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AS Level CS 9618 Paper 1 > communication > Flashcards

communication Flashcards

1
Q

WAN (wide area network)

A
  • network that connects devices within a larger geographical area
  • private or public ownership
  • transmission medium: PSTN or satellite link
  • lower data transfer rate
  • higher congestion
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2
Q

thin client

A
  • runs solely on the resources provided by the server and has no local storage
  • only provides input and receives output; processing done by server
  • less expensive
  • secure, cannot run unauthorized software
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3
Q

thick client

A
  • independent, does not require the server to run
  • processes most of the application
  • can function offline
  • no lag related to network problems
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4
Q

server

A

a computer or system that provides resources & data to other computers called clients
e.g: file server, print server, proxy server, web server, application server

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5
Q

pros of client server

A
  • files and resources are centralised
  • management of security
  • centralised back up
  • internet monitoring
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6
Q

client server applications

A
  • printer
  • file sharing
  • proxy server
  • email server
  • database server
  • domain controller server: management of user accounts (IDs & pswrds)
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7
Q

peer-to-peer model

A
  • all computers are of equal status
  • computers can communicate and share resources
  • each computer is responsible for its own security
  • lesser initial setup cost
  • can work even if a device goes down
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8
Q

benefits of peer to peer

A
  • parts are available from more than one host
  • allows users to download different parts of files separately
  • avoids possibility of congestion when more clients are simultaneously requesting to download a file
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9
Q

networking advantages

A
  • file sharing
  • software sharing
  • hardware sharing
  • higher storage
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10
Q

networking

A

the exchange of info and ideas among people with a common profession or special interest

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11
Q

network

A

two or more systems connected through wired or wireless means

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12
Q

LAN (local area network)

A
  • network that connects devices within a small geographical area
  • only private ownership
  • transmission medium: twisted pair cable, coaxial cable or wi-fi
  • higher data transfer rate
  • lesser congestion
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13
Q

internet

A

a global network providing communication facilities

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14
Q

drawbacks of peer to peer

A
  • reduced security, each computer is at risk from viruses from another computer
  • no central management of backup, if the data from one computer is not backed up, it is lost to all of them
  • no central management of file, consistency is difficult to maintain
  • individual computers may respond slower because they are being accessed by other computers
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15
Q

bus topology: how packets are transmitted

A
  • packets has address of recpient
  • sender transmits data through the bus
  • the bus carries data along the central cable
  • as the data arrives at each computer, the system compares the address to see if it matches
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16
Q

bus topology disadvantages

A
  • if the main cable breaks, the entire network goes down
  • difficult to detect and troubleshoot fault at an individual station
  • efficiency reduces as the number of devices connected increases
  • collisions, not suitable for network with heavy traffic
  • security is lower because several computers receive the sent signal from the source
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17
Q

bus topology advantages

A
  • easier to setup/extend
  • less cable required
  • less expensive
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18
Q

bus topology

A
  • uses a single central cable to which all computers and devices are connected
  • used when small and temporary network is needed, e.g: offices and schools
  • used for networks that dont rely on high data transfer speed
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19
Q

star topology

A
  • must have a central server that all devices are connected to
  • each node has a dedicated connection
  • each connection must be bi-directional
  • used when high performance is needed
  • found in homes where router acts as server, educational establishments, large organisations
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20
Q

advantages of star topology

A
  • signals only go to destinations (secure)
  • easy to connect/remove nodes
  • centralised management helps in monitoring the network
  • failure of one node or link doesn’t affect the rest of the network
  • fewer collisions
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21
Q

disadvantages of star topology

A
  • if the central device fails then whole network goes down
  • performance is dependent on capacity of central device
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22
Q

star topology: how packets are transmitted

A
  • packets have address of recipients
  • sender sends data to central devices
  • server reads address and finds where recipient is
  • server directly sends data recipient
  • server transmits packets only to recipient
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23
Q

mesh topology

A

all devices are interconnected with each other
- routing: gives nodes routing logic so data can be directed to its destination via the shortest route
- flooding: just sends data via nodes without routing logic
- used in establishments where communication is important, e.g: military organisations, emergency services

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24
Q

advantages of mesh topology

A
  • any broken links in the network don’t affect other nodes
  • good privacy and security
  • easy to expand
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25
Q

disadvantages of mesh topology

A
  • lot of cabling is needed (expensive and time consuming)
  • set up and maintenance is complex
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26
Q

mesh topology: how are packets transmitted

A
  • packets have address of recipients
  • sender transmit packets directly to node; each node is connected to at least one other node
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27
Q

mesh topology: how are packets transmitted

A
  • packets have address of recipients
  • sender transmit packets directly to node; each node is connected to at least one other node
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28
Q

hybrid topology

A
  • combination of two or more topologies
  • used in large organisations with different topologies in each building
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29
Q

cloud computing

A

refers to data and applications being stored and run on cloud so less storage is occupied and less processing is done on a local device

