Computer Networks Important Questions With Answers for Semester Exams: 2, 5 & 10 Marks
Computer Networks is one of those subjects where students understand the chapter while studying but get confused about what to write in the exam. A two-mark question needs a direct definition, a five-mark question needs explanation with important points, and a ten-mark question needs proper structure, working, diagram, advantages, differences or examples wherever required.
This question bank is designed for semester preparation. It covers the major Computer Networks topics from network fundamentals and the OSI model to routing, IP addressing, TCP, cryptography and the Application Layer. The answers are written in simple language so that you can understand them first and then write them comfortably in your own exam.
How Much Should You Write for 2, 5 and 10 Marks?
Writing more does not automatically give more marks. The answer should match the marks and directly cover what the examiner has asked.
Definition + Key Point
Usually write about 3–5 meaningful lines. Give the direct definition first and add one important feature, purpose or example.
Definition + Explanation
Start with a definition, explain 4–6 important points, and include a small example, table or diagram when the question needs it.
Complete Structured Answer
Use an introduction, proper headings, detailed working, diagram or table, important points, advantages or limitations where relevant, and a short conclusion.
Computer Networks 37-Chapter Study Map
If an answer below feels difficult, open the related detailed chapter. These links connect the question bank with the complete Computer Networks notes available on SahilDubey.com.
Computer Networks 2 Marks Important Questions With Answers
For a two-mark answer, write the definition first and then one or two important points. Do not turn a short-answer question into a full page.
1. What is a computer network?
A computer network is a group of two or more interconnected computers or devices that communicate with each other and share data, resources and services through communication links.
Examples include a home Wi-Fi network, a college LAN and the Internet.
2. State any four goals of computer networks.
The main goals are:
- Resource sharing.
- Data and information sharing.
- Communication between users.
- Improved reliability and availability.
3. What is network architecture?
Network architecture is the overall design of a computer network. It defines how devices, communication layers, protocols and services are organised and how they interact with one another.
4. What is a network protocol?
A protocol is a set of rules that controls communication between network devices.
It defines aspects such as message format, timing, addressing and error handling.
5. Name the seven layers of the OSI model.
The seven OSI layers are:
Physical → Data Link → Network → Transport → Session → Presentation → Application.
6. What is network topology?
Network topology describes the physical or logical arrangement of computers, networking devices and communication links in a network.
Examples include bus, star, ring, mesh and tree topology.
7. What is a backbone network?
A backbone network is a high-capacity central network that connects different smaller networks or network segments.
It carries a large amount of traffic between different parts of an organisation.
8. Differentiate between guided and unguided transmission media.
Guided media carries signals through a physical path such as twisted-pair cable, coaxial cable or optical fibre.
Unguided media carries signals through free space using radio waves, microwave or satellite communication.
9. What is circuit switching?
Circuit switching is a switching technique in which a dedicated communication path is established between sender and receiver before data transmission begins.
10. What is packet switching?
In packet switching, a message is divided into small packets. These packets travel through the network and are reassembled at the destination.
11. What is message switching?
Message switching is a store-and-forward technique in which an intermediate node receives the complete message, stores it temporarily and then forwards it to the next node.
12. What is ISDN?
ISDN stands for Integrated Services Digital Network.
It is a digital communication system designed to carry voice, data and other services over a digital telephone network.
13. What is terminal handling?
Terminal handling refers to the techniques used to manage communication between a user's terminal and a local or remote computer system.
It includes buffering, echoing, flow control, polling and terminal emulation.
14. What is the MAC sublayer?
The Media Access Control (MAC) sublayer is part of the Data Link Layer.
It controls access to a shared transmission medium and handles MAC addressing.
15. What is static channel allocation?
In static channel allocation, available communication capacity is permanently or pre-arranged among users or stations.
The allocation normally does not change dynamically with traffic demand.
16. What is dynamic channel allocation?
In dynamic channel allocation, communication capacity is assigned according to current transmission demand.
This allows stations to share the channel more flexibly.
17. What is ALOHA?
ALOHA is a random-access protocol in which stations transmit data over a shared channel without fixed scheduling.
If frames collide, they must be transmitted again.
18. What is the difference between Pure ALOHA and Slotted ALOHA?
In Pure ALOHA, a station may transmit at any time.
In Slotted ALOHA, transmission can begin only at the start of a fixed time slot, which reduces the collision period.
19. What are IEEE 802.3 and IEEE 802.11?
IEEE 802.3 is associated with Ethernet-based wired LAN communication.
IEEE 802.11 is associated with wireless LAN or Wi-Fi communication.
20. What is FDDI?
FDDI stands for Fiber Distributed Data Interface.
It is a high-speed network technology that traditionally uses optical fibre and a dual-ring architecture for improved reliability.
21. What is the Data Link Layer?
The Data Link Layer is Layer 2 of the OSI model.
It provides node-to-node delivery and performs functions such as framing, physical addressing, flow control and error control.
22. What is framing?
Framing is the process of dividing a continuous stream of bits into manageable units called frames at the Data Link Layer.
23. What is flow control?
Flow control regulates the rate of data transmission so that a fast sender does not overwhelm a slower receiver.
24. What is error control?
Error control refers to mechanisms used to detect transmission errors and, where required, recover or correct damaged or lost data.
25. What is ARQ?
ARQ stands for Automatic Repeat reQuest.
It uses acknowledgements, timeout and retransmission to provide reliable delivery when frames are lost or damaged.
26. What is CRC?
CRC stands for Cyclic Redundancy Check.
It is an error-detection technique that treats data as a binary polynomial and performs modulo-2 division using a generator polynomial.
27. What is checksum?
A checksum is an error-detection value calculated from a block of data and transmitted with it.
The receiver calculates the value again and compares it with the received checksum.
28. What is Hamming Code?
Hamming Code is an error-correcting code that adds redundant parity bits at specific positions.
It can locate and correct a single-bit error in a code word.
29. What is the Network Layer?
The Network Layer is Layer 3 of the OSI model.
Its important functions include logical addressing, routing and packet forwarding between different networks.
