Class 12 Computer Science Computer Network Notes

Class 12 Computer Science Computer Network Notes in Question and Answer form.

Q.1. What is a computer network ?

Two or more autonomous computing devices connected to one another to exchange information or share resources, form a computer network.

Q.2. What are the advantages and disadvantages of networks ?

Advantages of network-
Share resources : such as printers and scanners. This is cheaper than buying equipment for each computer.
Share storage : being able to access files from any machines on the network can share data.
Can share software : Software can be installed centrally rather than on a machine. Metering software can then be usednto limit the number of copies being run at any one time.
Improve communications: Messages can be sent

Disadvantages of network-
The system are more sophisticated and complex to run. This can add to costs and you may need specialist staff to run the network.
If networks are badly managed, services can become unusable and productivity falls.
If software and files are held centrally , it may be impossible to carry out any work if the center server fails. People become reliant on the communication, if these fail, it can cause havoc.
File security is more important especially if connected to WANs e.g.. protection from viruses.

Q.3.Write about the major component of computer networks.

(a) Host or Nodes. The term host or node refers to computers that are attached to a network and are seeking to share the resources of the network.
(b) Server. A server facilitates networking tasks like sharing of data, resource-sharing, communication among hosts etc.
(c)Clients. A client is a host computer that request from some service from a server.
(d)Network hardware. Establishing corrections, controlling network traffic etc. Example- NIC,HUB,SWITCH,ROUTER, many others.
(e)Communication channel. Can be wired or wireless.
(f) Software. The software layers of a network makes networking possible. These comprise of network protocols,network operating system etc.
(g)Network services- Application that provide different functionalities over a network, such as DNS(Domain name System),file sharing, VOIP and many more.

Class 12 Computer Science Computer Network Notes

Q.4.Types of networks based on Geographical Spread.

LAN(local area network) are confined to a localised area Network.
WAN(wide area network) is a group of computers that are separated by large distances and tied together.

Q.5. Types of network by component roles.

Peer – to – Peer networks: Each computer on a peer-to -peer network is equal. Each componenet can play the role of a client or a server.
Client- server network: Bigger networks prefer to have centralized control. They do this clearly designating servers and clients. Such network are called client-server networks oe even master-slave networks.

Q.6. Differences between client-server and P2P networks.


securityThe server controls security of the network.No central control over security
ManagementThe server manages the network. Need a dedicated team of people to manage the server.No central control over the network. Anyone can set up.
Dependencyclient are dependent on the server.clients are not dependent on a central server.
PerformanceThe server can be upgraded to be made more powerful to cope with high demand.If machines on the network are slow they will low down other machines.

Q.7. Type of network based on communication channel.

(i) Wired Computer Networks
a. Twisted pair cable- is a pair of insulated wires that are twisted together to improve electromagnetic capability and to reduce noise from outside sources.
b. Co-axial Cable- consists of a solid wire core surrounded by one or more foil or wire shields, each separated by some kind of plastic insulator.
c. Fibre Optic Cable- A fibre optic cable consists of a bundle of glass threads each of which is capable of transmitting messages modulated onto light waves.
(ii)Wireless computer network
a. Microwave- used in mobile phone
b. Radio- used in radio program.
(iii) Satellite- is a case of microwave relay system.

Q.8.Full form of NIC?use?

Answer: Network- interface -card is a device that is attached to each of the workstations and the server. NIC is also called Terminal Access Point (TAP).

Q.9. MAC adress ?

Answer: A unique physical address to each NIC , this physical address is known as Media Access control address.

Q.10.What is hub ? Types of hub?

A hub is a hardware device used to connect several computer together. A hub contains multiple independent but connected modules of network and inter-networked equipment. A similar term is concentrator. A concentrator is a device that provides a central connection point for cables from workstation, servers and peripherals.
Two type of hubs
Active hubs – electrically amplify the signal as it moves from one connected device to another.A ctive hubs are used like repeaters to extend the length of the network.
Passive hubs- allow the signal to pass from one computer to another without any change.

Class 12 Computer Science Computer Network Notes

Q.11.What is a Switch?

Answer: A switch is a device that is used to segment networks into different subnetworks called subnets or LAN segments.

Q.12. Working of a Bridge?

Answer: Bridges are smart enough to know which computers are on which side of the bridge, so they only allow those messages that need to get to the other side to cross the bridge.

Q.13. What is a Router?

Answer: Based on a network road map called routing table , routers can help ensure that packets are travelling the most efficient path to their destinations.

Q.14. What is a Gateway?

Answer: The gateway is the computer that routes the traffic from a workstation to the outside network that is serving the web pages.

Q.15. What is an Access point ?

Answer: An access point (AP), also called wireless access point(WAP), is a hardware device that establishes connections of computing devices on wireless LAN with a fixed wire network.

