Computer Networks

Welcome to the world of Computer Networks.  By the end of this guide you will learn the meaning and importance of Computer Networks.

  1. What is a Network?
    • A Network is two or more computers or other electronic devices connected together so that they can exchange data.
    • 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.
  2. What are the types of Network?
    • There are three types of Networks:
      • LAN
      • WLAN
      • P4+ WAN
  3. Why do we use Networks?
    • Using a computer connected to a network, allows us to:
      • Easily share files and data.
      • Share resources such as printer, scanner and internet connections.
      • Communicate with other network users (email, video conferencing, chatting, etc).
      • Store data centrally (by using server) for ease of access and backup.
      • Keep all of our settings centrally we can use any work station (PC).
    • If we use a computer connected to the internet, we can:
      • Make use of online services such as e-commerce (shopping), e-banking, etc.
      • Get access to a huge range of information.
      • Access forms of entertainment (games, music, videos, etc.)
      • Join online communities (e.g., Facebook, MySpace, etc.).
  4. What are the disadvantages of a Network?
    • Using a computer connected to a Network means that:
      • The computer is vulnerable to hackers.
      • If the network breaks, many tasks become very difficult to perform.
      • Your computer can more easily be attacked by a virus.
      • We have to be careful about revealing personal information.
      • We have to be careful to avoid suspect websites that might contain malware.
      • We have to be aware that information found on the internet is not always accurate or reliable.
  5. Explain the following terms.
    • Client:  Client computers are the normal computers that user can use it to get their work done.
    • Server:  Servers are special, powerful computers that provide services to the client computers .  The services are:
      • Providing a central, common file storage area.
      • Sharing hardware, such as printers.
      • Controlling who can or cannot have access to the network.
      • Sharing internet connections.
    • Servers are more expensive than normal computers.  In a small network, one server might provide all of these services.  In a larger network, there might be many servers sharing the work.
  6. What are the types of Network?
    • There are three types of Networks:
      • LAN – Local Area Network
      • WLAN – Wireless Local Area Network
      • WAN – Wide Area Network
  7. What is a 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.
      • A network Administrator to control and monitor all aspects of networking.
        • E.g., 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 must cases, the network will no longer function.
  8. What is a 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 pickup a signal.
      • There may be problems of interference, which can affect the signal.
      • Data transfer is slower than LAN.
  9. What is 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.
  10. Write the difference between LAN and WAN.
a. LAN is confined to a very small area. a. WAN covers wide geographical areas.
E.g. Between cities, countries and even continents.
b. Usually located in a single building. b. Usually located between many buildings and countries.
c. Uses cables, wireless, infra-red which are usually queued by the organisation. c. It uses wireless, satellite links, which are globally organised.
d. We can restrict or block any websites. d. WAN has very fast speed.
  1. Bluetooth (Personal Area Network)
    • Bluetooth is a wireless network technology designed for very short range connections (just a few metres).
    • The idea of bluetooth is to get rid of all those cables, that connects our computer to peripheral devices such as printers, mouse, keyboard, etc.
    • Bluetoowith devices contain small, low power, radio transmitters and receivers.
    • When devices are in range of bluetooth devices, they detect each other and can be connected.
    • With this system, it is possible to create small home networks.
    • The range is however quite small (about 10 metres).
    • Typical uses of Bluetooth
      • Connecting a wireless keyboard to a computer.
      • Connecting a wireless mouse to a computer.
      • Using a wireless headset with a mobile phone.
      • Printing wirelessly from a computer or PDA.
      • Transferring data or music from a computer to a MP3 player.
      • Transferring photos from a cell phone or camera to another device.
  2. WiFi
    • WiFi refers to any system, where it is possible to connect to a network or to single computer through wireless communication.
    • E.g., Laptop computers which are wifi enabled can connect to devices like printer, keyboard, etc.
    • Wifi system rely on some form of ‘AP’ (Access Point), which uses radio frequency technology to enable the device to receive and send signals.
    • It is not a short form of wireless Fidelity.
    • It is a trademark name for any product which is based on IEEE 802.11 standard.
    • Wifi hotspots are places where you can access wifi (free or paid).
    • They exist in public places such as airports, hotels, internet cafes’, etc.
    • It is possible to log on to free wifi unless they are protected by password.
    • Software exists which can be loaded in a laptop which then searches for non protected wifi system.
    • The practice of driving around in a car looking for these unsecured wifi hotspot is known as war driving and possess a security risk.
  3. Write short notes on networking hardware (devices).
    • Modem
    • Modem means modulator and demodulator and is a device which converts a computers digital signal into analogue signal and digital to analogue signal and transmission over existing telephone lines.
