Chapter No 4 – Networks and effects of using them
4.1
Networks
 Computer systems connected together in some way to form is known as a network.
 Network allows computers to share files, resources. A computer that is not connected to a network is known
as Stand-alone computer. Network connections are created using cables (wires), radio signals or by satellite
links.
4.1.1
Modems:
 Modem means ‘modulator demodulator’ and is a device that converts a computer’s digital signal into an
analogue signal for transmission over an existing telephone line.
 Modems are used to allow computers to connect to network over long distances using existing telephone
networks.
 Dial-up modem operate at the speed of about 60 kilobits per second, which is very slow. Modern broadband
operate at 11,000 kilobits per second.
4.1.1.1 HUB
 Hubs are hardware devices that can have a number of devices or computers connected to them. Hub is used at
the centre of star topology.
 Its main task is to take data which receives through one of the ports and then send out this data from all of the
ports. Each computer or device will receive the data, whether it is relevant or not.
 Hub is a dumb device, if it receives a message, it sends it to every computer on the network. This means that
hub-based networks are not very secure.
4.1.1.2 SWITCH
 Switch is like a hub which connects number of computers together to make a LAN. The use of a switch is at the
centre of star topology.
 The switch has cables plugged into computers to connect to a network. A switch is a more intelligent device than
a hub. If it receives a message, it checks who it is addressed and only sends it to that specific computer.
 Because of this, networks that use switches are more secure than those that use hubs, but also a little more
expensive.
 Switch only sends packets of data to the computer, it reduces the amount of data on the network, thus speeding
up the network.
4.1.1.3 Bridge
 Bridges are used to connect LANs together. When one of the LAN sends a message, all the devices on the LAN
receive the message.
 This increases the amount of data flowing on the LAN. Often a large LAN is divided into a series of smaller LANs.
 If a message is sent from one computer in a LAN to another computer in a different LAN, then the message
needs to pass between the LANs using the bridge.
 A bridge therefore, usually has only two ports in order to connect one LAN to another LAN.
4.1.1.4 Router
 Routers are hardware devices that read the address information to determine the final destination of the packets.
 Each computer linked to the internet is given a number which is called Internet Protocol address (IP address).
 When data is transferred from one network to another, the data is put into packets. The packets contain details
of the destination address of the network it is intended for.
 Computers on the same network have the same first part of the IP address and this is used to locate a particular
network.
 IT can be used to join wired or wireless networks together.
 Packets of data usually contain information such as:
 Sender’s IP address
 Receiver’s IP address
 Identity number of each packet
 Some form of header to identify the packets
 How many data packets make up the whole ‘message’.
4.1.1.5 Gateway
 A gateway is a network point or node that acts as an entrance to another network. It is a key point for data on its
way to or from other networks. All networks will have boundaries so that all communication within the network is
conducted using devices such as switches or routers. If a network node needs to communicate outside its
network, it needs to use a gateway.
4.1.1.6 Network interface card (NIC)
 A network interface card (NIC) is needed to allow a device to connect to a network. It is usually part of the device
hardware and frequently contains the MAC address generated at the manufactured stage.
4.1.1.7 Network cables
 Even though many computer systems use Wi-Fi, network cables are still used because they have the following
advantages over Wi-Fi:
 Faster data transfer rates
 Can be more secure than wireless networks.
 The cables can be either copper or fibre optics – the latter offers higher data transfer rates and also better security.
4.1.2 Internet protocol (IP) and media access control (MAC) addresses
4.1.2.1 Internet protocol (IP)
 Each device on the internet is given a unique address known as its internet protocol (IP) address. This is a 32bit number that is usually written in the form:
 Example: 109.108.158.1
 A home computer is given an IP address when it connects to the internet. This is assigned by the ISP and it is
unique for that particular internet session. The only IP addresses that remain fairly unchanged are web servers.
An IP address can be used instead of typing in the full URL; for example, http://109.108.158.1 would take you
straight to the device containing web page corresponding to this address.
4.1.2.2 Media access control (MAC)
 Each device or computer on a network has a media access control (MAC) address that uniquely a MAC address
identifying the source of the data should receive the data.
4.1.2.3 Differences between IP address and Media access control (MAC)
IP address
The IP address gives the location of a device on
the internet
Example:
You can think of the IP as the address of the house
you live in. IT is possible to move house (so your
IP address will change).
Media access control
MAC address identifies the device connected to the
internet.
Example:
MAC address can be thought of as a way of uniquely
identifying each person living in that house. The people
will be living in the new house. (So their MAC address will
remain unchanged).
