communication Flashcards
(83 cards)
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
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
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
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
5
Q
pros of client server
A
- files and resources are centralised
- management of security
- centralised back up
- internet monitoring
6
Q
client server applications
A
- printer
- file sharing
- proxy server
- email server
- database server
- domain controller server: management of user accounts (IDs & pswrds)
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
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
9
Q
networking advantages
A
- file sharing
- software sharing
- hardware sharing
- higher storage
10
Q
networking
A
the exchange of info and ideas among people with a common profession or special interest
11
Q
network
A
two or more systems connected through wired or wireless means
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
13
Q
internet
A
a global network providing communication facilities
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
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
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
17
Q
bus topology advantages
A
- easier to setup/extend
- less cable required
- less expensive
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
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
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
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
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
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
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
25
disadvantages of mesh topology
- lot of cabling is needed (expensive and time consuming)
- set up and maintenance is complex
26
mesh topology: how are packets transmitted
- packets have address of recipients
- sender transmit packets directly to node; each node is connected to at least one other node
27
mesh topology: how are packets transmitted
- packets have address of recipients
- sender transmit packets directly to node; each node is connected to at least one other node
28
hybrid topology
- combination of two or more topologies
- used in large organisations with different topologies in each building
29
cloud computing
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
30
advantages of cloud computing
- 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
31
disadvantages of cloud computing
- 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
32
private cloud
- owned by and only accessed by an organisation
- used by highly regulated industrives and govt agencies
33
public cloud
- owned by a cloud service provider
- for general user, grants access to multiple parties
34
pros of cloud computing
- less technical knowledge is required and easy to mplement
- flexibility: can be scaled to match organisation's growth
35
cons of cloud computing
- 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
World Wide Web (WWW)
- 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
internet
- 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
pros of wireless
- 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
pros of wireless
- 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
cons of wireless
- easier to hack
- interference
- signal degrades quickly
41
twisted pair cable
- 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
coaxial cables
- 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
fibre optic cables
uses pulses of light rather than electricity to transmit data
44
pros of fibre optic
- 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
cons of fibre optic
- high installation cost
- trained people are required to maintain and install
- breaks when bend
- uni-directional
- difficult to terminate
46
copper cable pros
- low installation cost
- more flexible
- vast knowlege as it has been around for years
- easier to terminate
47
copper cable cons
- less bandwidth rate
- needs repeaters (regenerates sent data signal over network before signal weakens)
- higher interference
48
radio waves
- 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
microwaves
- larger bandwidth, can transfer more data at a time
- used in TV and MRI
50
infrared
- electromagnetic waves
- high frequency
- used in TV remotes
51
satellites
- 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
switch
used to connect together a number of devices to form a LAN that directs incoming data packets to a specified destination address only
53
hub
hardware used to connect together a number od devices to form a LAN that directs incoming packets to all devices on the network
54
network interface card (NIC)
- provides device with a MAC address to uniquely identify it on the network
- allows each individual device to connect to the network
55
wireless network interface card (WNIC)
- 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
bridge
- 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
wireless access point (WAP)
- allowing devices to connect to the LAN instead of using a cable
- easy to move a device to a different location
58
repeater
device used to boost signals
59
router
- enables data packets to be routed between different networks
- acts as a default gateway
- can perform rotocol translation
- can move data between networks
60
gateway
- same as router except they connect dissimilar networks
61
how a video is sent using bit-streaming
- 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
on demand bit streaming
- 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
pros of bit streaming
- 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
cons of bit streaming
- 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
real time bit streaming
- 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
bit rate and bit streaming
- 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
CSMA-CD (carrier sense multiple access - collision detection)
- 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
functions of CSMA-CD
- 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
modem
converts digital data into analogue data which a computer can process -> connects router to the internet
70
PSTN (public switched telephone network)
- 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
pros of dedicated lines
- faster transmission of data
- more consistent transmission speed
- improved security
72
cons of dedicated lines
- expensive to setup/maintain
- disruption to the dedicated line would leave no alternative
73
IP address
- 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
public IP addresses
- can be reached across the internet
- provided by ISP
- unique
75
private IP addresses
- not publicly registered on the internet
- assigned by router
- more secure
- unique within their network but can be duplicated within another
76
static IP addresses
- when a computer disconnects and rejoins a network the address does not change
- address is assigned by ISP
77
dynamic IP addresses
- each time a computer rejoins a network the address changes
- address is assigned by the network OS
78
subnetting
- 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
IPV4
- 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
IPV6
- 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
domain name service (DNS)
- 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
uniform resource locator (URL)
- 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
how URL is converted to matching IP
- 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
