• Show understanding of the purpose and benefits of networking devices

• Show understanding of the characteristics of a LAN (local area network) and a WAN (wide area network)

• Explain the client-server and peer-to-peer models of networked computers

  • roles of the different computers within the network and subnetwork models

  • benefits and drawbacks of each model

  • justify the use of a model for a given situation

• Show understanding of thin-client and thick-client and the differences between them

• Show understanding of the bus, star, mesh and hybrid topologies

  • understand how packets are transmitted between two hosts for a given topology

  • justify the use of a topology for a given situation

• Show understanding of cloud computing

  • including the use of public and private clouds

  • benefits and drawbacks of cloud computing

• Show understanding of the differences between and implications of the use of wireless and wired networks

  • describe the characteristics of copper cable, fibre-optic cable, radio waves (including WiFi), microwaves, satellites

• Describe the hardware that is used to support a LAN

  • including switch, server, Network Interface Card (NIC), Wireless Network Interface Card (WNIC), Wireless Access Points (WAP), cables, bridge, repeater

• Describe the role and function of a router in a network

• Show understanding of Ethernet and how collisions are detected and avoided

  • including Carrier Sense Multiple Access/Collision Detection (CSMA/CD)

• Show understanding of bit streaming

  • methods of bit streaming, i.e. real-time and on-demand

  • importance of bit rates/broadband speed on bit streaming

• Show understanding of the differences between the World Wide Web (WWW) and the internet

• Describe the hardware that is used to support the internet

  • including modems, PSTN (Public Switched Telephone Network), dedicated lines, cell phone network

ADVANTAGES

• Computers that are connected together can communicate with each other. Stand-alone machines can't.

• Users on a network can easily share resources such as printers, scanners and modems. This means that a company doesn't have to buy so much equipment and users do not waste time moving files to different machines so they can use a piece of equipment that is only available on a particular PC.

• Users on a network can share data. For example, a team might be working on a project. They can all access and work on the same files easily without having first to back them up on floppy disks, for example, and then transport them to the next team member and then reload the files.

• New software need only be added once. It can then be distributed to all other PCs automatically.

• When data files are backed up they only need to be backed-up once, centrally, at the server. With stand-alone machines, you would have to back up the files on every machine. This would be very time-consuming!

• Users can retrieve and work on files from any machine on a network. If one machine is being used or breaks down, you simply move to a different machine!

• Networks can be managed. This means a network manager is able through the network software to control who can access the network, when they can access it, and what files and software and hardware they are allowed to use. An audit trail of each user can be built up so that projects can be more efficiently costed, for example, by keeping track of what printouts are done in connection with what project. Users, knowing that their activities are being monitored, will also be encouraged to stay on-task and not waste the organisation's time!

• Security can be centrally managed by the network manager. They can add patches centrally, ensure virus patterns are up-to-date centrally and so on.

DISADVANTAGES

• It costs more money to build a network than it does stand-alone machines. This is because you have to buy network cards, interconnections, a server and a Network Operating System.

• There is an additional support cost that is not insignificant. Networks are more complicated than sets of stand-alone machines. They need specialist knowledge to set them up and maintain them as well as time to maintain them. To do this, you would need to employ somebody with network management skills, usually a network manager.

• Networks have machines in different locations, each of which potentially could be used to gain access to the server's hard disk and the data stored on it. This is a security headache and the need to protect data on a network from hackers adds an extra degree of complexity to a network that doesn't exist with standalone machines.

• If the server on a client-server network goes down, the whole network will be out of action. It is also possible for one faulty machine on a network to cause other machines on the network to stop working. In addition, if the cables on a network fail, problems on either individual machines or on the whole network may occur.

• Viruses and other types of malware can spread very quickly across networks.

A Local Area Network (LAN) is a network where the workstations are 'close' together. It isn't strictly defined in terms of an exact distance but it is usually thought of as computers in the same room, or building or even in a number of buildings, which are next to each other.

A Wide Area Network (WAN) is where the workstations are 'further apart' from each other compared to a LAN. For example, the computers may be spread out over a town, a country or the world (like the Internet is).

