📘 PAPER 6 – DATA COMMUNICATION & NETWORKS ( UNIT 5 – APPLICATION LAYER & NETWORK APPLICATIONS )

 

🔴 UNIT 5 – APPLICATION LAYER & NETWORK APPLICATIONS

---

🟦 1. Application Layer – Introduction

✅ Definition

The Application Layer is the topmost layer of the OSI model.
It provides services directly to the user.

👉 It acts as an interface between:

• User

• Network

---

🟦 2. Functions of Application Layer

✔ File transfer
✔ Email communication
✔ Remote login
✔ Web browsing
✔ Network management

---

🟦 3. Application Layer Protocols

---

🔹 1. FTP (File Transfer Protocol)

Purpose:

Used to transfer files between client and server.

Features:

✔ Reliable
✔ Uses TCP
✔ Supports upload & download

Ports:

• Port 21 → Control

• Port 20 → Data

---

🔹 2. TFTP (Trivial File Transfer Protocol)

Features:

✔ Simpler than FTP
✔ Uses UDP
✔ No authentication
❌ Less secure

---

🔹 3. SMTP (Simple Mail Transfer Protocol)

Purpose:

Used to send emails

Characteristics:

✔ Push protocol
✔ Works on TCP
✔ Port 25

---

🔹 4. POP3 (Post Office Protocol)

Purpose:

Used to receive emails

Features:

✔ Downloads mail
✔ Deletes mail from server

---

🔹 5. IMAP (Internet Message Access Protocol)

Difference from POP:

✔ Emails remain on server
✔ Can access from multiple devices

---

🔹 6. HTTP (Hyper Text Transfer Protocol)

Used for:

✔ Web browsing
✔ Communication between browser and server

Features:

✔ Stateless
✔ Uses TCP
✔ Port 80

---

🔹 7. HTTPS

Secure version of HTTP

Uses:
✔ SSL / TLS encryption
✔ Port 443

---

🟦 4. DNS (Domain Name System)

Definition:

DNS converts:

Domain Name → IP Address

Example:

www.google.com → 142.250.192.14

---

DNS Hierarchy:

1. Root Server

2. TLD Server

3. Authoritative Server

---

🟦 5. SNMP (Simple Network Management Protocol)

Purpose:

Used to manage and monitor network devices.

Components:

✔ Manager
✔ Agent
✔ MIB

---

🟦 6. TELNET

Definition:

Allows remote login to another computer.

❌ Not secure
✔ Replaced by SSH

---

🟦 7. Network Applications

Common Applications:

✔ Email
✔ File sharing
✔ Video conferencing
✔ Web browsing
✔ Cloud services

---

🟦 8. Client–Server Model

Client:

Requests services

Server:

Provides services

Example:
Browser → Web Server

---

🟦 9. Peer-to-Peer Network

Features:

✔ No central server
✔ Each node is client & server
✔ Used in file sharing

---

🟦 10. Internet & Public Networks

Internet:

Global network of networks

Public Network:

Accessible by all users

---

📌 EXAM IMPORTANT QUESTIONS (UNIT 5)

✔ Explain FTP, SMTP, POP, IMAP
✔ Difference between HTTP & HTTPS
✔ DNS working
✔ Application layer protocols
✔ Client-server vs P2P
✔ SNMP explanation

📘 PAPER 6 – DATA COMMUNICATION & NETWORKS (UNIT 4 – TRANSPORT, SESSION & PRESENTATION LAYERS)

 

🔴 UNIT 4 – TRANSPORT, SESSION & PRESENTATION LAYERS

---

🟦 PART A: TRANSPORT LAYER

---

1️⃣ Transport Layer – Introduction

✅ Definition

The Transport Layer is responsible for:
✔ End-to-end communication
✔ Reliable data transfer
✔ Flow control
✔ Error control

