Computer Networks

Introduction

• Objective: Coverage of key points for semester exams
• Syllabus: Study of syllabi from various colleges and universities
• Topic: Coverage from the beginning to the end of computer networks
• Key Topics: ISDN, checksum, error checking, Ethernet, data link layer, application layer, Telnet, IGMP, etc.

Computer Networks

Definition

• Computer Network: A telecommunications network that allows autonomous digital devices to exchange data through wired or wireless means.
• Autonomous: Separate devices, no direct dependency.
• Resource: Hardware (printer), software (drive), etc.
• Diagram: Network connection of devices like printer, laptop, modem, router, etc.

Goal of Networks

1. Communication: Email, message, video conferencing
2. Resource Sharing: Files, data
3. Centralized Database: Centralized data storage
4. Cost Efficiency: Server access instead of multiple copies
5. Reliability: Better efficiency and reliability

Application

1. Business & Commerce: Online classes, meetings
2. Healthcare: Video consultation, robotic surgery
3. Governance: Aadhaar, PAN, digital wallet, etc.
4. Entertainment: Theater, hotel booking, online movies
5. Education: Online learning platforms

Data Communication

• Definition: Data exchange between two devices through a transmission medium
• Components:
  • Message: Data
  • Sender: Sends data
  • Receiver: Receives data
  • Transmission Medium: Wired or wireless medium
  • Protocols: Communication rules and regulations

Transmission Modes

1. Simplex: One-way communication
2. Half Duplex: Data communication in one direction at a time
3. Full Duplex: Simultaneous communication in both directions

Network Criteria

1. Delivery & Accuracy: Correct destination, error-free data
2. Performance: Data speed, bandwidth
3. Reliability: Network downtime, failure handling
4. Security: Protection of sensitive information

Types of Connections

1. Point-to-Point: Direct connection
2. Multi-Point: Multiple nodes connected in a shared medium

Topology

1. Mesh Topology: Every device connected to every other device
2. Star Topology: Connection through a central hub
3. Bus Topology: Connection through a central link
4. Ring Topology: Devices connected in a circular fashion
5. Hybrid Topology: Mixture of multiple topologies

Network Model

• OSI Model: Seven-layer model proposed by ISO
• Layered Architecture: Duties of each layer defined
• Key Layers:
  • Physical Layer: Representation of bits, data transmission rate, line configuration
  • Data Link Layer: Framing, physical addressing, flow control, error control
  • Network Layer: Logical addressing, routing
  • Transport Layer: Port addressing, segmentation and reassembly, Transmission Control Protocol (TCP)
  • Session Layer: Dialogue control, session establishment
  • Presentation Layer: Translation, encryption, data compression
  • Application Layer: High-level services, file transfer, email, virtual terminal

Transmission Medium

• Wired:
  • Twisted Pair Cable: Used in LAN and internet connections
  • Coaxial Cable: Cable TV connection
  • Optical Fiber: Long-distance communication
• Wireless:
  • Ground Propagation: FM radio, short distance
  • Sky Propagation: AM radio, long distance
  • Line of Sight Propagation: TV remote, short range
  • Spectrum: Radio waves, microwaves, infrared

Switching Methods

1. Circuit Switching: Establishing a physical connection
2. Packet Switching: Path-divided packet switching
3. Virtual Network: Using the same path

ISDN (Integrated Services Digital Network)

• Introduction: Integrated Services Digital Network
• Protocols: Protocols for circuit-switched connections
• Trend: Now outdated
• Categories: BRI (100-128 kbps), PRI (1.5-2 Mbps)

Data Link Layer

1. MAC (Media Access Control): Ethernet
2. LLC (Logical Link Control): Flow control, error control
3. Access Control Protocols (ALOHA, CSMA/CD, CSMA/CA): Collision detection and avoidance protocols

Flow Control

1. Stop and Wait: Sending one packet at a time
2. Go Back N: Sending multiple packets at a time, retransmitting all upon error
3. Selective Repeat: Retransmitting selected packets

Error Control

1. Parity Check: Single bit error detection
2. Two-Dimensional Parity Check: Two-bit error detection
3. Hamming Code: Single bit error correction
4. Checksum: Data error detection
5. CRC (Cyclic Redundancy Check): Cyclic redundancy check

Ethernet

• Introduction: Proposed by IEEE in 1980
• Physical Organization: Coaxial cables, twisted pair, optical fiber
• Data Rate: 1000 gigabytes per second
• Limitations: No anomaly service, improvements with Wi-Fi

Network Layer

1. Logical Addressing: Unique and universal IP address
2. Routing: Routing tables and algorithms
3. IPv4: 32-bit addressing
4. IPv6: 128-bit addressing
5. ICMP: Error reporting and congestion control

Transport Layer

1. TCP: Transmission Control Protocol, connection-oriented protocol
2. UDP: User Datagram Protocol, connectionless
3. Port Numbering: Service-to-service addressing

Application Layer

1. Email: SMTP, POP3, IMAP, MIME
2. Web-based Email: Operated through HTTP
3. FTP: File Transfer Protocol
4. Telnet: Remote server access protocol
5. IGMP: Internet Group Management Protocol
6. Voice over IP: Voice transmission over Internet Protocol
7. DNS: Domain Name System