A small accountant's business or a school probably have a LAN whereas a bank or a large travel agents company will have a WAN, as they have branches across the country and across the world, each with computers that can communicate with each other.

A Wide Area Network (WAN) connects geographically remote computers or networks. Connections between computers connected to a WAN may involve some of the following,

• Public switched telphone network

• Leased line

• Fibre optic

• Microwave

• Satellites

• Radio waves

Internetworking

An inter-network is a collection of connected networks which function separately. The Internet is obviously the largest example of such a thing. TCP/IP is the protocol used to connect networks. See the section on IP Addressing for more information.

Differences between LANs and WANs

• LANs are spread over a smaller area whereas WANs are spread over a larger area.

• WANs are usually made up of LANs connected together.

• LANs are usually much faster than WANs. LANs can usually send much bigger volumes of data in a second (known as 'bandwidth') than a WAN.

• Users generally share hardware on a LAN. On a WAN, however, the focus is all on communicating and sharing data.

Thin client – a computer that depends heavily on a more powerful computer that stores all the applications and data

Software example: mobile phone app that needs constant access to a server to work
Hardware example: POS terminal at a supermarket that needs constant access to a server to find prices etc

Thick client – a computer that relies on its own processing power, not that done by a server

Software example: a computer game that can run independently on a user’s computer.
Hardware example: normal computers

Introduction

The Internet is part of many people's lives across the globe now. It is used for socialising, education, business, news reporting and so on. It has so many uses that it is difficult now to imagine life without it. The following video adequately describes the difference between the Internet and the WWW.

What is the Internet?

The Internet is a set of networks, both Local Area Networks (LANs) and Wide Area Networks (WANs) which are connected together usually using telecommunications facilities. These include the phone lines but also such communication technologies as satellite.

The Internet allows everyone to communicate quickly and allows the transfer of files and data between computers. Data (an email, a file or a web site, for example) starts at one computer. It is broken down into digital 'packets' of information. Each packet is then passed through other computers, with each packet often going by a completely different route to the other packets. When all the packets reach the final destination, they are reassembled into the original communication and can then be read.

World Wide Web

The World Wide Web (WWW) is often used interchangeably with the 'Internet' but it does have a different meaning. The WWW is a collection (a very large collection) of information held on the Internet in multimedia form. This includes text, pictures, video, sound and animations.

Web pages and web sites

The information on the Internet is stored in 'web pages' and the web pages are themselves stored at places known as 'web sites'. Web pages can be very large so you often need to scroll down to be able to read them. A set of web pages on one web site can be very large so they are usually broken down into different web pages and linked together using 'hyperlinks', which are also known as 'hotlinks'. These can also be used to link to other completely different web sites. Because any individual web site can be large, it usually has a 'home page'. This is usually the starting point for any web site and helps the user quickly find their way around and navigate through the rest of the web site.

Browsers

A 'web browser' is a type of application, which has been written by an individual or organisation to allow a user to get back and display multimedia information on the Internet. It can be used to surf the WWW as well as to provide other facilities, such as transferring individual files. Web pages sent over the Internet use a communications protocol known as http. This isn't secure so that if anyone intercepts these pages, they can view them. You can send and receive encrypted web pages over the Internet using the communications protocol known as https. This is important if you are sending or receiving sensitive information e.g. logging into your bank account. Browsers typically have a range of features, such as navigation tools, to move forward and backwards between web pages, facilities to save web pages or print them out and security features, for example, the facility to block certain web sites or block certain types of file. Examples of Browsers include Firefox , Chrome, Sahara and Explorer but there are many many others. Try doing a Google search for web browsers and download and try out some of the less known ones at home.

Intranet

One word you may come across from time to time is 'Intranet'. An Intranet is very similar to the Internet, except that it exists purely within a company or other organisation. A company's Intranet is only accessible by authorised users, usually by using a system of logins, passwords and access rights (as opposed to the Internet, which anyone who has a connection can access). It allows a company to distribute information only to its own employees, information that it might not want its competitors to have, for example.

