COMPUTER O LEVEL(FORM TWO) NOTES -TOPIC 3: COMPUTER NETWORKS AND COMMUNICATIONS

TOPIC 3: COMPUTER NETWORKS AND COMMUNICATIONS

A network:

A network is a group of two or more devices or people connected to each other so that they can exchange information, such as e-mail messages or documents, or share resources such as disk storage or printers.

Computer network:

Refers to collections of computing devices that are connected in various ways to communicate and share resources. Usually, the connections between computers in a network are made using physical wires or cables. However, some connections are wireless, using radio waves or infrared signals. Networks are systems formed by links. The computers may be linked or connected to each other in the same building or different buildings. In most cases, this connection is made via electrical cables that carry information in the form of electrical signals. The cables transmitting the information are commonly known as transmission media or networking media. Networking media is the means by which signals or data are sent from one computer to another. The transmission media include unshielded twisted pair (UTP), coaxial cable, and fiber optic cable. Wireless transmission media include radio waves, infrared, and Bluetooth. When a computer is turned on and can be seen by all other computers, it is said to be online. If a computer is not turned on and is not visible to other networked computers, it is said to be offline.

Advantages of computer networks and communications

1. Networks are all about sharing three things: information, resources, and applications.

• Sharing information: Allows users to share information in several different ways. The most common way is to share individual files. For example, two or more people can work together on a word processing document.
• Sharing resources: Certain computer resources such as printers or hard drives can be set up so that network users can share them. Sharing these resources can result in significant cost savings. For example, it is cheaper to buy a single high-speed printer with advanced features that can be shared by an entire work group than to buy separate printers for each user in the group.
• Sharing applications: Several users can work together on a single business application. For example, an accounting department may have accounting software that can be used from several computers at the same time (database services).

2. High reliability: All data can be copied on two or three machines, so if one is unavailable, the other copies can be used.
3. Speed: Networks provide a very rapid method for sharing and transferring files. Without a network, files are shared by copying them to floppy disks, then carrying or sending the disk from one computer to another.
4. Reduced cost: Networkable versions of many popular software programs are available at considerable savings compared to buying individual licensed copies. Besides monetary savings, sharing a program on a network allows for easier upgrading of the program.
5. Sending messages such as electronic mail (E-mail): The presence of a network provides the hardware necessary to install an E-mail system. E-mail aids in personal and professional communication for all school personnel and facilitates the dissemination of general information to the entire school staff. Electronic mail on a LAN can enable students to communicate with teachers and peers at their own school. If the LAN is connected to the internet, students can communicate with others worldwide.
6. Flexible access: A school network, for example, allows students to access their files from computers throughout the school. Students can begin an assignment in their classroom, save part of it on a public access area of the network, and then go to the media center after school to finish their work. Students can also work cooperatively through the network.
7. Communication: A computer network can provide a powerful communication medium among widely separated employees or individuals, increasing communication capabilities.

Disadvantages of installing a network

1. Expensive to install: Although a network will generally save money and time, the initial cost of installation can be prohibitive. Cables, network cards, and software are expensive, and installation may require the services of a technician.
2. Requires administrative time: Proper maintenance of a network requires considerable time and expertise. Many schools have installed a network only to find that they did not budget for the necessary administrative support.
3. File server may fail: Although a file server is no more susceptible to failure than any other computer, when the file server “goes down,” the entire network may come to a halt. When this happens, the entire school or company may lose access to necessary programs and files.
4. Cables may break: Some configurations are designed to minimize the inconvenience of a broken cable, but with other configurations, one broken cable can stop the entire network.

What is a Network Interface Card?

• A network interface card (NIC) is a device that plugs into a motherboard and provides ports for the network media connections.
• It is the component that interfaces with the local-area network (LAN).