30. What is PPP?
PPP stands for Point-to-Point Protocol.
It is a Data Link Layer protocol used to establish and manage direct communication between two network nodes.
31. What is routing?
Routing is the process of selecting a suitable path through a network so that packets can move from the source to the destination.
32. What is Distance Vector routing?
Distance Vector routing is a routing method in which a router maintains information about destination distances and commonly exchanges routing information with neighbouring routers.
33. What is Link State routing?
Link State routing is a routing method in which routers collect information about network links, build a topology database and calculate suitable paths.
34. What is network congestion?
Network congestion occurs when the amount of traffic entering the network becomes greater than the capacity available to process and forward that traffic efficiently.
35. What is internetworking?
Internetworking is the process of connecting multiple independent networks so that devices in different networks can communicate with one another.
36. What is tunneling?
Tunneling is a technique in which one protocol packet is encapsulated inside another protocol packet so that it can travel through an intermediate network.
37. What is IP fragmentation?
IP fragmentation is the process of dividing an IP datagram into smaller fragments when the datagram is too large for the Maximum Transmission Unit of a network link.
38. What is the TCP/IP model?
The TCP/IP model is the protocol architecture used by the Internet.
It commonly includes Application, Transport, Internet and Network Access layers.
39. What is IPv4?
IPv4 is Version 4 of the Internet Protocol.
It uses 32-bit logical addresses and provides addressing and packet delivery across interconnected networks.
40. What is subnetting?
Subnetting is the process of dividing one IP network into smaller logical subnetworks by borrowing bits from the host portion of an address.
41. What is CIDR?
CIDR stands for Classless Inter-Domain Routing.
It represents a network by an address and prefix length, such as 192.168.1.0/24.
42. What is IPv6?
IPv6 is the newer version of the Internet Protocol that uses 128-bit addresses.
It provides a much larger address space than IPv4 and uses a simplified base header.
43. What is the Transport Layer?
The Transport Layer provides process-to-process communication between applications running on different hosts.
Its functions include segmentation, port addressing, multiplexing, reliability and connection management.
44. Differentiate between TCP and UDP.
TCP is connection-oriented and provides reliable, ordered data delivery.
UDP is connectionless, has lower overhead and does not provide built-in reliable delivery.
45. What are the Session and Presentation Layers?
The Session Layer manages communication sessions, dialogue control and synchronization.
The Presentation Layer handles data representation, translation, compression and related transformations.
46. What is the Application Layer?
The Application Layer is the top OSI layer and provides network services to user applications.
Examples of application-level services include web access, email, file transfer and remote terminal services.
Computer Networks 5 Marks Important Questions With Answers
For five marks, explain the concept instead of writing only definitions. Use headings and 4–6 strong points wherever possible.
1. Explain the goals and applications of computer networks.
A computer network connects devices so that they can communicate and share resources. The major goals and applications are:
- Resource sharing: Printers, storage, software and Internet connections can be shared.
- Communication: Users can communicate through email, messaging, voice and video calls.
- Data sharing: Files and information can be accessed by authorised users from different locations.
- Reliability: Multiple systems and communication paths can improve service availability.
- Remote access: Users can access services and systems from distant locations.
- Distributed processing: Work can be divided among multiple computers.
Therefore, networking reduces isolation between computers and allows resources and information to be used efficiently.
2. Explain the seven layers of the OSI model briefly.
- Physical Layer: Transfers raw bits through the physical medium.
- Data Link Layer: Provides framing, physical addressing, flow control and error control.
- Network Layer: Performs logical addressing, routing and packet forwarding.
- Transport Layer: Provides process-to-process communication and end-to-end transport.
- Session Layer: Manages communication sessions and synchronization.
- Presentation Layer: Handles data representation, translation and compression.
- Application Layer: Provides network services to user applications.
3. Compare Bus, Star, Ring and Mesh topology.
| Topology | Structure | Main Advantage | Main Limitation |
|---|---|---|---|
| Bus | All nodes share one backbone | Simple and economical | Backbone failure affects network |
| Star | All nodes connect to a central device | Easy fault isolation | Central-device failure is critical |
| Ring | Nodes form a circular path | Organised transmission path | A break can disturb communication unless protection exists |
| Mesh | Nodes have multiple direct paths | High reliability | Expensive and complex |
The correct topology depends on cost, reliability, scalability, performance and network size.
4. Explain important factors in network topology design.
Important topology-design factors include:
- Cost: Number of links, networking devices and installation cost.
- Reliability: Ability of the network to continue working after a failure.
- Delay: Time required for data to travel through the network.
- Traffic load: Amount of expected communication traffic.
- Scalability: Ease of adding new users and devices.
- Backbone design: Planning high-capacity central communication paths.
- Local access: Planning how users connect to the backbone.
5. Explain guided and unguided transmission media.
Transmission media provides the path through which communication signals travel.
Guided Media
Signals travel through a physical conductor.
- Twisted-pair cable
- Coaxial cable
- Optical fibre
Unguided Media
Signals travel through air or free space.
- Radio waves
- Microwave
- Satellite communication
Guided media usually offers a controlled transmission path, while unguided media provides mobility and wireless communication.
6. Explain circuit, message and packet switching.
Circuit Switching
A dedicated communication path is established before transmission. Resources may remain reserved during the communication session.
Message Switching
The complete message is stored at an intermediate node and then forwarded. A dedicated end-to-end path is not required.
Packet Switching
A message is divided into smaller packets. Packets are forwarded through the network and reassembled at the destination.
Modern data networks mainly use packet-based communication because network resources can be shared efficiently.
7. Explain ISDN architecture and its channels.
ISDN is a digital communication system designed to integrate services such as voice and data.
Important ISDN channel types include:
- B Channel: Bearer channel used to carry user information such as voice or data.
- D Channel: Used mainly for signalling and control information.
- H Channel: Higher-capacity channel used for higher data-rate services.
ISDN attempted to provide integrated digital services over telecommunications infrastructure and was important in the development of digital communication systems.
8. Explain terminal handling functions.
Terminal handling manages communication between terminals and a host system. Important functions include:
- Input handling: Accepting user input.