Extranet

Sometimes, an Intranet will allow part of itself to be viewed by the public from the Internet. This means that part of a company's Intranet could be used to advertise itself. If a part of an Intranet is accessible via the Internet then this part is sometimes called an 'extranet'.

Introduction

There are two types of network that we should know about: The first one is known as a 'client-server' network and the second type is known as a 'peer-to-peer' network.

The 'clients' on a client-server network are the individual computers or applications that authorised users log into and use. They are like the customers of the server and an authorised user can usually login to any of the clients on the network and use them.

In the next few years you are likely to see more and more software moving away from running on your desktop to running on remote servers and you accessing it as a client, this is called software as a service.

As an example of modern client server model consider a video sharing website. The website, let's call it MeTube, has a server that stores all the videos that are uploaded to the site. The website is used by millions of clients a day and each of them connects to the server to watch videos. When a client connects to MeTube the server and asks for a particular video, the server loads the video into RAM from a large array of hard disks and MeTube sends the video to the client. The client on receiving the video, presses play and watches the video.

Other examples of servers might be a shared printing service in a college. The print server will be hosted on a single computer, and when anyone in the college wants to print, the request is sent to the server. In this case the server will keep track of how much printing credit each user has and make sure that the print queue is dealt with properly.

These types of networks are quite simple and are fine for very small networks of about 10 computers or less. They aren't complicated to set-up but don't provide very many of the powerful features found in client-server networks. For example, client-server networks can provide sophisticated security from one point (the server) whereas security has to be set-up on individual computers on a peer-to-peer network (because they are all peers). You can back-up work easily on a central server but you have to back-up work on each computer in a peer-to-peer network.

Applications which use client-server model

For contrast it is worth mentioning client/server applications as a form of remote computing.

A client/server application is a piece of software that runs on a client computer and makes requests to a remote server. Many such applications are written in high-level visual programming languages where UI, forms, and most business logic reside in the client application. Often such applications are database applications that make database queries to a remote central database server (this can, however, get much more complicated than that and involve other communication methods).

In a database application, data related number crunching can occur on the remote database server where the processing is close to physical data. An example of a database query might be to return the sum of a field named "dollar amount" where the field name year is "2016". There may be hundreds of thousands of records but the client computer does not have to worry about fetching or sorting through all of them itself. The database server will sort through that and just return one small record with the result to the client.

There are a wide variety of other client-server applications such as email, network printing, MMORPG (massively multi-player on-line role playing games). etc.

Introduction

What hardware is needed to create a network and use the Internet?

Network hardware - servers

A client-server network is a way of organising computers (clients) so that they can make use of the resources of one or more servers. A server is simply a computer that has resources that can be used by clients. There are different types of server. As mentioned elsewhere, think of a server as a service rather than specifically a piece of hardware/software. It is not uncommon for small networks to have one computer running multiple servers.

• • • Domain server/authentication server. This is is the server that manages the security of the network. Different network platforms (e.g. Windows, Unix, Novel) use different terminology but effectively, this server is responsible for authenticating all users on the network and storing the users' network credentials (access rights).

    • A file server. This is a computer that stores all of the users' data files. The NOS (Network Operating System) allows accounts to be set up. Users have to enter in a user ID and password to gain access to the network and to their own files. This system also means that users cannot access other people's files.

    • A print server. This is a computer that allows clients to have access to a shared printer. Print servers usually come with spooler software. Spoolers collect any jobs that have been sent to the printer, queues them and then sends them to the printer. If you sent a file to be printed straight to the computer rather than the spooler program, your computer would slow down because the printer works much slower than the computer. The spooler program frees up an application so you can carry on working.

    • A CD-ROM server. This is a computer that has many CD drives (or one drive that can change CD -ROMs automatically). Clients can access the information from any of the CD -ROMs currently in this server. A mail server. This manages mail into and out of a network.

    • A web server. If a business wants to have an Intranet or wants to host its own web site then it will need a web server. This is responsible for storing web pages and distributing them in response to requests.

