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Network Architecture > Week 1: 3 > Flashcards

Week 1: 3 Flashcards

1
Q

What does data transmission require?

A
  • Encoding bits as energy
  • Transmitting energy through medium
  • Decoding energy back into bits
  • Energy can be electric current, radio, infared, light
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2
Q

What Radio Waves are?

A

Data transmitted using electromagnetic radio waves

  • Energy travels through the air
  • Conceptually similar to radio, TV, cellular phones
  • Can travel through walls and through an entire building
  • Can be long distance or short distance
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3
Q

What Microwaves are?

A

High frequency radio waves

Carry more information than lower RF transmissions

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4
Q

What does satellites do?

A
  • Can provide communications along longer distances
  • Transponder constists of radio receiver and transmitter
  • Grouped into categories according to the orbit height
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5
Q

List the categories of Satellites:

A
  • LEO: Low Earth Orbit
  • MEO: Middle Earth Orbit
  • GEO: Geostationary Earth Orbit
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6
Q

What is an analog signal?

A

It’s a continuous wave form that changes smoothly over time and includes an infinite number of values along its path

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7
Q

What is a digital signal?

A

It’s a discrete. It has only a limited number of defined values the transition of which is instantaneous.

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8
Q

How are the values of the electric current is determined to send bits?

A

Negative for 1. Positive for 0

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9
Q

What are the limitations of hardware?

A
  • How fast can hardware transmit across a wire
  • No electronic device can produce an exact voltage or change from one voltage to another instantly

Standards must specify how close to a
perfect waveform a transmitter must emit
and how tolerant of imperfection a receiver
must be.

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10
Q

What is a carrier?

A

A signal of a long distance communication

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11
Q

How can a carrier be described by?

A
  • Amplitude
  • Frequency
  • Phase
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12
Q

What is amplitude?

A

The value of the signal at any point on the wave (Equal to the vertical distance from the given point on
the wave to the horizontal axis.).

Measured in:
* Volts: voltage
* Amperes: current
* Watts: power

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13
Q

What is Frequency?

A

Period T: the amount of time, in seconds, a signal needs to complete one cycle: T = 1/F

Frequency F: the number of periods in one second: F = 1/T

F measured in:
* Hertz (Hz)

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14
Q

What is Phase?

A

The relative starting point of a wave cycle

Measured in:
* degrees

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15
Q

What is digital bandwidth?

A

In digital systems, bandwidth is expressed as data speed in bits per second

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16
Q

What is analog bandwidth?

A

In analog systems, bandwidth is expressed in terms of diffence between the highest-freuency signal and the lowest-frequency signal

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17
Q

What is bit rate?

A

The number of bits transmitted during one second

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18
Q

What is baud rate?

A

The number of signal units per second that are required to represent those bits

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19
Q

What it channel capacity?

A

The rate which data can be transmitted over a given communication path or channel, under given conditions.

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20
Q

List the underlying factors that limit the carrying capacity of a given circuit:

A
  • Delay
  • Bandwidth
  • Noise
  • Error-Rate
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21
Q

How can we use analog signals to represent binary data?

A

Thourgh the modulation of:
* Amplitude
* Frequency
* Phase

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22
Q

What does the amplitude modulation work?

Frequency and phase remain constant.

A

The strength of the carrier signal is vaired to represent binary 1 or 0

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23
Q

What does the frequency modulation work?

A

The frequency of the carrier signal is varied to represent binary 1 or 0.

Amplitude and phase remain constant.

24
Q

How does phase modulation work?

A

The phase of the carrier signal is shifted to represent binary 1 or 0

Amplitude and frequency remain constant.

25
Q

List the modes in which the transmission of binary data across a link can be accomplished:

A
  • Parallel
  • Serial
26
Q

How does parallel transmission work?

A

By sending data n bits at a time by grouping them

Use n wires to send n bits at one time

27
Q

What are the pros and cons of the parallel transmission?

A

Pros:
* Speed

Cons:
* Cost

28
Q

How does the serial transmission work?

A

One bit follows another so we need only one communication channel

Advantage: reduces cost of transmission

29
Q

What is a Modem?