- Buffering: Temporarily storing input or output data.
- Echoing: Displaying typed characters on the terminal.
- Flow control: Controlling transmission rate.
- Polling: Asking terminals whether they have data to send.
- Selection: Selecting a terminal to receive information.
- Terminal emulation: Software behaves like a physical terminal.
9. Explain the functions of the MAC sublayer.
The MAC sublayer controls access to a shared communication medium. Its main functions include:
- Providing MAC addressing.
- Deciding when a station may transmit.
- Coordinating multiple users sharing the same medium.
- Supporting LAN frame transmission.
- Helping manage collisions in shared-media technologies.
MAC rules are important because multiple devices may want to use the same network channel at the same time.
10. Explain Pure ALOHA and Slotted ALOHA.
Both ALOHA techniques allow multiple users to share a common channel.
Pure ALOHA
- A station transmits whenever it has data.
- Two overlapping frames may collide.
- After a collision, retransmission occurs after a random delay.
Slotted ALOHA
- Time is divided into equal slots.
- A frame can start only at the beginning of a slot.
- The vulnerable period is reduced compared with Pure ALOHA.
- Therefore, channel efficiency improves.
11. Explain IEEE 802.3, IEEE 802.11 and FDDI.
IEEE 802.3 defines standards associated with Ethernet and wired LAN communication.
IEEE 802.11 defines standards used for wireless LAN technologies commonly known as Wi-Fi.
FDDI is a high-speed network technology traditionally based on optical fibre and dual-ring communication.
These technologies represent different methods of providing local or metropolitan network connectivity.
12. Explain the functions of the Data Link Layer.
The Data Link Layer provides reliable node-to-node communication over a link. Its important functions include:
- Framing: Dividing data into frames.
- Physical addressing: Using link-layer addresses.
- Flow control: Controlling sender speed.
- Error control: Detecting or recovering from transmission errors.
- Access control: Deciding which device can use a shared medium.
13. Explain elementary Data Link protocols.
Elementary Data Link protocols are simplified protocol models used to understand reliable frame communication.
- Simplex unrestricted protocol: Assumes the receiver is always ready and the channel is perfect.
- Simplex Stop-and-Wait: Sender waits to ensure the receiver can process data.
- Noisy-channel protocols: Include acknowledgement, timeout and retransmission to handle lost or damaged frames.
These models form the foundation for understanding practical flow-control and ARQ protocols.
14. Differentiate between Go-Back-N and Selective Repeat.
| Point | Go-Back-N | Selective Repeat |
|---|---|---|
| Receiver window | Normally 1 | More than 1 |
| Out-of-order frames | Usually discarded | Can be buffered |
| Retransmission | Missing frame and later outstanding frames | Only required frames |
| Complexity | Lower | Higher |
| Efficiency | Lower when errors occur frequently | Better in many error conditions |
15. Explain CRC, checksum and Hamming Code.
These methods add redundancy so that transmission errors can be detected or corrected.
- CRC: Performs modulo-2 division using a generator polynomial. The remainder is transmitted with data.
- Checksum: Data words are added and a complement-type value is transmitted for verification.
- Hamming Code: Places redundant bits at specific positions and can locate and correct a single-bit error.
CRC is particularly strong for detecting burst errors, while Hamming Code provides error-correction capability.
16. Explain the functions of the Network Layer.
- Logical addressing: Provides addresses such as IP addresses.
- Routing: Selects paths between networks.
- Packet forwarding: Moves packets through routers.
- Internetworking: Supports communication across different networks.
- Fragmentation support: Handles packet-size limitations where required.
- Congestion-related mechanisms: Helps manage network traffic.
17. Explain PPP and its important features.
PPP is a Data Link Layer protocol used for direct communication between two nodes.
Important features include:
- Frame-based point-to-point communication.
- Link establishment and configuration.
- Support for authentication mechanisms.
- Ability to carry different Network Layer protocols.
- Error detection through frame-checking mechanisms.
18. Explain Distance Vector and Link State routing.
Distance Vector
Routers maintain information about destination distance and next hop and exchange routing information with neighbours.
Link State
Routers learn the state of network links, distribute link information, build a network map and calculate shortest paths.
Distance Vector is conceptually simpler, while Link State provides a more complete view of network topology.
19. Explain network congestion and its causes.
Congestion occurs when network traffic exceeds available resources.
Important causes include:
- Too many packets entering the network.
- Limited router buffer capacity.
- Low-bandwidth communication links.
- Slow packet processing.
- Bursty traffic.
- Poor traffic-management decisions.
Congestion can increase delay, packet loss and retransmission.
20. Explain internetworking, routers, gateways and tunneling.
Internetworking connects independent networks so that users can communicate across network boundaries.
- Router: Forwards packets between IP networks.
- Gateway: Can connect systems or networks that require higher-level protocol conversion or translation.
- Tunneling: Encapsulates one type of packet inside another so that it can cross an intermediate network.
These mechanisms make communication possible across heterogeneous network environments.
21. Differentiate between the OSI model and TCP/IP model.
| Point | OSI | TCP/IP |
|---|---|---|
| Nature | Reference model | Practical Internet protocol model |
| Layers | 7 | Commonly represented using 4 layers |
| Developed by | ISO | DoD/Internet research environment |
| Session/Presentation | Separate layers | Usually part of Application layer |
| Use | Mainly conceptual understanding | Widely used in real Internet communication |
22. Explain important fields of the IPv4 header.
Important IPv4 header fields include:
- Version: Identifies IPv4.
- Header Length: Size of the IP header.
- Total Length: Complete datagram length.
- Identification: Helps fragmentation and reassembly.
- Flags and Fragment Offset: Control fragmentation.
- TTL: Limits packet lifetime.
- Protocol: Identifies the upper-layer protocol.
- Source Address: Sender IPv4 address.
- Destination Address: Receiver IPv4 address.
23. Explain IPv4 classes, subnetting and CIDR.
Traditional IPv4 addressing divided addresses into classes such as A, B and C for different network sizes.
