1.3 Computer networks, connections and protocols

🎇1.3.1 Networks and topologies

This section covers:

  • Types of network:

    • LAN (Local Area Network)

    • WAN (Wide Area Network)

  • Factors that affect the performance of networks

  • The different roles of computers in a client-server and a peer-to-peer network

  • The hardware needed to connect stand-alone computers into a Local Area Network:

    • Wireless access points

    • Routers

    • Switches

    • NIC (Network Interface Controller/Card)

    • Transmission media

  • The Internet as a worldwide collection of computer networks:

    • DNS (Domain Name Server)

    • Hosting

    • The Cloud

    • Web servers and clients

  • Star and Mesh network topologies

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Other sections in this topic:

🔗1.3.2 Wired and wireless networks, protocols and layers

What is a Network?

We are all familiar with using a computer on its own, which is often referred to as a stand alone computer, or workstation. It is also very common for your computer system to be connected to a network, even though you may not have actually realised it. A network is when two or more computers are connected together and has these advantages:

  • Resources such as printers, central storage and internet connections can be shared, which saves money.

  • It is easy to communicate with other users using instant messaging, email and other similar methods

  • Software can be installed and updated remotely allowing admin staff to maintain large numbers of computers

  • Security measures such as anti-virus packages and secure passwords can be easily set up and enforced

  • Site licences for software are much cheaper than buying multiple licences for single machines.

  • Security is better as users cannot access each others files, unlike stand alone computers.

The disadvantages include:

  • Servers can be very expensive, and the network cabling and switches are also expensive.

  • Large network need dedicated staff to manage and maintain them.

  • Certain servers, such as the file server, are crucial and the network may cease to work if they break.

  • Large networks are a target for viruses, which can have a devastating effect.

  • Hackers sometimes target networks.


LAN (Local Area Network)

A Local Area Network, or LAN, is two or more computers connected together, either directly or through a central hub or router. The workstations may be connected with a cable (known as a wired network), or wireless connections can be used on a wireless network.

Other network devices such as printers, cameras and internet connections can also connect to the network through the hub.

There are several different ways (or topologies) that networks can be set up, but by far the most common is connecting them directly to the hub (known as a star topology)

Smart homes will also have many more devices connected, usually wirelessly. Smart bulbs, smart thermostats, doorbells, cameras and voice assistant devices (Google Home and Amazon Alexa) can also be connected.

Features of a LAN:

  • All of the network is usually in one location, such as a school, shop or business

  • The organisation owns all of the hardware (cabling, switches, servers etc.)

  • The organisation manages the LAN itself, i.e. employs staff to install, update and fix faults.

WAN (Wide Area Network)

When networks get larger, they inevitably get more complex. Sometimes, each building will have its own LAN, and each LAN will be connected to a central switch. Most schools, colleges and universities will use a WAN in this way. The network covers a much larger geographical area but resources such as printers, file servers etc are still connected and available as before.

The largest WAN is of course the Internet, which is made up of literally millions of LANs.

Features of a WAN:

  1. A WAN connects two or more LANs, which may be in different locations

  2. The connection between the LANs is usually owned by a separate company, and the organisation pays a subscription to use it.

  3. The connection is managed by the external company - they will install, maintain and update it.

Factors Affecting Network Performance.

Computer networks can have a huge effect on the experience of the computer users. There are many factors which can affect the speed that the network runs at. Some of these are down to the design of the network, and include:

  • Network Topology - as we have already seen, the most common way of connecting computers into a network is to use a star topology with a central hub or switch connecting all the computers together. The performance of switches varies, as does the price. Cheap switches may not be capable of handling large amounts of data and this will limit the speed of the whole network. There are also other topologies, such as ring and bus topology that cannot support as many computers as a ring, which is one reason why they are rarely used.
    A cheap switch or an overloaded switch will slow the network down for everyone.

  • Transmission Media - networks nearly always connected using metal cored ethernet cable, and there are different standards of cable that all support different maximum speed. It is also possible to use fibre optic cable, which is much thinner and can run a much higher speeds. Fibre optic cable also has the advantage of being able to transport data over much greater distances and also safely connect different buildings (There can be risks such as lightning strikes hitting the cable with a metal cored wire)
    Fibre optic connections will improve network performance because they are not affected by electrical interference.

This is CAT5 ethernet cable, which uses metal cored wire.

Fibre optics can carry data at much faster speeds, but needs special connectors and is more expensive to install.

You can buy cheap network switches for less that £50, but high performance ones may be thousands of pounds.

Central connections in a network can have thousands of cables connecting the switches and servers.

There are other factors that affect the performance of a network:

  • Number of users - if a large number of people are all using the network at once, and they are all performing data hungry tasks such as streaming video, then network speed can slow down.

