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3. Networks and communications

- types of network - methods of connecting computers and devices together - components of networks - communication appliances - how data is accessed on networks

Jumana Al-Kateb

on 18 May 2010

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Transcript of 3. Networks and communications

3. Networks and communications Introduction types of network
methods of connecting computers and devices together
components of networks
communication applications
how data is accessed on networks What is a network?
Standalone computers are not part of a network, but work indepedently.
They do not communicate with other computers.

A computer can be a standalone or connected to a network. A computer connected to a network can communicate with one of more computers in the network. Examples of communication include: messages or emails
file transfers
application sharing
print sharing (a) Local area network (a) A local area network is also known as a LAN. They are called 'local' as they are confined within a local geographic area. Characteristics of a LAN: Local geographic area
Workstations connect to the network using a network card or wirelessly.
Workstations and peripherals are also connected via cable or wireless devices.
Connection via cables is often to a switch or hub.
Peripherals can be shared such as printers and scanners.
Software and data can be shared within the network. For example, in this school, "student areas". (a) Wide area network (a) A wide area network is also known as a WAN. It consists of computers which are far away from each other, or geographically remote. Hence the term 'wide area'. It could even be as remote as worldwide. Characteristics of a WAN: Wide geographical area
External communications link is required to connect the workstations to the network. This may be a telephone line, leased line or mobile phone.
A modem, router or other device is also needed to connect to a WAN.

*Where can lans be found? schools, colleges, businesses, libraries and homes. a famous example of a wan: The internet! Millions of computers around the world are connected to this huge network via an external communications link (a common one is the telephone line).
An ISP (internet service provider) is also needed to connect to the internet.

Communication in the WAN includes-
- Information being shared via the World Wide Web
- Messages being sent via email and internet relay chat
- Web hosting
- File transfer [Workstations are connected to a switch or hub] [map of the internet] *Where can Wans be found? universities with multiple campuses far from each other,
local education authorities which connect many schools,
airline booking systems,
large businesses with many offices or shops. http://www.teachict.com/as_a2/topics/networks/networkswf/NWB_SIM.swf This link leads to a simulator that you can use to build a LAN: Connecting a LAN to a WAN Note: in this presentation, letters have been included next to certain pieces of text. These letters correspond to the letters on the specification for chapter 3. A LAN can be connected to a WAN directly via a router, as an external communications device. This router can often be connected to the switch via a cable.
When LANS connect to a WAN, they can connect with each other. The WAN brings, in effect, LANS in unison. (a) Virtual network In a virtual network, computers can communicate with each other as if they were in a LAN, but they may have no idea that they might be part of a larger network.

A virtual network in a LAN will include many computers. Only computers of a certain naming convention will be able to communicate with each other, but not with other computers of different conventions even if they are part of the same network. This means that the computers will appear 'invisible' to each other, even though they actually exist on the same network.

It is the switch device which actually 'hides' computers of specific conventions from each other. A virtual network can also exist within a WAN, but computers will operate as though they are part of a single LAN. If computers are not made to connect, then travelling data will not affect them.

Users will still have access to the same services as they would on a LAN, such as print sharing, data sharing and application sharing. *Where can a virtual network be found? online application software, such as prezi!
In a building with offices for multiple businesses,
storage of data concerning a certain entity in a different area or for remote employees for a company. PICTURE OF VIRTUAL NETWORK HERE (a) Compare the characteristics of a LAN, WAN and virtual network. (b) Compare the characteristcs and purpose of intranets, the internet and extranets (b) Internet Characteristics: The internet is the infrastructure provided to connect computers around the world using telecommunications such as telephone lines, leased lines, mobile phones and satellites. Don't forget that an external communications link was needed previously, to connect to a WAN.

