📖 Definition
The OSI (Open Systems Interconnection) Model is a 7-layer conceptual framework developed by ISO to explain how data moves from one device to another over a network.
It helps in understanding, designing, and troubleshooting networks.
| Layer | Name | Main Function |
|---|---|---|
| 7 | Application | User interaction & network services |
| 6 | Presentation | Data formatting, encryption, compression |
| 5 | Session | Session establishment & management |
| 4 | Transport | Reliable delivery (TCP/UDP, ports) |
| 3 | Network | IP addressing & routing |
| 2 | Data Link | MAC addressing & framing |
| 1 | Physical | Transmission of bits (signals, cables) |
🔝 Application (L7) – Provides services like HTTP, FTP, SMTP
🎨 Presentation (L6) – Encryption (SSL/TLS), format conversion
🔄 Session (L5) – Starts, manages & ends sessions
🚚 Transport (L4) – End-to-end delivery (TCP reliable, UDP fast)
🛣 Network (L3) – Routing using IP addresses
🔗 Data Link (L2) – MAC addressing, framing, switches
🔌 Physical (L1) – Cables, signals, hardware transmission
Sender:
Application → Presentation → Session → Transport → Network → Data Link → Physical
Receiver:
Physical → Data Link → Network → Transport → Session → Presentation → Application
👉 Called Encapsulation & Decapsulation
Standard reference model
Makes troubleshooting easy
Helps identify layer-wise problems
Vendor-neutral framework
👉 All People Seem To Need Data Processing
(Application → Presentation → Session → Transport → Network → Data Link → Physical)
Answer:
The OSI model is a 7-layer conceptual framework that defines how data moves from one device to another over a network. It helps in understanding and troubleshooting networking problems.
Answer:
Layer 3 – Network Layer.
It uses IP addresses and routers to forward packets.
Answer:
Layer 2 – Data Link Layer.
Answer:
Transport layer ensures reliable delivery using port numbers (TCP/UDP), while Network layer handles routing using IP addresses.
Answer:
Physical Layer issue (Layer 1 problem).
