Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Systems and Networks > Data Communications > Flashcards

Data Communications Flashcards

1
Q

Name some examples of transmission media.

A
  • Wire (copper)
  • Glass fibre
  • Infrared
  • Laser
  • EM radiation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are some pros and cons of copper wire as a transmission media?

A
  • common, inexpensive and easy to install
  • risk of interference
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How does optical fibre work as a transmission media?

A
  • thin glass tube coated in plastic
  • reflects light internally
  • transmitter uses LED or laser and receiver uses a light sensitive transistor
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the pros and cons of Optical fibre as a transmission media?

A
  • no electrical interference
  • signal can be carried further than by copper wire
  • can transfer more information at one time than copper
  • BUT hard to find breaks
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is a main example of infrared as a transmission media?

A

remote controls

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are some pros and cons of infrared as a transmission media?

A
  • portable and needs no antennae
  • cheap
    BUT
  • limited range
  • sensitive to orientation of transmitter to receiver and being blocked
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How does use of EM signals to transmit data vary between microwave and Radio?

A

Radio:
- small computer antennae
- can penetrate walls

Microwave:
- higher frequency
- carries more info than RF
- cannot penetrate metal so needs very tall towers and direct line of sight

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are six categories of trade-offs between media transmission types?

A

Cost
Data rate
Delay
Affect on signal
Environment interaction
Security

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What does a ‘communication system’ do?

A

Accepts input from one or more sources and delivers information from a given source to a specified destination

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What’s the difference between analogue and digital signals?

A

Analogue:
changes from one value to another via all possible intermediate levels (curvy)
Digital:
has fixed valid levels (straight flat lines with jumps between)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Most signals are _____ composite signals

A

composite (can be decomposed into a set of simple sine waves)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Why are signals typically modulated? What does this mean?

A

Signals are combined so they can share a communication medium
Modulation forms a composite signal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What energy type do each of these methods use?
- Wire (copper)
- Glass fibre
- Infrared
- Laser
- Radio / satellite

A

Copper wire: electrical
Glass fibre (fibre optic): light
Infrared: light
Laser: light
Radio / satellite : EM

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are the 3 categories of error?

A

Interference
Distortion
Attenuation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is a distortion error?

A
  • Physical systems distorting signals
  • wires have capacitance and inductance and will block signals at some frequencies
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is an attenuation error?

A

Weakening of signal with distance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is a single bit error?

A

A single bit in a block of bits is changed - normally due to short duration interference

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is a burst error?

A

Multiple bits in a block are changed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is an erasure error?

A

The the signal that arrives at the receiver is to ambiguous to be a 1 or 0
- can be caused by distortion or interference

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What are the trade-off considerations for error detection and correction?

A
  • Error detection adds overhead cost
  • single bit error is hugely important for some transmissions (bank transfer) but not others (pictures)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is forward error correction (FEC)?

A

Adding additional information to the data to allow the receiver to check if it’s transmitted correctly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What are some examples of FEC (forward error correction)?

A

Single parity bit checking
Row and column parity
Checksums

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What are Automatic Repeat reQuest mechanisms (ARQ)?

A

Using acknowledgment messages to check whether data has arrived at its destination

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is single parity bit checking?

A

The number of 1s is counted and an extra ‘parity’ bit is added to make this even or odd
- check at the other end that it’s still either even or odd as intended

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What are some limitations of single parity bit checking?

A
  • introduces additional costs
  • only detects limited types of errors
  • cannot be used to correct errors
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is row and column parity checking?

A

An even or odd parity bit is added to each row and column so that locations of errors can be identified and potentially resolved

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What are some pros and cons of row and column parity checking?

A
  • identifies exact error location
  • receiver can correct a single bit error
    But can only correct single-bit errors (can detect an odd number of errors if more than one bit changed)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What are some factors used to compare error detection/correction methods?

A
  • amount of extra data needed to be corrected
  • amount of extra computation needed
  • types of error detected
  • whether detected errors can be fixed
29
Q

What are checksums?

A

Data is interpreted as a sequence of integers and added together to get a ‘checksum’

30
Q

What are cyclic redundancy checks (CRCs)?

A

Bits are cycled through registers several times in several places
- detects more errors than checksums and especially good for burst errors

31
Q

What are ARQs good for?

A

When an underlying system detects error but doesn’t correct it and can guarantee delivery

32
Q

What does resistance in wires cause (to data)?