It is important to remember that the internet is not the same as the World Wide Web. The internet uses TCP/IP protocol for communication between devices. The internet can be termed an 'open network' as any computer can connect to the internet as long as it has an external communication link. Purpose: The internet provides users a wide range of services. Main ones are:
- Email
- World Wide Web
- Internet relay chat (instant messaging)
-File transfer

Software is required to access these services, however there are also dedicated web browsers. There are for example pieces of software for email, file transfer and internet relay chat. In an exam, do not give a brand name, but talk about the type of software. For example, do not say 'MSN' for internet relay chat software. (b) Intranet Characteristics: The intranet provides the same services as the internet, but it is limited to one organisation, hence the prefix 'intra'. It can only be accessed by authorised people in the organisation, and often require a username and password. It is different from the internet in the sense that it is not an open network.

It may be provided through a LAN or in a virtual network via a WAN. Only computers that are part of the LAN or virtual network can access the intranet, so it is a closed network. It uses the same TCP/IP protocol as the internet. Purpose: The intranet provides the same services as the internet, but only within a closed organisation. Services include:
- Internal email
- Internal web pages
- Internal chat
- File transfer

As with internet, software is required to access these services, but only within the organisation. For example, sending an email to a colleague at a separate office, information from internal web pages or downloading software specific to the organisation. An advantage of communicating across an intranet is that information can remain confidential as no-one outside of the organisation can gain access to it. (b) Extranet Characteristics: An extranet is an external intranet. Users can access an intranet away from an organisation via the internet. The extranet will have the same features as the intranet, and users will see exactly the same thing as though they were in the organisation.

Access can be provided via a web page through a secure server which does not provide access for everyone. Access could also be granted by secure software which has to be installed onto a computer. Purpose: The same services as intranets and the internet are provided by an extranet. The main differences are that they are limited within an organisation and the services can be accessed off-site. Services can be accessed from internet connection and are useful for contact with colleagues who are far from the organisation.

For example, an employee may want to email a colleague who is far from them, if they are on business or working from home. They can even download files from web page. Information remains confidential within the organisation just like in an intranet. In this way, confidentiality can be maintained as access is limited, however there is an added risk of someone hacking into the extranet as it is available from every computer with internet connection. (b) Comparing the internet, intranet and extranet. In the exam, you may be asked to discuss/compare the characteristics and purposes of the internet, intranet and extranet. This should be a balanced argument of both advantages and disadvantages. Characteristics: Internet Intranet Extranet Allows computers across the globe to connect by providing the infrastructure.
Uses telecommunications systems to connect
Web pages are available to everyone however some may require a username and password.
Uses the TCP/IP protocol
Available to the whole world.
Communication with the organisation
Uses LANs or virtual networks through a WAN.
Requires a username and password to access.
Uses the TCP/IP protocol.
Available only to registered users and within the physical network of an organisation.
Communication with the organisation from any internet-connected computer.
Uses internet to provide access to the extranet.
Requires a username and password to access, so access is limited.
Uses the TCP/IP protocol.
Available only to registered users even though it can be found on the internet.
purpose: Internet Email communication with other users with internet connection
Web pages can be accessed for information
Chat conversations can take place.
Files can be transferred to and from sites.
Intranet Email communication only with members of the organisation
Web pages can be visited for internal information regarding the organisation.
Chat conversations can only take place with those on the intranet.
Files can be downloaded only within the organisation.
Information is secured in the organisation so external users cannot gain access to it.
Extranet Employees working far from office can send and recieve internal emails.
Employees working far can also access internal webpages for information.
They can also chat with colleagues,
They can download files needed for their tasks.
Employees can access all services of the intranet without physically being in the organisation's premises but there is the security risk of hacking.
(c) Describe client-server and peer-to-peer networks giving advantages and disadvantages of each. (c) Client-server network A client-server network involves a server and a client! A server is composed of at least one powerful computer which perfoms certain roles to control the network itself. The clients are the workstation computers connected to the network via a switch or other communication device.

The roles of the server include:
- File storage
- Back - up
- Application sharing
- Printer management.

Client computers:
Clients are connected to the server via a switch, hub, etc. Files and peripherals will be available for use on the network, however uses must log on with a specific username and password to make use of these. Some client computers use swipe cards or finger print recognition to connect to the server. Once the user is connected, they can make use of the facilities that the server provides, such as:
- A dedicated amount of storage space for each user.
- Printers (only certain clients may make use of certain printers)
- Files (if permission is granted)
- Sharing software and other peripherals.

