OSI Model & TCP/IP Model

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🌐 OSI Model & TCP/IP Model

Networking models explain how data travels from one computer to another in layers.

🧱 OSI Model (Open Systems Interconnection)

👉 Developed by ISO.
👉 Has 7 Layers.

🔹 OSI 7 Layers (Top to Bottom)

7️⃣ Application Layer

👉 User interacts with network.

Examples:

  • HTTP

  • FTP

  • SMTP

6️⃣ Presentation Layer

👉 Data formatting and security.

Functions:

  • Encryption

  • Compression

  • Translation

5️⃣ Session Layer

👉 Manages sessions.

Functions:

  • Session setup

  • Control

  • Termination

4️⃣ Transport Layer

👉 End-to-end delivery.

Protocols:

  • TCP

  • UDP

Functions:

  • Flow control

  • Error control

3️⃣ Network Layer

👉 Routing and addressing.

Protocols:

  • IP

  • ICMP

Devices:

  • Router

2️⃣ Data Link Layer

👉 Node to node delivery.

Functions:

  • Framing

  • MAC addressing

  • Error detection

Devices:

  • Switch

1️⃣ Physical Layer

👉 Actual transmission.

Examples:

  • Cable

  • Signals

  • Voltage

Devices:

  • Hub

🧠 Memory Trick (Top → Bottom)

👉 All People Seem To Need Data Processing

🌍 TCP/IP Model

👉 Developed by DARPA.
👉 Has 4 Layers.

🔹 TCP/IP Layers

4️⃣ Application Layer

👉 Combines OSI’s top layers.

Protocols:

  • HTTP

  • FTP

  • SMTP

  • DNS

3️⃣ Transport Layer

👉 Data transfer.

Protocols:

  • TCP

  • UDP

2️⃣ Internet Layer

👉 Routing.

Protocols:

  • IP

  • ICMP

  • ARP

1️⃣ Network Access Layer

👉 Hardware + data link.

Includes:

  • Ethernet

  • MAC

🔹 Difference Between OSI & TCP/IP

OSI ModelTCP/IP Model
7 Layers4 Layers
TheoreticalPractical
ISO developedDARPA developed
Used for teachingUsed in real networks

🔹 OSI to TCP/IP Mapping

OSITCP/IP
ApplicationApplication
PresentationApplication
SessionApplication
TransportTransport
NetworkInternet
Data LinkNetwork Access
PhysicalNetwork Access

🔹 Important Exam Points

  • OSI has 7 layers.

  • TCP/IP has 4 layers.

  • TCP works at transport layer.

  • IP works at network layer.

  • OSI is reference model.

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