Subnetting divides one larger network into smaller subnetworks by extending the network prefix into host bits.
CIDR removes dependence on fixed class boundaries and uses prefix notation such as /24 or /26.
CIDR improves address allocation flexibility and supports route aggregation.
24. Differentiate between IPv4 and IPv6.
| Point | IPv4 | IPv6 |
|---|---|---|
| Address size | 32 bits | 128 bits |
| Representation | Dotted decimal | Hexadecimal groups |
| Address space | Smaller | Extremely large |
| Base header | More variable | Simplified fixed base-header structure |
| Broadcast | Supported | Traditional broadcast is not used in the same way |
25. Explain the functions of the Transport Layer.
- Process-to-process delivery.
- Port addressing.
- Segmentation and reassembly.
- Multiplexing and demultiplexing.
- Connection establishment and termination.
- Flow control.
- Error control and reliable delivery where supported.
TCP and UDP are the two most familiar Transport Layer protocols in the TCP/IP protocol suite.
26. Explain TCP connection establishment and termination.
Connection Establishment
TCP normally uses a three-way handshake:
- Client sends SYN.
- Server sends SYN-ACK.
- Client sends ACK.
Connection Termination
TCP connection release commonly uses FIN and ACK messages from both directions so that each side can close its sending direction properly.
27. Explain TCP flow control and congestion window.
TCP controls how much data a sender can place in transit.
- Receiver Window: Advertised by the receiver and helps prevent receiver-buffer overflow.
- Congestion Window: Maintained by the sender according to perceived network congestion.
- Effective sending limit: Is influenced by both receiver capacity and congestion conditions.
Therefore, TCP attempts to protect both the receiving host and the network.
28. Explain the Session Layer and synchronization.
The Session Layer manages communication sessions between applications.
Important functions include:
- Session establishment.
- Session maintenance.
- Session termination.
- Dialogue control.
- Synchronization using checkpoints.
- Recovery from certain communication interruptions.
Checkpoints can reduce the need to restart a long operation completely after failure.
29. Explain Remote Procedure Call (RPC).
RPC allows a program to request a service from a program running on another computer while making the call appear similar to a local procedure call.
Basic flow:
- Client program calls a client stub.
- Arguments are converted into a transmittable form.
- Request is sent to the server.
- Server stub receives and interprets the request.
- Server procedure executes.
- Result is returned to the client.
30. Explain Presentation Layer functions.
The Presentation Layer deals with the representation of information exchanged between systems.
Its functions include:
- Data format translation.
- Character-code conversion.
- Serialization or representation changes.
- Data compression.
- Supporting encryption-related data transformation in conceptual OSI discussions.
31. Explain symmetric encryption, asymmetric encryption and hashing.
- Symmetric encryption: The same shared secret key is used for encryption and decryption.
- Asymmetric encryption: Uses a mathematically related public-key and private-key pair.
- Hashing: Converts data into a fixed-size digest using a one-way function.
Encryption is used to protect confidentiality, while hashing is widely used to support integrity verification and password-processing systems.
32. Explain important Application Layer services.
The Application Layer provides services used directly by network applications.
- FTP: File transfer.
- Email services: Sending and receiving electronic messages.
- Web services: Accessing web resources through web protocols.
- Virtual terminal: Remote terminal access.
- Name and directory services: Help identify or locate network resources.
These services connect users and application software with the underlying network infrastructure.
Computer Networks 10 Marks Important Questions With Detailed Answers
For ten marks, write in a proper structure. Start with a definition or introduction, draw a diagram where possible, explain each part with headings, and end with a short conclusion.
1. Explain the OSI model in detail with functions of all seven layers.
Introduction
The OSI model, or Open Systems Interconnection model, is a seven-layer reference model used to understand how data moves from one computer to another through a network. Instead of treating communication as one large task, the model divides it into seven smaller layers. Each layer performs a specific set of functions and provides services to the layer above it.
1. Physical Layer
The Physical Layer is responsible for transmitting raw bits over a physical medium. It deals with electrical, optical or radio signals, connectors, transmission rate and physical communication characteristics.
2. Data Link Layer
The Data Link Layer provides node-to-node delivery over a link. Important functions include framing, physical addressing, flow control, error control and medium-access control.
3. Network Layer
The Network Layer provides logical addressing and routing. It decides how packets should move from the source network to the destination network. Routers primarily work at this layer.
4. Transport Layer
The Transport Layer provides process-to-process communication. It performs segmentation, reassembly, port addressing, multiplexing and connection management. TCP and UDP are common Transport Layer protocols in the TCP/IP suite.
5. Session Layer
The Session Layer establishes, manages and terminates communication sessions. It may provide dialogue control and synchronization checkpoints.
6. Presentation Layer
The Presentation Layer handles the representation of data. It can perform translation between formats, character-code conversion, compression and other data transformations.
7. Application Layer
The Application Layer provides network services to user applications. Services such as file transfer, electronic mail, web communication and virtual-terminal access are associated with the application level.
Advantages of Layering
- Makes network design easier to understand.
- Separates different communication responsibilities.
- Supports modular protocol development.
- Makes troubleshooting easier because problems can be associated with a particular layer.
- Allows technologies at one layer to change without redesigning every other layer.
2. Explain different network topologies with advantages and disadvantages.
Introduction
Network topology describes how devices and communication links are arranged in a network. A topology may be discussed physically, according to cable and device arrangement, or logically, according to the communication path followed by data.
1. Bus Topology
In a bus topology, all computers are connected to a common backbone cable.
Advantages:- Simple structure.
- Requires less cable for small networks.
- Low installation cost.
- Backbone failure can affect the entire network.
- Fault isolation may be difficult.
- Performance may decrease as traffic increases.
2. Star Topology
In a star topology, all devices connect to a central device such as a switch.
Advantages:- Easy to install and manage.
- Failure of one end device or cable normally does not stop other devices.
- Fault detection is easier.
- Central-device failure can affect the network.
- Requires more cable than basic bus topology.
3. Ring Topology
Devices are connected in a circular structure. Data moves through the ring according to the network design.
