OSI Model

✍️ OSI Model — Layers Explanation

✅ OSI Model क्या है

OSI (Open Systems Interconnection) model networking communication को 7 layers में divide करता है ताकि data transmission व्यवस्थित तरीके से हो सके।

---

🔵 1️⃣ Physical Layer (Layer 1)

✔ Function

Data को bits (0,1) में transmit करना

Electrical signals / cables / hardware

✔ Examples

Cable, Hub, Repeater

👉 यह hardware layer है।

---

🔵 2️⃣ Data Link Layer (Layer 2)

✔ Function

Error detection

Framing

MAC addressing

✔ Examples

Switch, Ethernet

👉 Reliable node-to-node communication।

---

🔵 3️⃣ Network Layer (Layer 3)

✔ Function

Routing

Logical addressing (IP address)

Path selection

✔ Examples

Router, IP protocol

👉 Best path decide करता है।

---

🔵 4️⃣ Transport Layer (Layer 4)

✔ Function

End-to-end delivery

Error control

Flow control

Segmentation

✔ Examples

TCP, UDP

👉 Reliable communication सुनिश्चित करता है।

---

🔵 5️⃣ Session Layer (Layer 5)

✔ Function

Session establish, maintain, terminate

Synchronization

👉 Devices के बीच connection manage करता है।

---

🔵 6️⃣ Presentation Layer (Layer 6)

✔ Function

Data format conversion

Encryption / Decryption

Compression

👉 Data को readable format में बदलता है।

---

🔵 7️⃣ Application Layer (Layer 7)

✔ Function

User services

Network applications

✔ Examples

HTTP, FTP, SMTP, Email, Browser

👉 User interaction layer।

---

✅ Data Flow (Exam Concept)

Application → Presentation → Session → Transport → Network → Data Link → Physical

(Receiving side पर reverse)

---

✅ Mnemonic (Exam Trick)

⭐ Please Do Not Throw Sausage Pizza Away

---

✅ Conclusion

OSI model communication को modular बनाता है, troubleshooting आसान करता है और networking standards define करता है।

---