📘 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