Chapter 3 82-87 Flashcards
What is data modulation?
converting analog to digital signals
what modulates data in your home?
the modem
what is a carrier wave?
a wave with preset properties (frequency, amplitude, phase)
How is data transferred
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
how much is modified by the information wave?
only one property of the wave is modified by the information wave when added to the carrier wave
What is FM
FM is frequency modulation.The data wave must conform to a certain frequency.The carrier wave’s frequency is modified by a data signal
What is AM
AM is amplitude modulation, the amplitude of the carrier wave is modified by the data wave
Simplex
one way communication, cannot get a message back
Half-duplex
two way communication, but only one way at a time (walkie talkies)
Duplex
full duplex, phone lines, two way communication at the same time
what is a channel?
a channel is a distinct transportation path
multiplexing?
allowing multiple signals to travel simultaneously over one medium
Sub-channel
a medium’s channel is divided into subchannels
what is a mux and demux
the device that separates the signals or combines the signals
multiplexer
at the transmission end of the signal, combines many signals on a channel
demultiplexer
At the receiving end separates the signals on the channel
What is the purpose of multiplexing?
multiplexing allows more data to be transmitted in a given span of time over a given bandwidth
TDM
Time division multiplexing
what is TDM
channel is divided into intervals of time,or time slots. Each node on the network gets its own slot.
Why can TDM be inefficient?
because if all nodes are not transmitting data, then that spot is wasted it is not shared with other users
What is statistical multiplexing?
slots are assigned according to priority or need
How is statistical multiplexing different from TDM?
when a node is not using its slot, the space is reassigned to a node that can use it.
What is a benefit of statistical multiplexing?
it maximizes available bandwidth on a network
what is FDM
Frequency division multiplexing
What happens in FDM?
a unique frequency band is assigned to each communication sub channel
When was FDM used?
in the earth 20th C for telephone lines rather than stringing a line per house, they merged the signals
How many signals were sent on telephone wire?
24
How are telephone wires used differently these days?
we can only hear 300-3400 MHz, so they use the remaining bandwidth to send other signals
What happens when the telephone signal gets to your house?
It is demultiplexed into only your signal
What is WDM?
Wavelength division multiplexing
What does WDM do?
uses fiber optic cable,
How many conversations can a WDM signal carry?
20000
How does WDM work?
a beam of light, divided into 40 carrier waves with different wavelengths, thus different colours
What can each WDM carry?
10Gbps on one channel
What happens to the data?
Each channel is given its data signal, then a mutliplexer combines all the waves into one white light. Like a prism
What happens to the WDM signal when it arrives?
a demultiplexer separates it into channels again
What can boost the signal?
an amplifier might boost a weak signal
What is DWDM?
Dense wavelength division multiplexing
What does DWDM do?
a single fiber in a fiber optic cable can carry 80-160 channels
How does DWDM get so much signal?
DWDM uses more wavelength for signals
when is DWDM used?
between ISP providers and their providers, very long distance WAN for high bandwidth uses