4.1.3 Wi-Fi and Bluetooth
4.1.3.1 Wi-Fi
 A wireless transmitter receives information from a network via its connection. This transmitter converts the
received information into radio waves and then transmits them.
 A device receives the radio waves via an installed wireless adaptor which allows it to download the information
from the data source.
 Wi-Fi is best suited to operating full-scale networks since it offers much faster data transfer rates, better range
and better security than Bluetooth.
4.1.3.2 Bluetooth
 Bluetooth sends and receives radio waves in a band of 79 different frequencies. Devices using Bluetooth
automatically detect and connect to each other, but they don’t interfere with other devices since each
communicating pair uses a different channel.
 When a device wants to communicate, it picks one of the 79 channels at random. If the channel is already being
used, it randomly picks another channel. This is known spread-spectrum frequency hopping.
4.1.3.3 Differences between Wi-Fi and Bluetooth
Features
Transmission frequency used
Data transfer rate (maximum)
Maximum effective range (metres)
Maximum number of devices
connected
Type of data transmission security
4.1.4
Wi-Fi
Bluetooth
2.4 Ghz
25 Mbits/second
(~3.1 Mbytes/second)
30m
Up to 7
2.4, 3.6, 5.0 Ghz
250 Mbits/second (~31 Mbytes/second)
Key matching encryption
WEP (Wireless equivalent privacy) and WPA (Wi-Fi
protected access) are the most common security
systems.
100m
Depends on the router used
How to setup a small network?
 If you want to set up a small network, you will need the following hardware and software:
 Hardware requirements:
 One or more switches or hub to link devices together.
 Network cables to connect devices to the switch.
 A separate wireless access point to allow wireless devices to connect to the network.
 A router to connect your LAN to the WAN.
 A firewall to protect your network from the hackers.
 A bridge is required if you already have a section of the network and you want new network to connect
to it.
 Software requirements:
 Web browser to access internet
 Firewall – if it is software
 Anti-virus to protect your network
 Apart from the hardware and software, you would also have to think about doing the following:
 Set up an account with an ISP
 Set up the system.
 Configure hardware and software so that everything works with the network.
 Get an internet connection installed from the ISP.



4.1.5
Putting all common software onto a server and making sure that network license is acquired.
Set up privileges so that each user can only access their own area or common shared area.
Servers to network-manager-level of privilege so that they can monitor network usage, change
passwords, etc.
Internet, Intranet and Extranet: Refer Chapter 10
4.1.6 Types of network
4.1.6.1 Local Area Network (LAN)
 Local Area Network or LAN is usually within one building or not over a large geographical area. A LAN consists
of a number of computers and devices, e.g., printers, which will be connected to hubs or switches.
 Advantages:
 The sharing of resources (such as expensive peripherals and application software).
 Communication between users is easy.
 A network administrator to control and monitor all aspects of networking (For example, changing
password, monitoring internet, etc.)
 Disadvantages:
 Easier spread of viruses through the whole network.
 The development of queues for printer, which can be frustrating.
 Slower access to networks, such as internet.
 Increased security risk as compared to stand-alone computers.
 If the main server breaks down, in most cases, the network will no longer function.
4.1.6.2 Wide Area Network (WAN)
 A Wide Area Network is formed by a number of LANs being connected together through either a router or
modem. Some companies setup private WANs. This is expensive but comes with an advantage of much
enhanced security and speed. It is common to use an Internet Service Provider (ISP) for connections to the
internet and communicate through this network system.
 Advantages:
 A WAN is a network that extends over a large area.
 WAN can be connected using optical fibre cable, satellite link, radio signals, etc.
 Disadvantages:
 Very expensive.
 Limited access.
 Data access slows down if spread over huge area.
4.1.6.3 Wireless Local Area Network (WLAN)
 Wireless Local Area Networks or WLANs are similar to LANs, but there are no wires or cables.
 They provide wireless network communication over very short distances (a few metres) usually radio or infra-red
signals instead of cables.
 Devices known as access points are connected into the wired network, at fixed locations.
 Because of the limited range, most commercial WLANs need several access points, to permit uninterrupted
wireless communication.
 The access point receives and transmits data between the WLAN and the wired network structure.
 Advantages:
 All computers can access the same services and resources. E.g., printers, scanners, internet access,
etc.
 There is no cabling to individual computers and devices so safety is improved.
 The system is more flexible since, users can move their laptops from their desks.
 Adding new computers and devices is a very easy task and costs are reduced, since no extra cabling is
needed.