    • A proxy server. The proxy server acts as a security buffer between the main file server and the users on a computer system. A user requests data held in a file server. The proxy server intercepts this request. The proxy server checks that the user is a valid user and is making a request for data that he/she is entitled to. If the user passes these checks, the proxy server gets the requested data from the file server an d passes it to the user. The user cannot access the file server directly. They must go via the proxy server. Proxy servers are mainly used as a security buffer between a computer network and the Internet, to stop threats from the Internet entering the computer system.

Network hardware - additional equipment

In addition to clients and various kinds of servers, a network will also need additional equipment. You should read widely to understand fully what the components that make up a network actually do because their definitions and functions are blurred and are constantly changing! If in doubt as to what any particular piece of equipment does then stick to the definitions given by the British Computer Society!

Hub

A hub is used to connect many computers to one place. For example, in a star network, all the cables from each individual computer go back and connect to a hub. The hub then connects to the server. Hubs can also boost signal strength if needs be.

Gateway

Gateways and routers are often seen as doing the same job, but there is an important different. Gateways regulate traffic between two dissimilar networks (enable them to be connected), while routers regulate traffic between similar networks (i.e. same protocol). Gateways convert data from dissimilar network's format into the other, so that each network can send and receive information to the other, usually using the public telephone network.

You might have come across the term 'default gateway' and this is used in IP networks as a catch-all for addresses that cannot be located on the local area network. The default gateway's address is almost always the address of the router, or proxy server.

Unfortunately, the terms gateway and bridge (not covered here) are often among those whose meanings vary between different communities of users.

Router

A router takes a ‘packet’ of data, looks at its IP address and then redirects it, or routes it, to the correct destination on a network (or different network running the same protocol). The network might be a LAN or WAN, such as the Internet. You can think of a router as a post office that knows all the addresses of any equipment on the network, whether it is a computer or a printer or a scanner, for example. Every time the post office receives some information from inside or outside the network, it knows exactly where to redirect it to. Routers are discussed in more detail in the next section, on IP addresses.

Routers can be called a gateway, but they are not. They are merely acting as a default gateway.

Network card (or Network Interface Card – NIC)

Each computer that is going to be part of a network needs to be actually connected up to the network. To do this, you will need to buy and fit a network card into an expansion slot in each computer. The network card inside a computer provides:

• • • a means of connecting a computer to a network

    • a way of splitting up data that you want to send across a network and then getting that data actually onto the network successfully

    • a way of collecting ‘packets’ of data addressed to that particular computer from the network. Each network card has a unique identifier called a ‘MAC address’ that enables this to happen.

Introduction

If you want to connect a single computer or a network to the Internet then you need to use some specialised equipment. There are a number of choices, including a modem, a broadband modem, a broadband router and a wireless broadband router (although there are other pieces of equipment you can use).

Public Service Telephone Network (PSTN)

PSTN is the network of the world’s public circuit-switched telephone networks. The PSTN is made up of fiber optic cables, microwave transmission links, communications satellites, undersea telephone cables, telephone lines and cellular networks. All of this equipment is inter-connected by switching centres which subsequently allows any telephone in the world to communicate with another. One benefit is that the PSTN connection remains active even during a power outage as its power is fed in separately to the building. When you make a telephone call, a direct channel is used between the devices used in the call and for the entire duration of the call.It is full duplex data transmission, with data passing through different switching centres.

Voice calls (and video) can also be made using Internet based systems (such as voice over IP (VoIP)). The benefit of using Internet based systems is that the connection is in use as long as data is being sent (e.g. there is sound). The connection can be used for other data in-between voice data packets being sent. This type of system can also make use of encoding and compression.

Advantages and disadvantages of modems

In this way, the existing, widespread phone network, which only uses analogue signals, can be used by computers, which are digital devices. On the other hand, modems cannot send large volumes of data at once. They are therefore of little use when streaming files, and the time taken to download files such as music or films may make them frustrating. In addition, the phone line, just like making a phone call, is engaged whilst the modem is in use. This is why it is also known as a 'dial-up' modem; you have to dial up the phone number provided by your Internet Service Provider (ISP) to make a connection to the Internet and all the time you are on the phone using the Internet, your phone cannot be used for other things, such as making and receiving phone calls or sending faxes.