It works between:
➡ Application Layer and Network Layer

---

2️⃣ Functions of Transport Layer

✔ Segmentation & Reassembly
✔ Service point addressing (Port numbers)
✔ Flow control
✔ Error control
✔ Connection control

---

3️⃣ Transport Layer Protocols

🔹 1. TCP (Transmission Control Protocol)

Features:

✔ Connection-oriented
✔ Reliable
✔ Error-free transmission
✔ Flow control
✔ Congestion control

---

TCP Services:

• Sequencing

• Acknowledgment

• Retransmission

• Full-duplex communication

---

TCP Header Contains:

• Source port

• Destination port

• Sequence number

• Acknowledgment number

• Flags

• Window size

---

4️⃣ TCP Connection Management

🔹 Three-Way Handshake

1️⃣ SYN →
2️⃣ SYN + ACK →
3️⃣ ACK →

✔ Connection established

---

🔹 Connection Termination

Uses:

• FIN

• ACK

---

5️⃣ UDP (User Datagram Protocol)

Features:

✔ Connectionless
✔ Fast
✔ No error checking
✔ No flow control

---

Used In:

• Video streaming

• Online games

• Voice calls

---

6️⃣ TCP vs UDP

TCP	UDP
Reliable	Unreliable
Connection-oriented	Connectionless
Slower	Faster
Error control	No error control
Used for emails	Used for video

---

🟦 PART B: SESSION LAYER

---

7️⃣ Session Layer – Introduction

Definition:

Session layer manages:
✔ Session establishment
✔ Session maintenance
✔ Session termination

---

Functions:

• Dialog control

• Synchronization

• Session checkpointing

---

Example:

✔ Video conferencing
✔ Online login sessions

---

🟦 PART C: PRESENTATION LAYER

---

8️⃣ Presentation Layer – Introduction

Definition:

Presentation layer is responsible for:
✔ Data formatting
✔ Encryption
✔ Compression

---

Functions:

---

🔹 1. Data Translation

Converts data format (ASCII, EBCDIC)

---

🔹 2. Encryption

Provides security

---

🔹 3. Compression

Reduces data size

---

9️⃣ Encryption Techniques

🔹 Symmetric Encryption

• Same key for encryption & decryption

• Example: AES

---

🔹 Asymmetric Encryption

• Public key + Private key

• Example: RSA

---

🔟 Comparison of Layers

Layer	Main Function
Transport	End-to-end delivery
Session	Session control
Presentation	Data formatting & security

---

📌 EXAM IMPORTANT QUESTIONS (UNIT 4)

✔ Explain TCP/IP
✔ TCP vs UDP
✔ Three-way handshake
✔ Functions of session layer
✔ Functions of presentation layer
✔ Encryption techniques

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

 

🔴 UNIT 3 – NETWORK LAYER

---

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.

---

2️⃣ Functions of Network Layer

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

---

3️⃣ Network Layer Services

🔹 Connection-Oriented Service

• Establishes connection before transmission

• Reliable

• Example: Virtual circuits

---

🔹 Connectionless Service

• No prior connection

• Fast but unreliable

• Example: Internet (IP)

---

4️⃣ Routing

✅ Definition

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

---

5️⃣ Types of Routing

---

🔹 1. Static Routing

• Fixed routes

• Manually configured

• Used in small networks

---

🔹 2. Dynamic Routing

• Routes change automatically

• Uses routing algorithms

---

6️⃣ Routing Algorithms

---

🔹 1. Distance Vector Routing

Features:

• Based on distance and direction

• Uses Bellman-Ford algorithm

Example:

RIP (Routing Information Protocol)

---

Problems:

❌ Count to infinity
❌ Slow convergence

---

🔹 2. Link State Routing

Features:

• Each node knows full topology

• Uses Dijkstra’s algorithm

Example:

OSPF (Open Shortest Path First)

---

Advantages:

✔ Fast
✔ Accurate

---

7️⃣ Congestion Control

✅ Definition

Congestion occurs when:

Network traffic exceeds capacity.

