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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
twisted pair
commonly used for networks and wired LANs bandwidth: 500 MHz
26
coax cable
commonly used for telephone networks, cable television, wired MANs bandwidth: GHz
27
optical fiber
commonly used for: long-distance network, wired MANs, high-performance MANs bandwidth: 100 GHz
28
radiowave
advantage: can travel reasonably long distances
29
microwave
satellite dishes disadvantage: needs a line of sight
30
infrared
remote controls
31
satellite networks
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
baseband transmission
idea: send signals that represent one or more bits
33
Non-Return to Zero
clock problems
34
Manchester encoding
halves the available bandwidth
35
passband transmission
idea: move from [0, B] Hz to [S, S+B] Hz - the passband
36
grey encoding
every adjacent pair of symbols only differs by one bit
37
simplex channels
only allow data to pass in one direction
38
duplex channels
allows data to pass through in both directions at the same time
39
half-duplex channels
allow data in both directions, but not at the same time
40
FDM
all stations send at the same time, at different frequencies
41
CDMA
stations send at the same time, at the same frequency receiver figures out who sent what
42
TDM
stations take turns on a fixed schedule
43
How does static multiplexing affect apps?
inefficient resource usage video streaming no longer works
44
acknowledgements
let the sender know it does not need to retransmit
45
ARQ
keeps track of frames using sequence numbers wait until previous frame has been accepted adds error control (ACK)
46
stop-and-wait
1-bit sliding window protocol half the bandwidth is wasted on retransmissinos
47
when using stop-and-wait, data rate decrease when:
latency increases frame size decreases
48
sender window
specifies how many frames a sender is allowed to send before waiting for an acknowledgement
49
receiver window
specifies the range of frames that the receiver is allowed to accept small window reduces performance
50
CRC vs checksum
can detect all double bit errors detect all bit errors <= r not vulnerable to systematic errors
51
parity reliably detects any __ number of errors
odd
52
checksum vs parity
improved error detection detects burst up to N errors, N - num of words
53
convolutional codes
operate on a stream of bits, keeping internal state determines most likely input for given output
54
contented approach
if there is data to send, send it collisions are a fact of life keep trying until sending successful
55
coordinated approach
if there is data to send, let other stations knows send when it is your turn
56
ALOHA
in pure ALOHA, users transmit frames whenever they have data; if a collision occurs, users retry after a random delay
57
slotted ALOHA
reduced frame of collisions, frames overlap completely or not at all
58
CSMA
senders detect if the channel is in use protocols that apply it: 1-persistent nonpersistent p-persistent
59
CSMA/CD
idea: when collision is detected, do not finish sending, stop transmission instead separates contention periods from transmission periods -> saves time and bandwidth
60
contention period
check if it is safe to send data
61
transmission period
send data
62
classic ethernet
uses 1-persistent CSMA/CD large frames → less time spent in connection periods uses CRC
63
ethernet frames
preamble: 8 destination: 6 source: 6 T/L: 2 Data: 0-1500 Pad: 0-46 CRC: 4
64
ethernet evolution
1. classic ethernet 2. fast ethernet 3. gigabit ethernet 4. 10-Gigabit ethernet
65
properties of wireless channels affect
MAC protocol design
66
MACA
an approach to solve the hidden and exposed terminal problem
67
CSMA/CA
starts with back-off regardless of collision
68
stop and wait
poor utilisation of bandwidth one frame at a time
69
sliding window protocol
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
controlled access protocols
reservation polling token passing

computer networks (6 decks)

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