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Network Architecture > Week 1: 3 > Flashcards

Week 1: 3 Flashcards

(56 cards)

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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?

Study These Flashcards
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?

Study These Flashcards
A

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

Amplitude and frequency remain constant.

25
List the modes in which the transmission of binary data across a link can be accomplished:
* Parallel * Serial
26
How does parallel transmission work?
By sending data n bits at a time by grouping them | Use n wires to send n bits at one time
27
What are the pros and cons of the parallel transmission?
Pros: * Speed Cons: * Cost
28
How does the serial transmission work?
One bit follows another so we need only one communication channel ## Footnote Advantage: reduces cost of transmission
29
What is a Modem?
Stands for **Mo**dulator/**Dem**odulator and is the most familiar type of Data Communication Equipment (DCE)
30
What does a modem do?
Converts a digital signal to analog signal and vice versa
31
What is multiplexing?
It's the set of techniques that allows the simultaneous transmission of multiple signals across a single data link
32
Why does multiplexing work?
Because: Two or more signals that use different carrier frequencies can be transmitted over a single medium simultaneously without interference. ## Footnote Computer networks use the principle of separate channels to permit multiple communications to share a single physical connection.
33
What does a multiplexer do?
Combines singals into a single stream
34
What does a demultiplexer do?
Seperates the stream back into each component transmissions
35
Does a path have just a single or many channels?
Many
36
List the three basic techniques of multiplexing:
* FDM: Frequency Division Multiplexing * TDM: Time-Division Multiplexing * WDM: Wave-Division Multiplexing
37
How does FDM and WDM work?
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
List the two categories of TDM:
* Synchronous TDM * Statistical TDM
39
How does Synchronous TDM work?
It arranges for sources to proceed at round-robin scheme ## Footnote Provides absolute guarantee of fairness
40
How does Statistical TDM work?
The same as Synchronous TDM but the multiplexor skips the source if there is not data to send
41
List the two classes of transmission media:
* Guided: Thoser a provide a conduit from one device to another * Unguided: Transport electromagnetic waves without using physical conductor
42
What is UTP?
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
What is STP?
Shielded Twisted Pair * Has a metal foil covering each pair of insulated conductors * Eliminates crosstalk * Less susceptible to noise * More expensive
44
How does a coaxial cable to a twisted one
* 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
How do optical fibers works
They use light to transport data
46
What is the protection of optical fiber cables
A plastic jacket
47
How does a fiber optic transmitter work?
It uses a light emitting diode (LED) or laser to send pulses of light down the fiber
48
How does an optical fiber receiver work
It uses light sensitive transistor to detect pulses
49
What are the pros and cons of optical fibers
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
List the five factors for medium evaluation:
* Cost * Speed * Attenuation * Electromagnetic Interference * Security
51
Why does much of the complexity in computer networks arises?
Because digital transmission systems are susceptible to interference that can cause random data to appear or transmitted data to be lost or changed
52
What is thermal noise?
* Also known as white noise * Relatively constant and can be reduced * If it gets too strong, it can completely disrupt the signal
53
What is impulse?
* 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
What is crosstalk?
* Unwanted coupling between two different signal paths * Relatively constant and can be reduced with proper measures
55
What is echo?
* 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
What is jitter?
* 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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