Introduction to Computer Networks

Introduction to Computer Networks

Computer Networks enable communication between devices. Understanding network concepts is essential for GATE CS.

What is a Computer Network?

Computer Network is a collection of interconnected devices that can share resources and communicate.

Purpose:

• Resource sharing
• Communication
• Data exchange
• Remote access

Network Types

1. LAN (Local Area Network)

• Small geographic area
• High speed
• Example: Office network

2. MAN (Metropolitan Area Network)

• City-wide coverage
• Medium speed
• Example: City-wide network

3. WAN (Wide Area Network)

• Large geographic area
• Lower speed
• Example: Internet

4. PAN (Personal Area Network)

• Very small area
• Personal devices
• Example: Bluetooth

Network Topologies

1. Bus Topology

• Single cable (bus)
• All devices connected to bus
• Simple but single point of failure

2. Star Topology

• Central hub/switch
• All devices connected to center
• Easy to manage, hub failure affects all

3. Ring Topology

• Circular connection
• Data travels in one direction
• Token passing

4. Mesh Topology

• Every device connected to every other
• Full mesh: n(n-1)/2 links
• Partial mesh: fewer links

5. Tree Topology

• Hierarchical structure
• Root and branches
• Scalable

OSI Model

OSI (Open Systems Interconnection) model has 7 layers:

Layer 1: Physical Layer

• Transmits raw bits
• Hardware: cables, hubs
• Functions: Bit transmission, encoding

Layer 2: Data Link Layer

• Error detection/correction
• Framing
• MAC addressing
• Hardware: Switches, bridges
• Functions: Framing, error control, flow control

Layer 3: Network Layer

• Routing
• Logical addressing (IP)
• Hardware: Routers
• Functions: Routing, forwarding, fragmentation

Layer 4: Transport Layer

• End-to-end communication
• Segmentation
• Error recovery
• Functions: TCP, UDP

Layer 5: Session Layer

• Session management
• Synchronization
• Functions: Establish, manage, terminate sessions

Layer 6: Presentation Layer

• Data translation
• Encryption/decryption
• Compression
• Functions: Data format conversion

Layer 7: Application Layer

• User interface
• Network services
• Functions: HTTP, FTP, SMTP

TCP/IP Model

TCP/IP model has 4 layers:

1. Network Interface Layer

• Physical and data link
• Corresponds to OSI layers 1-2

2. Internet Layer

• Routing
• IP protocol
• Corresponds to OSI layer 3

3. Transport Layer

• TCP, UDP
• Corresponds to OSI layer 4

4. Application Layer

• Applications
• Corresponds to OSI layers 5-7

Protocol

Protocol is a set of rules for communication.

Examples:

• HTTP: Web browsing
• FTP: File transfer
• SMTP: Email
• TCP: Reliable transport
• UDP: Unreliable transport
• IP: Internet protocol

GATE CS Weightage

Computer Networks typically accounts for:

• 8-12 marks out of 100 in GATE CS
• Medium priority subject
• Requires understanding of protocols and layers

Important Topics for GATE CS

1. OSI/TCP-IP Models (High Priority)

• Layer functions
• Protocol mapping

1. Network Layer (High Priority)

• IP addressing
• Routing algorithms

1. Transport Layer (High Priority)

• TCP, UDP
• Flow control, congestion control

1. Data Link Layer (Medium Priority)

• Error detection
• MAC protocols

1. Application Layer (Medium Priority)

• HTTP, DNS
• Application protocols