Examples of Network Devices

• Switch
• Bridge
• Server
• Fiber optic cable
• Hub
• Router
• Twisted cable
• Coaxial cable
• Repeater

Importance of Network

Network enables:

1. Sharing of devices (e.g., network printer)
2. Sharing of information
3. Easy communication
4. Online shopping
5. SIM banking
6. Easy transfer of data through network devices

Types of Network

1. LAN (Local Area Network)
2. WAN (Wide Area Network)
3. MAN (Metropolitan Area Network)
4. Internet
5. Intranet

Homework

Mention and explain network devices according to their respective types of network:

1. Switch: A computer networking device that links networks; the respective type of network used is LAN.
2. Bridge: A network device that connects multiple network devices (LAN).
3. Fiber optic cable: A cable containing one or more optic fibers; used in internet networks.
4. Server: A large computer that stores websites on the internet.
5. Hub: A device for connecting multiple Ethernet devices together and making them act as a single network segment (LAN).
6. Router: A device that is connected to two or more data networks for different networks (WAN).
7. Twisted cable: A type of wiring in which two conductors of a single circuit are twisted together (used in LAN, MAN, WAN, internet, intranet).
8. Coaxial cable: A type of cable that has an inner conductor surrounded by a tubular insulating layer; used in LAN, WAN, MAN, Internet, Intranet.
9. Repeater: A network device to regenerate or replicate a signal; used in LAN, WAN, MAN, Internet, Intranet.

Explain 5 types of network

1. LAN – Local Area Network: Connects network devices over a relatively short distance. A network office building, school, or home usually contains a few small LANs (perhaps one per room) and occasionally a LAN will span a group of nearby buildings. TCP/IP networking LAN is often but not always implemented as a single IP subnet.
2. MAN – Metropolitan Area Network: A large computer network which extends to a city or to a large university campus. The purpose of MAN is to provide the link to the internet in the long run. A MAN usually incorporates a number of LANs to form a network. This large MAN’s backbone comprises an optical fiber setup.
3. WAN – Wide Area Network: A broad network whose communication is wider than LAN, MAN, and CAN. The application of WAN is not limited to a room, building, or specific vicinity. The basic purpose of WAN is to maintain a number of LAN networks to increase the efficiency of the network. Different LAN networks are connected to establish a network which will enable the user of one location to communicate with users present in other locations. Internet service providers usually help and guide to establish WAN networks. However, many large organizations develop their own private WANs.
4. Intranet: The internal network of an organization which allows access to specific authorized users.
5. Internet: An interconnected network worldwide.

Network Topology

Is how devices are connected in a given network.

Types

• Logical
• Physical

The Advantages of Networking

• Sharing of data
• Sharing of hardware (e.g., printer)
• Easy transferring of data
• Easy communication
• Enable e-learning
• Enables e-commerce
• Exchange of information

Disadvantages of Networking

• Security of data
• Cost of installing nodes is very high
• If server fails, all the nodes will be affected
• Virus attack

Types of Network

• LAN – Local Area Network
• WAN – Wide Area Network
• MAN – Metropolitan Area Network
• Intranet
• Internet

LAN (Local Area Network)

A LAN connects network devices over a relatively short distance. A network office building, school, or home usually contains a few small LANs (perhaps one per room) and occasionally a LAN will span a group of nearby buildings. TCP/IP networking LAN is often but not always implemented as a single IP subnet.

MAN (Metropolitan Area Network)

A large computer network which extends to a city or to a large university campus is termed a metropolitan area network or MAN. The purpose of MAN is to provide the link to the internet in the long run. A MAN usually incorporates a number of LANs to form a network. This large MAN’s backbone comprises an optical fiber setup.

What is WAN?

Wide Area Network is a broad network whose communication is wider than LAN, MAN, and CAN. The application of WAN is not limited to a room, building, or specific vicinity. The basic purpose of WAN is to maintain a number of LAN networks to increase the efficiency of the network. Different LAN networks are connected to establish a network which will enable the user of one location to communicate with users present in other locations. Internet service providers usually help and guide to establish WAN networks. However, many large organizations develop their own private WANs.

INTRANET

Is the internal network of an organization which allows access to specific authorized users.

Advantages

1. Intranet is free because it does not involve phone links.
2. Easier updating.

Disadvantage

1. Information cannot be shared outside the local network.

EXTRANET

Is a private network that extends to users outside the company, usually via the internet.

Advantages

1. Share of information between companies.
2. Collaboration with other companies.
3. Communication between companies.
4. Jointly develop and use training programs with other companies.