When using this type of network, resources will remain the same no matter which client/workstation users connect to. This is the same system we have in school!

In large organisations, there may be several serves for certain tasks. This include print servers, file servers, back-up servers and proxy servers. Software can be shared with all clients including anti-virus software.

Serves require specialist technicians to manage and if a server fails, all clients will be affected.

(c) Peer-to-peer network There is no central server in this type of network. Computers are connected to each other and govern themselves, rather than being governed by a server. Resources may also be shared with other computers.

All computers have the same roles and rights, therefore they are 'peers'. No computer acts as the leader. Each computer may have different files or resources, that other computers may have to individually access. There is no server controlling files.

A peer-to-peer network is easier and cheaper to set up, and is often found in homes and small businesses. However each computer has to be maintained individually, so software for example has to be installed onto each computer.

(c) Advantages and disadvantages of each. (c) Client-server network (c) Peer-to-peer network Back-ups are managed centrally so users do not have to worry about that.
Anti-virus and general software is managed centrally and so can be shared amongst clients.
Network processing is done by the server, so clients have more processing power.
Data and applications be involved from any client.
Security and permissions are managed centrally.
Servers require a lot of processing power, large disks and lots of memory so they can be very expensive.
If the server fails, user lose access to certain resources.
A network manager is required to maintain the server.
There can be a lot of network traffic if applications are run directly from the server.

Each user is responsible for backing up their own data.
Anti-virus and other software has to be installed individually on each computer which can be time consuming.
This is a problem with anti-virus software as it has to be installed regularly to keep up to date.
All processing is done by computers, so they use more processing power.
The user has to access the same computer each time for resources and files.
Difficult to set up security.
No reliance on a central server, so it if fails, only shared resources are lost.
They can be set up by competent people.
Network traffic is minimal as most resources are provided by each computer.

QUESTIONS! 1) describe 3 characteristics of a lan
2) describe 3 characteristics of a wan
3) where will you most likely find a lan and wan?
4) Give an example of a wan
5) describe the purpose of a virtual lan
6) identify 4 services offered bn an isp. QUESTIONS! 1) describe 3 facilities available from the internet, intranet and extranet.
2) how does an intranet differ from the internet?
3) describe the purpose of an extranet QUESTIONS! (d) Explain the importance of bandwidth when transmitting data and how different types of communication media (cables, wireless and optical) govern the bandwidth available. Knowledge of different communication media is required. (d) Bandwidth Bandwidth is the measure of how much data can be transferred along a communications channel at one time.
The more frequencies available to the channel, the more data can be transferred at once. Bandwidth is officially measured in frequency (Hz) however it is more commonly reported in bits per second (bps).

This is often written as Mbps (mega bits per second). So 8 mega bits per second would be written as 8 Mbps.

A higher bandwidth means more data can flow through the channel at one time (per second). This means the speed of data transfer is a lot faster.
Visualise bandwidth.... Imagine a busy motorway with many cars in a traffic jam. The motorway has 4 lanes, and in each lane, there are many cars travelling one after the other. Four cars can travel at once along the motorway, so the motorway has a bandwidth of 4 cars.

Increase the number of lanes to 6 lanes on the motorway. Now 6 cars can travel along the motorway at one time, so the number of cars that the motorway can carry has increased. The same applies to a channel. The motorway would be a channel and the frequencies would be the lanes. As said before, the more frequencies available, the more data can travel. The cars would mimic data. So data travels along a channel, and the more frequencies available, the more data can travel at one time.
(d) Bottlenecks You might have been through a bottleneck whilst downloading from the internet. Your bandwidth may be higher than your download speed because of a bottleneck made somewhere within the internet. This means downloads are slower.

A bottleneck: is the smallest bandwidth that exists between the user and the origin of data (the channel). Think of it in terms of the smallest width in a channel.

