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computer networks > midterm > Flashcards

midterm Flashcards

1
Q

AM radio

A

f ≈ 1 MHz

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2
Q

FM radio

A

f ≈ 100 MHz

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3
Q

wave properties and which are dependent

A

A
f
phase
dependent: A and phase

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4
Q

physical layer function

A

converting data into electrical, radio or optical signals
it is responsible for the transmission and reception of raw data streams over a physical medium

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5
Q

data link layer function

A

to provide node-to-node transfer-a link between two directly connected nodes
responsible for communications between adjacent network nodes by handling the data moving in and out of a physical link in a network

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6
Q

packet-switched

A

data packets take various routes to the destination

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7
Q

circuit-switched

A

create a dedicated path for the entire communication session

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8
Q

CDMA

A

allows multiple users to share the same bandwidth simultaneously; each user is assigned unique code to differentiate their data from others on the same channel
allows stations to transmit at the same time and over the same frequency

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9
Q

function of CSMA

A

detecting signals from other devices before transmitting

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10
Q

CSMA

A

protocol that helps devices sense whether the medium is in use or not -> prevents data collisions

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11
Q

role of MAC

A

controlling how devices access the shared physical medium

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12
Q

sliding window: high latency ->

A

decreased efficiency
messages containing ACKs to the previous message take longer to transmit, and the sender can not send another frame until it has received the ACKs for the previous frame

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13
Q

Ethernet Frames use ____ for error detection

A

CRC

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14
Q

Which collision-free protocol is most efficient in terms of bandwidth utilisation and minimising time for collision resolution?

A

binary countdown

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15
Q

Big Endian

A

most significant byte at the lowest address

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16
Q

1 KiB = __ bytes

A

2^10

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17
Q

kibi

A

2^10

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18
Q

ASCII

A

a character encoding standard used to represent text in computers and other devices. It encodes 128 specified characters into seven-bit integers, including letters, numerals, and special symbols

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19
Q

Why choose layered over monolithic architecture?

A

A layered architecture breaks down a system into manageable parts, making it easier to understand, maintain, and develop, as opposed to a monolithic architecture which is typically a single, indivisible unit

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20
Q

What is the purpose of framing?

A

Splitting data into manageable units.

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21
Q

What is the OSI model primarily used for?

A

Designing layered network architectures
OSI model is a conceptual framework used to understand and standardise the functions of a telecommunication or computing system without regard to its underlying internal structure and technology. It is organised into seven layers, each specifying particular network functions

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22
Q

OSI layers

A

application
presentation
session
transport
network
data link
physical

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23
Q

TCP/IP layers

A

application
transport
internet
host-to-network

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24
Q

modulation

A

putting information into a signal

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25
Q

twisted pair

A

commonly used for networks and wired LANs
bandwidth: 500 MHz

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26
Q

coax cable

A

commonly used for telephone networks, cable television, wired MANs
bandwidth: GHz

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27
Q

optical fiber

A

commonly used for: long-distance network, wired MANs, high-performance MANs
bandwidth: 100 GHz

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28
Q

radiowave

A

advantage: can travel reasonably long distances

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29
Q

microwave

A

satellite dishes
disadvantage: needs a line of sight

30
Q

infrared

A

remote controls

31
Q

satellite networks

A

radio waves allow for a high bit rate and have low attenuation
sending signals to artificial satellites and back has significant latency
lower latency requires lower orbits requires more satellites

32
Q

baseband transmission

A

idea: send signals that represent one or more bits

33
Q

Non-Return to Zero

A

clock problems

34
Q

Manchester encoding

A

halves the available bandwidth

35
Q

passband transmission

A

idea: move from [0, B] Hz to [S, S+B] Hz - the passband

36
Q

grey encoding

A

every adjacent pair of symbols only differs by one bit

37
Q

simplex channels

A

only allow data to pass in one direction

38
Q

duplex channels

A

allows data to pass through in both directions at the same time

39
Q

half-duplex channels

A

allow data in both directions, but not at the same time

40
Q

FDM

A

all stations send at the same time, at different frequencies

41
Q

CDMA

A

stations send at the same time, at the same frequency
receiver figures out who sent what

42
Q

TDM

A

stations take turns on a fixed schedule

43
Q

How does static multiplexing affect apps?

A

inefficient resource usage
video streaming no longer works

44
Q

acknowledgements

A

let the sender know it does not need to retransmit

45
Q

ARQ

A

keeps track of frames using sequence numbers
wait until previous frame has been accepted
adds error control (ACK)

46
Q

stop-and-wait

A

1-bit sliding window protocol
half the bandwidth is wasted on retransmissinos

47
Q

when using stop-and-wait, data rate decrease when:

A

latency increases
frame size decreases

48
Q

sender window

A

specifies how many frames a sender is allowed to send before waiting for an acknowledgement

49
Q

receiver window

A

specifies the range of frames that the receiver is allowed to accept
small window reduces performance

50
Q

CRC vs checksum

A

can detect all double bit errors
detect all bit errors <= r
not vulnerable to systematic errors

51
Q

parity reliably detects any __ number of errors

A

odd

52
Q

checksum vs parity

A

improved error detection
detects burst up to N errors, N - num of words

53
Q

convolutional codes

A

operate on a stream of bits, keeping internal state
determines most likely input for given output

54
Q

contented approach

A

if there is data to send, send it
collisions are a fact of life
keep trying until sending successful

55
Q

coordinated approach

A

if there is data to send, let other stations knows
send when it is your turn

56
Q

ALOHA

A

in pure ALOHA, users transmit frames whenever they have data; if a collision occurs, users retry after a random delay

57
Q

slotted ALOHA

A

reduced frame of collisions, frames overlap completely or not at all

58
Q

CSMA

A

senders detect if the channel is in use
protocols that apply it:
1-persistent
nonpersistent
p-persistent

59
Q

CSMA/CD

A

idea: when collision is detected, do not finish sending, stop transmission instead
separates contention periods from transmission periods -> saves time and bandwidth

60
Q

contention period

A

check if it is safe to send data

61
Q

transmission period

A

send data

62
Q

classic ethernet

A

uses 1-persistent CSMA/CD
large frames → less time spent in connection periods
uses CRC

63
Q

ethernet frames

A

preamble: 8
destination: 6
source: 6
T/L: 2
Data: 0-1500
Pad: 0-46
CRC: 4

64
Q

ethernet evolution

A
  1. classic ethernet
  2. fast ethernet
  3. gigabit ethernet
  4. 10-Gigabit ethernet
65
Q

properties of wireless channels affect

A

MAC protocol design

66
Q

MACA

A

an approach to solve the hidden and exposed terminal problem

67
Q

CSMA/CA

A

starts with back-off regardless of collision

68
Q

stop and wait

A

poor utilisation of bandwidth
one frame at a time

69
Q

sliding window protocol

A

noiseless channels, no error control
multiple frames at a time
data loss -> sender waits for data an infinite amount of time and receiver waits for ack

70
Q

controlled access protocols

A

reservation
polling
token passing

computer networks (6 decks)

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