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30
Q

advantages of cloud computing

A
  • files stored on the cloud can be accessed at any time from any device
  • no need to carry external storage device
  • cloud storage can be free
  • security can be better
  • most cloud server providers have inbuild backup
  • data can be easily shared
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31
Q

disadvantages of cloud computing

A
  • can only access the cloud with internet
  • no control over security
  • can take a long time to upload/download data
  • can be more expensive in the long term
  • could be a limit to amount of storage unless paid for
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32
Q

private cloud

A
  • owned by and only accessed by an organisation
  • used by highly regulated industrives and govt agencies
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33
Q

public cloud

A
  • owned by a cloud service provider
  • for general user, grants access to multiple parties
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34
Q

pros of cloud computing

A
  • less technical knowledge is required and easy to mplement
  • flexibility: can be scaled to match organisation’s growth
35
Q

cons of cloud computing

A
  • cannot access the data stored on the cloud if there are bandwidth issues
  • poor data privacy since there may be data leakage in public clouds
36
Q

World Wide Web (WWW)

A
  • collection of web pages stored on websites
  • protocols are used to transmit data across the WWW
  • web pages are written in HTML
  • URLs specify the location of web pages
  • stored on website
37
Q

internet

A
  • massive open network of networks
  • uses TCP/IP protocol, uses IP addresses to identify devices connected to the internet
  • access provided by ISP
  • communication used: wired, radio and satellite
38
Q

pros of wireless

A
  • devices are more mobile
  • easier to set up
  • additional devices can easily be added
  • many different types of devices can be connectd at the same time
39
Q

pros of wireless

A
  • devices are more mobile
  • easier to set up
  • additional devices can easily be added
  • many different types of devices can be connectd at the same time
40
Q

cons of wireless

A
  • easier to hack
  • interference
  • signal degrades quickly
41
Q

twisted pair cable

A
  • most commonly used in LANs
  • lowest data transfer rate
  • suffers most from external interference
  • cheapst option
  • shielded cables are used commercially as it cancels out some interference
42
Q

coaxial cables

A
  • most commonly used in MANs and by cable TV companies
  • cost is higher than TPC
  • offers better transfer rate
  • greatest signal attenuation
  • less affected by external interference
43
Q

fibre optic cables

A

uses pulses of light rather than electricity to transmit data

44
Q

pros of fibre optic

A
  • less interference in the signal
  • greater bandwidth -> faster transmission
    difficult to hack so more secure
  • consumes less power
  • lighter in weight -> easier to install
45
Q

cons of fibre optic

A
  • high installation cost
  • trained people are required to maintain and install
  • breaks when bend
  • uni-directional
  • difficult to terminate
46
Q

copper cable pros

A
  • low installation cost
  • more flexible
  • vast knowlege as it has been around for years
  • easier to terminate
47
Q

copper cable cons

A
  • less bandwidth rate
  • needs repeaters (regenerates sent data signal over network before signal weakens)
  • higher interference
48
Q

radio waves

A
  • electromagnetic waves, can travel over long distances
  • used for TV siglans + mobile phone comms
  • low frequency so transmits less data at a time, affected by radio stations with similar frequencies
49
Q

microwaves

A
  • larger bandwidth, can transfer more data at a time
  • used in TV and MRI
50
Q

infrared

A
  • electromagnetic waves
  • high frequency
  • used in TV remotes
51
Q

satellites

A
  • easy to interfere
  • expensive to set up
  • satellites boost signals that need to reach antennas that are unreachable due to the curvature of the earth
52
Q

switch

A

used to connect together a number of devices to form a LAN that directs incoming data packets to a specified destination address only

53
Q

hub

A

hardware used to connect together a number od devices to form a LAN that directs incoming packets to all devices on the network

54
Q

network interface card (NIC)

A
  • provides device with a MAC address to uniquely identify it on the network
  • allows each individual device to connect to the network
55
Q

wireless network interface card (WNIC)

A
  • provides device with a MAC address to uniquely identify it on the network
  • allow each individual device to connect to the network wirelessly instead of a cable
  • use antenna to communicate with networks via microwaves
56
Q

bridge

A
  • connects two LANs which work using the same protocol, which can be two segments of the same network
  • stores mac addressed of all devices between both networks
  • used to reduce traffic
57
Q

wireless access point (WAP)

