Unit 2



LAN (Local Area Network)

  • covers a small geographical area .
  • located on a single site.
  • all hardware for LAN owned by organisation that uses it.
  • are wired or wireless.
  • various devise can connet to a lan, e.g PCs, smart TV, printers.
  • sharing files are easy.
  • share same hardware.
  • internet connection can be shared between all devices.
  • install and update software on all computers at once.
  • user account can be stored centally.

WAN (Wide Area Network)

  • conects LANs that are in different geographical areas.
  • more expencive than a LAN.
  • may be connected using fiber or copper telephone lines, satellite links or radio links.
  • the internet is an example.
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Affecting Network Performance


  • amount of data that can be transfered at a single time.
  • shared between users of a network and so if too many users or heavy use may cause congestion can cause a slow network connection.
  • you can limit the use of bandwidth for each person in the network

wired connections

  • are generally faster 
  • more reliable 
  • fiber optic cables can give much better performcance than copper cables 
  • wireless singnal depends on signal quality 
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NICs, Switches and Routers

Network Interface controller (NIC) 

  • internal piece of hardware that allows a device to connect to a network
  • wired and wireless 
  • built into a motherboard


  • connect devices on a LAN
  • recieve and transmit data to the decixe on the network with correct MAC address


  • transmitting data between networks 
  • connected to at least 2 different networks
  • direct data packets to their destination 
  • connect LAN to the internet
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Ethernet, coaxial and fibre-optic


  • twisted pair cables containing 4 pairs of copper wires which are twisted together to reduce internal interface


  • single copper wire surrounded by a plastic lay of insulation and metallic mesh, provding a shield from outside interference


  • transmit data as light, high performance
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  • managed by a server
  • devices connected to the server are clients 
  • files and software stored centrally 
  • the client sends requests to the server asking for data, the server processes the request and responds, which is known as the client-server relationship 
  • stores user profiles, passwords, and access information.


  • easy to keep track of files
  • easy to perform backups
  • easy to install and update software
  • easy to manage network security
  • very reliable


  • expensive
  • server dependence
  • overloaded 
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  • all devices are equal 
  • store files on individual devices
  • may be used at home to share data/files


  • easy to maintain
  • no dependence on server


  • no centralized management
  • can create duplicate files, easy to lose track of what's stored where and which files are up to date
  • less reliable and data may be lost if one fails
  • slow down when other devices access them
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Star topology

  • all devices are connected to the central switch or server that controls the network.
  • a central switch allows many devices to access the server simultaneously. 


  • if the device fails or is disconnected then the rest of the network is unaffected.
  • simple to add more devices 
  • better performance than other setups


  • expensive
  • if there is a problem with switch or server then the whole network affected 
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Mesh topology

  • network devices are either directly or indirectly connected to every other one without need for a central switch or a server.
  • work by sending data along the fastest route from one device to another
  • no single point where it can fail
  • if one device fails then data is sent along a different route so that it can reach its destination.
  • wired mesh networks are more expensive but wireless ones are more practical. 
  • full mesh topology is where all devices are connected together but a partial mesh topology is where not all devices are connected. 
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Network protocols

  •    Set of rules
  •   How communication between 2 devices should start and end
  •     How the data should be organized and what devices should do if data goes missing
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MAC Address

  •  Unique identifier
  •    Assigned to all network-enabled devices
  •    48 or 64-bit binary number into hexadecimal
    • E.g 10011000 10000001 01010101 11001101 11110010 00101111 =98-81-55-CD-F2-2F
  •  the Ethernet protocol on LANs allow the switches to read MAC Address and direct them to a device
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IP Address

  • Used when sending data between TCP/IP networks
  • Aren’t linked to hardware – can be assigned manually or automatically before the device can access network
  • STATIC – permanent addresses used to connect printers on a LAN and for hosting websites on the internet
  • DYNAMIC – assigned every time it logs onto a network so could get a different one each time you connect.
  • It may change if you take a laptop to a new country and connect to a network over there.It may change if you take a laptop to a new country and connect to a network over there. 
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Packet switching

·       Broken into equal packet sizes

·       Given a header containing;

o   IP its going to

o   IP its come from

o   Sequence/order

o   Number of packets in sequence

o   Error checking data

·       Sent across internet separately following different routes

·       Reassembled once it has reached the destination/recipient

·       Any packets not received will be resent

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Types of protocols

·       HTTP (Hyper Text Transfer Protocol) – access to websites and communication with web server

·       HTTPS (Hyper Text Transfer Protocol Secure) – a secure version of HTTP, encrypts all information it sends and receives.

