📘 PAPER 6 – DATA COMMUNICATION & NETWORKS (UNIT 3 – NETWORK LAYER) university of allahabad

 

🔴 UNIT 3 – NETWORK LAYER

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1️⃣ Network Layer – Introduction

✅ Definition

The Network Layer is responsible for:

• Routing packets

• Logical addressing

• Path selection

• Congestion control

👉 It ensures data reaches the correct destination network.

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2️⃣ Functions of Network Layer

✔ Logical addressing
✔ Routing
✔ Packet forwarding
✔ Congestion control
✔ Internetworking

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3️⃣ Network Layer Services

🔹 Connection-Oriented Service

• Establishes connection before transmission

• Reliable

• Example: Virtual circuits

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🔹 Connectionless Service

• No prior connection

• Fast but unreliable

• Example: Internet (IP)

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4️⃣ Routing

✅ Definition

Routing is the process of selecting the best path to transfer data from source to destination.

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5️⃣ Types of Routing

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🔹 1. Static Routing

• Fixed routes

• Manually configured

• Used in small networks

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🔹 2. Dynamic Routing

• Routes change automatically

• Uses routing algorithms

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6️⃣ Routing Algorithms

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🔹 1. Distance Vector Routing

Features:

• Based on distance and direction

• Uses Bellman-Ford algorithm

Example:

RIP (Routing Information Protocol)

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Problems:

❌ Count to infinity
❌ Slow convergence

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🔹 2. Link State Routing

Features:

• Each node knows full topology

• Uses Dijkstra’s algorithm

Example:

OSPF (Open Shortest Path First)

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Advantages:

✔ Fast
✔ Accurate

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7️⃣ Congestion Control

✅ Definition

Congestion occurs when:

Network traffic exceeds capacity.

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Causes:

• Too many packets

• Limited bandwidth

• Slow routers

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Congestion Control Techniques:

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🔹 Open Loop

• Prevent congestion

• No feedback

Examples:
✔ Traffic shaping
✔ Admission control

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🔹 Closed Loop

• Detect & correct congestion

• Uses feedback

Examples:
✔ Backpressure
✔ Choke packet

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8️⃣ Internetworking

Definition:

Connecting multiple networks together to form the Internet.

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Devices Used:

• Router

• Gateway

• Bridge

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9️⃣ Internet Protocol (IP)

✅ IP

Responsible for:

• Logical addressing

• Packet delivery

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🔹 IPv4 Address

• 32-bit address

• Written in dotted decimal

• Example: 192.168.1.1

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IPv4 Classes

Class	Range
A	1–126
B	128–191
C	192–223
D	Multicast
E	Experimental

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🔹 IPv6

Features:

✔ 128-bit address
✔ Larger address space
✔ Better security
✔ No NAT needed

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Example:

2001:0db8:85a3::8a2e:0370:7334

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🔟 Difference Between IPv4 and IPv6

IPv4	IPv6
32-bit	128-bit
Limited addresses	Large address space
NAT required	No NAT
Less secure	More secure

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📌 EXAM IMPORTANT QUESTIONS (UNIT 3)

✔ Explain Network Layer
✔ Routing algorithms
✔ Difference between distance vector & link state
✔ Congestion control
✔ IPv4 vs IPv6
✔ IP addressing