Chapter 3 82-87

Question 1

What is data modulation?

Answer 1

converting analog to digital signals

Question 2

what modulates data in your home?

Answer 2

the modem

Question 3

what is a carrier wave?

Answer 3

a wave with preset properties (frequency, amplitude, phase)

Question 4

How is data transferred

Answer 4

another wave is combined with the carrier wave to create a new wave, then another data wave is added to this. The modem separates them when the message arrives

Question 5

how much is modified by the information wave?

Answer 5

only one property of the wave is modified by the information wave when added to the carrier wave

Question 6

What is FM

Answer 6

FM is frequency modulation.The data wave must conform to a certain frequency.The carrier wave’s frequency is modified by a data signal

Question 7

What is AM

Answer 7

AM is amplitude modulation, the amplitude of the carrier wave is modified by the data wave

Question 8

Simplex

Answer 8

one way communication, cannot get a message back

Question 9

Half-duplex

Answer 9

two way communication, but only one way at a time (walkie talkies)

Question 10

Duplex

Answer 10

full duplex, phone lines, two way communication at the same time

Question 11

what is a channel?

Answer 11

a channel is a distinct transportation path

Question 12

multiplexing?

Answer 12

allowing multiple signals to travel simultaneously over one medium

Question 13

Sub-channel

Answer 13

a medium’s channel is divided into subchannels

Question 14

what is a mux and demux

Answer 14

the device that separates the signals or combines the signals

Question 15

multiplexer

Answer 15

at the transmission end of the signal, combines many signals on a channel

Question 16

demultiplexer

Answer 16

At the receiving end separates the signals on the channel

Question 17

What is the purpose of multiplexing?

Answer 17

multiplexing allows more data to be transmitted in a given span of time over a given bandwidth

Question 18

TDM

Answer 18

Time division multiplexing

Question 19

what is TDM

Answer 19

channel is divided into intervals of time,or time slots. Each node on the network gets its own slot.

Question 20

Why can TDM be inefficient?

Answer 20

because if all nodes are not transmitting data, then that spot is wasted it is not shared with other users

Question 21

What is statistical multiplexing?

Answer 21

slots are assigned according to priority or need

Question 22

How is statistical multiplexing different from TDM?

Answer 22

when a node is not using its slot, the space is reassigned to a node that can use it.

Question 23

What is a benefit of statistical multiplexing?

Answer 23

it maximizes available bandwidth on a network

Question 24

what is FDM

Answer 24

Frequency division multiplexing

Question 25

What happens in FDM?

Answer 25

a unique frequency band is assigned to each communication sub channel

Question 26

When was FDM used?

Answer 26

in the earth 20th C for telephone lines rather than stringing a line per house, they merged the signals

Question 27

How many signals were sent on telephone wire?

Answer 27

24

Question 28

How are telephone wires used differently these days?

Answer 28

we can only hear 300-3400 MHz, so they use the remaining bandwidth to send other signals

Question 29

What happens when the telephone signal gets to your house?

Answer 29

It is demultiplexed into only your signal

Question 30

What is WDM?

Answer 30

Wavelength division multiplexing

Question 31

What does WDM do?

Answer 31

uses fiber optic cable,

Question 32

How many conversations can a WDM signal carry?

Answer 32

20000

Question 33

How does WDM work?

Answer 33

a beam of light, divided into 40 carrier waves with different wavelengths, thus different colours

Question 34

What can each WDM carry?

Answer 34

10Gbps on one channel

Question 35

What happens to the data?

Answer 35

Each channel is given its data signal, then a mutliplexer combines all the waves into one white light. Like a prism

Question 36

What happens to the WDM signal when it arrives?

Answer 36

a demultiplexer separates it into channels again

Question 37

What can boost the signal?

Answer 37

an amplifier might boost a weak signal

Question 38

What is DWDM?

Answer 38

Dense wavelength division multiplexing

Question 39

What does DWDM do?

Answer 39

a single fiber in a fiber optic cable can carry 80-160 channels

Question 40

How does DWDM get so much signal?

Answer 40

DWDM uses more wavelength for signals

Question 41

when is DWDM used?

Answer 41

between ISP providers and their providers, very long distance WAN for high bandwidth uses