I.

Networks and connectivity basics

We live in a connected world – almost all digital devices are part of a network. It’s this very function of devices being connected with each other that has enabled the digital revolution to transform our societies.

Why is that? Because it’s actually really convenient to have your computer be able to talk to your colleagues' computers. If your computer is connected to all of your colleagues' computers, you can share all of your files. That saves a lot of time emailing. Also, with computers networked, an entire office can use a single device like a printer. This cuts down on costs and makes different tasks very convenient for everyone. Having computers networked increases productivity and enhances the possibilities and capabilities of any computer. Just think about all the data and information you have access to on the internet because you are able to network with all those other computers. Could your own computer ever store that much information on its own? Never.

Note

If things are connected together for a specific purpose, we refer to it as a network. There can be many types of networks, like a telephone network, a television network, a computer network or even a people network. The biggest computer network of all is the internet.

When you are connected to the internet and you use your web browser to visit a website or you use your email client to read your emails, your computer is constantly receiving and sending data and files to special computers called servers hundreds or thousands of kilometres away (more on that later).

We will now focus on computer networks, as they constitute the infrastructure of our connected societies and we will look more closely at what they are and how they keep everything connected.

Simply put, a computer network is a setup that connects two or more computers to share a range of services and information in the form of digital video, digital audio, shared use of application and storage servers, printers, use of email and instant messaging applications, access to the internet, and so on.

Three elements are needed for two computers to talk to each other to form a network:

1) A connection through a connection media

The connection media is a carrier used to interconnect computers in a network, such as coaxial cable, twisted-pair wire or optical fibre cable. The connection can also be done wirelessly using radio signals, laser or infrared technology or satellite transmission.

2) A common language, which in networking is known as a protocol

A protocol is the set of defined rules that allows two entities to communicate across the network. Without protocols it wouldn’t be possible for computers to exchange and make use of information; this is referred to as interoperability. There are different protocols for different applications, such as: wired networking (Ethernet), wireless networking (e.g. 802.11ac), and internet communication (e.g. IP).

Note

Usually, protocols work in the background – so it is not necessary for us to know how each protocol works. However, it may be useful to get familiar with some common protocols to better understand settings in software programs, such as web browsers and email clients.

  • Transmission control protocol (TCP): divides the message into a series of packets and sends them from source to destination to be reassembled at the destination.

  • Internet protocol (IP) is an addressing protocol and is mostly used with TCP. TCP/IP is the most common protocol that connects networks.

  • Post office protocol (POP): is designed to receive incoming emails.

  • Simple mail transport protocol (SMTP): sends and distributes outgoing email.

  • File transfer protocol (FTP): transfers files from one system to another, such as multimedia files, text files and documents, etc.

  • Hypertext transfer protocol (HTTP): transfers hypermedia documents, such as HTML. It was designed for communication between web browsers and web servers, but it can also be used for other purposes. Similar to HTTP, HTTPS also transfers the data in the hypertext format but in an encrypted format.

3) A unique address

An important relationship when we talk about networks is that of the server and the client.

A server is a computer that holds content and services such as a website, a media file or a chat application. A good example of a server is the computer that holds the website of an SME and that you can visit by using your web browser and typing the name of the website. The server holds that page, and sends it out when requested.

A client is a different computer, such as your laptop or cell phone, that requests to view, download, or use the content. The client can connect over a network to exchange information. For instance, when you request Google’s search page with your web browser, your computer is the client. This is the networking model used on the web and the internet.

The sending back and forth of messages between the two is known as a request-response messaging pattern. Using a specific protocol, the client will send a request and the server must return a response.

This relationship is important for several reasons. First, all the data needed can be contained in one place on the server, making it is easier to protect and provide authorisation. Also, the server does not need to be located close to the client for the data to be accessed. And finally, it is easy to upgrade the modes in the client-server model because everything is independent of each other.

Note

A brief overview of common network terminology

Packet: When data has to be transmitted, it is broken down into small segments of a larger message before transmission, called packets, which are reassembled to the original data chunk once they reach their destination.

Media access control or MAC address: The MAC address or physical address uniquely identifies each host. It is associated with the network interface card (NIC).

IP address: The IP address is an identifying number that is associated with a specific computer or computer network. When connected to the internet, the IP address allows the computers to send and receive information and makes it possible to identify destinations and origins. An IP address is just a set of four numbers between 1 and 254, separated by dots. An example of an IP address is 192.084.15.1.

An IP address is similar to a street address. There are different classifications, or types, of IP address. A network can be public, or it can be private. Public IP addresses are accessible anywhere on the internet, while private IP addresses are not.

Router: Routers are pieces of hardware that transfer data between networks, allowing different networks to communicate. Routers allow the end-to-end transmission of data by establishing routes between end devices and forwarding data along the route, from the emitting node to the destination. This route usually requires multiple hops between routers. This may be between your private network and the internet, your private network and your server, or different networks that are connected to each other.