Advantages:- Organised transmission path.
- Can provide controlled access to the medium.
- A link or node failure can disturb communication in a simple single-ring design.
- Expansion and maintenance can be more difficult.
4. Mesh Topology
In mesh topology, devices are connected using multiple communication paths.
Advantages:- High reliability.
- Alternative paths may remain available after a link failure.
- Good fault tolerance.
- High cable and hardware cost.
- Complex installation.
5. Tree Topology
Tree topology uses a hierarchical structure. Different star-like branches may connect through backbone links.
6. Hybrid Topology
Hybrid topology combines two or more topology designs to meet the needs of a larger network.
Conclusion
There is no single topology that is best for every network. The choice depends on cost, reliability, traffic, scalability, physical location and maintenance requirements.
3. Explain transmission media in detail. Compare guided and unguided media.
Introduction
Transmission media is the communication path through which data signals travel between network devices. It is broadly classified into guided media and unguided media.
A. Guided Media
In guided media, signals travel through a physical conductor.
1. Twisted-Pair Cable
Two insulated copper wires are twisted around each other. Twisted pair is inexpensive and widely used in telephone and Ethernet networks.
Advantages:- Low cost.
- Easy installation.
- Widely available.
- More affected by interference than optical fibre.
- Distance and bandwidth are limited compared with fibre.
2. Coaxial Cable
Coaxial cable has a central conductor surrounded by insulation and shielding. It provides better shielding than basic twisted pair.
3. Optical Fibre
Optical fibre carries data using light. It provides high bandwidth, supports long distances and is resistant to electromagnetic interference.
B. Unguided Media
In unguided media, signals travel through free space.
1. Radio Waves
Radio communication can cover large areas and can often penetrate buildings depending on frequency.
2. Microwave
Microwave transmission can provide high-capacity point-to-point wireless links and commonly requires suitable line-of-sight conditions for terrestrial links.
3. Satellite Communication
Satellites relay signals over very large geographical areas and are useful where terrestrial communication infrastructure is difficult.
| Point | Guided | Unguided |
|---|---|---|
| Path | Physical conductor | Free space |
| Examples | Twisted pair, coaxial, fibre | Radio, microwave, satellite |
| Mobility | Lower | Higher |
| Interference | Depends on medium; fibre is highly resistant | Wireless environment can be affected by interference |
Conclusion
The correct transmission medium is selected according to bandwidth, distance, cost, security, mobility and installation requirements.
4. Explain circuit switching, message switching and packet switching in detail.
Introduction
Switching is used to move data through a network containing multiple intermediate nodes. The three important approaches are circuit switching, message switching and packet switching.
1. Circuit Switching
A dedicated end-to-end path is established before actual communication begins. The path remains reserved for the session.
- Predictable path after establishment.
- Continuous communication.
- Useful for traditional real-time circuit-based services.
- Reserved capacity may remain unused.
- Connection setup is required.
- Less efficient for bursty computer data.
2. Message Switching
The complete message is treated as one unit. Each intermediate node stores the full message and forwards it when the next link becomes available.
Advantages:- No dedicated path required.
- Network links can be shared.
- Large storage requirements.
- High delay.
- Not suitable for many real-time applications.
3. Packet Switching
The message is divided into small packets. Packets are transmitted through the network and reassembled at the destination.
Advantages:- Efficient sharing of communication links.
- Suitable for bursty data traffic.
- Many users can share network capacity.
- Delay may vary.
- Packets may require buffering and routing.
- Protocols are required to handle delivery and ordering when necessary.
Conclusion
Packet switching is the basic communication approach used by modern data networks and the Internet because it shares network resources efficiently.
5. Explain MAC sublayer, channel allocation and ALOHA protocols.
MAC Sublayer
The Media Access Control sublayer is the lower part of the Data Link Layer in IEEE LAN architectures. Its main job is to control how multiple devices share a communication medium.
Important MAC functions include:
- MAC addressing.
- Medium-access control.
- Frame transmission.
- Collision-related handling depending on the LAN technology.
Channel Allocation
When many users share one channel, a mechanism is required to decide who may use the channel.
Static Allocation
Channel capacity is divided in advance. Each user receives a predetermined share even if the user has no data at a particular moment.
Dynamic Allocation
Channel access is provided according to traffic demand. This approach is generally more flexible for bursty computer communication.
ALOHA
ALOHA is a random-access protocol designed for a shared communication channel.
Pure ALOHA
- Transmit whenever data is ready.
- Collisions occur if frames overlap.
- After collision, wait a random time and retransmit.
Slotted ALOHA
- Time is divided into fixed slots.
- Transmission starts only at a slot boundary.
- The collision vulnerable period is reduced.
- Efficiency improves compared with Pure ALOHA.
Conclusion
MAC protocols are necessary because many devices may compete for the same channel. Dynamic allocation and random-access protocols allow shared media to be used more efficiently.
6. Explain Sliding Window Protocol, Go-Back-N and Selective Repeat ARQ in detail.
Introduction
Sliding Window Protocol improves link utilisation by allowing the sender to transmit multiple frames before receiving acknowledgements for all previously sent frames.
Basic Idea
Frames are identified using sequence numbers. The sender maintains a sender window, and the receiver maintains a receiver window. As acknowledgements arrive, the window moves forward.
Stop-and-Wait ARQ
Only one frame is sent at a time. The sender waits for acknowledgement. If the frame or ACK is lost, timeout causes retransmission.
Go-Back-N ARQ
- Several frames may remain outstanding.
- The receiver window is normally one.
- Out-of-order frames are normally discarded.
- Cumulative acknowledgements may be used.
- If one frame is missing, the sender retransmits the missing frame and subsequent outstanding frames.
For an m-bit sequence number, the classical maximum sender window is:
Selective Repeat ARQ
- The receiver can accept and buffer out-of-order frames.
- Only missing or damaged frames need retransmission.
- Individual frame tracking is required.
- It is more efficient but also more complex.