A

Signal loss

33
Q

What type of signal will propagate further than other signals?

A

A continuous oscillating signal

34
Q

What type of signals is the term modulation used for? What is the equivalent for the other type of signal?

A

Analogue signals
- called shift keying for digital signals

35
Q

What are the two types of modulation?

A

Frequency modulation (FM)
Amplitude modulation (AM)

36
Q

What is modulation in a general sense?

A

An oscillating carrier wave is sent and modulated in some way - the receiver picks this up and discards the carrier (which is known)

37
Q

What is shift keying?

A

The modulation of a carrier wave to encode a digital signal

38
Q

What is amplitude modulation?

A

The amplitude of a carrier wave is adjusted to match the amplitude of a wave to be transmitted

39
Q

What are ASK and FSK?

A

Amplitude shift keying
Frequency shift keying

40
Q

Why do we never reach the theoretical limit of max data speed?

A

because of noise (caused by interference)

41
Q

What is Nyquist’s theorem?

A

Suggests if you are more clever in encoding data you can send more data per unit time e.g. changing phase of a signal

42
Q

What is PSK?

A

Phase shift keying
- timing of the carrier is changed so several bits can be sent per cycle

43
Q

How many wave cycles are needed to send a bit using AM and FM?

A

at least one

44
Q

How can PSK carry more bits?

A

Each phase shift represents more than bit.
e.g. 00 - no shift
01 - 1/4
10 - 1/2
11 - 3/4

45
Q

What is QAM?

A

phase and amplitude are changed to encode even more data

46
Q

What is a modem?

A

A combined modulator-demodulator
(can apply modulation and extract bits from a modulated wave)

47
Q

What is a dial-up modem?

A

A modem using audio tone on a telephone
Uses QAM to increase data rate

48
Q

When are optical modems vs RF (radio frequency modems) used?

A

optical: for optical fibres
RF: for radio e.g. wifi networks

49
Q

What is multiplexing? What is demultiplexing?

A

multiplexing: combining information streams from several sources to transmit on a shared medium
demultiplexing: separating the combined stream

50
Q

What are the 4 types of multiplexing?

A

FDM (frequency division)
- widely used
WDM (wavelength division)
- form of FDM
TDM (time division)
- uses time slots
CDM (code division)
- mathematical approach

51
Q

When is WD multiplexing used?

A

With optical fibres

52
Q

What are the requirements of FDM?

A

Requires high bandwidth and coaxial cables as it’s sensitive to interference

53
Q

Using FDM, data is sent on _______ frequencies

A

several

54
Q

Explain WDM.

A

Application of FDM to optical fibre
prisms are used to combine beams of light of different wavelengths into a single beam

55
Q

What is TDM?

A

Alternate to FDM where sources sharing the medium take turns

56
Q

What differentiates statistical TDM?

A

A source with nothing to send is skipped

57
Q

What is the most important basic component of a WAN? What does it do?

A

Packet switches that connect local computers (LANs) to other computers and other packet switches

58
Q

Briefly describe the concept of store and forward.

A

Each packet switch in a WAN receives packets, queues them in its memory and sends out when possible (available destination)

59
Q

How does addressing work in a WAN?

A

A WAN defines it’s own frame format and assigns an address to each computer

60
Q

How does hierarchical addressing work in a WAN ?

A

The first part identifies which packet switch the computer is connected to and the second part defines the actual computer

61
Q

Explain next hop forwarding in a WAN.

A

Each packet only has the information for the next packet switch it can send to, so the frame hops from packet to packet til it reaches the packet its destination is connected to.
e.g. london to NY to Dallas to San Francisco to computer

62
Q

What does source independence mean in a WAN?

A

The next hop in a forwarding path only depends on the destination not on source address

63
Q

What is routing (in WAN context)?

A

Routing is the process of forwarding a packet to its next hop

64
Q

What must WAN routing tables guarantee?

A
  • Universal routing (next hop for every possible destination)
  • Optimal routes - next hop must point to the shortest path to the destination
65
Q

What are the two types of routing for a WAN?

A

Static routing - program computes and installs routes when a switch boots and they don’t change
Dynamic routing - program builds an internal table which alters as condition changes

66
Q

Describe static routing.

A

program computes and installs routes when a switch boots and they don’t change

67
Q

Describe dynamic routing.

A

program builds an internal table which alters as condition changes

68
Q
A

Systems and Networks (4 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions