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What is a LAN?
local area network
a network over a small geographical area such as a single site
the network infrastructure is usually owned and managed by the organisation
What is a WAN?
wide area network
a network over a large geographical area such as multiple sites, towns, cities countries or continents
requires third party connections such as phone lines and satellite
What is the role of a client in a client-server network?
a less powerful computer that relies on servers to provide and manage data
they have no control over the network as a whole or over individual computers
to send requests to a server, wait for a response, and then receive the response
What is the role of a server in a client-server network?
a more powerful computer that manages and stores files (provides services) to other computers on the network
to wait for requests from clients, to perform the request and to send a response back to the client
What are the advantages and disadvantages of a client-server network?
advantages
can be controlled centrally from the server which also backs up all software and file servers as well as controls security
hardware, software and resources can be shared across the network (e.g printers, applications and files)
allows for improved scalability - more clients can be easily added to the central server
disadvantages
large amounts of traffic congestion will cause it to slow down
all users are reliant on the central server so if there is a fault with it, the whole network will fail and if a back up has not been made to a back up server, all files will be lost
servers are expensive
hard to manage and maintain - IT technicians needed
malware can spread quickly across the network
What are the roles of computers in a peer to peer (P2P) network?
there is no central server so data is shared directly between systems and all computers have equal status
each requests and performs tasks on the network - serve each other
all responsible for providing data
What are the advantages and disadvantages of a peer to peer network?
advantages
simpler and cheaper to set up than client server - no dedicated equipment like a server needed and no specialist staff
direct communication - optimal for quickly sharing files between systems, especially media files
computers are not dependent on a single server
if a computer goes down, only its files are lost
disadvantages
no central device to manage backups or security so it must be performed on each individidual computer - less secure
decreased scalabilty and ability to manage beyond a few computers
files on individual computers may be hard to locate as each user is responsible for their own filing so it may be unorganised
if a computer is switched off, the data can’t be retrieved at all.
computer performance will decrease with more connected devices, especially if those are slow
How does bandwidth affect network performance?
it is the max amount of data that can be transferred through a connection at a time
bandwidth of the medium is shared between all connected devices
as the number of devices increases, bandwidth per device decreases so the network is slower
How does latency affect performance?
the length of time a packet of info sent from one device takes to travel through the network to another device (delay in receiving it)
a higher latency slows the network performance
How does the number of collisions (error rate) affect network performance?
when devices try to communicate with each other at the same time, the signals collide
the transmission fails and the signal must be re sent which slows the network
What are all of the factors that affect network performance?
the bandwidth available
number of users at the same time
number of data collisions
latency
interference
distance to travel/signal strength
amount of data to transfer
applications being used
server/CPU performance
When is a client-server network used?
best suited to organisations with many computers, or to situations where many computers need access to the same information. Many schools use this type of model.
When is a peer to peer network used?
best suited to smaller organisations that have fewer computers, or where fewer computers need access to the same data.
What is the role of a wireless access point?
to provide a link between wireless and wired networks
creates a wireless LAN that allows wifi enabled devices to connect to a wired network
e.g a wifi or bluetooth hotspot
may be a seperate device or built into another device such as a router
uses a a radio transceiver
What is the role of a router?
to transfer data packets between networks
receive data packets and use the IP address in the packet header to determine the best/most suitable route for transmission (quickest and shortest)
data is transferred from router to router across the internet towards the destination
it stores the IP address of each computer connected to it
What is the role of a switch?
to connect devices together on a LAN
recieves data packets from a connected node, reads the destination address in the packet header and forwards the data directly to its destination
generates a list of the MAC addresses of all devices connected to it when it receives data
scans for a matching destination address before sending
What is an alternative to a switch?
hub
forwards a copy of the received data to all connected nodes
less secure
slower - unneccessary signals are sent
What is the role of a network interface controller/card?
internal piece of hardware (embedded on the motherboard) required for a device to connect to a network
includes a MAC address which is used when sending data across a LAN
ethernet cable plugged into it to allow data to be exchanged between the device and the network
What is transmission media?
the communication channel along which data is transferred
carries data signals
can be wired or wireless
type used afffects performance
What are the advantages and disadvantages of copper cables?
use electricity
advantages
tried and trusted technology
relatively inexpensive
disadvantages
signal affected by electric
and magnetic fields
low bandwidth
heavy cables
trailing cables
What are the advantages and disadvantages of fibre optics?