Disadvantages

1. Expensive to implement.
2. Requires network security.

INTERNET

Is an interconnected network worldwide.

Advantages

1. Sharing of information.
2. Data can be easily updated.

Disadvantages

1. Security of data.
2. Virus attack.

The Network Topology

The network topology is defined as the layout of the network. It is the way in which nodes are connected in a network.

Nodes: are the network devices e.g., computer, switch, hub, server, or router.

Nodes can be connected physically or logically.

Physical Topology

Refers to the actual physical layout of the devices in a network or the way in which nodes are connected physically.

Logical Topology

Refers to the paths that signals take from one point in the network to another.

Types of Physical Topology

• Bus Topology
• Star Topology
• Ring Topology
• Hybrid Topology

Bus Topology

Commonly referred to as linear bus, all the devices on a bus topology are connected by one single cable which runs from one computer to the next.

This topology is rarely used and would only be suitable for a home office or small business with few hosts.

Advantages

• The thin net cabling it uses is quite inexpensive.
• It uses less cable compared to other physical topologies like star or extended star.
• It works well for small networks.
• It doesn’t need a central device such as hub, switch, or router.

Disadvantages

• It results in slower access to the network and less bandwidth due to the sharing of the same cable by all devices.
• It is challenging to identify and isolate problems.
• A break at any point in the bus can disable the entire bus network.
• It needs termination.

Star Topology

All nodes are connected to a central device.

Advantages

• It is upgradable, flexible, and reliable.
• It is easy to design and install.
• This topology makes diagnosing problems relatively easy since the problem is localized to one computer or device.
• This topology allows for more throughput than any other topology.

Disadvantages

• It requires a lot of cable to connect computers since a cable is required between each device and the central location.
• It is more expensive to build because of the additional cost of cables and devices like hubs and switches needed to run between devices.

Ring Topology

Nodes are connected in a circle whereby all devices have equal importance.

• A frame called a token travels around the ring and stops at each node.
• If a node wants to transmit data, it adds that data and the addressing information to the frame.
• The frame continues around the ring until it finds the destination node which takes the data out of the frame.

Advantages of Ring Topology

• Growth of system has minimal impact on performance.
• All stations have equal access.
• No one computer monopolizes the network.

Disadvantages of Ring Topology

• Most expensive topology.
• Failure of one computer may impact others.
• Complex in configuration.
• Difficult to troubleshoot a ring network.
• Adding or removing a computer disrupts the network.

Types of Ring Topology

1. Single ring topology: The entire device on the network shares a single cable, and the data travels in one direction only.
2. Dual ring topology:
   • Two rings allow data to be sent in both directions.
   • This creates redundancy (fault tolerance), meaning that in the event of a failure of one ring, data will still be transmitted on the other ring.

Advantages of Ring Topology

• Very fast because data flows in one direction.
• Less expensive than star topology.

Disadvantages

• If one node fails, it will affect the whole network.

Mesh Topology

• The mesh topology connects all devices (nodes) to each other for redundancy and fault tolerance.
• It is used in WANs to interconnect LANs and critical networks.
• The mesh topology is expensive and difficult to implement.

Advantages

• Redundancy
• Fault tolerance

Disadvantages

• More cable needed
• Very expensive
• Needs more skills
• Difficult to implement

Hybrid Topology

Combines more than one type of topology.

Advantages

• Redundancy
• Fault tolerance
• Efficient
• High speed

Disadvantages

• More cables are needed
• More complicated
• Very expensive
• Difficult to implement
• Hard to troubleshoot

TOPIC 4: THE INTERNET

What is the Internet?

The Internet is a worldwide connection of computers which enables sharing of resources like files and folders, pictures and music, teaching materials like notes/tutorials, and computers.

Communication between networks is called internetworking. Therefore, internet comes from the word internetworking, meaning a connection of data communication. The communication in which the end instruments are computers.

The internet is a worldwide public network that interconnects thousands of smaller networks to form one large “web” of communication. Many private networks, some with thousands of users of their own, connect to the internet by using the services of internet service providers (ISPs).

In simple words, the internet is a huge number of computers that are connected to each other throughout the world.