A
  • allowing devices to connect to the LAN instead of using a cable
  • easy to move a device to a different location
58
Q

repeater

A

device used to boost signals

59
Q

router

A
  • enables data packets to be routed between different networks
  • acts as a default gateway
  • can perform rotocol translation
  • can move data between networks
60
Q

gateway

A
  • same as router except they connect dissimilar networks
61
Q

how a video is sent using bit-streaming

A
  • data is compressed before transmitting
  • video is transmited continously as a series of bits
  • video is hosted on media server
  • on download, server sends data to buffer on client’s computer
  • buffer stores data from the server
  • user’s stream software receives bit stream from the buffer
62
Q

on demand bit streaming

A
  • existing digital files converted to encoded bit streaming format
  • link for encoded video is placed on website and user clicks on link to view encoded streaming video
  • can be paused, rewinded, fast-forwarded and rewatched
63
Q

pros of bit streaming

A
  • no need to wait for the whole file to be downloaded
  • no need to store large files on user’s computer
  • allows on demand playback
  • no specialist software is required for playback in browser
64
Q

cons of bit streaming

A
  • video lags if internet is slow, if inadequete buffering capacity
  • loss of internet means can’t access films
  • may require specific software to run the file
  • viruses can be downloaded from the websites
65
Q

real time bit streaming

A
  • event is captured live with a video camera
  • the video camera is connected to a computer
  • video signal is vonverted to streaming media file, encoded on the computer
  • encoded feed is then uploaded from the computer to the dedicated streaming server
  • server sends the live images to all users requesting it as real time video streaming
  • cannot be paused
66
Q

bit rate and bit streaming

A
  • bit rate determines how quickly the data is sent over the internet to the viewers
  • higher the bitrate or broadband speed, the better the quality of bis streaming and there will be no buffering
67
Q

CSMA-CD (carrier sense multiple access - collision detection)

A
  • before transmitting the data, a device checks if the channel is busy
  • if channel is free the data is sent
  • when transmission begins, it listens to the other device
  • if there is a collision, transmission is stopped
  • both device wait a different random time, then try again
68
Q

functions of CSMA-CD

A
  • monitor traffic
  • only allow data to be sent when the line is idle
  • detects collision on the network
  • halts transmissions when a collision occurs
  • calculates random wait time
  • allows re-transmission after wait time
  • collisions are detected due to voltage change
69
Q

modem

A

converts digital data into analogue data which a computer can process -> connects router to the internet

70
Q

PSTN (public switched telephone network)

A
  • PSTN consists of many different types of communication line
  • data is transmitted in both directions at the same time
  • communication passes through different switching centres
  • lines always remain active
71
Q

pros of dedicated lines

A
  • faster transmission of data
  • more consistent transmission speed
  • improved security
72
Q

cons of dedicated lines

A
  • expensive to setup/maintain
  • disruption to the dedicated line would leave no alternative
73
Q

IP address

A
  • stands for internet protocol
  • used to locate a device on a netowrk - gives each device an identifier
  • each address on network is unique
  • allows a device to send data to the correct destination
74
Q

public IP addresses

A
  • can be reached across the internet
  • provided by ISP
  • unique
75
Q

private IP addresses

A
  • not publicly registered on the internet
  • assigned by router
  • more secure
  • unique within their network but can be duplicated within another
76
Q

static IP addresses

A
  • when a computer disconnects and rejoins a network the address does not change
  • address is assigned by ISP
77
Q

dynamic IP addresses

A
  • each time a computer rejoins a network the address changes
  • address is assigned by the network OS
78
Q

subnetting

A
  • split a large network into a grouping of smaller network to help minimize traffic
  • improving speed and performance
  • IP addresses are broken down into 3 parts by partitioning the host ID into subnet ID and host ID
79
Q

IPV4

A
  • each IP address should contain 4 numbers
  • should be in range 0-255
    separated by full stops
  • address should not be more than 32 bits
  • 4 groups
  • e.g: 192.168.0.1
80
Q

IPV6

A
  • valid hex number
  • only one double colon is allowed
  • 8 groups
  • separate by colon
  • each number is 4 hex digit
  • needed when no. of IP addresses needed will exceed number available using IPV4
  • e.g: 2001:0800:0000:0000:0000:0000:0000:0000
81
Q

domain name service (DNS)

A
  • naming system used for computers or resources with and internet connection
  • consists of a hierarchy of DNS servers which have a URLs database of their corresponding IP addresses
82
Q

uniform resource locator (URL)

A
  • unique reference address for the exact location of an internet resource on the WWW
  • e.g: http://cie.org.uk/computerscience.html
    http : enables browser to know what protocol is being used to access information in the domain
    cie.org.uk : the domain name
    computerscience.html : file name which is being viewed
83
Q

how URL is converted to matching IP

A
  • URL is parsed to obtain the domain name
  • domain name is sent to nearest DNS server
  • DNS holds a list of domain name and matching IP
  • domain name resolver searches its database for the domain name
  • if DNS doesnt find it, request is forwarded to higher level DNS
  • if domain name is found IP address is returned
  • if not, error message is output

AS Level CS 9618 Paper 1 (9 decks)

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