use light
advantages
very fast data transmission
low loss of signal over distance
not affected by magnetic or
electric fields
require very little power
more difficult to intercept than copper cables
disadvantages
high investment cost
need for expensive optical
transmitters and receivers
What are the advantages and disadvantages of wireless
transmission?
uses radio waves
advantages
allows devices to be used
anywhere provided there is a
signal
no need for trailing wires (safer)
easier to add devices to a
network
disadvantages
data transmission rate less
than that of wired systems
signal can be blocked by
objects or walls
increased risk of security issues
What is a network topology?
the layout of computer systems (nodes) on a LAN
star and mesh
What is a star topology?
nodes are connected to each other through a central switch through which all communication passes
What are the advantages and disadvantages of a star topology?
advantages
improved security - data packets sent directly to and from the switch in the centre and not necessarily all devices
new nodes can be added directly and easily to the central switch - network will not need to be shut down to modify it
if an attached node or cable fails, the rest of the network is not affected
faster data transfer speeds - data goes to intended recipient with minimal collisions - higher performance
disadvantages
requires additional hardware which is expensive and needs to be maintained
single point of failure - if the central device fails, the whole network will become unusable until fixed
What is a mesh toplogy?
no central connection point - each node is connected to at least one other node
each acts as a router to relay data
full mesh - each node is connected to every other node
What are the advantages and disadvantages of a mesh toplogy
advantages
if one cable or node fails, the data packets can take an alternative route - no single point of failure
many possible connections allow data transmission from multiple devices simultaneously - can withstand large amounts of data traffic - messages more likely to get through and do so quickly
modification and expansion can be done without disrupting the entire network
disadvantages
large amount of cabling needed in a full mesh especially - expensive to install and maintain - difficult to maintain
may involve redundant connections (those that will never be needed)
Where is a star toplogy found?
smaller businesses
schools
wireless home networks
Where is a mesh toplogy found?
large organisations that require reliable communication
e.g military or emergency services
What are the advantages anmd disadvantages of using networks over having stand alone computers?
advantages
file sharing
hardware sharing
communication - email, chat, video etc
roaming access - users can sign in to any computer on the network and be able to access their files
on larger networks (businesses and schools)
centralised maintenance and updates - network managers can apply software updates across a network, removing the need for individual users to do it
centralised security - anti-virus software
and firewalls can be implemented across a network, helping to protect user files from risks
user monitoring
levels of access - different users can be given different access rights.
disadvantages
cost - additional equipment is needed
require management by technical staff
malware can easily spread across an improperly secured network
hacking once a device is connected to another device, it is possible that data may be accessed without the device owner's permission
What is the internet?
a worldwide collection of interconnected computer networks
What is web hosting?
a service offered by companies that will host web pages and files
a website must be hosted (stored) on a web server to be able to be accessed by others on the internet
How does web hosting work?
a web server responds to the web browser (client’s) request to display a web page
the web server processes the request by preparing the web page and then returning it to the web browser
it is then displayed to the user
What are the advantages of web hosting?
advantages
web hosts have far more bandwidth - can serve more users
able to monitor their equipment 24/7
web hosts will back up sites remotely
What is the domain name system?
every web page has a domain name that is easy to remember and type in as well as a unique IP address for the device that the web page is stored on
a DNS server stores a list of domain names and a list of corresponding IP addresses
13 DNS root servers worldwide - complete list of all domain names and their IP addresses
What are the steps taken to display a web page?
a domain name is typed into the address bar of a browser
a query is sent to the local DNS server for the corresponding IP address of the domain name
it will check if it holds the corresponding IP address. if it does, it passes it to your browser
the browser then connects to the IP address of the server and accesses the website
if the local DNS server does not hold the IP address, the query is passed to another DNS server at a higher level
if found, the address is passed down to servers lower in the hierarchy until it passes the local DNS server and then your browser
What is the cloud?
a network of servers accessed on the internet
example of a remote service provision
software as a service
purposes include running applications, storing data and processing
data stored on large servers owned by a hosting company
What are the advantages and disadvantages of cloud storage?
advantages
huge capacity and ability to upgrade your subscription for more storage
free for a certain amount of storage
access can be granted to another user and people can work on a file simultaneously
can be accessed from anywhere on demand with an adequete internet connection
no need for a powerful computer to store data
back ups are supposed to be done by the service provider
disadvantages
unusable without a good enough internet connection
no guarantee that data is being backed up
personal data will be stored on another company’s servers - data protection risk
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