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ITN 100 - Intro to Telecom > Chapter 3 - Physical Layer > Flashcards

Chapter 3 - Physical Layer Flashcards

1
Q

Physical Circuit

A

The physical media that connects devices (twisted pair wire, coaxial, etc)

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2
Q

Logical Circuit

A

The transmission characteristics of a connection (like T1)

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3
Q

Modem

A

Turns sender’s digital data into an analog signal, turns received analog signal into digital data

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4
Q

Codec

A

Turns sender’s analog data into a digital signal, turns received digital signal into analog data

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5
Q

Symbol

A

An agreed-upon standard between sender and receiver of what constitutes a 0 and what constitutes a 1

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6
Q

Symbol Rate

A

How many symbols will be sent over the circuit per second, in kilohertz

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7
Q

Circuit Configuration

A

The physical layout of the circuit

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8
Q

Point to Point Circuit

A

Direct connection between two devices, also known as dedicated circuit. Best used when two computers generate enough data to use the full capacity of the circuit.

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9
Q

Multipoint Circuit

A

Many computers on the same shared circuit. Only one computer can send at a time. Less cabling to run, more efficient when no one computer needs the full circuit capacity.

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10
Q

Simplex Transmission

A

One way transmission, like TV and radio

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11
Q

Half-Duplex Transmission

A

Two way transmission, but one way at a time. Control signals help decide who’s sending and who’s receiving.

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12
Q

Turnaround Time/Retrain Time

A

Time taken for a half-duplex circuit to change directions.

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13
Q

Full-Duplex Transmission

A

Two way transmission, devices can transmit in both directions simultaneously

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14
Q

Multiplexing

A

Break one high-speed physical circuit into several slower logical circuits, so many devices can use the circuit at the same time.

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15
Q

Frequency Division Multiplexing

A

Circuit divided horizontally so many signals can travel at once. Circuit divided into channels, each on a different frequency - like radio stations or TV channels.

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16
Q

Time Division Multiplexing

A

Circuit shared by computers taking turns, dividing circuit vertically.

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17
Q

Statistical Time Division Multiplexing

A

Uses statistical analysis of usage needs of the circuit to make more efficient use of circuit capacity.

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18
Q

Wavelength Division Multiplexing

A

Similar functionally to Frequency Division Multiplexing, but for fiber-optic cables. Uses full spectrum of light instead of just one color.

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19
Q

Digital Subscriber Line (DSL)

A

Uses FDM to split physical circuit into phone, upstream data, and downstream data logical circuits, then uses TDM to provide channels within the up and downstream data circuits.

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20
Q

Guided Media

A

Message flows through a physical medium that guides the signal - twisted pair wire, coaxial cable, or fiber-optic.

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21
Q

Wireless Media

A

Message is broadcast into the air - microwave or satellite

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22
Q

Twisted Pair Cable

A

Insulated pairs of wires twisted together within a cable. Two pairs in phone cables, four pairs in network cables.

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23
Q

Coaxial Cable

A

Copper core, outer shell for insulation, and outer shield. Less interference than twisted pair cable, but much more expensive.

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24
Q

Fiber-Optic Cable

A

Signals carried through thin strands of glass by high-speed pulses of light from lasers or LEDs.

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25
Q

Multimode Fiber

A

Light reflects inside cable at different angles. Signal weakened (attenuation) and didn’t all arrive together (dispersion). Max length 500 meters.

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26
Q

Graded-Index Multimode Fiber

A

Refractive properties of the glass fiber were changed to ensure the signal all arrives at once. Max length 1,000 meters.

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27
Q

Single-Mode Fiber

A

Narrower fiber, more concentrated light, faster over longer distances up to 100 KM. Alignment of light with cable must be perfect, lasers must be used. More expensive.

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28
Q

Radio Transmission

A

Each device on circuit has radio transmitter/receiver. Low power transmissions, short effective range.

29
Q

Microwave Transmission

A

Extremely high-frequency wireless, line of sight between two points 25-50 miles apart. Towers used to keep clear line of sight.

30
Q

Satellite Transmission

A

Similar to microwave, but involves a satellite as a midpoint instead of going directly to another point on earth.

31
Q

Propagation Delay

A

The time taken for data to transmit to a satellite and come back.

32
Q

Raindrop Attenuation

A

When heavy rain absorbs signals from satellite transmission.

33
Q

Coding scheme

A

Assigning groups of bits to a set of characters within a system (ASCII, Unicode)

34
Q

ASCII

A

Code for data communications, assigns letters to a 7 or 8 bit number.

35
Q

ISO 8859

A

Expands on ASCII, allows for non-English characters with accents.