---

Causes:

• Too many packets

• Limited bandwidth

• Slow routers

---

Congestion Control Techniques:

---

🔹 Open Loop

• Prevent congestion

• No feedback

Examples:
✔ Traffic shaping
✔ Admission control

---

🔹 Closed Loop

• Detect & correct congestion

• Uses feedback

Examples:
✔ Backpressure
✔ Choke packet

---

8️⃣ Internetworking

Definition:

Connecting multiple networks together to form the Internet.

---

Devices Used:

• Router

• Gateway

• Bridge

---

9️⃣ Internet Protocol (IP)

✅ IP

Responsible for:

• Logical addressing

• Packet delivery

---

🔹 IPv4 Address

• 32-bit address

• Written in dotted decimal

• Example: 192.168.1.1

---

IPv4 Classes

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

---

🔹 IPv6

Features:

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

---

Example:

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

---

🔟 Difference Between IPv4 and IPv6

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

---

📌 EXAM IMPORTANT QUESTIONS (UNIT 3)

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

📘 PAPER 6 – DATA COMMUNICATION & NETWORKS (UNIT 2 – DATA LINK LAYER & MEDIUM ACCESS CONTROL) university of allahabad

 

🔴 UNIT 2 – DATA LINK LAYER & MEDIUM ACCESS CONTROL

---

1️⃣ Data Link Layer – Introduction

✅ Definition

The Data Link Layer is the second layer of the OSI model.
It is responsible for reliable data transfer between two directly connected nodes.

---

✅ Main Functions

✔ Framing
✔ Error control
✔ Flow control
✔ Access control
✔ Physical addressing

---

2️⃣ Framing

🔹 Definition

Framing divides the data stream into manageable units called frames.

---

🔹 Methods of Framing

1. Character Count

• Frame size specified in header
  ❌ Error-prone

---

2. Byte Stuffing

• Special character added to data
  ✔ Used in HDLC

---

3. Bit Stuffing

• Extra bit inserted after 5 consecutive 1s
  ✔ Used in modern networks

---

3️⃣ Error Detection Techniques

---

🔹 1. Parity Check

• Adds 1 parity bit

• Detects single-bit error

---

🔹 2. Checksum

• Sum of data bits

• Used in TCP/IP

---

🔹 3. Cyclic Redundancy Check (CRC)

• Most powerful method

• Uses polynomial division

✔ Highly reliable
✔ Widely used

---

4️⃣ Error Control

Error control ensures reliable data delivery.

Methods:

✔ Error detection
✔ Error correction
✔ Retransmission

---

5️⃣ Flow Control

Definition:

Controls the amount of data sent to avoid receiver overflow.

---

Methods:

1. Stop-and-Wait

2. Sliding Window

---

6️⃣ Sliding Window Protocol

Types:

---

🔹 1. Stop-and-Wait ARQ

• Send one frame

• Wait for ACK

• Simple but slow

---

🔹 2. Go-Back-N ARQ

• Sends multiple frames

• Retransmits all frames after error

---

🔹 3. Selective Repeat ARQ

• Retransmits only erroneous frame

• Efficient but complex

---

7️⃣ Medium Access Control (MAC)

Definition:

MAC controls who can transmit data on shared medium.

---

8️⃣ Channel Allocation Methods

---

🔹 1. Static Channel Allocation

• Fixed bandwidth

• Inefficient for bursty traffic

---

🔹 2. Dynamic Channel Allocation

• Bandwidth allocated as needed

• Used in LANs

---

9️⃣ Multiple Access Protocols

---

🔹 ALOHA Protocol

Types:

1. Pure ALOHA

2. Slotted ALOHA

---

Pure ALOHA

• Send anytime

• High collision

• Low efficiency (~18%)

---

Slotted ALOHA

• Time divided into slots

• Higher efficiency (~36%)

---

🔹 CSMA (Carrier Sense Multiple Access)

Types:

1️⃣ CSMA/CD (Collision Detection)

• Used in Ethernet

• Detects collision and stops transmission

---

2️⃣ CSMA/CA (Collision Avoidance)

• Used in Wi-Fi

• Avoids collision before transmitting

---

1️⃣0️⃣ IEEE Standards

Standard	Description
IEEE 802.3	Ethernet
IEEE 802.11	Wi-Fi
IEEE 802.5	Token Ring
IEEE 802.15	Bluetooth

---

1️⃣1️⃣ Data Link Layer Protocols

✔ HDLC
✔ PPP
✔ Ethernet

---

📌 EXAM IMPORTANT QUESTIONS (UNIT 2)

✔ Explain Data Link Layer
✔ Framing techniques
✔ Sliding Window Protocol
✔ ALOHA vs CSMA
✔ Error detection methods
✔ CRC explanation

📘 PAPER 6 – DATA COMMUNICATION & NETWORKS (UNIT 1 – INTRODUCTION & PHYSICAL LAYER) university of allahabad

 

📘 PAPER 6 – DATA COMMUNICATION & NETWORKS

🔴 UNIT 1 – INTRODUCTION & PHYSICAL LAYER

---

1️⃣ Introduction to Data Communication

✅ Definition

Data Communication is the process of transferring data from one device to another using a transmission medium.

---

Components of Data Communication

1. Sender

2. Receiver

3. Message

4. Transmission Medium

5. Protocol

---

Characteristics of Data Communication

✔ Delivery
✔ Accuracy
✔ Timeliness
✔ Jitter-free communication

---

2️⃣ Goals of Computer Networks

✔ Resource sharing
✔ Communication
✔ Reliability
✔ Cost reduction
✔ Scalability

---

3️⃣ Network Structure & Architecture

Network Architecture:

Defines how network is designed and how devices communicate.

---

4️⃣ OSI Reference Model

OSI has 7 Layers

Layer	Name	Function
7	Application	User interface
6	Presentation	Encryption
5	Session	Session control
4	Transport	Reliable delivery
3	Network	Routing
2	Data Link	Framing
1	Physical	Transmission

---

👉 Exam Tip:

Remember as:
A-P-S-T-N-D-P

---

5️⃣ Services Provided by OSI Model

✔ Data transmission
✔ Error control
✔ Flow control
✔ Connection management

---

6️⃣ Network Topologies

🔹 1. Bus Topology

• Single cable

• Low cost

• Difficult troubleshooting

---

🔹 2. Star Topology

• Central hub

• Easy maintenance

• High reliability

---

🔹 3. Ring Topology

• Circular connection

• Data flows in one direction

---

🔹 4. Mesh Topology

• Each node connected to every other

• High cost

• Highly reliable

---

7️⃣ Network Design

Network Design Factors:

✔ Delay
✔ Bandwidth
✔ Cost
✔ Reliability

---

8️⃣ Physical Layer

Functions:

✔ Bit transmission
✔ Electrical specifications
✔ Data rate control

---

9️⃣ Transmission Media

---

🔹 Guided Media

1. Twisted Pair Cable

• UTP

• STP
  ✔ Cheap
  ❌ Noise sensitive

---

2. Coaxial Cable

✔ Better shielding
✔ Used in cable TV

---

3. Optical Fiber

✔ High speed
✔ Long distance
✔ Secure

---

🔹 Unguided Media

✔ Radio waves
✔ Microwave
✔ Infrared

---

🔟 Switching Techniques

---

🔹 Circuit Switching

• Dedicated path

• Used in telephone network

---

🔹 Packet Switching

• Data divided into packets

• Used in Internet

---

🔹 Message Switching

• Store and forward technique

• Not used now

---

📌 EXAM IMPORTANT QUESTIONS (UNIT 1)

✔ OSI model with diagram
✔ Transmission media
✔ Network topology
✔ Switching techniques
✔ Physical layer functions