These computers are situated in many different countries and are connected through telephone lines, cables in the ground, and even satellites in space.

Development of the Internet

The internet evolved from a US Department of Defense project called ARPANET (Advanced Research Project Agency Network) in 1969. The main reason was to exchange information between researchers in this project.

Browsers and the World Wide Web (WWW) were introduced in the early 1990s.

Using the Internet

(i) Why do people use the internet?

• To find general information about a subject: The web is like a huge encyclopedia of information; in some ways, it’s even better. The volume of information you will find on the web is amazing. For every topic that you’ve wondered about, the web offers many different perspectives on a single topic.
• To find information not easily available elsewhere: It puts information into your hands that you might otherwise have to pay for or find out by less convenient means.
• To correspond with faraway friends: Email offers a cheap and easy alternative to traditional methods of correspondence. It’s faster and easier than writing snail mail and cheaper than using the telephone.
• To meet people: People love getting e-mail from strangers and friendships are quick to form from casual correspondence. Many people have even found love on the Net and have gone on to marry their cyber-partner.
• To discuss: To discuss their interests with like-minded people.
• To have fun: There’s plenty to keep you occupied on a rainy day.
• To learn: Online distance education courses can give you an opportunity to gain a qualification over the internet.
• To read the news: People all over the world access news through the internet. For example, a Tanzanian living in London can read Tanzanian newspapers on the internet and be updated every day.
• To find software: The internet contains a wealth of useful downloadable shareware. Some pieces of shareware are limited versions of the full software; others are limited trials (you should pay once the time limit is up). Other shareware is free for educational institutions or non-commercial purposes.
• To buy things: The security of online shopping is still questionable, but as long as you are dealing with a reputable company or website, the risks are minimal.

(ii) Why do people put things on the web?

• To advertise a product.
• To sell a product.
• To make money.
• To share their knowledge with the world.

The application of the internet

Electronic mail (e-mail or email) is a store and forward method of composing, sending, storing, and receiving messages over electronic communication systems.

What makes the internet different?

• This is an electronic communication.
• Its speed and broadcasting ability are fundamentally different from paper-based communication. This is because turnaround time can be so fast—mail is more conversational than traditional paper-based media.

Computers on the internet may use the following internet services:

• Electronic mail (e-mail) to send and receive mail.
• Telnet or remote login to log onto another computer and use it as if you were there.
• File Transfer Protocol (FTP) to rapidly download complex files intact from a remote computer to a local computer or upload from a local computer to a remote computer.
• Web browsing.
• Social networks (Facebook, Twitter, LinkedIn).
• Online shopping.
• Search engines.
• Resource distribution (hosting).
• Video conferencing.
• Games.

Terms used in the internet

WWW (World Wide Web)

Web: Is the collection of websites on the internet.

Website: Is a collection of web pages linked to each other.

Web page: Is a single page on a website.

Homepage: The first page of a particular website.

Web browser: Software that enables users to retrieve and view HTML documents. Examples include Internet Explorer, Safari, Mosaic, Netscape Navigator.

Web Server: Large computer that stores websites on the internet.

Hypertext: The document that contains hyperlinks.

Hyperlink: The shortcut from one webpage to other web pages.

HTML (Hyper Text Markup Language): Computer language used to make web pages.

URL (Uniform Resource Locator): This is the address of a website on the internet.

Online: Connected to the internet.

Offline: Not connected to the internet; e.g., http://www.sirpatrick.com.

Parts of URL

1. Protocol
2. Web
3. Host
4. Domain

Example: http://www.sirpatrick.com

1 2 3 4

HTTP – Hypertext Transfer Protocol

IP – Internet Protocol

POP – Pointing Information Protocol

ISP – Internet Service Provider

Protocol:

Is a set of predetermined rules used to facilitate communication over data networks.

Importance

1. Used to allow devices to communicate successfully.
2. Provide structure and format of the message.
3. To set up and terminate the data transfer session.

Search Engine

Is a website that helps users to find information/material on the internet. Examples include Google, Yahoo!, Go, Mamma, Metacrawler, Lycos, etc.

