CM VIII - Inside internet

Illustration of a network in a school with three labs interconnected and an internet connectivity.

Tejas: In our school till now we had only one computer lab. This year we will have 2 more such labs. And all of them will be interconnected and we can also access internet from any of the computers.Jyoti: The computers in our school office and library, will be also on this network. We can issue books from our library using the lab computer. We can share printers. If one printer has a problem we can print on the printer in another lab.

Recall: 1) Computer Network, 2) Advantages of a computer network.A computer network is two or more computers, or other electronic devices, connected together so that they can exchange data.

Recall uses of networks: A computer network allows computers to share files, and applications, Users to communicate with each other, Share devices, ......

LAN, WLAN and WANTejas: We would like to understand the connections and hardware used to connect the computers in the

lab, office and library.Moz: How are the computers and devices connected in your lab?

Jyoti: Using network cables. One side of the cable is connected to a network port (recall Motherboard) on the computer and the other side to a rectangular box with several ports. Recall Motherboard: Any computer that needs to be connected to the network has a NIC (network interface card) which is usually built into the motherboard.Moz: The rectangular box is called a switch. A switch is used to interconnect computers in a small area and create a network called LAN (local area network).Tejas: Suppose, I want to copy a file from Jyoti's computer. When I perform the actions does the switch pass on the file to my computer? Moz: Right. The switch has built in software which knows exactly to which computer the data has to be directed to. Jyoti: I have seen laptops connecting to the network without a cable.Moz: Right. These are called wireless connections. Radio signals are used to connect to the network. A wireless antenna to send and recieve data is built into the laptops. But you also need a

switch which can receive and send data. We will see this soon.

Concept LAN:

A Local Area Network interconnects computers in a limited area such as a home, school, computer laboratory, or office building.

In a LAN cables or low-power radio (wireless) are used for the connections.

Tejas: In some places like airports and some offices, cables are not required at all. Anyone who walks in with a laptop or a tablet can access internet but in a limited area.Moz: Right such a LAN is called WLAN (Wireless local area network). The switch in such a network has antennae and receives and sends data through radio signals.

Concept WLAN: A LAN that uses radio signals (called WiFi) to connect computers is called WLAN

(wireless local area network). A wireless switch with one or two antennas sticking out the back of the switch, is used for

sending and receiving data to the computers. Devices which have a wireless technology capable of sending and receiving data can

become part of the WLAN. The range of wireless connection is around 50 meters.

Tejas: How do computers from one country to another connect? Moz: Computers and LANs between long distances are usually connected with optical fibre (glass) cables, satellite radio links, microwave radio links, etc. Such a network is called WAN (wide area network). Internet is an example of WAN.Jyoti: Is there a switch between the LANs or computers between long distances?Moz: Yes. The switch is called a router. It is a special switch and much more powerful with software connects long distance LANs, internet and computers.

Info: Router A router is a network device that connects together two or more networks. A common use of a router is to join a home or business network (LAN) to the Internet

(WAN). The router will typically have the Internet cable plugged into it, as well as a cable, or cables

to computers or switch on the LAN.

Concept WAN: A Network which is geographically spread over large areas and links between computers is

called a WAN (wide area network). The long distance connections are done using technologies like optical fibre (glass) cables,

satellite radio links, microwave radio links, etc.

Moz: Now, let us see two types of computers which communicate with each other on a network. Where is the information that you access on internet stored? Tejas: On a computer?Moz: This computer is called a server. It is a special, powerful computer. Next, where do you type the web address (URL)?

Jyoti: We use a web browser on our computer, to enter the address. Moz: The computer you are using is called a client computer. When you type in a web address in the web browser, you are providing the address of a Web server. The web browser (client), asks the web server for the web page that you want, and the server serves back the page that you requested. This was an example of accessing web pages. Give a few more examples, of what can be stored or accessed from a server.

Tejas: We can also save and retrieve files which contain for example, photographs, documents.Moz: Right. Servers give file sharing services. Jyoti: Our mail is also saved on some server on the internet. Moz: Right. Several other services provided by a server on a network are, information on who can access the internet, and shared devices access permissions. For eample can everyone print on the printer in your school?Tejas: No. Only some students can print and the permissions are given by our teacher.Jyoti: Servers have to work without failure since they provide so many important services. Moz: Correct. They are built to be very reliable and hence they are more expensive than client computers.