Using the motorway analogy, think of a motorway having 4 ordinary lanes. What if road works occur and a lane is closed? The motorway will now have 3 lanes, so less cars can travel through it at a time, so the journey time for cars will be longer. This is the same idea with data, less data can travel through the channel at one time because of the reduced space.

Also, with a bottle, water can only pour down the neck, which is the narrowest part, so it slows down the flow of water.

When does this occur? Well, imagine you are connected to your own ISP with a bandwidth of 8 Mbps. If you are trying to download a file from a website which is connected to their ISP with a bandwidth of 2 Mbps, the bottleneck will be 2 Mbps. This means that even your bandwidth is 8 Mbps, you can only download the file at a rate of Mbps due to the bottleneck. If more than one person is downloading from the website at once, bandwidth will be even lower.
(d) Importance of bandwidth The amount of bandwidth is important in determining download speed, and how much data can be downloaded at once. It depends on the application (software) the user is running and how much data is being downloaded at once. For example, if a user wants to send an occasional email with no attachments, a small bandwidth is suitable.

Instances where a large bandwidth may be required include a video conference or live radio. In a video conference, lots of data will need to be transferred at once as video and sound consist of large packets of data. These need to be delivered in time to avoid lagging which may result in broken or missing picture/sound.

Live radio is streamed. A high bandwidth is require to deliver the sound on time so that breaks are not experienced during broadcast.

However pre-downloads are not affected as much. For example is a radio programmed is pre-downloaded, actual download time may take long and be inconvenient, but once it has been downloaded, it can be listened the whole way through without disruption.

The importance of bandwidth:
- accessing content being delivered in real time
- downloading large amounts of data
- to avoid broken pictures, sound, becoming out of sync and freezing

communication media- cables (d) Cable The copper cable is one of the oldest methods for transmitting data. Older networks used co-axial cables and are still used within the television industry due to it's capacity for high bandwidths. The co-axial cable can be seen in pictures on the left <<<.

The outer cable acts as a shield or insulator to electromagnetic interferece, which reduces signal loss. Electromagnetic radiation can be easily absorbed by copper.

Copper cables in modern networks are now usually in the form of twisted pairs of wire. They are narrow strands of copper wire, insulated with plastic and then twisted together.

Unshielded pairs form most of the twisted copper cables and can result in data packets being lost especially at higher frequencies. These cables are known as 'unshielded twisted pair' (UTP) or Ethernet cables.

'Shielded twisted pair' (STP) cables have a shield for each pair of wires. The shield is made of metal and reduces electromagnetic inteference. These cables are often used in high-speed networks where a higher bandwidth is required.
WHY? Copper cables are used in local area networks.
Can support data transmission of up to 1 Gbps using CAT 5e cables (four twisted pairs). CAT 6 and cat 7 can transmit up to 10 Gbps.
Cheaper than optical cables
Limited to a maximum of 100 metres, otherwise the signal becomes too weak
Prone to electrical interference, so data packets are lost , reducing overall transmission rate.

Unshielded twisted pair. Shielded twisted pair. (d) Optical Fibre-optical cables are very thin glass tubes which reflect light along the length of the tube. The are used where more than 100m of cable is required and in modern cable TV networks. As they use light, they do not suffer electrical interference and very little loss of data, so bandwidth is a lot higher than copper cables.

In 2008, Virgin Media were offering 20 Gbps broadband connections using fibre-optic cable, however in 2000 Siemens carried out a test of transmitting 7.04 Tbps along a single cable.

However, optical cables can be easily damaged due to their delicacy. Installation is also more expensive than copper cabling.
1) describe 3 advantages of networking computers
2) compare peer-to-peer networks and client-server networks
3) describe 2 advantages of a peer-to-peer, and 2 advantages of client-server
4) describe 2 disadvantages of client-server, and 2 disadvantages of peer-to-peer QUESTIONS! 1) describe the term bandwidth
2) if a user has a 8 mbps connection, why may it take longer to download than the speed that the actual connection dictateS?
3) give 2 examples when it is important to have a high bandwidth
(d) Wireless There are many methods for wireless communication, including radio, satellite and infrared methods.