  • Bandwidth - this is the term used to specify exactly how much data the network is capable of transmitting. If one section of the network, such as the connection between different LANs in a WAN, has a large amount of data being transmitted, then all users may notice a reduction in network speed.

Client-Server and Peer to Peer networks

Client-Server

On the school network, you will probably have heard the teachers talk about "the server". That is because our network, like most larger networks, runs on a client server model. This means that certain computers, often very powerful ones, will provide a service to the other computers, called the clients. When you logon, a logon server will check that you have a valid account and then the storage server will connect you to your user area and any other storage areas such as the student shared area. Our website is stored on a web server and email comes from the email server. It is not uncommon to have thirty or more servers running on a network. The main server is extremely powerful, using four xenon 16 core processors and 256gb of RAM. It has twin power supplies in case one fails and a UPS battery back up. The secondary storage is a RAID drive which will notify the admin team if there is a fault and allow them to "hot swap" a drive if the fault is serious.

Servers do not all have to be so powerful. You could easily set up a server running on a raspberry pi which would be accessible by all network users, but only provide a low bandwidth service such as a small web server.

The key point about a client-server model is that the client is dependent on the server to provide and manage the information.

A good example is how websites are stored and accessed. Websites are stored on web servers. A web browser is the client which makes a request to the server, and the server sends the website to the browser.

Popular websites need powerful servers to serve thousands or millions of clients, all making requests at the same time. The client side of a web application is often referred to as the front end. The server side is referred to as the back end.

Peer to Peer

In a P2P network, no single provider is responsible for being the server. Each computer stores files and acts as a server. Each computer has equal responsibility for providing data.In the client-server model, many users trying to access a large file, such as a film, would put strain on one server. In the peer-to-peer model, many users on the network could store the same file. Each computer can then send sections of the file, sharing the workload. Each client can download and share files with other users.

P2P is ideal for sharing files. P2P would be unsuitable for a service such as booking tickets, as one server needs to keep track of how many tickets are left. Also, on P2P networks no single computer is responsible for storing a file - anyone can delete files as they wish

Hardware Required to Connect to a Network

Network Interface Card

To connect any computer system to a network, the computer system needs a special device called a NIC or Network Interface Card. This device can be for connecting via a cable to a wired network, or wirelessly to a wi-fi network. The NIC has a circuitry to convert the signals from the network into a form that can understand.

Wireless Access Point

On a wired network, the NIC will use an RJ45 connector on an ethernet cable. The cable may plug into a wall socket, but will eventually connect to a hub or switch. If a system uses a wireless NIC, then there will be one or more Wireless Access Points (WAP) The WAP is often called other names, which are not as accurate, such as wireless router or modem. The WAP transmits signals from the network so that they can be read by the wireless NIC on the computer system.

Router

On a wireless network, the computers will connect to a wireless router. A router is a device that can join different networks together. You will probably have one on your home network, which may also be combined with a small hub that can connect four or five ethernet cabled devices.

When you ask what the wifi password is and connect to a coffee shop's wireless network, you will have connected to their WAP. You should still be very careful with your personal data on a public network because you trust that they will keep it secure, and that they will not use it themselves, and neither of these things are guaranteed.

The wires, cables and fibre (the actual connection) is referred to as the access medium. This may be a wired (ethernet cable), fibre optic cable, or even wireless, which uses radio waves to connect devices together.

Switch

Networks also have a very similar device to a router, called a switch. A switch allows the devices to connect to the network. It will typically have many sockets which allow ethernet cables to be plugged in. Expensive switches will have control circuitry that examines all of the traffic that is being sent to the switch, and will redirect it to the correct device.

In a home network, the router, switch and wireless access point are often contained in the same box.

Transmission Media

All wired networks use transmission media to connect the network components. This has an impact on how well the network performs and how easy it is to maintain. The simplest transmission media is an ethernet cable which has a standard plug at each end and is very simple to configure.

Fibre optic cables can also be used, which are more difficult to install and need special equipment but offer far higher speeds and can be used over much greater distances.

The Internet

The Internet is a very special and massive Wide Area Network. There are a huge number of services which run on the Internet, including email, messaging services, information services and of course the world wide web.

The Internet is the huge wide area network that has millions of servers and billions of computers connected to it. It is the actual hardware that makes up the network and can run many different services. One of those services is the World Wide Web which is the web service that runs on the Internet and allows you to look at web pages.

The Internet is the hardware that connects computers.

The World Wide Web is the services including web pages that uses the internet to distribute its content.