Broadband modem

For many years, most homes used dial-up modems but as we have seen, these are slow and you cannot use your phone line for making or receiving phone calls whilst you are connected to the Internet. As technology advanced, many homes and businesses now make use of broadband modems. These pieces of equipment work in much the same way as dial-up modems, connecting to your phone line, converting digital signals into analogue signals and back again. However, they make use of a much wider range of frequencies than dial-up modems. Some of those frequencies can be used for the Internet but crucially, the frequencies that we use for speaking can be reserved for speaking. This means that we can now use both the Internet and make and receive phone calls at the same time.

One thing to note about broadband modems - they are designed to allow you to connect only one computer to your broadband connection. For many homes and businesses these days, that is a problem, as they have many devices that need to access the Internet!

Broadband router

Another piece of equipment in wide use is a 'broadband router'. This piece of equipment combines a broadband modem with a switch, so that you can connect not one computer but many computers or a whole network to your broadband connection. The router usually has an 'Admin' area. You can log in to this area using a login and password and set up the router and any security features, such as a 'firewall'. This is a piece of software that stops unauthorised users getting access to the network.

Wireless broadband router

If it weren't enough to have broadband routers, it is very common to find 'wireless broadband routers' in homes and businesses today. These work in the same way as a broadband router but you can connect devices wirelessly to the router as well as physically, using cables. That means that those wireless devices can also use the broadband connection to access the Internet.

Using wireless broadband router software, you can login using the administrator's login and password and set up the firewall. You can also set up the wireless security features that are commonly found. There are two features you are likely to find:

A password. You set up a password for wireless users. That means that anyone with a wireless device has to enter the correct password into their device before they can get access to the Internet connection.

MAC addresses. Allowable MAC addresses are entered into a table. Every device that can connect to the Internet has a MAC (Media Access Control) address. If you put the addresses of only the devices you want to allow to make a connection, then any device with a MAC address not in this table will not be allowed access to the Internet connection.

It is always a good idea to prevent unauthorised users from getting access to your network. One reason is they might be up to no good. The second reason is they might be downloading large files, which could slow your own use of the Internet down or even cost you money if you are paying for how much data is downloaded.

Leased line (dedicated line)

An alternative to a dial-up connection is a leased line connection. In this type of connection, you pay a fixed fee for a permanent Internet connection. You have access to the Internet 24 hours a day. You do not need to dial-up a phone number because you are always connected! Modems used in dial-up connections work at speeds of up to 56 Kbytes. This may be fine for light Internet use. However, leased lines typically give much higher bandwidths and this may be necessary if there is heavy use in the office by a lot of people or use involving large multimedia files

Mobile phone networks (cell modems)

Cellular modems are an alternative to these other types of network modems. They enable computers and other devices for Internet access. Instead of connecting to some cable that serves as the network pipe, though, cellular modems communicate over wireless links to the Internet via cell phone towers. Using cell modems offers several benefits over other modems:

• digital cellular service is faster than dial-up Internet

• cellular Internet access can be used while traveling and from any location the cell signal is available

Although their network speeds have increased substantially in the past several years, cell connections to the Internet typically offer somewhat slower data rates than other forms of broadband Internet, sometimes even below 1 Mbps. When tethered, a cell phone cannot receive voice calls.

Internet providers typically enforce strict limits on the daily or monthly data utilisation of their cellular service. Exceeding these bandwidth quotas results in high fees and sometimes even termination of service.

The following video gives an interesting history to undersea communication. This video does contain some useful facts for the exam (all of which are already on this page), but is here for those interested.

Coaxial copper cable

It is made up of a central conducting core covered with some protective insulation. Wrapped around the insulation is a thin metal sheath that provides the electrical interference protection. Finally, the cable has an outer covering. Coaxial cable is the cable used to connect your television aerial to the television.

It is heavier and less easy to manipulate than UTP. It is also more expensive. You can have longer cable runs than for UTP but still not as long as for fibre optic. This means that you may need fewer repeaters compared to UTP cable, but more than for a fibre optic cable. It is mechanically strong and resistant to interference.