There tends to be less bandwidth with wireless networks as there is a smaller range of frequencies than for copper cables and fibre optic cables. This means that the speed of data transfer is lower.

Obstacles may also intefere with signals such as walls and steel, leading to lost data packets. Wireless can also be susceptible to other interference which reduces transmission rate and can lead to loss of data.
picture here (e) Compare the role of network components: switches, hubs, WAPs, NICs, WNICs, routers, repeaters, bridges, servers and identify where their use would be appropriate. (e) Switch A switch is a device which connects several devices, allowing communication to take place between them. Such devices include printers and computers. It consists of a number of ports to which cables are connected to. Those cables are connected to the device from the other end.

Switches are useful because when they recieve data packets, they examine their destination and send the packets to the port connected to the recipient device. So data packets are only sent to target computers which is much more efficient.

Large organisations often have many switches which are connected to a core switch. The core switch manages data recieved by other switches and sends the data to other switches connected to it (the core switch).

Data recieved by each port can be controlled using various methods. A common way is to assign different amounts of bandwidth to different ports. They can also be configured to QoS (quality of service) which is when priority is given to certain applications whicyh require a certain bandwidth such as video conferencing or VoIP (voice over internet protocol). Another method is to set up a virtual LAN to monitor traffic. This can allow two ports to communicate at the same time as two other ports without collisions.

(e) Hub A hub looks physically the same as a switch and can allow devices connected to it to communicate with each other, however it uses a different method.

It does not examine data packets and sends them to specific ports, but rather sends them to every port connected to the data packets. This means that recipient devices have to filter data rather than being filtered by the switch or hub. This means that data can be disrupted and be susceptible to interception (preventing correct data arriving).

Sending data out through all parts can also cause collisions and delays. There is no indepedence between ports, therefore collisisons may occur.
(e) Wireless access point (WAP) A wireless access point is a hub which connects devices wirelessly so there are no physical connecitions at ports.

The WAP is connected to the main network infrastructure by a single cable connected to a switch. Wireless enabled devices such as laptops, mobile phones and PDAs can connect to a WAP. These devices send radio signals to the WAP and the signals are then sent to the network or another wireless device.

When a signal is sent from a wireless device to the WAP, the WAP recieves the signal, broadcasts it and the recieiving wireless device collects the data packets.

A problem with WAPs is that there is a high potential for hackers to intercept data. WAPs use encryption methods to encrypt data, making it harder for hackers to access. WAPs are often found in homes, small organisations and large organisations where wireless devices need to connect to the network.
(e) Network interface card (NIC) Network interface cards are often found on motherboards of computers. A NIC enables a computer to be connected to a network using a cable. Even though the cards are often found as part of the circuitry of the motherboard, it is possible to add them to computers.

Each NIC has a media access control (MAC) address which is unique to that card. Other devices with a NIC connected to networks also have unique MAC addresses so they can be identified uniquely.
(e) Wireless network interface card (WNIC) Just as devices communicate wirelessly with WAPs, and WAPs communicate wirelessly themselves, a wireless network interface card is needed to communicate with a WAP.

WNICs can be found as:
- part of the internal circuitry of a laptop computer or printer (inside)
- a USB wireless dongle which can be connected to any USB port on a computer or other device.
- an adapter card that fits into the PCMCIA slot on a laptop or expansion slot on a desktop computer.

The WNIC must have the same communication method as the WAP to transfer data correctly and will also have a MAC address just as a normal NIC.
(e) Router A router is an advanced version of a switch. It stores addresses of devices connected to it, and sends data to recipient devices using the address via an efficient route.
It is usually used to connect a LAN to a WAN (such as the internet).

Routers were once used exclusively by large organisations but can now be found in home computers in smaller versions.
(e) Repeater USB dongle Repeaters are able to amplify signals. Signals deteriorate along long cables, so the quality of the signal decreases and data can be lost. A device is needed to extend the range of the cables and to ensure the signal remains as it is.