Concept: Client and ServerComputers connected together to create a network fall into two categories: servers and clients (workstations).

ClientComputers or workstations, that people use to get their work done like accessing internet, communicating with others, sharing their work, are called Client computers.

ServerServers are special, powerful computers that provide ‘services’ to the client computers on the network. Servers are built to be very reliable. This means that they are much more expensive that normal computers.

These services might include: Controlling who can or can’t have access to the network. Sharing Internet connections. Providing a central, common file storage area. Mail. Sharing hardware such as printers.

Tejas: What is done if the power goes off where the server is located?

Moz: The servers are protected from power disruptions with a UPS (uninterrupted power supply). UPS is an electrical apparatus that provides emergency power to the server . UPS provides power by means of one or more attached batteries and associated electronic circuitry.

Info: UPSUninterrupted power supply (UPS), an electrical equipment is used to protect the servers from power disruptions. UPS provides power by means of one or more attached batteries and associated electronic circuitry.

Moz: What are the different methods of connecting to the internet? You must have used atleast one method.

Jyoti: At home we have to connect a dongle (with USB connector) to the computer to connect to the internet.

Moz: From where do you get this dongle?

Jyoti: We have to buy from the internet service provider. Recall: ISP

Recall ISP: An Internet service provider (ISP) is an organization that provides access to the Internet.

Moz: Right. The dongle is a mobile broadband USB device that can be plugged into a computer for internet access.

Tejas: On a mobile phone, we can also access the internet by enable some settings.

Moz: Right. You can also access internet through some mobile phones with 3G technology. This service is available at any area where the mobile phone coverage is available.

Jyoti: I have seen some connections that use telephone lines. A device called modem is connected to the computer in such connections.

Moz: Right. This is called a

Tejas: When many computers have to be connected to internet, like in our lab or a big building what is the method of getting internet access?

Moz:

Info: Internet access – Single user and multiusers

Single user internet connection

DSL (digital subscriber line) Modem - is a device used to connect a computer or router to the internet through a telephone circuit that has digital subscriber line service configured.

Broadband Modem uses DSL or a cable Internet service to go online. Here, the DSL line connects to your phone jack and the USB line or Ethernet to your computer.

Mobile broadband service requires the use of a wireless internet card such as a USB dongle to connect to the internet. The USB dongle is a plug and play device connected to a USB port of laptops or computers, to provide broadband internet access.This dongle can be used anywhere, where there is the ISP providers coverage, just by plugging into the USB port on a netbook, PC or laptop.

Portable Internet Devices like smartphones use WiFi and WiMAX technology to connect to the Internet.

Multi user internet connections

Fiber-to-the-building Broadband (FTTH) uses fiber optic cables to connect to the Internet. Such optics-based systems can deliver digital information very efficiently.

WiFi can provide Internet access throughout cities. Routers, like the one above, are mounted on light poles and a wireless mesh network is created.

Wireless mesh networks: In these, the network connection is spread out among dozens or even hundreds of wireless mesh nodes that "talk" to each other to share the network connection across a large area.

Satellite dish: Internet connection through a satellite dish to upload and download data communications is recommended for rural areas, or areas with no other connection option as it isn't the fastest.

Jyoti: What is a firewall? We have heard that firewalls protect the computers.

Moz: Yes. A firewall secures a network from unauthorized access and communication. A firewall is a device, or a piece of software that is placed between your computer and the rest of the network. Normal data like emails and webpages can be allowed through the firewall. Data for example like advertisements, spams mails, abusive mails, and even viruses, can be blocked through the firewall software that is provided

through the OS on the computer or through the device (router).

Network Security: Firewall

Concept: A firewall blocks unauthorised connections being made to a computer or LAN. Normal data is allowed through the firewall (e.g. e-mails or web pages) but all other data is blocked. To protect whole LAN from hackers out on the Internet, a firewall is placed between the LAN and the Internet connection.

The firewall is a device like a router or software built into the OS of a computer. Several setting can be made in the firewall software to protect the computers from unauthorized access and communication.

Hardware Firewall – Router Software Firewall –-Windows

Jyoti: On internet when we register to a website, we have to give some personal information, like email address, phone number and we have to also enter password. How is this secret?

