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Learners should have studied the following:
a) Types of networks:
b) Factors that affect the performance of networks
c) The different roles of computers in a client-server and a peer-to-peer network
d) 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
e) The internet as a worldwide collection of computer networks:
What is a Network?
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)
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.
WAN (Wide Area Network)
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.
Factors Affecting Network Performance.
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.
- 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)
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 and Peer to Peer networks
Client-Server
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
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.
Information taken from https://www.bbc.com/bitesize/guides/zh4whyc/revision/7
Hardware Required to Connect to a Network
Hardware Required to Connect to a Network
The computers (all computers, including clients, servers and peer to peer computers) will need a NIC (Network Interface Card) to connect to the network. On a wired network, this is usually done via a RJ45 connector on an ethernet cable. The cable may plug into a wall socket, but will eventually connect to a hub or switch. 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.
The actual connection is called the access medium. This may be a wired (ethernet cable), fibre optic cable, or even wireless, which uses radio waves to connect devices together.
A WAP (wireless access point) is a device that allows wireless connections, usually using some for of encryption. 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 Internet
The Internet
We have already seen that the Internet is a very special and ginormous 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. Many people think that the world wide web is the same as the Internet but it isnt.
The Internet is the huge wide area network that has millions of servers and billions of computers connected to it.
The World Wide Web is the web service that runs on the Internet and allows you to look at web pages.
The web pages are stored on web servers and we need to know precisely which web server holds and page that we are searching for. This is done using another service called the Domain Name Service.
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!
Here are two explanations of how DNS works, watch them both!
Hosting
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.
Cloud Storage
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:
Virtual Networks
Virtual Networks
Virtual networks make use of software to divide devices on a LAN into smaller groups.
The whole LAN is still physically connected by cables, but the 'virtual network' of devices created through software are restricted from accessing any of the other computers on the LAN. So they appear to be a completely separate network within the larger one.
In school, we may configure the network so that all of the administration team appear to be on one virtual network, all the teachers computers may be on another virtual network, and the students computers on a third virtual network.
Devices on the administration office virtual network can see all of the files and folders they need and can easily share data with anyone else on their network. However, they cannot see teacher or student files stored on the other virtual networks. Likewise, students on the virtual network cannot see resources stored on the other two networks.
It is possible to pay to join a VPN over the Internet, so that your computer appears to be in another country. This is sometimes done in order to access services which are not yet available in this country.
In this virtual network, three groups of users access three different virtual networks. Even though they are all on actually on the same network, they cannot see each others computers and files.
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