36
Q

Unicode

A

Expands on ASCII. UTF-8 is similar, UTF-16 has more space and can handle Cyrillic and Chinese characters.

37
Q

Parallel Transmission

A

Transmits an entire data unit at once across a wide number of connections. A 32 bit data unit is transmitted simultaneously across 32 connections.

38
Q

Serial Transmission

A

A stream of data is sent sequentially, one bit at a time.

39
Q

Digital Transmission

A

Transmission of data as 1s and 0s through electrical or light pulses.

40
Q

Unipolar Signaling

A

Voltage is always positive or negative to represent 1, no voltage represents 0.

41
Q

Bipolar - NRZ

A

Positive voltage represents a 1, negative voltage represents a 0. Voltage is always positive or negative, never 0.

42
Q

Bipolar - RZ

A

Positive voltage represents a 1, negative voltage represents a 0. Voltage always returns to 0 between bits.

43
Q

Bipolar - AMI

A

0 volts always represents 0, 1s alternate between positive and negative voltage.

44
Q

Manchester Encoding

A

Change from high to low voltage is 0, change from low to high voltage is 1. Less susceptible to undetected errors - if there’s no transition midsignal, there must be an error.

45
Q

POTS

A

Plain Old Telephone Service - the telephone system

46
Q

Analog Transmission

A

Signal over transmission media continuously varies from one state to another, in wave pattern.

47
Q

Amplitude

A

Height of wave, measured in decibels. Two parts of wave - half above 0 amplitude mark, half below, both must be the same.

48
Q

Frequency

A

Number of waves per second, measured in hertz. High frequency = many short waves, low frequency = fewer long waves.

49
Q

Phase

A

Direction in which the wave begins, measured in degrees. Up and to the right is 0°, down and to the right is 180°.

50
Q

Carrier Wave

A

Simple sound wave sent through telephone line circuit

51
Q

Modulation

A

Changing the shape of the carrier wave to represent 1 and 0

52
Q

Amplitude Modulation/Amplitude Shift Keying

A

Different heights of the wave are symbols - taller wave can mean 1, shorter wave can mean 0.

53
Q

Frequency Modulation/Frequency Shift Keying

A

Different number of waves per second are symbols - higher frequency can mean 1, lower frequency can mean 0.

54
Q

Phase Modulation/Phase Shift Keying

A

Different directions of the start of the wave are symbols - phase of 0° can mean 0 and phase of 180° can mean 1.

55
Q

Quadrature Amplitude Modulation

A

Combines phase modulation and amplitude modulation for one symbol to represent 16 values

56
Q

Sending Multiple Bits

A

Using AM, FM, or PM, define more than two symbols. Four different amplitudes can represent 00, 01, 10, or 11. Can combine modulation techniques.

57
Q

Bit Rate/Data Rate

A

Capacity of circuit in bits per second - calculated by bits per symbol x symbols per second.

58
Q

Baud Rate

A

Number of symbols per second - same as symbol rate, deprecated term. Bit Rate and Baud Rate are only the same if each symbol only carries one bit.

59
Q

Bandwidth

A

Difference between highest and lowest frequencies in a band

60
Q

Data Compression

A

Increases throughput of data by making the data smaller

61
Q

V.44/Lempel-Ziv encoding

A

Creates dictionary of two-, three-, and four-character combinations in a message. When that character pattern reoccurs, the index of that data in the dictionary is sent rather than the data itself.

62
Q

Quantizing Error

A

Difference between analog signal and closest digital value available - like a rounding error

63
Q

Converting Analog to Digital

A

Samples are taken and amplitude is recorded. More frequent samples, and more bits to store amplitude data, yield better quality transmission.

64
Q

Local Loop/Last Mile

A

The analog bit of a common carrier network running from a building to the telephone switch

65
Q

Telephone Switch

A

Turns the analog signal from the phone through the local loop into a digital signal to be sent through the network.

66
Q

Pulse Code Modulation (PCM)

A

Input voice sampled 8,000 times per second, each sample stored as 8 bits. Network must transmit at 64,000 bps.

67
Q

Adaptive Differential Pulse Control Modulation (ADPCM)

A

Used by lower-speed digital circuits. Generates same number and bits of samples as PCM, but only transmits the change from one to the next rather than sending each sample. The change only needs 4 bits to be expressed, and can be used on 32,000 bps digital circuits.

68
Q

VoIP

A

Phone contains codecs built in, so the phone itself transmits digital data. Less wiring, doesn’t require a separate network.

69
Q

G.722

A

Version of ADPCM used by VoIP. Samples 8,000 times per second, each sample stored as 8 bits.

ITN 100 - Intro to Telecom (2 decks)

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