COMPUTER NETWORKS
UNIT I & UNIT II – DETAILED POINT-WISE EXAM NOTES
Prepared strictly from the prescribed textbook (Kurose & Ross: Computer Networking – A Top-Down
Approach) and aligned with the TY ETC NEP syllabus. The content is written in clear, professional,
academic language, in point format, while maintaining depth and conceptual completeness. These
notes are suitable for printing and direct exam writing.
UNIT I – INTRODUCTION
1. Computer Networks
• A computer network is an interconnection of multiple autonomous computing devices called hosts
or end systems.
• These devices are connected using communication links and networking devices to exchange data
and share resources.
• The primary goal of computer networking is to enable reliable, efficient, and scalable
communication between geographically distributed systems.
• Computer networks support resource sharing, including hardware resources, software applications,
and data stored on remote systems.
• Networks improve system reliability by providing alternative communication paths in case of failure.
• Scalability is achieved by allowing new devices to be added with minimal impact on existing network
operations.
Applications of Computer Networks
• Electronic mail and instant messaging systems.
• World Wide Web and cloud-based services.
• Video conferencing and multimedia streaming.
• Online gaming and distributed computing.
• File transfer and remote data access.
2. Components of a Computer Network
(A) End Systems (Hosts)
• End systems are devices located at the edge of a network.
• They run application programs and act as the source or destination of data communication.
• Examples include desktop computers, laptops, smartphones, servers, and IoT devices.
• End systems are classified into clients and servers.
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• Clients initiate requests for network services, while servers respond by providing services such as
web pages, email delivery, and file storage.
(B) Network Hardware Devices
Hub
• A hub is a physical layer device.
• It broadcasts incoming data to all connected ports.
• It does not perform filtering, addressing, or error detection.
• The use of hubs increases network collisions and reduces efficiency.
Switch
• A switch operates at the data link layer.
• It forwards frames based on MAC addresses.
• It maintains a MAC address table for efficient forwarding.
• Switches reduce collisions and improve network performance.
Bridge
• A bridge connects multiple LAN segments.
• It filters traffic using MAC addresses.
• Bridges reduce network congestion and collisions.
Repeater
• A repeater is a physical layer device.
• It regenerates and amplifies weakened signals.
• It extends the physical length of a network.
Router
• A router operates at the network layer.
• It uses IP addresses for packet forwarding.
• Routers determine the best path using routing algorithms.
• They connect different independent networks.
Gateway
• A gateway performs protocol conversion.
• It enables communication between dissimilar networks.
Comparison: Hub vs Switch
• Hub operates at the physical layer, whereas a switch operates at the data link layer.
• Hub broadcasts data to all ports, whereas a switch forwards data selectively.
• Hub causes more collisions, whereas a switch minimizes collisions.
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3. Network Software and Protocols
Protocol
• A protocol is a set of rules governing communication between network entities.
• It defines the format of messages, the order of message exchange, and the actions taken upon
transmission or reception.
• Protocols ensure interoperability between devices from different manufacturers.
Standards Organizations
• The Internet Engineering Task Force develops Internet standards and publishes RFCs.
• The IEEE defines standards for LAN and MAN technologies such as Ethernet and Wi-Fi.
4. Types of Networks
Local Area Network (LAN)
• Covers a small geographical area such as a building or campus.
• Provides high data transfer rates and low delay.
Metropolitan Area Network (MAN)
• Covers a city or large campus.
• Interconnects multiple LANs.
Wide Area Network (WAN)
• Covers large geographical areas.
• Connects networks across cities, countries, or continents.
• The Internet is the largest WAN.
5. Switching Techniques
Circuit Switching
• A dedicated physical path is established before data transmission.
• Bandwidth is reserved for the entire duration of communication.
• It provides constant data rate and low delay.
• Communication occurs in three phases: connection establishment, data transfer, and connection
release.
• Example: Traditional telephone network.
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Packet Switching
• Data is divided into small units called packets.
• Packets are transmitted independently over the network.
• Different packets may follow different routes to reach the destination.
• Packet switching ensures efficient bandwidth utilization.
• Example: Internet.
Virtual Circuit Switching
• A logical path is established prior to data transmission.
• All packets follow the same route during communication.
• Combines features of circuit and packet switching.
6. Delay, Loss, and Throughput
Types of Delay
• Processing delay occurs due to packet header examination at routers.
• Queuing delay occurs when packets wait in buffers.
• Transmission delay is the time required to push all packet bits onto the link.
• Propagation delay is the time taken by the signal to travel through the medium.
End-to-End Delay
• Total delay is the sum of processing, queuing, transmission, and propagation delays.
Throughput
• Throughput is the rate at which data is successfully delivered over the network.
• It is measured in bits per second.
7. Layered Architecture
• Layering divides network functionality into manageable components.
• Each layer provides services to the layer above and uses services of the layer below.
• Layered architecture simplifies design, implementation, and troubleshooting.
8. OSI Reference Model
OSI Layers
• Application Layer: Provides network services to end users.
• Presentation Layer: Handles data encryption, decryption, and compression.
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• Session Layer: Manages session establishment and termination.
• Transport Layer: Provides reliable end-to-end communication.
• Network Layer: Performs routing and logical addressing.
• Data Link Layer: Responsible for framing and error detection.
• Physical Layer: Transmits raw bits over the medium.
