towers

Characteristics:

Distance- 60km
Use- trunk line/backbone, long distance

Question 21

Serial transmission

Answer 21

• Sends but by bit over a single wire sequentially

- slower than parallel mode

Question 22

Parallel transmission

Answer 22

• uses several wires, each wire sending one bit at the same time as the others
• multiple bits transmitted simultaneously

Question 23

Unipolar signal

Answer 23

Voltage is 0 or positive representing binary bits

Question 24

Bipolar Nonreturn to zero (NRZ)

Answer 24

Voltage is positive or negative but not zero

Question 25

Bipolar return to zero (RZ)

Answer 25

Voltage is positive or negative, returning to zero between each bit

Question 26

Manchester signal

Answer 26

Voltage is positive or negative and bits are indicated by a mid-bit transition (used by Ethernet)

Question 27

Plain old telephone service (POTS)

Answer 27

Enables voice communications between two telephones.

-human voice (sound waves) concerted into electrical signals by the sending telephone and converted back to sound waves at the far end

Question 28

Modulation

Answer 28

Technical term used to describe the “shape changes” of waves when transmitting

Question 29

Amplitude Modulation (AM)

Answer 29

The amplitude or height of the wave is changed

-more susceptible to noise (more errors) during transmission than FM

Question 30

Frequency Modulation

Answer 30

Modulation technique where each 0 or 1 is represented by a number of waves per second (different frequency)

Question 31

Phase Modulation (PM)

Answer 31

Phase refers to the direction in which the waves begin

Question 32

Local loop

Answer 32

The wires that run from your home or business to the telephone switch that connects your local loop into the telephone network (sometimes called the last mile)