Using satellite communications

Satellites are used widely for communication in the media, navigation, video conferencing, data transfer and for military purposes, for example. A transmitter on the ground sends signals to a satellite using microwaves or some other form of transmission. Using a different frequency to avoid interference, the signals are then redirected back to the planet. If it doesn’t reach the intended recipient, it is then bounced to other satellites and on to its destination.

Pros and cons of using satellites for communication

If you transfer data using satellite technology, the cost of data transfer is not dependent on distance. A short distance transfer costs the same as a long distance one. Overall, the cost of transfer is higher than non-satellite methods. Satellites can handle a very high number of simultaneous communication lines (they can handle a large bandwidth). Satellite communications can be used in the remotest parts of the world, from the arctic to mountainous areas to deserts although the actual equipment is very expensive. One use of this technology has been to provide up-to-date educational materials for schools in remote parts of Africa. Because of the distance between the surface of the planet and the satellites, there is a short delay in any communication. Weather conditions can also affect the quality of transmission.

Using WIFI - a wireless LAN (microwave frequency range 2.4 GHz - 5GHz)

You can connect up networks without using cables! For example, you can use lasers to 'fire' data signals between different parts of a network or use radio signals to send information across a LAN. You could use lasers to link two buildings onto one network, for example. Of course, you must have a clear view between the sending and receiving equipment in each building or the laser signal will be blocked.

Consider a school. The school has a couple of computer rooms linked using UTP. What happens when one department wants to use a computer room and it is booked? What happens when a teacher wants to use the computers in their own area rather than the computer room? One answer is to use wireless technology to provide a 'roaming computer room' like this:

• • • Buy laptop computers. Most laptops these days have a wireless card in them.

    • Set up Access Points around the school in all departments. (These hardware devices are 'black boxes' fixed to the wall. They relay signals from the server to each laptop's radio network card).

    • Use the laptops as if they were part of the main network!

The beauty of this system, also known as Wi-Fi, is that you can move the laptops around the school to different departments (so long as you have remembered to install a transceiver there). You also don't have to worry about cable installation. One drawback is that the bandwidth of these systems may not perform as the main part of the network does. For example, you should be able to run generic applications such as a word processor or a spreadsheet but multimedia or bandwidth-intensive Internet applications may be slower than networks that use physical connections. They also suffer from electrical interference problems far more than cable-based networks and they are potentially very insecure! Signals can be easily intercepted if the network has not been set up with security in mind. If this is a problem for an organisation than it should consider other technologies or think about encryption, perhaps PGP.

MAC addresses and security of wireless networks

All wireless devices, such as an IPOD, a laptop or a wireless printer, come with a MAC address, or Media Access Control address. When setting up a secure wireless network, you need to know the MAC address of the device you want to connect with. When you have this number, you have to access the wireless router using the administration login account. You then add the MAC address to the wireless router's list of allowable MAC addresses. The router will then only allow those MAC addresses to access the network and then only if they have the right password.

Of course, you may want to set up a wireless network which will allow any user to access the network, usually by giving them a password. These types of wireless network are known as 'Hotspots' and you can find them everywhere these days, from MacDonalds and Starbucks to airports and schools. Sometimes they are free and sometimes you have to pay. If you are setting up your own hotspot, the password chosen should be a good, long one using a mixture of upper and lower characters, numbers and punctuation and should use the latest WAP encryption methods. Older types of encryption like WEP aren't secure.

If you need to send information over longer distances then satellite, cellular phone technology and microwave technology should be looked at.

Live streaming and on-demand streaming: Differences

The two types of webcasting are live streaming media and VOD or video on-demand streaming media. Both types of webcasting will give a great smooth picture with audio. Live streaming media is the transmission of specially encoded digital content. In many ways, on-demand and live streaming are very similar. Live streaming is the broadcast of an event in real time over the Internet. On-demand streaming is the playback of an archived file that is accessed via a link embedded on a Web page. With on-demand streaming, a website visitor can access a streaming file at any time. In addition, both live streaming and on-demand streaming can be protected so it can not be shared by the use of DRM - Digital Rights Management.