Discover the basics of computer networks in 9th class computer science (new syllabus). Understand networking types, protocols, security, and real-world applications with simple explanations.
MCQs
1. What is the primary objective of computer networks?
Options:
(a) Increase computational power
(b) Enable resource sharing and data communication ✅
(c) Enhance graphic capabilities
(d) Improve software development
Explanation:
The primary goal of computer networks is to allow multiple devices to communicate and share resources such as files, printers, and the internet.
Tip:
Always focus on the main purpose—data sharing and communication in networks.
2. Which device is used to connect multiple networks and direct data packets between them?
Options:
(a) Switch
(b) Hub
(c) Router ✅
(d) Modem
Explanation:
A router connects different networks and determines the best path for forwarding data packets between them.
Tip:
- A switch is used within a network to connect devices.
- A hub is a basic networking device that broadcasts data to all connected devices.
- A modem connects a network to the internet.
3. Which layer of the OSI model is responsible for node-to-node data transfer and error detection?
Options:
(a) Physical Layer
(b) Data Link Layer ✅
(c) Network Layer
(d) Transport Layer
Explanation:
The Data Link Layer ensures error detection and node-to-node data transfer, using protocols like Ethernet and MAC addressing.
Tip:
- Physical Layer deals with hardware transmission (cables, signals).
- Network Layer handles IP addressing and routing.
- Transport Layer ensures end-to-end delivery (e.g., TCP/UDP).
4. What is the function of the Domain Name System (DNS)?
Options:
(a) Assign IP addresses dynamically
(b) Translate domain names to IP addresses ✅
(c) Secure data communication
(d) Monitor network traffic
Explanation:
DNS translates human-readable domain names (e.g., google.com) into IP addresses (e.g., 8.8.8.8), allowing browsers to access websites.
Tip:
- DHCP assigns IP addresses dynamically.
- DNS only translates domain names.
5. Which method of data transmission uses a dedicated communication path?
Options:
(a) Packet Switching
(b) Circuit Switching ✅
(c) Full-Duplex
(d) Half-Duplex
Explanation:
Circuit Switching establishes a dedicated communication path between sender and receiver (e.g., traditional telephone calls).
Tip:
- Packet Switching (used in the internet) divides data into packets sent over different routes.
- Full-Duplex & Half-Duplex relate to communication direction.
6. What is encapsulation in the context of network communication?
Options:
(a) Converting data into a secure format
(b) Wrapping data with protocol information ✅
(c) Monitoring network traffic
(d) Translating domain names to IP addresses
Explanation:
Encapsulation is the process of adding protocol-specific headers and trailers to data as it moves through network layers.
Tip:
Encapsulation follows the OSI model:
- Application Layer (data)
- Transport Layer (segments)
- Network Layer (packets)
- Data Link Layer (frames)
- Physical Layer (bits)
7. Which protocol is used for reliable data transfer in the TCP/IP model?
Options:
(a) HTTP
(b) FTP
(c) TCP ✅
(d) UDP
Explanation:
TCP (Transmission Control Protocol) ensures reliable data transmission using error checking and acknowledgment.
Tip:
- UDP (User Datagram Protocol) is faster but unreliable (used in streaming).
- HTTP & FTP are application-layer protocols.
8. What is the main purpose of a firewall in network security?
Options:
(a) Convert data into a secure format
(b) Monitor and control network traffic ✅
(c) Assign IP addresses
(d) Translate domain names
Explanation:
A firewall acts as a security barrier, filtering incoming and outgoing traffic based on predefined rules.
Tip:
Firewalls prevent unauthorized access and cyber attacks.
9. Which network topology connects all devices to a central hub?
Options:
(a) Ring
(b) Mesh
(c) Bus
(d) Star ✅
Explanation:
In a Star Topology, all devices are connected to a central hub or switch, which manages communication.
Tip:
- Ring Topology: Devices are connected in a loop.
- Mesh Topology: Every device is interconnected.
- Bus Topology: A single central cable connects all devices.
10. What is a key benefit of using computer networks in businesses?
Options:
(a) Increase computational power
(b) Enable resource sharing and efficient communication ✅
(c) Enhance graphic capabilities
(d) Improve software development
Explanation:
Computer networks enhance communication and allow resource sharing, reducing costs and improving efficiency.
Tip:
- Always focus on connectivity and resource-sharing when answering network-related benefits.
Short Questions with Answers
1. Define data communication and list its key components.
Answer: Data communication is the exchange of data between devices through a transmission medium. The key components are:
- Sender (originates data)
- Receiver (accepts data)
- Transmission Medium (carries data)
- Message (actual data being transmitted)
- Protocol (rules governing communication)
Key Words: Data exchange, sender, receiver, transmission, protocol
2. Explain the role of routers in a computer network.
Answer: Routers direct data packets between networks, ensuring efficient data transmission by selecting the best path. They connect different networks, manage traffic, and provide security features like firewalls.
Key Words: Data packets, network connection, routing, path selection, traffic management
3. What are the main functions of the Network Layer in the OSI model?
Answer: The Network Layer is responsible for:
- Logical addressing (assigning IP addresses)
- Routing (determining the best path)
- Packet forwarding (moving data across networks)
- Fragmentation (breaking data into smaller packets)
Key Words: IP addressing, routing, forwarding, fragmentation
4. Describe the difference between packet switching and circuit switching.
Answer:
- Packet Switching: Data is broken into packets, which travel independently and reassemble at the destination (e.g., Internet).