The repeater receives the signal from one cable and re-sends it along the next cable. This ensures that the signal continues unaffected by distance, so no data is lost. It is used when copper cable is needed for a distance of over 100 metres.

Visualise: Imagine people standing in a line with a large distance between them. The first person shouts something, and the sound begins to fade after a distance. The next person then shouts the next thing, and the sound is repeated.

defintion: to increase in size, to strengthen, to make bigger. http://www.wordle.net/create (e) Bridge Used to connect two LANs together. It is different to a router because it does not store addresses of the devices connected to it.

(e) Servers A server is a powerful computer that is able to perform many functions. Such functions are performed on behalf of clients/workstations connected to it. For example, controlling printing. There are many different types of server and the size and functionality (tasks) of a network will dictate how many servers are required. There are various types of servers including:
(e) File server Stores files available on the network for all clients to access. It often has storage areas for each user in the network that only they can access, (for example with student accounts) and shared areas available to all or some users (for example student areas).

examples Shared areas in a school are very common. Some examples of shared areas in a school area:

Student - all users of the network can view all files in this area.
ICT- only ICT staff can make changes to files
History - only History staff can make changes to files.
Staff - staff can read all files, but students cannot access the files.
Secure - only staff who have been given permission can read or change files in this area.
Finance - only finance staff can read or change files.
Admin - only administrative staff can read or change files.

It is important that users can access their own and shared files on all clients due to the server. This is a huge advantage of a client-server network.

(e) Application server In client-server networks, software can be installed once and then be used on all workstations. This is due to an application server. The application server stores all software for use across the network. It performs two main functions:

- storing software so that it can be run from the application server by a client computer.
- storing software installation files so that software can be shared among client computers.

The advantage of using an application server to store software is that all client computers can use the software without having to install the software individually on all computers. It saves storage space, memory and processing power on client computers, however can also increase network traffic.

(e) Mail server The mail server manages email for an organisation. It recieves incoming emails and then allocates them to an appropriate inbox depending on the recipient address. It only allows a certain user to access an account. Emails sent by the mail server by users will go to another user on the LAN or via a router to a WAN or the internet. The mail server will also has the following functions:

- checking incoming emails for viruses
- filtering out SPAM emails
- providing a central address book for the organisation (stores addresses)
- setting limits to the size of mailboxes
- calendars.

(e) Proxy server A proxy server manages access to the internet within an organisation. It has the following functions:

- stores web pages visited in a cache so that the next user to visit web pages stored in the cache has faster access to them.
- a firewall that examines incoming data coming in to (and sometimes outgoing data) the network and blocks access to unacceptable internet traffic.
- filters access to webpages so that undesirable web pages are blocked.

definition: a collection of duplicated data stored elsewhere for faster, future access. (e) Print server A print server manages print access within a LAN. Print requests are sent by client computers to the print server which processing the request and also assigns the printer for the request. This reduces processing required by client computers. The print server puts all print jobs in a queue and deals with them individually. It can also restrict printing access. Features are:

- prioritise print jobs so 'urgent' ones can jump the queue.
- charges users for print jobs
- restrict the number of pages that can be printed at once to a printer
- restrict access to certain printers so that they can only be used by specific users.
- provide reports of print jobs.

(e) Back-up server A back-up server backs-up all data on a network so that users do not have to back-up their own data. This means that even if a file is accidently deleted, the user can recover the file using the back-up server. Even though users can rely on the back-up server to back-up their files, it is usually recommended for users to back-up their personal files incase the back-up server were to fail, or just as good practice.

A back-up server often has tape drives connected to it. Back-up jobs are often performed automatically each day overnight when there is less strain on the network. Tape drives are often stored elsewhere.

(f) Describe optical communication methods (infrared, fibre optic, laser), their advantages and disadvantages and typical applications. (f) Infrared Infrared has been a method of communication for many years with remote controls for use with televisions, video recorders and CD players. Infrared was also used in early laptops to enable the to communicate with printers and other laptops. It is also used by mobile phones, enabling them communicate with each other to share files and play games. Before Bluetooth, infrared was the main method for wireless communication between a laptop and mobile phone.