The web pages are stored on web servers, and there are hundreds of millions of web servers on the Internet. When we want to look as a website, we type in the web address (called the URL - Uniform Resource Locator), and a system of computers called Domain Name Servers are used to find the IP address of the actual web server that has the web pages that we need.

Each computer on a network has to have a unique "address" so that information, files, and messages can be correctly delivered. The address is known as its I.P.(Internet Protocol) address and is currently made up of four eight bit binary numbers (which are the same as denary numbers 0 to 255), separated by a dot.

The current IP4 system is actually right at the end of its life because all of the possible IP4 addresses have been used and the system is "full". It has already started to be replaced with a compatible and similar system called IP6, which uses six eight bit binary numbers and will allow a very much larger number of computers to connect to it.

In practice, we do not type in an IP4 address, we use a domain name such as www.bbc.co.uk instead of its IP address of 151.101.192.81

Here are two explanations of how DNS works, watch them both!

DNS
DNS Explained.mp4

Hosting

It is quite easy to set up a web server that can serve web pages from a very simple computer, even a raspberry pi. This would be able to serve web pages to a small number of computers and could be made to work quite well. Of course, websites can get very busy and may require a huge amount of bandwidth and very powerful computers just to cope with the massive amount of data that needs to be delivered. In the case of the bbc website shown above, a whole network of servers (called a server farm) will be used to distribute the load across many powerful computers.

This server farm is said to be hosting the bbc web site. If you have a website that you want to be accessible on the world wide web, then you will probably pay a commercial company to host the web site for you. They will make sure that there is another computing power available and that the web site will be safe and secure so that it cant be hacked.

Hosting can also be provided for other services, such as file hosting (known as cloud storage - see below)

Cloud Storage

Many of these hosting companies will also provide cloud storage. This is a form of secondary storage that can be accessed from any web enabled computing device. The largest cloud hosting companies are well known names such as Google, Amazon, Facebook and Microsoft. These companies invest billions of pounds in complex data centres which are situated all over the world. The data centres are incredibly secure, have their own cooling systems and power supplies and achieve extremely reliable levels of service.

You will not be able to watch these Youtube videos in school, but they are fascinating and well worth having a look at:

Star Topologies

In the past, there were several different ways of connecting computers and devices together, two of which were known as known as ring and bus topologies. These are rarely used today and by far the most common network topology in use today is the star topology.

A star topology connects each computer or device to a central hub or switch. You can connect as many devices as you like, but due to practical limits imposed by the size of the RJ45 connectors, this is usually limited to 24 or 30 devices. When you need to connect more workstations than that, you need to connect two or more hubs together which is usually done by simply plugging them into each other, which is referred to as daisy-chaining or piggy-backing.

One very important point about star topologies is that the centre "hub" of the star is the hub or switch. Textbooks and websites sill sometimes show a server as being the centre, but this is incorrect - the server is just like any other computer and connects to the central hub in exactly the same way.

Mesh Topologies

A disadvantage of connecting computers to a central hub is that the hub itself may fail or become overloaded. Wireless networks can overcome this by allowing connections directly between each other as well as through a hub. It is also possible to connect a wired network in this way, but the amount of cable and individual network connectors that are needed rapidly become unmanageable.

In this diagram you can see how complex the connections between computers can become. In a network with just nine computers, each one would need eight network interface cards.

In a Full Mesh network, every computer is connected to every other one. This means that the amount of connections are very large and this can quickly become unpractical and will even start to slow the network down.

A half or partial mesh network will have many less connections. Computers will generally be connected to two or more other computers but it is unlikely that any one computer has a direct connection to every other one.

Smart homes are now becoming popular, and there are many kinds of device which will connect to your home network such as light bulbs, sensors, fans etc. These are often capable of connecting to each other to form a mesh network.

The Internet is another example of a partial mesh network. There are several connection to each node of the network, which means that if one of them were to fail, the Internet node would still be able to function normally.

When you use wireless connections instead of physical wires, mesh topologies become a lot more practical. It is also possible to set up a partial mesh topology where the computers are only connected to a few other computers. This is how the Internet is configured, with large central "nodes" having many connections to each other, and many of the connected computers only having one network connection.

Advantages of a mesh topology

  • Multiple devices can transmit data at the same time, which may travel via a different route to its destination and means that a mesh network can handle high amounts of traffic.

  • If one device on the network fails, the network can still function because alternative connections are available.

  • Adding additional devices does not disrupt data transmission between other devices.

Disadvantages of a mesh topology

  • The cost to implement is higher than other network topologies, making it a less desirable option. (this is especially true in a wired mesh network

  • Building and maintaining the topology is difficult and time consuming.

  • The chance of redundant connections is high, which adds to the high costs and potential for reduced efficiency.


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