Q.16. What is cloud computing?

Answer: Cloud computing is Internet-based computing, whereby shared resources, software and information are provided to computers and other devices on demand.

Q.17. Type of clouds ? Explain them.

1. Private clouds-These are the clouds for exclusive use by a single organization and typically controlled, managed and hosted in private data centers.
2. Public clouds- These are the clouds for use by multiple organization (tenants) on a shared basis and hosted and managed by a third party service provider. clouds- These are the clouds for use by a group of related organizations who wish to make use of a common cloud computing environment
4.Hybrid clouds- When a single organization adopts private and public clouds for a single application in order to take advantage of the benefits of both.

Q.18. What is Internet of Things?

Answer- IOT is a technology that connects the things to the internet over wired or wireless connections

Class 12 Computer Science Computer Network Notes.

Q.19. What is RFID ?

Answer: RFID (Radio Frequencies Identification) is designed to use radio waves to read and capture information stored on a tag, called an RFID tag attached to an object.

20.Which devices can form IOT?

a) Home appliances
b) Wearables
c) Vehicles
d) Factories
e) Agriculture
f) Food

Q.21. What is modulation and demodulation?

Answer: A message signal that carries the data to be transmitted, needs to be imposed on top of the carrier signal. These process is termed as modulation. Demodulation is the reserve process of modulation where data is extracted from the received signal.

Q.22. Working of amplitude and frequency modulation?

Amplitude modulation-That amplitude is the height of the carrier wave, if, we can tweak the height of the carrier so that it shows the impact of data/message signal.
Frequency modulation- The frequency modulation, the frequency of the carrier signal is varied as per the changes in the amplitude of the modulating signal.

Q.23. What is collision in wireless network?

Answer: Transmitting over a shared communication medium requires that at a time, only one sender and one receiver use the communication medium. If multiple nodes on the same network transmit data at the same time, it leads to a condition called collision and data gets lost. In a computer network , collision is a specific condition that occurs when two or more nodes on a network transmit data at the same time.

Q.24.Difference between full Duplex and Half-Duplex COMMUNICATION.

Two way communication where sending and receiving takes place simultaneously, is called full Duplex.
Wireless network cannot listen while transmitting is called Half Duplex.

Q.25. Which method is used for collision detection in wired and wireless ?

CSMA/CA(carrier sense multiple access/ collision avoidance) for wireless , CSMA/CD (carrier sense multiple access/collision detection for wired.

Q.26. How CSMA/CA works ?

1. Node ready to tansmit/talk.
2. Listen for other nodes, if any transmission is taking place.
2.1 BUSY. A transmission is taking place.
2.1.1 Increase back off or wait time
2.1.2 Sleep as per BEB (Binary Exponential Backoff ))
2.2 Free. No transmission is taking place.
2.2.1 Send Message
2.2.2 Verify it proper transmission has taken place using one of the following methods:
(a) ACK (acknowledgement) Method
(b)Request to send / clear to send (RTS/CTS) Method.
Two version of CSMA/CA
1.with ACK (Acknowledgement) method
1.Transmits data to another node, the receiving node must send an acknowledgement signal called ACK, once it has received the data.
2.with RTS/CTS
1. The sender node first sends an RTS signal to its receiver. Reciever confirms its readiness to receives by sending a CTS signal to the sender as well as all other nodes.

Q.27. Explain Single-bit , Multiple-bit and Burst error ?

Single-bit error- If only one bit of the transmitted data got changed from 1 to 0 or from 0 to 1.
Multiple-bit error- If two or more consecutive bits in data changed from 0 to 1 or from 1 to 0.
Burst Error- If two or more consecutive bits in data got changed from 0 to 1 or from 1 to 0.

Q.28. What is Single Dimensional Parity Checking? Advantages and disadvantages?

Numbers of 1’s is counted in the actual data unit
Add an extra bit called the parity bit to actual data so that the number of 1 ‘s along with the extra bit, become or remain even.
1) It is a simple mechanism, which is easy to implements.
2) It is an inexpensive technique for detecting the errors in data transmission.
1)It can detect only single-bit errors which occur rarely.
2) If, in the data transmitted , two bits gets interchanged then even through data gets affected , but the parity bit remain correct . In such cases , this technique cannot detect the errors.

Q.29. What is two- Dimensional Parity checking? Advantages and disadvantages ?

Calculating the parity bits for each data unit row- wise and column-wise.
Advantage of two- Dimensional –
(I) It is more efficient than single dimensional parity technique.
(ii) It can detect multiple bit error also, which sometimes single dimensional parity checking technique cannot.
(I) Cannot detect compensating multiple bit errors.
(ii) This technique cannot detect 4 – or more-bits errors in some cases.