- Circuit Switching: A dedicated communication path is established for the entire session (e.g., telephone calls).
Key Words: Packet-based, independent transmission, dedicated path, real-time communication
5. What is the purpose of the Dynamic Host Configuration Protocol (DHCP)?
Answer: DHCP automatically assigns IP addresses to devices in a network, reducing manual configuration and ensuring efficient IP management.
Key Words: IP assignment, automation, network configuration, address management
6. How does encapsulation ensure secure communication in a network?
Answer: Encapsulation wraps data with headers and encryption, protecting it during transmission. It helps maintain integrity, confidentiality, and proper data routing.
Key Words: Data protection, headers, encryption, security, integrity
7. Differentiate between TCP and UDP in terms of data transfer reliability.
Answer:
- TCP (Transmission Control Protocol): Reliable, connection-oriented, ensures data delivery with error checking.
- UDP (User Datagram Protocol): Faster, connectionless, no guarantee of delivery but efficient for real-time applications.
Key Words: Reliable, connection-oriented, error checking, fast, connectionless
8. Explain the importance of encryption in network security.
Answer: Encryption converts data into an unreadable format, preventing unauthorized access and ensuring confidentiality, integrity, and secure communication.
Key Words: Data security, confidentiality, encryption, unauthorized access
9. What are the advantages of using a star topology in a network?
Answer:
- Easy Troubleshooting: Faults are isolated to a single device.
- Scalability: Easy to add new devices.
- Better Performance: Dedicated links prevent data collisions.
Key Words: Central hub, easy maintenance, scalability, reliability
10. How do firewalls contribute to network security?
Answer: Firewalls monitor and filter incoming/outgoing traffic, blocking unauthorized access and preventing cyber threats like malware and hacking attempts.
Key Words: Traffic filtering, security, unauthorized access, malware prevention
Here are the detailed answers for your long questions, suitable for a 9th-grade level:
1. Objectives of Computer Networks and Resource Sharing
Objectives:
- Communication: Networks allow users to send emails, messages, and video calls.
- Resource Sharing: Users can share printers, files, and internet access.
- Data Storage and Retrieval: Cloud storage helps store and retrieve data from anywhere.
- Centralized Management: Large organizations manage data through servers efficiently.
- Security and Access Control: Networks enable secure data access through authentication.
Examples of Resource Sharing:
- A school shares one printer for all classrooms.
- Offices store employee data on a shared database.
- Students access online study materials through networked computers.
2. Simplex Communication – Time Calculation
Given:
- Data Rate = 500 bps
- Message Sizes: (a) 10 kilobits, (b) 10 kilobytes
(a) Transmission time for 10 kilobits Time=Total bits/Transmission Rate=10,000/500=20 seconds
(b) Transmission time for 10 kilobytes
1 Byte = 8 Bits → 10 KB = 10,000×8= 80,000 bits
Time=80,000/500=160 seconds=2 minutes 40 seconds
3. Packet Switching vs. Circuit Switching
Packet Switching
- Data is divided into packets and sent through different routes.
- Efficient use of bandwidth.
- Used in the Internet (e.g., emails, web browsing).
Circuit Switching
- A dedicated path is established for the whole communication.
- More reliable but less efficient.
- Used in traditional telephone systems.
4. Importance of Protocols and Key Protocols
Role of Protocols:
- Standardize communication between devices.
- Ensure data is transmitted accurately.
- Manage error detection and correction.
Key Protocols:
- TCP/IP: Manages internet communication.
- HTTP: Transfers web pages.
- DNS: Converts website names to IP addresses.
- DHCP: Assigns IP addresses to devices.
5. Network Security Methods
- Firewalls: Block unauthorized access to networks.
- Encryption: Converts data into unreadable code to protect privacy.
- Antivirus Software: Detects and removes malicious software.
6. Real-World Applications of Networks
- Business: Online banking, e-commerce.
- Education: E-learning platforms like Google Classroom.
- Healthcare: Online patient records and telemedicine.
7. Comparison of Network Topologies
| Topology | Structure | Advantages | Disadvantages |
|---|---|---|---|
| Star | Central hub connects devices | Easy troubleshooting | Failure of hub affects all |
| Ring | Each device connected to two others | Less data collision | Failure of one node affects all |
| Bus | Single central cable | Cost-effective | Slow with high traffic |
| Mesh | Every node connects to multiple others | High reliability | Expensive to set up |
8. Shift Cipher with Shift Amount = 4
Encryption:
SECURITY → WMXYVMI
(S → W, E → I, C → G, etc.)
Decryption:
WMXYVMI → SECURITY
(W → S, M → I, etc.)
9. IPv4 Address Calculation
(a) Total Unique IPv4 Addresses
IPv4 uses 32 bits, so the total addresses: 232=4,294,967,296
(b) Addresses Left After Reserving 10%
10%×4,294,967,296=429,496,729.6≈429,496,72910
Remaining=4,294,967,296−429,496,729=3,865,470,567