·       FTP (File Transfer Protocol) – edit and move files on a network

·       POP3 (Post Office Protocol – version 3) – retrieve emails from a server, server holds until you download it at which point it is deleted from the server

·       IMAP (Internet Message Access Protocol) – retrieve email from server, server hold until you delete it and you only download a copy

·       SMTP (Simple Mail Transfer Protocol) – Used to send emails, and used to transfer emails between servers

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·       A layer is a group of protocols with similar functions

·       They are self contained – they do not need to know what is happening in other layers in order to function

·       Each layer serves the layer above it.

Layer 4 – Application layer

Layer 3 – Transport layer

Layer 2 – Network layer

Layer 1 – Link layer


·       Communication is in manageable pieces

·       Self contained – edit one and not affect the others

·       Makes compatible universal hardware

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The internet is a worldwide web

·       The internet is a network of networks

o   A WAN that connects devices and networks all over the world, it is based around the protocol TCP/IP.

·       The World Wide Web (WWW) is a collect on websites that are hosted on web servers using the HTTP protocol.

·       URLs are addressed used to access web servers and resources on them.

·       A Domain Name Server (DNS) translate a website’s domain name into its IP address. The internet has a network of DNSs meaning you don’t have to remember the IP Address to  access a website so you can use a domain name instead.

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·       Hosting is when a business uses its servers to store files of another organisation.


  • Users can access files from any connected device.
  • Easy to increase storage availability
  • No expensive hardware
  • No IT staff needed to manage storage
  • Cloud host provides security and backups for you
  •  Cloud software will be updated automatically


  • Need connection to internet to access files
  •  Dependant on host for security and backups
  • Vulnerable to hackers
  • Unclear who has ownership of data
  • Expensive
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Virtual Networks

·       A network that is entirely software-based.

o   Created by partitioning off some of a physical network's bandwidth to form a separate network.

·       Several virtual networks exist on the same physical network. These networks all share the same hardware making virtual networks more efficient.

·       Has own security including its own firewall so can only be access with certain software or login details.

·       A VPN is a Virtual Privet Network that can be used to send data securely over a large network, like a WAN or the Internet.

·       A virtual LAN allows you to split up a network into several separate networks using the same hardware.

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Network attacks

·       Passive attack – where someone monitors the data traveling on a network and intercepts any sensitive data that they find. Network monitoring software is used to see what each type of data is being transferred.

·       Active attack – someone attacks a network with malware or other planned attacks. These are easier to detect and can be stopped with a firewall.

·       Insider attack – someone within a network uses their access to steal information.

·       Bruit force attack – gaining information by cracking passwords using trial and error. Normally they are automated software that produces hundreds of likely password combinations. By locking accounts after a certain number of attempts and using strong passwords will stop or so down the process.

·       Dos attack – stopping a user from accessing a part of the network or website, by flooding with useless traffic making network really slow or making it crash.

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People are the weak points of a system

·       People can give personal information in many ways:

o   Social engineering – influencing people and gaining personal information

o   Telephone – someone pretends to be a person from well known business requesting personal information.

o   Phishing – getting emails suggesting something bad will happen if you don’t click on the link.

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SQL Injection

·       Data base query language

·       One of the main coding languages used to access information in databases

·       SQL typed into a websites input box which then reveals sensitive data/information 

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Good network policy

·       Will have:

o   Regular tests to find and fix security weaknesses and investigate any problems

o   Use passwords to prevent unauthorised access

o   User access levels to limit number of people who can access sensitive information

o   Install anti-malware and firewall software to prevent and destroy software attacks.

o   Encrypt sensitive data

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Penetration testing

·       Also known as pentesting is when organisations employ specialists to simulate potential attacks on their network

·       Used to identify possible weaknesses in a networks security

·       The results are then resulted back 

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Networks Forensics

·       Investigations undertaken to find out the cause of attacks on networks

o   Need to have system of capturing data packets as they enter a network

·       After a network is attacked these packets can be analysed to discover how a network was attacked and decide how to prevent future attacks.

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·       Prevent unauthorised users accessing a network

·       Passwords need to be strong in order to protect peoples sensitive data – should be a long consist of a range of letters and numbers, in both capital and lowercase 

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User Access levels

·       Controls which group of people can access which information on a network

·       Helps to limit the number of people with access to important information

o    prevent insider attacks

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·       Find and stop malware from damaging a network

·       Lots of different types like anti-virus softer, which isolate and destroy and infected data.

·       Companies use firewalls to block unauthorised

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·       Data transferred into code, where someone with the encryption key and access

·       Text called cipher text is encrypted and plain text is the opposite

·       Essential for sending data over a network securely. 

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