 Disadvantages:
 Security is a big issue, since anyone with a WLAN enabled laptop or computer, can access a network if
it can pick up a signal.
 There may be problems of interference, which can affect the signal.
 Data transfer is slower than LAN.
4.1.7 Accessing the internet
4.1.7.1 Mobile phones and tablets
 Advantages:
 Very portable; can be used almost anywhere provided phone network signal can be accessed.
 A person is more likely to have a mobile phone with them at all times.
 It is easier to use a mobile phone while on the move than the other devices.
 Disadvantages:
 Expensive to use if Wi-Fi hot spot not available.
 Signal less likely to be as stable or reliable as a wired system.
 Not all websites are mobile friendly.
 Keyboards are very small – it is therefore more difficult to type in messages or navigate web pages.
 The displays on mobile phones are smaller than no other devices – this makes it more difficult to read
web pages.
4.1.7.2 Mobile phones and tablets
 Advantages:
 Laptops are more mobile than desktops.
 Touchpads on laptops are not as easy to use as a mouse when navigating web pages, but much easier
than mobile phones.
 The keyboards on laptops are not as easy as a desktop but are much better than those on a mobile
phone.
 Disadvantages:
 Heavier and less portable than tablets and mobile phones.
 Although the screen size is usually bigger than a mobile it is not usually a large as than on a desktop
computer.
 Laptops require expensive ‘dongles’ to access phone networks.
 Processors used in laptops are not usually as powerful as those in desktops, so access speed is not as
quick.
4.1.7.3 Mobile phones and tablets
 Advantages:
 Tend to have more powerful/ faster processors than other devices.
 Usually have a more stable and reliable internet connection since they use a wired system rather than
Wi-Fi.
 All web pages are accessible due to larger screen size than other devices.
 Use of full-sized keyboard and pointing devices, such as a mouse, make web page navigation much
easier.
 Disadvantages:
 Desktops require expensive dongles to access the phone network.
 As all the parts are separate and because of the large size, desktop computers are not very portable.
4.2
4.2.1
Network issues and communication
Network security
 The security problems when using network such as the internet are well documented. There are various security
threats to network and there are many equally varied ways of combating the threats.
4.2.1.1 Should the internet be policed?
 The internet doesn’t presently have any controlling body that ensures that it conforms to certain standards.
 There are many arguments in favour of having control, and as many arguments against it.
 Arguments in favour of some form of control:
 It would help to prevent illegal material being posted on websites.
 People find it much easier to discover information that can have serious consequences; although most
of this information can be found in books, it is much easier to find it using a search engine.
 It would help to prevent children and other vulnerable groups from being subjected to undesirable
websites.
 It would help to stop incorrect information being published on websites.
 Arguments against some form of control:
 Material published on websites is already available from other sources.
 It would be very expensive to ‘police’ all websites and users would have to pick up the bill.
 It would be difficult to enforce rules and regulations on a global scale.
 It can be argued that policing would go against freedom of information.
 Laws already exist to deal with those who post illegal material/ comments on websites.
 Social divide:
 One more issue is the social divide created by computer technology and ICT. This is often referred to as
the digital divide: those people who have the necessary IT skills and/ or money to purchase and use
computer equipment will benefit from the new technology; those who are not able to access this new
technology, either through lack of money, skills or simply because they don’t live in a country with the
necessary infrastructure, are left further behind, leading to this social divide.
4.2.1.2 Inappropriate sites and the accuracy of information
 It is important to look at the quality of information found on the internet when using a search engine. There are
three main aspects to consider:
 Reliability of information:
 Information on the internet is more likely to be up to date than in books.
 It is much easier to get information from websites.
 There is a vast amount of information on the internet that is easier to locate than using the indices in
several books.
 Information could also be incorrect, inaccurate or even biased, since it doesn’t go through any checking
process.
 There is a real risk of information overload, even if the search engines are used properly; it is possible to
get millions of hits.
 Undesirability of certain websites:
 There is always a risk of finding undesirable websites.
 There is also risk of connecting to websites that are not genuine.
 Security risks will be there.
 Security issues:
 Passwords are used in many instances when accessing the internet, for example when:
o Accessing your email account.
o Carrying out online banking.
o Accessing social networking sites.
 IT is important that passwords are protected; some ways of doing this are described below:
o Run anti-spyware software to make sure that your passwords aren’t being relayed back to
whoever put the spyware on your computer.
o Change passwords on a regular basis.
o Passwords should not be easy to guess or break.
o Strong passwords should contain:
 at least one capital letter.
 at least one digit
 at least one special character
 Example: Syttt$1299TY
4.2.2
Authentication
 Authentication is used to verify that data comes from a secured and trusted source.