Moz: Good point. Let us take an example. I want to pass on a message “Leaving for Delhi today”, to you. Now let us encrypt this using a code also called cipher, so that others cannot understand.

Jyoti: What is the code.

Moz: You can build your own code. For example, we can decide that every letter in A-Z is represented by the fourth letter from its position.

Tejas: That means instead of 'A' we write 'D'. Instead of 'L' we write 'O'. This is fun. Let us encrypt this line. Let us first write this code (cipher)!Plain: ABCDEFGHIJKLMNOPQRSTUVWXYZCipher: DEFGHIJKLMNOPQRSTUVWXYZABC

Plain text: Leaving for Delhi today

Ciphertext: OHDYLPJ IRU GHOL WRGDB

Moz: Good. Note that the encrypted text is called ciphertext. By the way, this is called ceaser cipher as Julius Ceaser was the first one to use this cipher to pass on messages.

Tejas: Sometimes we too use code language among a group of friends, so that others do not understand what we are saying.

Moz: Right. Several algorithms are used for the encryption and decryption of information and you can build your own cipher. Now, let us look at examples of information which needs to be kept secret.

Jyoti: Credit-card information, Identification information like passport numbers.

Tejas: Personal details, bank account information.

Moz: Right. Did you observe https in the URL, for some of the sites which ask you for this information?

Jyoti: Yes. When we want to book train ticket online the URL used is: https://www.irctc.co.in/

What does https mean?

Moz: On the train ticketing website the information that you provide is encrypted. Since for ticketing, sensitive information like your email id, your date of birth need to be provided the website is configured with security and is indicated by https.

Concept: Internet Security

Encryption: Encryption is the conversion of data (plain text) into a form, that cannot be easily understood by unauthorized people. Decryption is the process of converting encrypted data (ciphertext) back into its original form, so it can be understood. The code or the algorithm used in the encryption and decryption of data is called cipher.

(HTTPS) provides encrypted communication and secure identification of a network web server. HTTPS connections are often used for payment transactions on the internet, and where sensitive information is needed on some information systems.

Moz: Now that you are familiar with all the aspects of network, security setup and the hardware related to networks go ahead and design a network for the school with the three labs, library and office.

CMVIII – Inside network/Internet – Worksheets and activity

Work sheets.

1. Match the following

LAN Internet browser

WAN Wireless LAN

WLAN Local Area Network

Server Wide Area Network

Client a powerful computer that provides a service, such as centralised file storage

2. Fill in the blanks

i. Following hardware is used to setup networks: network cables, ______, ______, ________.

ii. In a network resources such as _____ and ______ can be shared. iii. A wireless lan (WLAN) uses _________ to connect computers.iv. Network setup in a small office is called _______.v. The internet is an example of ___________ .vi. A powerful computer that provides a service, such as centralised file storage is called _____.vii. A computer that connects to internet to fetch mails is called a _________.viii. Websites that transfer information use ______.ix. A ________ is used to protect the computer from unauthorised use.

3. Label each part of the network from 1 – 10

Let us give here a network WAN with LANs and also WLAN. The components switch, router, server, client, satellite, radio waves, network cable, need to have a place for labelling them. Also put a dotted line around LAN, WLAN and an arrow pointing to the same with a place for labelling.

4. Complete the following LAN, WLAN and WAN by drawing the missing hardware, labelling the hardware Label client and server Making appropriate connections.

Sandeep: For the following please discuss with me a) LAN - Provide a box with 4 computers (one computer bigger than the other 3 and labelled server), and a printer. b) WLAN – same as above. c) WAN – two of the above + satellite

5. A cipher with an example is given below:

Cipher :

1 2 3 4 5

1 A B C D E 2 F G H I/J K3 L M N O P4 Q R S T U5 V W X Y Z

Example:

Plaintext: HELLO

Ciphertext: 32 52 13 13 43

a. Encrypt your name using the above code.

c. Build a cipher of your own. Encrypt your name using the cipher. Show this to your friends. Write a message using your cipher. Ask your friends to decrypt the message.

-------------------Activity:

Design a network for your school which shows: The network in each of the three labs, office, library, Interconnect the above networks. Provide a connection to the internet through one of the ISPs. Include a firewall in your design. Label the LANs, WAN, WLAN, in your network by putting a dotted line around. Label the type of computers (client or server) and the other hardware used in your design. Indicate labs, office and library in your design by labelling.