A common maximum-window condition is:
Go-Back-N vs Selective Repeat
Go-Back-N uses simpler receiver logic but can retransmit many correct frames after an error. Selective Repeat requires more memory and control but retransmits only the necessary frames.
Conclusion
Sliding-window protocols improve performance when propagation delay is significant because multiple frames can be in transit at the same time.
7. Explain error detection and correction techniques: Parity, Checksum, CRC and Hamming Code.
Introduction
During data transmission, noise and other communication problems can change transmitted bits. Error-control methods add redundant information so that the receiver can detect or correct these errors.
1. Parity
A parity bit is added to a group of bits.
- Even parity: Total number of 1s is made even.
- Odd parity: Total number of 1s is made odd.
Simple parity can detect many single-bit errors but cannot detect every possible multi-bit error pattern.
2. Checksum
Data is divided into words. These words are added using a defined arithmetic method, and a checksum value is generated. The receiver repeats the calculation and checks the result.
3. Cyclic Redundancy Check
CRC treats the data bits as a polynomial. The sender divides the data by a generator polynomial using modulo-2 arithmetic. The remainder is appended to the frame.
The receiver performs the same division. A non-zero remainder normally indicates an error.
4. Hamming Code
Hamming Code adds redundant bits at positions that are powers of two, such as 1, 2, 4 and 8.
For m data bits and r redundant bits:
The parity-check results form a syndrome that can identify the position of a single-bit error. The receiver can then flip that bit and correct the data.
Conclusion
Parity and checksum are simple error-detection methods, CRC provides strong detection capability, and Hamming Code provides single-bit error correction.
8. Explain the Network Layer and major routing algorithms.
Introduction
The Network Layer is responsible for moving packets between different networks. It provides logical addressing and selects communication paths through routers.
Main Functions
- Logical addressing.
- Routing.
- Packet forwarding.
- Internetworking.
- Fragmentation-related processing where required.
- Supporting traffic-management functions.
Routing
Routing is the process of selecting a suitable path from the source network to the destination network.
Distance Vector Routing
Each router maintains a table containing destination information, distance or cost and next-hop information. Routers exchange their routing information with neighbouring routers.
Advantages:- Conceptually simple.
- Lower initial complexity.
- Convergence may be slower.
- Routing loops and count-to-infinity problems may occur in basic forms.
Link State Routing
Each router learns the state and cost of its links, distributes this information and builds a topology database. A shortest-path algorithm is then used to calculate routes.
Advantages:- Provides a detailed network view.
- Can converge quickly after changes when correctly implemented.
- Requires more processing and memory.
- More complex than basic Distance Vector operation.
Conclusion
Routing allows packets to reach remote networks. Distance Vector learns routes mainly through neighbour information, while Link State builds a broader map of the network.
9. Explain congestion in computer networks and methods used to control it.
Meaning of Congestion
Network congestion occurs when too many packets compete for limited network resources such as bandwidth, router buffers and processing capacity.
Causes
- Sudden increase in traffic.
- Limited link bandwidth.
- Insufficient router buffers.
- Slow packet-processing capability.
- Bursty applications.
- Excessive retransmission after packet loss.
Effects
- Long queuing delay.
- Packet loss.
- More retransmissions.
- Reduced useful throughput.
- Poor application performance.
Congestion-Control Approaches
Congestion can be handled using preventive and feedback-based mechanisms.
- Traffic shaping: Controls the rate at which traffic enters the network.
- Admission control: Restricts new traffic when sufficient resources are not available.
- Queue management: Manages router queues to reduce uncontrolled buffer growth.
- Feedback: Network or receiver information may tell senders to reduce transmission rate.
- TCP congestion control: TCP changes its congestion window according to perceived network conditions.
Flow Control vs Congestion Control
Flow control protects the receiver from a fast sender, while congestion control protects the network from excessive traffic.
Conclusion
Effective congestion control improves throughput and reduces packet loss and delay by matching offered traffic with available network capacity.
10. Explain internetworking, routers, gateways, tunneling and fragmentation.
Internetworking
Internetworking means connecting multiple independent networks so that devices in those networks can communicate as part of a larger system.
Router
A router operates mainly at the Network Layer and forwards packets between IP networks. It uses routing information to select the next hop toward a destination.
Gateway
The term gateway may refer to a device or software system that connects different environments. A gateway can perform protocol conversion, representation changes or other translation depending on the system design.
Tunneling
Tunneling encapsulates a packet of one protocol inside another packet so that it can cross an intermediate network that may not directly support the original protocol.
Fragmentation
Different networks may support different Maximum Transmission Unit sizes. If an IP datagram is too large for a link, fragmentation may divide it into smaller pieces where the protocol and path permit it.
The receiving side uses fragmentation-related information to reconstruct the original datagram where required.
Conclusion
Routers provide packet forwarding, gateways connect dissimilar systems, tunneling carries one protocol through another network, and fragmentation handles packet-size limits.
11. Explain the TCP/IP model and compare it with the OSI model.
TCP/IP Model
The TCP/IP model describes the protocol architecture used by the Internet. It is commonly represented using four layers.
1. Network Access Layer
Handles communication over the local network and physical transmission medium.
2. Internet Layer
Provides logical addressing and packet delivery across interconnected networks. IP operates here.
3. Transport Layer
Provides process-to-process communication. TCP and UDP are important protocols at this layer.
4. Application Layer
Provides services for applications and combines roles that are represented separately in the upper OSI layers.
| OSI | TCP/IP |
|---|---|
| Seven layers | Commonly four layers |
| Reference model | Practical Internet protocol architecture |
| Separate Session and Presentation layers | Functions generally included in Application layer |
| Useful for conceptual learning | Widely used in actual Internet communication |
Conclusion
The OSI model is extremely useful for learning network responsibilities, while the TCP/IP model reflects the protocol architecture that powers the Internet.
12. Explain the IPv4 datagram format and IP fragmentation.
Introduction
IPv4 carries data across interconnected networks using datagrams. Each datagram contains a header followed by payload data.
Important Header Fields
- Version: Identifies IPv4.
- IHL: Specifies header length.
- Total Length: Size of the complete datagram.