9. TCP/IP Reference Model
Layers of TCP/IP Model
• Application Layer
• Transport Layer
• Internet Layer
• Network Access Layer
OSI vs TCP/IP
• OSI model consists of seven layers, while TCP/IP consists of four layers.
• OSI is a conceptual model, whereas TCP/IP is a practical implementation.
10. Addressing in Networks
• Physical addressing uses MAC addresses at the data link layer.
• Logical addressing uses IP addresses at the network layer.
• Port addressing identifies specific application processes at the transport layer.
UNIT II – PHYSICAL LAYER
1. Data Communication Concepts
• Data refers to the information to be transmitted from sender to receiver.
• Signals are the physical representation of data.
• Analog signals are continuous, whereas digital signals are discrete.
2. Transmission Media
Guided Transmission Media
Twisted Pair Cable
• Consists of two insulated copper wires twisted together.
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• Low cost and easy to install.
• Widely used in local area networks.
Coaxial Cable
• Consists of a central conductor surrounded by shielding.
• Provides better noise immunity than twisted pair cable.
• Used in cable television and broadband networks.
Optical Fiber Cable
• Transmits data using light signals.
• Provides very high bandwidth and low attenuation.
• Immune to electromagnetic interference.
Unguided Transmission Media
Radio Waves
• Support omni-directional communication.
• Used in radio and television broadcasting.
Microwaves
• Require line-of-sight communication.
• Used in satellite and cellular systems.
Infrared Waves
• Used for short-range communication.
3. Transmission Impairments
• Attenuation refers to the reduction in signal strength.
• Distortion occurs when different frequency components experience different delays.
• Noise refers to unwanted disturbances that degrade signal quality.
4. Performance Parameters
• Bandwidth represents the maximum data-carrying capacity of a channel.
• Throughput represents the actual achieved data rate.
• Latency is the total time taken for data to travel from source to destination.
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5. Transmission Techniques
Parallel Transmission
• Multiple bits are transmitted simultaneously.
• Suitable for short-distance communication.
Serial Transmission
• Bits are transmitted sequentially.
• Suitable for long-distance communication.
6. Numerical Concepts (Delay Analysis)
• Transmission delay is calculated as packet size divided by transmission rate.
• Propagation delay is calculated as distance divided by propagation speed.
• End-to-end delay analysis helps in evaluating network performance.
These notes provide deep, point-wise coverage of Unit I and Unit II as per the TY ETC NEP syllabus and
are suitable for printing and direct use in examinations.
EXAM DIAGRAMS (NEAT, HAND-DRAWABLE)
1. OSI Reference Model Diagram
+------------------+
+------------------+
+------------------+
+------------------+
+------------------+
+------------------+
+------------------+
Application
Presentation
Session
Transport
Network
Data Link
Physical
How to draw in exam: Draw 7 horizontal blocks, label from bottom (Physical) to top (Application).
2. TCP/IP Reference Model Diagram
+------------------+
+------------------+
Application
Transport
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+------------------+
+------------------+
Internet
Network Access
3. Packet Switching vs Circuit Switching Diagram
Circuit Switching
Sender ==== Dedicated Path ==== Receiver
Packet Switching
Sender -> R1 -> R2 -> R3 -> Receiver
-> R4 -> R2 -> R3
4. Network Edge and Core Diagram
Client ---- Access Network ---- Router ---- Core Network ---- Router ---- Server
5. Transmission Media Diagrams
Twisted Pair Cable
~ ~ ~ ~ ~
~ ~ ~ ~ ~
Coaxial Cable
| Insulation |
| Shield
|
| Conductor |
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Optical Fiber
| Cladding |
| Core
|
NUMERICALS (STEP-BY-STEP, EXAM ORIENTED)
1. Transmission Delay
Formula: Transmission Delay = Packet Size / Transmission Rate
Example: - Packet size = 1500 bytes = 12,000 bits - Transmission rate = 2 Mbps = 2 × 10⁶ bps
Solution: Transmission Delay = 12,000 / (2 × 10⁶) = 0.006 seconds = 6 ms
2. Propagation Delay
Formula: Propagation Delay = Distance / Propagation Speed
Example: - Distance = 3000 km = 3 × 10⁶ meters - Propagation speed = 2 × 10⁸ m/s
Solution: Propagation Delay = (3 × 10⁶) / (2 × 10⁸) = 0.015 seconds = 15 ms
3. End-to-End Delay
Formula: End-to-End Delay = Processing + Queuing + Transmission + Propagation
Example: - Processing delay = 2 ms - Queuing delay = 5 ms - Transmission delay = 6 ms - Propagation delay
= 15 ms
Solution: End-to-End Delay = 2 + 5 + 6 + 15 = 28 ms
4. Throughput Calculation
Formula: Throughput = Data Transferred / Time Taken
Example: - Data = 10 MB = 80 Mb - Time = 8 seconds
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Solution: Throughput = 80 / 8 = 10 Mbps
5. Bandwidth vs Throughput (Conceptual Numerical)
• Bandwidth = 100 Mbps
• Achieved throughput = 40 Mbps
Reason: Throughput is lower due to congestion, protocol overhead, and transmission delays.
EXAM TIP (VERY IMPORTANT)
• Always draw diagrams using a ruler.
• Label each part clearly.
• Write formula first in numericals.
• Mention units in final answer.
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