Types

1. Individual
2. Meta

E-mail Address:

An e-mail address is a string that identifies a user so that a user can receive Internet e-mail.

They are composed of:

• User ID
• The symbol @
• Domain name

The domain:

• It is located after @
• Tells the location and type of address
• Provides information about where the message should be delivered

Root Domain:

Describes the type of location; currently there are six root domains:

1. .com: commercial organization
2. .edu: education/research organization
3. .gov: government organization
4. .mil: military organization
5. .net: gateway host network
6. .org: non-profit or miscellaneous organization

Some domain names will also include the country name, e.g., .uk: England or .tz: Tanzania.

Examples of e-mail addresses are:

(a) [email protected]

• User ID: janetjackson
• Domain name: yahoo.com
• Domain (location): yahoo

(b) [email protected]

• User ID: pavinistanley
• Domain name: udsm.edu.tz
• Domain (location): udsm
• Root domain (domain type): edu
• Country: tz

Advantages of E-mail

1. Convenience: There are no trips to the post office, no need to search for stationery and stamps. A message can be formal or informal. It makes it very easy to publish and discuss.
2. Speed: E-mail is very fast.
3. Inexpensive: Once you are online, the cost of sending a message is small.
4. Printable: The hard copy is easy to obtain; you may save on natural resources for your own records.
5. Reliable: Although messages are occasionally lost, these are rare. Many mail systems will notify the sender if an email message was undelivered.
6. Generality: It is not limited to texts; it allows the transfer of graphics, programs, and even sounds.

Electronic Learning (E-Learning)

E-Learning is the effective teaching and learning by using electronic media.

E-Learning can occur in or out of the classroom. It is suited to distance learning and flexible learning but can also be used in conjunction with face-to-face teaching.

Advantages of E-learning

• Reduces traveling costs and time to and from school.
• Learners can study whenever they access a computer and internet.
• Self-paced learning models allow learners to work at their own pace.
• Classwork can be scheduled around personal and professional work, resulting in flexible learning.

Disadvantages of E-learning

• Students may feel isolated or miss social interaction.
• Unmotivated learners or those with poor study habits may fall behind.
• Instruction may not always be available on demand.
• Slow or unreliable internet may be frustrating.
• Some courses, such as traditional hands-on courses, can be difficult to simulate.

E-Commerce

The buying and selling of products and services by businessmen and consumers through an electronic medium without using any paper documents.

E-Commerce is widely considered the buying and selling of products over the internet, but any transaction that is completed solely through electronic measures can be considered e-commerce.

Advantages of E-commerce

• Faster buying and selling procedures as well as easy to find products.
• More reach to customers; there is no geographical limitation.
• Lower operational costs and better equality of services.
• No need for physical company setups.
• Easy to start and manage a business.
• Customers can easily select products from different providers without moving around physically.

Disadvantages

• Perishable goods: Goods bought and sold via the internet tend to be durable and non-perishable.
• Lack of personal service: Although some human interaction can be facilitated via the web, e-commerce cannot provide the richness of interaction provided by personal service.
• Security: Security of data moved across some mobile and wireless network participants.

Types

• Business-to-Consumer (B2C)
• Consumer-to-Consumer (C2C)
• Business-to-Business (B2B)

Negative effects of the internet

Cultural Issues

Information presented on the internet should carefully consider the audience and not offend because of cultural beliefs. Pornographic materials are offensive to most African cultures, and other cultures dislike particular ways of dressing which may portray an image not intended by the dissemination of information.

Religious

In some religions, rituals and symbols are serious matters to tamper with. The information that involves those symbols or rituals must be carefully treated to avoid disharmony in the concerned audience. Other religions have important considerations in disseminating information such as dressing code and place of worship. But the internet does not take care of the effect on the audience.

Political

Political issues can affect information from the internet. Political affiliation can affect proper dissemination of information as the information may be biased to favor certain political views.

Social

When information is corrupted by predators on the internet, they mislead and bring confusion to the audience. For example, in a children’s social network, appropriate information for the particular age is useful. Also, other societies have certain agreed codes of conduct which have particular information expectations, so internet information is advised to be highly important to ensure expected ethical codes of conduct by the audience.