- Identification: Helps identify fragments belonging to the same original datagram.
- Flags: Control fragmentation behaviour.
- Fragment Offset: Indicates fragment position.
- TTL: Prevents packets from circulating indefinitely.
- Protocol: Identifies the encapsulated upper-layer protocol.
- Header Checksum: Checks the IPv4 header.
- Source Address: Sender address.
- Destination Address: Receiver address.
Fragmentation
A datagram may encounter a network whose MTU is smaller than the datagram size. IPv4 fragmentation can divide the datagram into smaller fragments where permitted.
Important fields used for fragmentation include Identification, Flags and Fragment Offset.
Conclusion
The IPv4 header contains the information needed for addressing, forwarding, protocol identification, lifetime control and fragmentation-related processing.
13. Explain IPv4 addressing, subnetting and CIDR with an example.
IPv4 Addressing
An IPv4 address is 32 bits long and is normally written using four decimal octets, for example:
An IP address contains a network portion and a host portion. The subnet mask or prefix length tells the system which bits belong to the network.
Traditional Classes
Earlier IPv4 networks were commonly divided into address classes such as Class A, B and C. Modern networks mainly use classless prefix-based allocation.
Subnetting
Subnetting divides one network into smaller subnetworks. Bits are borrowed from the host part to create additional network prefixes.
Example
Suppose the network is:
A /24 prefix leaves 8 host bits. If we create /26 subnets, two additional bits are used for subnetting.
Each /26 subnet contains 64 total addresses.
Possible network blocks are:
- 192.168.10.0/26
- 192.168.10.64/26
- 192.168.10.128/26
- 192.168.10.192/26
In traditional subnet calculations, each /26 block provides 62 usable host addresses because the network and broadcast addresses are not assigned to normal hosts.
CIDR
CIDR stands for Classless Inter-Domain Routing. It represents networks using a prefix length such as /24, /26 or /20 instead of depending on fixed class boundaries.
Advantages
- Flexible address allocation.
- Efficient use of IPv4 space.
- Supports route aggregation.
- Allows subnet sizes to match actual requirements more closely.
Conclusion
Subnetting divides networks internally, while CIDR provides flexible prefix-based addressing and routing.
14. Explain IPv6, its features and differences from IPv4.
Introduction
IPv6 is the newer version of the Internet Protocol developed to provide a very large address space and improve several aspects of IP networking.
IPv6 Address
IPv6 uses 128-bit addresses written in hexadecimal notation.
Example:
Main Features
- 128-bit address space.
- Simplified base-header design.
- Support for extension headers.
- No traditional broadcast addressing.
- Improved support for automatic address configuration.
- Better long-term scalability for Internet growth.
IPv4 vs IPv6
| Feature | IPv4 | IPv6 |
|---|---|---|
| Address length | 32 bits | 128 bits |
| Notation | Dotted decimal | Hexadecimal |
| Address space | Limited compared with IPv6 | Extremely large |
| Broadcast | Supported | Not used in the traditional IPv4 broadcast manner |
| Base header | Includes several fields and optional length | Simplified fixed-size base header |
Need for IPv6
The most important reason for IPv6 is the limited IPv4 address space. Growth in computers, smartphones, cloud systems and connected devices requires a much larger number of globally unique addresses.
Conclusion
IPv6 provides a very large address space and a modernised Internet Protocol design while remaining focused on packet delivery across interconnected networks.
15. Explain the Transport Layer, its functions and TCP vs UDP.
Introduction
The Transport Layer provides logical communication between application processes running on different hosts. While the Network Layer delivers packets between hosts, the Transport Layer identifies the correct application processes.
Main Functions
- Process-to-process delivery: Delivers data to the correct application process.
- Port addressing: Uses port numbers to identify applications.
- Segmentation: Breaks large application data into smaller transport units.
- Reassembly: Reconstructs application data at the destination.
- Multiplexing: Allows multiple applications to share network communication.
- Connection management: Establishes and releases connections when required.
- Flow control: Prevents overwhelming the receiver.
- Error control: Reliable protocols can detect losses and recover through retransmission.
TCP
TCP is a connection-oriented transport protocol that provides reliable and ordered byte-stream delivery.
UDP
UDP is a connectionless transport protocol with low protocol overhead. It does not provide TCP-style connection establishment, retransmission or ordered reliable delivery.
| TCP | UDP |
|---|---|
| Connection-oriented | Connectionless |
| Reliable delivery mechanisms | No built-in reliable delivery |
| Ordered byte stream | Datagram-based |
| Higher overhead | Lower overhead |
Conclusion
TCP is useful when reliable ordered communication is important. UDP is useful when lower overhead or application-controlled reliability is preferred.
16. Explain TCP segment format, three-way handshake and connection termination.
TCP Segment
TCP adds a header to application data. Important fields include:
- Source Port.
- Destination Port.
- Sequence Number.
- Acknowledgement Number.
- Header Length.
- Control flags such as SYN, ACK and FIN.
- Window Size.
- Checksum.
Three-Way Handshake
The handshake synchronizes connection information and confirms that both sides are ready to communicate.
Connection Termination
TCP supports full-duplex communication, so each direction is closed independently.
A common simplified sequence is:
Importance of Sequence and Acknowledgement Numbers
Sequence numbers identify byte positions in the TCP data stream. Acknowledgement numbers indicate the next expected byte and help provide reliable ordered delivery.
Checksum
TCP uses a checksum to detect corruption in the TCP segment.
Conclusion
TCP uses structured headers, acknowledgements, sequence numbers and explicit connection establishment to provide reliable communication.
17. Explain TCP window management, flow control and congestion control.
Introduction
TCP should not send unlimited data without considering receiver capacity and network conditions. Window management controls how much data can remain in transit without acknowledgement.
Sliding Window Concept
TCP uses a byte-oriented sliding-window mechanism. As data is acknowledged, the sending window moves forward and more data can be transmitted.
Receiver Window
The receiver advertises how much buffer space is available. This value helps the sender avoid overflowing the receiver.
This mechanism is mainly associated with flow control.