    • 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.
    • Hub
      • Hubs are hardware devices that can have a number of devices or computers connected to them.
      • 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 used at the centre of star topology.
      • 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.
    • Switch
      • Switch is like a hub.
      • It is a device 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.
    • Bridges
      • 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 usng the bridge.
      • A bridge therefore, usually has only two ports in order to connect one LAN to another LAN.
    • 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).
      • This address is like 123.456.7.89 and is unique for each device.
      • 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.
      • Can be used to join wired or wireless networks together.
    • HTTP Proxoy Servers
      • This is a special type of server that acts as a protector between WAN and LAN.
      • A Proxy Server can be a major component of a firewall.
      • The Proxy Server is able to modify request and responses.
      • Organisations such as schools, libraries, business centres, use Proxy Servers to block offensive web contents.
    • They can be used to protect data on the internet.
      • A Proxy server is a computer set up, to share resources usually and internet connections.
      • Other computers can request a web page via the Proxy Server.  The Proxy Server will get a web page by using internet connection and pass it back who ask for it.
      • Proxy Servers are often used instead of a router since additional software can be easily installed on the computer such as antivirus, web filtering, etc.
    • Firewall
      • Is a device or a piece of software that is placed between your computer and the rest of the network (where the hacker is).
      • If you wish to protect your whole LAN from the hacker on the internet.  You would place a firewall between the LAN and internet connection.
      • A firewall blocks un-authorised connections being made to your computer or a LAN.
      • Normal data is allowed through the firewall,  e.g., Emails, Web pages, but all other data is blocked.
  4. What is internet?
    • The internet is the world wide collection of networks which allows a user to send and receive emails, chat or browse the World Wide Web (WWW).
    • WWW or web is the part of the internet which the user can access by using web browsers.
    • A web browser is a s0ftware that allows a user to access and interact with web pages and files on the web.
    • Web Page
      • Web pages are documents on a computer screen which may consist of text, pictures, sound, video, etc.
    • Web Site
      • Web site consists of many of he web pages linked together.  A web is made up of millions of websites and web pages.
      • E.g.
      • The web site shows the hyperlink to allow user to navigate between web pages.  These hyperlinks are often shown as Blue underlined text or sometimes a small hand appears under a picture or under some text indicating that link to web pages or web sites.
      • Web browsers use URL (Uniform Resource Locator) to retreive files.
      • URL’s are a standard way of locating resources on the internet.
      • They are usually a set of four numbers.
      • The URL indicates
        • Protocol://site address/Path/Filename where
        • Protocol is usually HTTP
        • Site address consists of host computer name, domain name, domain type and the country name.
          • Computer name is usually www
          • Domain name is name of website
          • Domain type is commonly one of the following
            • .com, .org, .net, .mil, .gov
          • country name .in, .uk
          • file path is a URL of the web page
          • file name is the name of the document
          • Thus, full url could be
  5. How to access internet?
    • An ISP is a company that provides access to the internet to the user and usually a paid service.
    • When a user registers with an ISP, an account is set up and they are given login details which include username and password.
    • There are three common ways of accessing the internet offered by service providers.
      • Dial up internet access
      • Cable internet access
      • DSL (Digital Subscriber line)
      • Dial up internet access
        • It is the slowest internet connection (60 kbps).
        • The user connects to the internet via telephone lines by dialing one of the number supplied from the ISP.
        • ISP contracts are usually for hours per month of internet access time and additional charges are incurred if this is exceeded.
        • A big disadvantage is that if the telephone line is tied up while a dial up modem is in operation.
      • Cable internet access
        • Local cable television operators give a user access to the internet through their own cable network using a cable network model.
      • DSL – Digital Subscriber Line
        • The fastest download speed can be obtained by using DSL broad band connection (about 11,000 kbps)
        • This is often offered through wireless interface which requires an access point and a router.
        • Broadband has the advantage of always being on because it does not tie up the telephone line.
  6. What is intranet?
    • An intranet is the name given to a private network that provides similar services to the internet like email, messaging, web page, etc.
    • Intranet is a computer network based on internet technology that is designed to meet the internal need for sharing information within a single organisation or company.
    • However, these services are only for the users of intranet, they are private not public.
    • Businesses and other organisations often have intranet, for use by their employees.
  7. Write advantages of intranet.
    • It is safer since there is less chance of external hacking or viruses.
    • It is possible to prevent employees accessing unwanted websites.
    • Companies can ensure that information available is specific to their needs.
    • It is easier to send sensitive messages that will remain within the company.