Infrared however, requires a direct line of sight, so if the device is blocked, the signal cannot be retrieved. It can only work at short distance of no more than 10 metres, usually less.
Bandwidth is also restricted to 115.2 kbps.

(f) Fibre optic Fibre optic makes use of tiny glass tubes which make use of light for data transmission. Data therefore travels at the speed of light and bandwidth is very high. It is the highest among optical communication methods. They are used in LANs were more than 100 metres is needed and in WANs.
Virgin Media use fibre optics for cable television and broadband across the UK.

(f) Laser Laser communication involves having two laser devices in direct line of sight with each other, so that they face each other with no obstruction. One device sends a laser beam to the other, which recieves the laser beam from the other device.

Data travels at the speed of light just as fibre optic, and does not require a physical connection such as a cable with fibre optic. However, laser communications only work in line of sight.

Laser communications can be set up quickly and are portable, and are often used at live sporting events to transmit live video from an aircraft. Live video can be transmitted due to the high bandwidth. However, atmospheric conditions can intefere with laser.

Laser is also used in tag games in which laser guns are used to aim a laser beam at other contenders. If the laser hits the contender's laser reciever, a point is scored.

Laser communications are not as common as the other two forms of communication described, however there have been experiments for laser communication between satellites in space. In 2008, the TS4B company were offering bandwith of 1.5 Gbps for up to 4 kilometres.

For use with... (g) Describe wireless communication methods (Bluetooth® and radio), their advantages, disadvantages and typical applications. (g) Bluetooth® Bluetooth® is a protocol for wireless communication. It uses short-length radio waves. It has a range of 10 metres and does not require a line of sight (it does not have to be directly infront of another device). It was created to enable widespread communication between portable devices.

The first bluetooth protocol enabled data transfer rates of up to 1 Mbps which was suitable for data transfer between laptops and mobile phones. A later version enabled transfer rates of up to 2 Mbps which was suitable for laptops connecting to 3G mobile phones. In 2009, there were plans to make a third version with transfer rates of up to 480 Mbps.

Typical applications include:

- Bluetooth® headset for a mobile phone
- transferring files between mobile phones
- connecting a mobile phone with a laptop to enable file transfers, using the mobile as a modem for the laptop and connecting the phone to a GPS reciever for satellite navigation.

definition: standard rules for data transmission. advantages and disadvantages: Advantages Disadvantages Widely available on many portable devices
A radio frequency licence is not required
Does not require line of sight
Pass key can be used to prevent unauthorised devices from connecting

Current data transfer rates
Maximum range of 10 metres
Can connect only one device to another device at a time (e.g. a Bluetooth® headset cannot be connected to a laptop and mobile at the same time).

(g) Radio Radio is a common method of wireless communication, also known as wi-fi. It supports three main standards: 802.11a, 802.11b and 802.11g. 80.2.11b supports bandwidths up to 11 Mbps, whereas 802.11g supports bandwidth up to 54 Mbps.

There is also 802.11n, which supports a higher bandwidth but at the time of writing, the standard was not universally accepted.

Typical applications include:

- wireless-enabled laptops being able to connect to an organisation's network
- laptops connecting to the internet in wireless hotspots in places such as hotels, airports etc.
- laptops connecting to home networks
- PCs with a wireless NIC being able to connect to a network where cabling would be expensive and difficult to install.
- mobile phones and PDAs being able to access the internet via wireless networks instead of being chrged per minute or megabyte.
- game consoles connected to internet without cable
- printers can be connected to a wireless network.

advantages and disadvantages: Advantages Cable not required for connection
Portable devices not restricted to a particular location for network access
Money can be saved by using mobile phones and PDAs on wireless networks at home and work
No line of sight required
Transfer rates sufficient for internet communication
Wi-fi standards mean any laptop can connect to any compatible wireless network across the world.