A

Stands for Modulator/Demodulator and is the most familiar type of Data Communication Equipment (DCE)

30
Q

What does a modem do?

A

Converts a digital signal to analog signal and vice versa

31
Q

What is multiplexing?

A

It’s the set of techniques that allows the simultaneous transmission of multiple signals across a single data link

32
Q

Why does multiplexing work?

A

Because:
Two or more signals that use different carrier frequencies can be transmitted over a single medium simultaneously without interference.

Computer networks use the principle of separate
channels to permit multiple communications to
share a single physical connection.

33
Q

What does a multiplexer do?

A

Combines singals into a single stream

34
Q

What does a demultiplexer do?

A

Seperates the stream back into each component transmissions

35
Q

Does a path have just a single or many channels?

A

Many

36
Q

List the three basic techniques of multiplexing:

A
  • FDM: Frequency Division Multiplexing
  • TDM: Time-Division Multiplexing
  • WDM: Wave-Division Multiplexing
37
Q

How does FDM and WDM work?

A

By using carrier frequencies to allow independent signals to travel through a medium, and reserve sufficient space to separate frequency channels to avoid interference.

WDM is FDM but uses light signals though fiber optic channels instead

38
Q

List the two categories of TDM:

A
  • Synchronous TDM
  • Statistical TDM
39
Q

How does Synchronous TDM work?

A

It arranges for sources to proceed at round-robin scheme

Provides absolute guarantee of fairness

40
Q

How does Statistical TDM work?

A

The same as Synchronous TDM but the multiplexor skips the source if there is not data to send

41
Q

List the two classes of transmission media:

A
  • Guided: Thoser a provide a conduit from one device to another
  • Unguided: Transport electromagnetic waves without using physical conductor
42
Q

What is UTP?

A

Unshielded Twisted Pair
* Most common medium
* Used in telephone system
* Transmit both data, voice
* Twisting the wires helps to eliminate electromagnetic interference between wires

43
Q

What is STP?

A

Shielded Twisted Pair
* Has a metal foil covering each pair of insulated conductors
* Eliminates crosstalk
* Less susceptible to noise
* More expensive

44
Q

How does a coaxial cable to a twisted one

A
  • Carries signals of higher frequency ranges than twisted pair cable
  • More protection from interference that twisted pair
  • A single wire surrounded by a heavier metal shield
45
Q

How do optical fibers works

A

They use light to transport data

46
Q

What is the protection of optical fiber cables

A

A plastic jacket

47
Q

How does a fiber optic transmitter work?

A

It uses a light emitting diode (LED) or laser to send pulses of light down the fiber

48
Q

How does an optical fiber receiver work

A

It uses light sensitive transistor to detect pulses

49
Q

What are the pros and cons of optical fibers

A

Pros:
* Doesn’t cause electrical interference nor are theey susceptible to it
* Can carry a pulse of light much further than a copper wire can carry a signal
* Can carry more information than a wire
* Most secure medium

Cons:
* Cost
* Installation/Maintenance
* Fragility

50
Q

List the five factors for medium evaluation:

A
  • Cost
  • Speed
  • Attenuation
  • Electromagnetic Interference
  • Security
51
Q

Why does much of the complexity in computer networks arises?

A

Because digital transmission systems are susceptible to interference that can cause random data to appear or transmitted data to be lost or changed

52
Q

What is thermal noise?

A
  • Also known as white noise
  • Relatively constant and can be reduced
  • If it gets too strong, it can completely disrupt the signal
53
Q

What is impulse?

A
  • One of the most disruptive forms of noise
  • Random spikes of power that can destroy one or more bits of information
  • Can damage more bits if they are closer together
54
Q

What is crosstalk?

A
  • Unwanted coupling between two different signal paths
  • Relatively constant and can be reduced with proper measures
55
Q

What is echo?

A
  • The reflective feedback of a transmitted signal as the signal moves through the medium
  • Most often occurs in coaxial cable
  • If echo is bad enough it could interfere with original signal
56
Q

What is jitter?

A
  • The result of small timing irregularities during the transmission of signals
  • Occurs when a digital signal repeated over and over
  • If serious enough jitter forces system to slow down their transmission

Network Architecture (4 decks)

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