    • Typical uses of intranet
      • Internal emails and instant messaging between the workers.
      • Company’s workers or employees can view internal web pages only.
      • E.g., Company’s calender, Company’s strategies, etc
      • Sharing of internal documents
    • Difference between internet and intranet
    • Internet Intranet
      The term internet comes from the phrase ‘International Network’. The term intranet comes from the phrase ‘Internal restricted access network’.
      Covers topics of global interest Used to give local information relevant to the company.
      It is difficult to block certain web sites from internet. Possible to block certain internet web sites using intranet.
      Can be accessed from anywhere provided user has an ISP account. An intranet requires password entry and can only be accessed from agreed points.
      Will not give full protection against hackers and viruses. An intranet is behind the firewall which gives protection against hackers and viruses.
      Information cannot be stored on local server. Information used in intranet is stored on local servers which makes it more secure from outside agencies.
  8. Explain 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.  Some are
      • User ID
      • Password
      • Encryption
      • Authentication techniques
      • User ID
        • When logging on to any network system, a user will be asked to type user id.  This assigns the user privileges, once the log-on procedure is successful.  E.g, On a network, top level privileges are for an administrator, who is able to set passwords, delete files, etc., whilst the user privileges may only allow access to their own work area.
      • Password
        • After keying in the user id, the user will be requested to type their password.  This should be combination of letters and numbers which would be difficult for somebody else to guess.  For example, weak password
          • 123456
          • Apple
          • 6.12.00
        • Strong passwords are     Rag73Su
      • Encryption
        • It is the process which converts information into a form that is meaningless to anyone except holders of the key.
        • For example, sent email message by using encryption which is meaningless to others and provide description key.
        • Encryption is used by countries to protect secrets.  Military use encryption to protect important messages sent to the armies.
        • These messages are secret messages and confidentiality to protect it or guard it from enemies.
  9. How to setup a small network?
    • If you want to set up a small network, you will need the following hardware and software
    • Hardware
      • One or more switches or hub, tooling devices together.
      • Network cables to connect devices to the switch.
      • A separate wireless access point to allow wireless devices to connect to the network.
        • E.g. Laptops, smartphones, etc
    • 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.
    • Servers to manage network functions such as network security, shared resources like network file storage, etc.
    • You would also need to organise some other things like:
      • Set up an account with an ISP
      • Get an internet connection installed from the ISP, to install your line in your location.
      • Configure various bits of hardware and software so that everything works with the network.
    • Software
      • Web browser to access internet
      • Firewall – if it is software
      • Anti virus to protect your network
  10. What are the methods of Communication?
    • The different methods of communication are:
    • Fax
    • E-Mail
    • Video Conferencing / Teleconferencing
    • Fax
      • Is the long distance photcopier
      • You put the documents in the fax machine and enter the telephone number of the fax machine to which it is to be sent.
      • The page is scanned and converted to a bit map (.bmp) image and sent past the telephone line and is printed out on the recipient’s fax machine.
      • Documents as well as diagram, drawings can be sent by fax.
      • Fax is rapidly being replaced by e-mail as much of the information such as letters, contracts, building plans is already in digital form so it can be attached to email.
      • Software can also be used to convert files and send them directly to a fax machine.
      • Advantages
        • Does not spread virus
        • Cannot be hacked into
        • Fax and documents are legally acceptable
      • Disadvantages
        • Usually printed out in an area shared by other employees so they can be seen by others.
        • Paper jam causes wastage of time.
        • The receiver’s fax machine may not be turned on.
        • The receiver’s fax machine may be out of paper.
        • Information received is not normally a computer file and cannot be edited by the receiver.
    • E-Mail
      • It is electronic message sent from one communication device to other.
      • A web browser software has email facilities.
    • Video Conferencing
      • Video conferencing allows two or more people situated at different places to talk to each other and see each other at the same time.
      • They are also able to exchange electronic files with each other and also pass electronic documents around rather than paper based documents.
      • If meetings need to be conducted between people in different countries, a WAN is used such as the internet.
      • Desktop video conferencing, in addition to PC, includes video compression card, sound card, microphone, web camera and special software.
      • 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.
        • More environment friendly as there are people in smaller numbers travelling to meetings, this cuts down carbon dioxide emission.
        • Few journey means few traffic jams and hence less pollution.
      • Disadvantages
        • Needs good, powerful connectivity of internet, otherwise output would not be as desired.
        • Needs good quality camera or else output would not be of desired quality.
        • Also needs good microphone for high quality sound.
        • All the above mentioned points will need extreme expenditure.

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