Disadvantages Transfer rates restricted for network communication
Range is 30 metres indoors and restricted by walls and steel construction
if many laptops or other devices are connect to a single WAP, bandwidth is shared so transfer rates are reduced.
If encryption is not set up properly, wireless networks are susceptible to hacking.

(h) Describe the facilities of the following communication applications: fax, email, bulletin (discussion) boards, tele/video conferencing and internet relay chat (IRC) and compare their use for a given application. QUESTIONS! 1) why can't copper cable be used over long distances?
2) what is the difference between utp and stp
3) what an advantage of stp over utp?
4) Why are fibre-optic bandwidths higher than copper bandwidth
5) Why are wireless bandwidths lower than cable bandwidths?
QUESTIONS! 1) identify three items needed for a network
2) compare a switch and hub
3) list the hardware needed for a wireless network
4) what is a mac address?
5) which device is used to connect a lan to a wan?
QUESTIONS! 1) describe the purpose of a file server
2) describe the purpose of an application server
3) list 3 functions of a mail server
4) describe a proxy and print server

QUESTIONS! 1) give 3 situations when infrared might be used
2) when might fibre-optic cables be useful?
3) describe laser communications

QUESTIONS! 1) discuss advantages and limitations of bluetooth
2) describe three applications of radio
3) describe two applications of bluetooth
4) discuss advantages and disadvantages of radio

(h) Fax A fax (facsimile) machine is used to produce outputs on the form of hardcopies. They look similar to printers and have a number pad for dialling telephone numbers and a scanner.

A document is fed through the fax machine which scans the document, and it is then sent electronically via a telephone line to another fax machine which will print the document. The quality of the document received is considerably less than the original. The cost of sending a fax is the same as a telephone call for the same duration.

An advantage is that documents can be sent instantenously to the recipient. Confidentiality can be difficult to maintain as fax machines are often found in shared office areas. There is also debate as to whether faxed documents are legally binding, i.e. whether or not faxed documents can be used as contracts.

Typcial uses of a fax include:
- advertising material to potential customers
- draft copies of contracts
- directions (pre-drawn and hand-drawn maps)
- printed diagrams

Facilities of a fax machine include:
- send and recieve 2D documents (hardcopies)
- send to multiple recipients using auto-dial, however documents are sent one recipient after the other
- receive faxed documents automatically
- block unrecognised callers
- produce delivery receipt
- produce a summary of faxes sent and recieved over a period of time.

(h) Email Email is the most popular method of communication in the developed world. Messages can be sent to a recipient, or multiple recipients, and attached files can also be included and received instantaneously. Emails are stored in an inbox, and can be available for the user to access whenever required, so emails do not have to be opened straight away.

Confidentiality can be maintained as the user needs to log into their email account in order to view emails. Quality of original documents is not lost, as documents are sent as digital documents electronically. They are received exactly how they are sent. The cost of sending an email is negligble assuming that a broadband connection is used.

A similar debate with faxes also exists with email about legally binding contracts. UK law allows the use of electronic signatures but they must be recognised in the law. The requirements of electronic signatures under the Electronic Communications Act (ECA) are very complex. While it is possible to use emails as contractual documents, they should not be relied on completely.

Emails can be sent using computers, mobile phones and email-enabled landline telephones. Also, cable television providers offer email services through television via a digi-box.

Typical uses include sending:
- advertising material to potential customers
- newsletters to members of an organisation
- messages to friends and family
- documents to suppliers and clients

Facilities of email include:
- send and receive messages
- send messages to multiple recipients at once
- address book
- electronic signature
- attachments
- reply to emails
- forward emails to other recipients
- request a read receipt
- filter out junk email
- encryption.

N.B. many emailsystems also include a personal calendar and task management facilities.

(h) Bulletin boards Bulletin (discussion) boards are used to enable to discuss topics with other people based on a certain topic. The could be for leisure purposes or business reasons. Users can post a message asking a question which other users can read and respond to. Messages are then posted in turn on the discussion board. A discussion board often has the following structure:

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