Congestion Window
The sender maintains a congestion window based on perceived network conditions. When congestion is detected, the sender may reduce its sending rate.
Effective Transmission
The sender must respect both:
- Receiver capacity.
- Network congestion limits.
Flow Control vs Congestion Control
| Flow Control | Congestion Control |
|---|---|
| Protects receiver | Protects network |
| Based strongly on receiver buffer availability | Based on congestion conditions |
| Receiver window is important | Congestion window is important |
Conclusion
TCP window management balances performance and reliability by allowing multiple bytes to be in transit while limiting transmission according to receiver and network conditions.
18. Explain Session Layer and Remote Procedure Call (RPC) in detail.
Session Layer
The Session Layer is Layer 5 of the OSI model. Its role is to establish, manage and terminate communication sessions between applications.
Main Functions
- Session establishment.
- Session maintenance.
- Session termination.
- Dialogue control.
- Synchronization.
- Checkpoint management.
Synchronization
For a long data-transfer operation, checkpoints can be inserted at intervals. If communication fails after a checkpoint, recovery may continue from an appropriate checkpoint instead of restarting the complete operation.
Remote Procedure Call
RPC is a distributed-computing mechanism in which a program calls a procedure located on another machine while programming interfaces attempt to make the call look similar to a local procedure call.
RPC Working
- Client calls the client stub.
- The stub packages procedure parameters.
- The request is transmitted across the network.
- The server stub receives the request.
- The server procedure executes.
- The result is packaged and sent back.
- The client receives the result.
Advantages
- Simplifies distributed application design.
- Provides an abstraction over low-level network communication.
- Allows services on remote computers to be invoked programmatically.
Conclusion
The Session Layer conceptually manages communication sessions, while RPC provides a practical mechanism for requesting remote computation.
19. Explain Presentation Layer and cryptography in computer networks.
Presentation Layer
The Presentation Layer is Layer 6 of the OSI model. It ensures that data produced by one system can be represented in a form understandable by another system.
Main Functions
- Data translation.
- Character-code conversion.
- Representation conversion.
- Data compression.
- Conceptual support for encryption-related transformation.
Data Compression
Compression reduces the number of bits required to represent information. This can reduce storage requirements and the amount of data transmitted through a network.
Cryptography
Cryptography protects information using mathematical techniques.
Symmetric Encryption
The sender and receiver use the same secret key for encryption and decryption.
Advantages:- Fast for bulk data encryption.
- Efficient processing.
The secret key must be shared securely.
Asymmetric Encryption
Uses a public key and a private key. The two keys perform related but different cryptographic operations.
Hashing
A hash function converts data into a fixed-size digest. It is designed as a one-way process and is useful for integrity checks and many security mechanisms.
Digital Signature
A digital signature uses asymmetric cryptography to support authenticity, integrity and non-repudiation-related security goals.
Conclusion
The Presentation Layer focuses on data representation, while cryptography protects network information against unauthorised reading or modification and supports trusted communication.
20. Explain Application Layer services and the working of the Internet and public networks.
Application Layer
The Application Layer is the top layer of the OSI model. It provides network services directly to user applications.
Important Services
1. File Transfer
File-transfer services allow users to upload and download files between systems. FTP is a traditional protocol associated with file transfer.
2. Electronic Mail
Email systems use application protocols to send, relay and retrieve messages. Different protocols may be used for sending and receiving mail.
3. Virtual Terminal
Virtual-terminal services allow a user to interact with a remote computer as though a terminal were connected to that remote system.
4. Web Communication
Web applications use application-layer protocols to request and deliver web resources.
Internet
The Internet is a global internetwork made from a very large number of independently managed networks connected through routers and common protocol standards.
Major Components
- End devices and hosts.
- Routers.
- Communication links.
- Internet service providers.
- Network protocols.
- Servers and cloud infrastructure.
- Addressing and routing systems.
Basic Communication Flow
- An application generates data.
- Transport protocols prepare process-to-process delivery.
- IP provides logical addressing and packet forwarding.
- Routers move packets across networks.
- The destination host receives the data.
- The destination application processes the information.
Conclusion
The Application Layer provides user-facing network services, while the Internet connects networks globally and uses layered protocols to deliver information from one application to another.
Last-Minute Computer Networks Revision Checklist
If the exam is close and you cannot revise every chapter again, focus on the concepts below first.
Must-Revise Topics
- Seven OSI layers and their functions.
- OSI vs TCP/IP model.
- Bus, Star, Ring, Mesh, Tree and Hybrid topology.
- Guided vs Unguided transmission media.
- Circuit vs Message vs Packet switching.
- MAC sublayer and channel allocation.
- Pure ALOHA vs Slotted ALOHA.
- IEEE 802.3 and IEEE 802.11.
- Data Link Layer functions.
- Stop-and-Wait, Go-Back-N and Selective Repeat.
- CRC, Checksum, Parity and Hamming Code.
- Network Layer functions.
- Distance Vector vs Link State routing.
- Congestion control.
- Routers, gateways, tunneling and fragmentation.
- IPv4 packet format.
- Subnetting and CIDR.
- IPv4 vs IPv6.
- Transport Layer functions.
- TCP vs UDP.
- TCP three-way handshake.
- TCP receiver window and congestion window.
- Session Layer and RPC.
- Presentation Layer and compression.
- Symmetric vs Asymmetric cryptography.
- Hashing and Digital Signature.
- FTP, Email and Application Layer services.
- Basic Internet architecture.
Conclusion
Computer Networks becomes much easier when you prepare according to the marks instead of reading the complete textbook repeatedly. Two-mark questions test whether your basic definitions are clear. Five-mark questions test whether you can explain and compare concepts. Ten-mark questions test whether you understand the complete topic and can present it in a structured way.
Use this page for question practice and use the linked 37 Computer Networks chapters whenever you need a deeper explanation. Before the semester exam, practise diagrams, comparisons, protocol flow and important numerical concepts along with these theory answers.
Do not memorise every sentence exactly. Understand the concept first and then practise writing the same idea in clear points. That is usually much easier to remember in the examination hall.