 It works with encryption to strengthen internet security, for example: User ID and passwords are authentication
techniques.
 Some forms of authentication include:
 Digital certificates
 Biometrics
 Magnetic stripe cards/ id cards/ passports.
 Example: Passport control at an airport
 The passport page containing the photograph is placed face down on a reader.
 A microchip embedded in the page is now read by a reader and the facial image on the passport is also
scanned in.
 The owner of the passport now looks up at a digital format and a photograph is taken.
 The photograph is converted into a digital format so that it can be compared to the scanned facial image.
 The data read from the microchip is also compared to data stored on a central database.
 The scanned image from the passport and photograph just taken by the camera must match and the
data stored on the microchip must also match up with the data on a central database; if either produces
any differences the passport is rejected.
4.2.3
Viruses
 This section considers how the risk of viruses can be minimized when using the internet or any situation where
data is transferred from computer to computer or other electronic devices – it is important to point out that tablets
and mobile phones can be infected by viruses. Ways of preventing or minimizing the risk of viruses are outlined
below:
 Antivirus software:
 Running antivirus software in the background on a computer will constantly check for virus attacks.
 Common features of antivirus software is as follows:
 Check software or files before they are run or loaded on a computer
 Antivirus software compares a possible virus against a database of known virus.
 Heuristic check is carried out.
 Any files that are infected are put into quarantine that:
o Allows the virus to be automatically deleted or
o Allows the user to make the decision about deletion.
 Antivirus software needs to be kept up to date.
 Full system checks need to be carried out once a week.
 Avoiding viruses when accessing the internet:
 Avoid looking into unknown or suspicious websites.
 Look for security indicators such as https or padlock symbols.
 While accessing a new website, instead of clicking the link sent to email, copy paste the URL into the
address bar. This can help you to avoid links to bogus/ fake websites.
 Viruses from hardware devices:
 It is unsafe to plug in a device from an unknown source.
 Even memory sticks or DVDs from friends could still be infected unless they have also carried out all the
necessary precautions.
4.2.4
Data protection acts (DPA)
 DPAs are designed to protect individuals and to prevent incorrect or inaccurate data being stored.
 General guidelines about how to stop data being obtained lawfully:
 Don’t leave personal information lying around on a desk when not attended.
 Lock filing cabinets at the end of the day or when the room is unoccupied.
 Do not leave data on a computer monitor if it is unattended; log off from the computer if away from your
desk for any length of time.
 Use passwords and user ids, which should be kept secure; passwords should be difficult to guess/ break
and should be changed frequently.
 Make sure that anything sent on fax or email is not of a sensitive nature.
 Eight principles of DPAs:
 Data must be lawfully protected.
 Data can only be processed for the stated purpose.
 Data must be adequate and not excessive
 Data must be accurate.
 Data must not be if unnecessary
 Data must be processed in accordance to subject’s rights
 Data must be kept secure
 Data must not be transferred to other country unless they have adequate protection.
4.2.5 Network Communication
4.2.5.1 Faxes and email
 There are two different ways of sending a fax:
 A physical fax:
 Standard fax machines have been used for many years to send and receive paper documents through
a telephone line.
 The user places the document in the fax machine tray, lifts the receiver and dials the fax number of the
recipient and then presses <send>.
 At the receiving end, the document is printed on another fax machine.
 It is a slow process if the fax line is busy.
 Electronic faxing:
 Electronic faxing or online faxing makes use of computer technology and internet to transfer the
documents.
 The fax number needs to be used by the sender to send the fax messages to the recipient.
 Once the fax is received, the online fax provider sends an email with the fax message attached in pdf
format.
 The sender of the fax can either use an email account or log into any online account to send the fax.

Advantages of fax machine when compared with traditional method:
o Costs are reduced as there is no need to buy a fax machine
o Transfers using electronic methods are encrypted, improving security.
o Transmissions are sent to an email account, which is password protected.
o There is no issue of a ‘busy signal’.
 Differences between traditional fax and electronic faxing:
 Online faxing or electronic faxing is associated with an email address and a fax number whereas
traditional faxing needs fax number.
 Emails:
 Emails are used when sending/ receiving attachments to/ from any device connected to the internet.
 It is important to have a good and stable internet connection.
 Email require an account with an ISP.