Firewall: A firewall is a network security device that controls incoming and outgoing traffic based on predetermined rules. This can protect any network that is connected to the internet. They can be set to block or allow traffic based on state, port or protocol. Some firewalls also have antivirus software and threat detection built in. A firewall can be placed before or after a router to protect against external threats.

Internet service providers (ISP): ISPs are companies that provide everyone with their internet connections, both to individuals and to businesses and other organisations.

Broadband: The transmission of wide bandwidth data over a high-speed internet connection. Broadband provides high speed internet access via multiple types of technologies including fibre optics, wireless, cable, DSL and satellite.

Ethernet: A technology that connects wired local area networks (LANs) and enables the devices to communicate with each other through a protocol which is the common network language.

Hub: A network device that repeats the traffic it receives to all connected devices.

Switch: A network device that sends traffic it receives to a specific connected device, such as a single desktop computer or laptop.

Types of networks

As technologies have improved, various versions of these three elements have been developed to better support diverse connectivity needs, all with very precise functions that can be combined to define different types of networks.

  • Not all computer networks are the same. The network we use to link a computer to a phone via Bluetooth is the smallest imaginable. This is sometimes called a PAN (personal area network); as the name suggests, a one-person network.

  • If you work in an office, you probably use a LAN (local area network), which is typically a few separate computers linked to one or two printers, a scanner, and a shared local storage device. Networks can be much bigger than this.

  • At the opposite end of the scale, we talk about MANs (metropolitan area networks), which cover a whole town or city, and WANs (wide area networks), which can cover any geographical area. The internet is a WAN that covers the entire world but, in practice, it's a network of networks as well as individual computers.

Another way of differentiating network types is by their public or private character.

  • A public network is a network to which anyone can connect. The best example of such a network is the internet, where people can visit public servers via their public IP addresses or via their assigned domain name.

  • A private network is any network to which access is restricted and servers only have a private IP address. A corporate network or a network in a school are examples of private networks. Sometimes the difference between public and private networks gets a little blurred. For example, using the World Wide Web, you may come across password-protected files or subscription-only websites. So even on a completely public network, it's possible to create a degree of selective, private access.

If you work for a big corporation, you're probably used to the idea that much of the information you share with your colleagues is accessible only over internal machines; if it's accessed in a web-like way, what you have there is called an intranet (a kind of private, internal internet/web not accessible over the public internet). But what if you're working from home and you need to access the private bits of your corporate network over the public internet? Then you can use something called a VPN (virtual private network), which is a secure tunnel that gives you access to the private network at your work over a public one (we’ll discuss that more later).

Next, we will illustrate how a network works by looking at one type of network that is the most familiar to us, namely the home network.

Home networks

We can set up two kinds of home network. One with internet access, or one without internet access. In both cases, a home network allows us to connect all our devices that have a connectivity function to communicate with each other, and also with other devices over the internet or over other networks. Below you can see a home network that has access to the internet, as it has a cable modem that connects to the internet service provider (ISP) that provides that service. If this diagram did not have the cable modem, the home network would still operate but it would not have internet access; it would be purely a home network with private connectivity.

A home network

A. Internet service provider; B. Mobile phone; C. Wi-Fi modem; D. Smart TV; E. Laptop computer

Since for most of us, having access to the internet at home is essential, we will explain the devices needed to have such a network at home. It's important to know exactly what kind of equipment you need to have a home network. Let’s start.

Essential home network devices

The essential device that will provide you with an internet connection is called a modem.

In a small home or apartment, the minimum you need is an ISP modem and Ethernet cables to set up a simple and small network. Depending on how many ports that ISP modem has, you can connect that many wired devices via Ethernet cables. If a Wi-Fi router is connected to the modem, the Wi-Fi router provides connectivity to more devices via wired and wireless connection.

ISP modems exist that have an in-built Wi-Fi router, and they are called Wi-Fi modems.

You can set up a home network with internet connectivity that is fully wireless and that only uses one network device, the Wi-Fi ISP modem. When you buy such a device, make sure that the range is sufficient to cover your house and that the signal is strong enough to go through walls. If that is not the case, you will need more Wi-Fi routers to expand your Wi-Fi experience at home. Some internet service providers can offer you a rental service for a Wi-Fi modem.

What are hotspots?

The term hotspot is used to define an area where Wi-Fi access is available. It can either be through a closed wireless network at home or in public places such as restaurants or airports. In order to access hotspots, your device should include a wireless adapter. If it doesn't, you can purchase a wireless adapter that will plug into the PCI slot or USB port. Once installed, your system should automatically detect the Wi-Fi hotspots and request a connection.