Class 12 Computer Science Computer Network Notes

Q.30. What is check sum and how does it operates ?

The checksum refers to a sum of data bits calculated from digital data that is used to ensure the data integrity at the reciever’s end.
Operates like-
a) At the sender node , before transmission
(i) The data being transmitted is divided into equal sized k number of segments , where each segment contains m number of bits.
(ii) The divided k segments are added using 1’s complement arithmetic and extra bits are added back to the sum.
(iii)The final sum’s complement is calculated . This is the checksum.
(iv) Now all the data segment is sent along with the checksum.
b) At the reciever node, after transmission
(V) Step (II) is repeated at the reciever end , all the data segments are added using 1’s complement arithmetuic to get the new sum.
(vi) This calculated new sum is added with the recieved check sum and then complemented.

(a) If the result is all 0’s, the transmission is successful- Accept the data.
(b) If the result is not all 0’s, the transmission is Erroneous – Reject the data.

Q.31.What is routing and routing table.

Routing is the process of efficiently selecting a path in a network along which the data packets will travel to their destination.
A routing table is a table maintained by routers that maintains routing information based on which router determines best path to reach a network.

Q.32. What is router goal?

Answer: Finding the best route from every destination for data transmission.

Q.33. What is TCP/IP ?

Answer: TCP/IP suite is the current standard for both local and wide area networking. TCP/IP is a collection of protocols that includes TCP, IP ,UDP(USER DATAGRAM PROTOCOL) and many other.
TCP – TCP ensures reliable communication and uses ports to deliver packets. It is a connection- oriented protocol. TCP also fragments and reassembles messgaes, using a sequencing function to ensure that packets are reassembled in the correct order. In TCP, a connection must be built using a handshake process before information is sent or received.
UDP- UDP is a connectionless protocol. It allows information to be sent without using a handshake process.
IP- IP is a connectionless protocol responsible for providing address of each computer and performing routing.

Q.34. Symptoms of Network Congestion?

(i) Excessive packet delay
(ii) Loss of data packets
(iii) Retransmission

Q.35. What is Metering technique that is implemented to control network congestion?

Answer: Metering technique is implemented to control network congestion
(i) It ensures that the sender does not overflow the network and it is done by controlling the flow of data packets. With this measure, the sender maintains a value indicating the limit of data that can be sent into the network without being acknowledged.
(ii)It ensures that the routers along the path work as per their capacity to handle network traffic and do not become overflowed.
(a) Rerouting the data packets
(b) Informing the senders about the congestion to control the transmission rate.
(c)Delaying the transmission / retransmission depending upon the congestion levels.

Q.36. What is URL ?

HTTP(Hypertext Markup Language (HTML) uses Internet addresses in a special format called Uniform Resource locator or URL.
Elements of a URL –
(a) The type of server or protocol.
(b) The name/address of the server on the Internet.
(c) The location of the file on the server.

Q.37. What is internet server and what they provide.

ServerProtocolInformation it provides
ftpFile transfer protocolText and binary files that are organized in a hierarchical structure, much like family tree.
gopherTransfer control protocol/internet procol(TCP/IP)Text and binary files that are organized in a menu structure.
httpHypertext Transfer ProtocolHypertext/hypermedia files

Q.38. What is IP address. What are different version of it.

IP address is a unique numerical label as a string of numbers separated by dots , used to identify a device on the internet.
IPV4- uses a 32-bit address scheme allowing for a total of 2**32 address (just over 4 billion addresses).they have reached limit
IPV6- uses a 128 bit long IP addreses. They are being assigned.
IPV6(DUAL) uses IPV6 and IPv4 address combined.

Q.39. What is DNS? Explain.

Answer: The url of a website is also known as its domain name. The domain name is unique name of a website.
(i) www
(ii) name describing the website purpose.
(iii)TLD (Top Level Domain) such as .com,.net,.org etc.

Q.40.Explain features of cellular or wireless networks depend hevily on wireless connectivity protocols such as 2G,3G,4G etc?

2G GSM (1992) – the second generation: Allows data along with calls in the form of text messages.GSM can handle data speed of upto 250 kbps.
The GSM standard is transmitted at the frequencies between 900 Mhz and 1800 Mhz.
3G(2000)- the third generation – 3G offers speed of 500 Kbps to 2 Mbps. 3G is transmitted at frequency 2100 Mhz.
4G(2013)-the fourth generation- Range of 10-15 Mbps which can go upto 50 Mbps and even higher. The frequency range are 1800 Mhz to 2300 Mhz.

Q.41. What is wi-fi .

Answer: Wi-Fiprotocol governs the rules to connect to the Internet without a direct line from our PC to the ISP.