 When sending an email, it is necessary to include the email address, a subject line and any attachment
required.
 The recipient simply has to log on to their account and read the emails in their inbox.
 Differences between email and electronic faxing:
 Online faxing or electronic faxing is associated with an email address and a fax number whereas email
process needs email id of sender and receiver.
 Comparison of traditional faxes and emails:
Traditional faxes
They are more likely to be intercepted
Quality of documents can be poor at times.
If the telephone line is busy, there can be a
considerable delay in sending the fax.
It can be a slow process if several documents are to be
sent.
No modifications possible.
Emails
They are more secure
The document is usually of a much better quality.
No delay if stable internet connection is there.
Could send several attachments together in a faster way.
Can be modified or easily copied and pasted into other
documents.
4.2.5.2 Video Conferencing
 Video conferencing is a communication method that allows two or more people situated at different places to talk
to each other and see each other at the same time. If meetings need to be conducted between people in different
countries, a WAN is used such as the internet.
 They are also able to exchange electronic files with each other and also pass electronic documents around rather
than paper based documents.
 The basic hardware includes:
 Microphone
 Web camera
 Speakers
 Large monitors/ television screens.
 The basic software includes:
 Webcam and microphone software drivers
 CODEC (Coder-Decoder/ Compression Decompression)
 Echo cancellation software.
 There are few things to consider when a conference is about to begin:
 Agree a time and date for the conference to take place.
 The delegates in each conference room must log in to the video conference system.
 Video conference set-up needs to be checked before the meeting goes live.
 Webcams need to be placed in the correct position so that all the delegates in the room are within visual
contact.
 Microphones need to be placed centrally so that all the delegates can speak.
 Advantages:
 Saves money as business does not have to spend money on travelling, hotel rooms, meals, etc.
 Less stress as employees don’t have to experience delays at airports, accidents, road work, etc.
 Meeting can be called at very short notice without too much planning.
 Improved family life as less time spent away from homes, staying in hotels.
 Improved productivity of employees as they are not wasting time in travelling.
 Disadvantages
 Delays when talking.
 Jerking images due to poor internet.
 Can be very expensive to set up.
 There will be problems if the delegates live in different countries where the time zone differences are
large.
 Training people to use the system can be costly and time consuming.
4.2.5.3 Audio Conferencing
 Audio conferencing refers to meetings held between people using audio equipment.
 The equipment used can be as follows:
 Telephone
 A computer (with built-in microphones and speakers) or
 An internet phone.
 Audio conferencing using telephone line:
 Audio conferencing (also known as phone conference) can be done over the telephone line. The
procedure to be carried out when a phone conference is detailed below:
 The organizer of the phone conference is given two PINs by the phone company.
 One PIN is the personal PIN given to the organiser and the second PIN is the participants’ PIN.
 The organiser contacts all of the participants and informs them of their PIN and the date and time of the
phone conference.
 When the phone conference is about to start, the organiser dials the conference phone number and,
once he/she is connected, keys in his/her personal PIN.
 The participants then call the same conference number to join in – once they get through they each input
the PIN given to them by the organiser. Without this PIN, it will be impossible to join the phone
conference.
 Conferencing using VOIP:
 It is possible to hold an audio conference using a computer provided a microphone and speakers are
connected. This makes use of VOIP (Voice Over Internet Protocol).
 VOIP allows an organiser to create a group of people to take part in conference call. The group is created
by dragging and dropping user names and telephone numbers into the group. When the conference is
to take place, the organiser clicks on the group and the conference is initiated.
 VOIP allows communication using voice, instant messaging and video.
 Internet connection has to be stable for better quality.
4.2.5.4 Web Conferencing
 Web conferencing (also known as webinar) uses the internet to permit conferencing to take place. It allows the
following types of meeting to take people:
 Business meetings
 Presentations
 Online education or training.
 The only requirement is a computer and a high-speed, stable internet connection.
 To carry out web conferencing, each user either downloads an application or logs in to a website from a link
supplied in an email from the conference organiser.
 Delegate can leave or join the conference as they wish. The organiser can decide on who can speak at any time
using the control panel on their computer.
 If the delegate wishes to speak, they raise a flag next to their name. Delegates can post comments using instant
messaging for all delegates to see at any time.
 Some of the main features include:
 Slide presentation that can be posted and documents can be uploaded on the conference website before
the conference starts.
 Draw or write on a whiteboard using their own keyboard or mouse.
 Transmit images or videos using webcam throughout the conference.
 Possible to chat verbally or by instant messaging throughout the conference.