Setting up a WiFi hotspot from mobile phone

Another option for connecting our devices is using Bluetooth wireless technology. If you have a smartphone, laptop, tablet or similar device, it is probably equipped with both Bluetooth and Wi-Fi wireless capabilities. Bluetooth allows for short-range data transfer between devices. As an example, it is commonly employed in headsets for mobile phones, enabling hands-free phone use. Wi-Fi, on the other hand, allows devices to connect to the internet. Bluetooth limits the number of devices that can connect at any one time, whereas Wi-Fi is open to more devices and more users. In addition, Bluetooth tends to be simpler to use and needs less power than Wi-Fi. However, this is achieved at the expense of range and speed of data transfer, which is why Wi-Fi typically exceeds Bluetooth’s capabilities.

Once your devices are connected, they are ready to communicate with each other and with devices over other networks. For this, they will need an IP address and a MAC address. When you connect to the internet your device will use an external IP address. This address is the IP address of the router.

How about network security?

In the same way we secure our physical goods against thieves, we should also secure our virtual goods – that is the information we store or transmit over computer networks. As we use our computers more and more to store our personal information in digital formats or to access important services such as our bank accounts via the internet, computer network security is vital.

There are many entry points to a network. These entry points include the hardware and software that comprise the network itself as well as the devices used to access the network, like computers, smartphones and tablets. Because of these entry points, network security requires the use of several defence methods.

Example

Here are five ways to secure your home network:

  • Change the name of your default home network: This makes it harder for malicious attackers to know what type of router you have. If a cybercriminal knows the manufacturer name of your router, they will know what vulnerabilities that model has and then try to exploit them.

  • Set a strong and unique password to secure your wireless network: Every wireless router comes pre-set with a default username and password, which is needed in the first place to install and connect your router, making it easy for hackers to guess it if they know the manufacturer. The first thing to do is to change this key and choose a password that is at least 15 characters long.

  • Always keep your device software up to date: Software is an essential part of your wireless network security. Software updates can contain security updates and neglecting this can leave open doors for cybercriminals to exploit various vulnerabilities.

  • A firewall can help secure your Wi-fi network: Firewalls aren’t just software programs used on your PC, they are also part of hardware. A hardware firewall is similar to the software version – it monitors network traffic and prevents access to parts of the network based on security rules – but its biggest advantage is that it adds one extra layer of security for all the devices in the network.

  • Turn off the wireless home network when you are not at home: It’s recommended to disable the wireless home network in case of extended periods of non-use. This closes any opportunity for malicious hackers who might attempt to get access to it while you are away.

Another threat is posed by public networks. Free public Wi-Fi is available in a lot of places — airports, restaurants, coffee shops, libraries, public transit, hotel rooms and so on. While connecting to these networks sometimes proves to be very convenient to access online accounts or catch up on work, be aware of the privacy and security risks they pose. The same features that make free Wi-Fi hotspots desirable for consumers make them desirable for hackers; namely, that it requires no authentication to establish a network connection. This creates an opportunity for the hacker to get access to unsecured devices on the same network.

Example

Here are five ways to keep you secure on public networks:

  • Never use public networks to access sensitive information: If you need to get online to browse for directions or do something else that’s less sensitive, it’s less risky. But if you’re trying to access your bank account or buy something, wait until you’re connected to a network that you know is safe.

  • Use HTTPS: Look for HTTPS at the beginning of a website’s address. This means the connection between the browser and the web server is encrypted, so any data that is submitted to the website will be safe. Most browsers also include a padlock symbol at the beginning of the address to indicate that the site uses encryption.

  • Protect your passwords: When you’re using public Wi-Fi, hackers could gain access to your passwords. One way to enhance your protection is by enabling two-factor authentication on any services that offer it. When enabled, this added protection ensures that even if someone gains access to your password while you’re using public Wi-Fi, they still won’t be able to access your accounts.

  • Turn off file sharing: Do this before accessing public Wi-Fi. If you keep file sharing on, it’s possible your folders may be accessible to anyone connected to the same public network.

  • Log out: When you’re done browsing, be sure to log out of any services you were using. Also check your settings to make sure your device will "forget the network” and not automatically reconnect to that network again without your permission if you’re within range.

What is a VPN and why use it?

A VPN, or virtual private network, provides an easy-to-use solution to ensure our privacy, security or content access. A VPN transmits your data via an encrypted connection – think of it as a secure tunnel between you and the internet. Here are a few things you should know about VPNs:

  • A VPN is a service that you sign up for online from a VPN provider, so you don’t need any other equipment.

  • Once you have an account, your VPN service should be active when you're online.

  • A VPN takes your internet connection and makes it more secure by giving you a temporary IP address, hiding your real one from every website you connect to, encrypting all your internet activity.

Network threats constantly evolve, which makes network security a never-ending process that we should be aware of. You can learn more about this in our Cybersecurity course.

Next section
II. World Wide Web and the internet revolution