Q.42 . What are the following commands and their uses?
(a) PING
(b) Traceroute
(f) Speed test

(a)To test the connectivity between two hosts, you can use the PING command. PING determines whether the remote machine can receive the test packet and reply. Ping serves two purposes:
1. To ensure that a network connection can be established.
2. Timing information as to the speed of the connection.
(b)traceroute or tracert is very similar to ping, expect that it identifies which network pathways it takes along each hop, rather than the time it takes for each packet to return.
(c)NSLOOKUP: Displays the name and IP address of your computer default DNS server.
(d) IPCONFIG: Command gives more detailed information such as DNS servers, DHCP enabled or not, MAC Address along with other helpful information.
(e)WHOIS : is used to get information on a specific domain name such as who registered it , when was it registered and when the domain will expire etc.
(f)To check the download and upload speed of your network go to the site click on Go. It will check the current speed and show.


(a)HTTP: The Hyper text Transfer Protocol is an application-level protocol with the lightness and speed necessary for distributed, collaborative, hypermedia information systems. It is a generic , stateless, object-oriented protocol which can be used for many tasks.

(b)FTP: File Transfer Protocol.
(i) It is very useful to transfer files from one network in an organisation to another.
(ii) It is an effective way to get a geographically dispersed group to co-operate on a project.
(iii) It is a potent and popular way to share information over the internet.

(c) POP(post office protocol): The POP3 has become a standard mail protocol.POP3 protocol works on two ports:
1.Port 110-default pop3 non -encrypted port.
2.Port 995-the encrypted port used for secure email communication.

(d)IMAP(internet message access protocol)
The IMAP is another mail protocol used in conjunction with pop3 protocol for accessing emails on a remote web server and downloads them to a local client.
port 143-the default non-encrypted
port 993-encrpted port used for secure communication.

(e) SMTP (Simple Mail Transfer Protocol)
The SMTP is used for sending emails across the internet.
port 25- the default , SMTP non- encrypted port
port 465-encrypted port

(f)VOIP (voice over Internet Protocol)
VoIP is a technology that enables voice communications over the Internet through the compression of voice into data packets that can be efficiently transmitted over data networks and then converted back into voice at the other end. The most common protocol used for communicating on these packet- switched network is internet protocol.

(g)NFC (Near Field communications)
used to provide short- range wireless connectivity between two electronic devices that within the distance of 4-5 centimeters.

Q.44. Basic idea of how HTTP works.

Answer: Protocol HTTP works over the protocol TCP/IP. There are HTTP clients that make requests via HTTP protocol and HTTP servers that respond to HTTP requests. Working-
(i) For web communications, the request message , is sent to an HTTP server in the form of URLs by the HTTP client.
(ii) The HTTP server receives the HTTP request, fetches the information as per the request and sends it to the HTTP client.
(iii)The HTTP client receives the response message, interprets the message and displays the contents of the message on the browser’s window.

Q.45. Basic idea of working of E-MAIL.

(i) You compose and send an email from your email client. Your email has the recipient’s email address along the email message.
(ii) Now your email client connects to the outgoing SMTP server and hands over the email message in the required format.
(iii) The outgoing SMTP first validates the sender details and if valid processes the message for sending and places it in outgoing queue.
(iv) Next DNS look up takes place. The SMTP server based on the domain details in the recipient address, looks up the DNS server of the domain and retrieves the recipient server information of the recipient domain
(v) Then the SMTP serve connects with the Recipient email server and sends the email through SMTP protocol.
(vi) The Recipient server in turn validates the recipient account and delivers the email to the users mail account.
(vii) The user logs into own email account and views the received email using e-mail client that will use POP3/IMAP protocol.

Q.46. How to obtain secure communication?


1)Encryption is one of such measures and highly recommended too. Encryption is a technique that translates the original data into a form which is not a usable form of data. To decrypt the data, a specific code called the decryption key is required.
2)HTTPS stans for hyper text transfer protocol secure and is a combination of HTTP and SLS/TLS protocols. HTTPS provides encrypts communication and secure identification of a network web server. HTTPS encrypts your data and establishes a secure channel over a non secure network to ensure protected data- transfer. Thus data is protected from eavesdroppers and hackers who want to intercept and access your data. That is why most banks apply HTTPS because HTTPS connections are more secure for online payment transactions compared to HTTP connections.

Q.47.Describe Remote login ?

Person can work on the desktop of another computer in the same manner as if that computer is right in front of the person. There are two programs: TELNET and SSH that facilitate remote login on the internet. Specify the remote machine on which you want to work and these programs will help you connect to it.

Thank you, for reading Class 12 Computer Science Computer Network Notes post. Below is useful material for Python.

We are also providing the solutions of all the chapters of Computer Science (Python) in this site. the links of relevant topics are provided below:

Computer Science with Python Class 12 Sumita Arora Solutions – CS Study

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