Chapter 5: Communication and the internet

5.1 Networks

• Network: An arrangement of computers and other devices connected together to share resources and data.
• Why are networks used?
  • To access shared files among several users
  • To download data or updates to computer programs
  • To access the internet
  • To communicate with each other
• Types of network
  • Local area network (LAN): A network that covers a relatively small geographical area, often a single site.
  • Wireless local area network (WLAN): A local area network in which connected devices use high frequency radio waves to communicate.
  • Wide area network (WAN): A network that covers a large geographical area. It connects together two or more LANs and is usually under collective ownership. The largest wide area network is the internet.
• Client-server network: A network that has at least one server to provide services to the client computers.
• Peer-to-peer network: A network that doesn’t have any centralised servers. Each computer in the network can act as client and server.
• Network topologies: Describes how the devices on a network are connected together.
• Bus topology

Advantages

Disadvantages

Relatively cheap to install since only one cable is needed

Whole network will fail if the cable Is cut or damaged

Easy to add extra network devices

Can be difficult to identify where a fault is on the cable

 

• Ring topology

Advantages

Disadvantages

Adding extra devices does not affect the performance of the network

Whole network will fail if the cable is cut or damaged or a device on the network fails

Easy to add extra networks

Can be difficult to identify where a fault is on the network.

 

• Star topology

Advantages

Disadvantages

A damaged cable will stop the whole network from working, just the network device connected to it

If the hub or switch fails then the whole network fails

Easy to locate faults because they will normaly only involve one device

Expensive to install due to amount of cable needed and the hub or switch

 

• Internet: A worldwide system of interconnected networks that enables information to be exchanged and shared.
• Mesh topology

Advantages

Disadvantages

Very fault tolerant, especially in the case of a fully connected mesh network — if one device fails, messages can be rerouted

Difficult and expensive to install wire mesh networks

In a wirless mesh network each node extends the range of the network

Can be difficult to manage due to number of connections within the network

 

• Communication media: The means by which data is transmitted between devices on a network. Coaxial cable, fibre-optic cable and microwaves are all forms of communication media.
  • Wired connectivity

Advantages

Disadvantages

Faster than wireless connectivity

Expensive to install and reconfigure

Not easy to intercept or eavesdrop on data

Requires many cables at a premises

Less susceptible to interference that wireless connectivity

 

 

• • Wireless connectivity

Advantages

Disadvantages

No need for a cable to connect device or to the internet

Data transmission speeds can be slower than wired connectivity

Allows users to use their own device

Interference from other wireless device can adversely affect performance

A wider range of devices can communicate with each other/a network because it is not dependant on having the correct table.

Walls and other physical objects can adversely affect performance

 

• Network data speed

Unit

Abbreviation

Bits per second

Bits per second

bps

1

Kilobits per second

kbps

1,000

Megabits per second

Mbps

1,000,000

Gigabits per second

Gbps

1,000,000,000

•  
• Protocols: A set of rules that govern how communications on a network should be formatted and what data they should include.
• Email protocols
  • Simple Mail Transfer Protocol (SMTP): Used when sending email through the internet.
  • Post Office Protocol, Version 3 (POP3): Current version of Post Office Protocol that is used for retrieving email from an email server.
  • Internet Message Access Protocol (IMAP): Allows emails to be accessed using multiple email clients.
• Network protocols
  • Ethernet: Family of protocols that are used in wired LANs. Physical parts of a network.
  • Wi-Fi: A digital communications protocol that sets out how data is transmitted on wireless LANs.
  • Transmission Control Protocol (TCP): Provides a reliable connection between computers.
  • Transmission Control Protocol/Internet Protocol (TCP/IP): A protocol stack, a collection of protocols that work together.

Layer

Description

Application

The top layer of the stack. Layer which interacts with the user to provide access to services and data is sent/received over a network.

Transport

This layer manages end-to-end communication over a network. There are two main protocols that operate at this layer - TCP and UDP

Internet

This layer deals with sending data across multiple networks, from the source network to the destination network.

Link

This layer controls the transmission and reception packets of data to/from a local network.

• • HyperText Transfer Protocol (HTTP): Used when sending and receiving data between web browsers and web servers.
  • HyperText Transfer Protocol Secure (HTTPS): The secure version of HTTP.
  • File Transfer Protocol (FTP): Used to transfer files over a network that uses TCP protocol, such as the internet.

5.2 Network security

• Network security: Activities designed to protect a network and its data from threats such as viruses, hacker attacks, denial of service attacks, data interception and theft.
• Access control: This determines which users have access to which data, and what they are allowed to do with it.
• Firewall: A network security system that monitor and control data that is moving from one network to another.
• Physical security: Controlling access to critical parts of a network using physical methods rather than software.
• Authentication is the process of checking the identity of someone trying to use a computer system.
• Cloud storage is storing data using a third party, usually in a system connected to the internet.
• A cyberattack is any kind of electronic attack on a computer system, server, network or other IT device.
• Many different measure need to be taken to prevent cyber attacks from being successful. These start at the design stage of system and include keeping systems up to date, training staff and proactively testing security if the network regularly.
•  

5.3 The internet and the World Wide Web

• The internet is a global network of networks. It is used to transfer data between different computer systems.
• The internet has many different services running on top of it. Two common services are the World Wide Web and email.
• The World Wide Web runs on top of the internet. Although people often mix the two terms up, they are not the same.