OSI Reference Model - Define Open Systems Interconnection Model (MCQ)

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  Category:  NETWORKING | 9th July 2025, Wednesday

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What Is OSI Model?

The OSI Model (Open Systems Interconnection Model) Is A conceptual Framework That Explains how Data Travels From One Computer To Another In A Network.

It divides The Process Of Communication Between Two Devices Into 7 Different Layers, Where each Layer Has A Specific Task.

This Model Was Developed By The International Organization For Standardization (ISO) To Help standardize Networking Protocols.

Why OSI Model?

  • To standardize Communication Between Different Devices & Systems.

  • To understand Network Functions Clearly.

  • To design And Troubleshoot Networks Effectively.

7 Layers Of OSI Model (Mnemonic: All People Seem To Need Data Processing)

Layer Number Layer Name Purpose (in Simple Words)
7 Application Layer User-facing Layer: Apps Like Browser, Email, Etc.
6 Presentation Layer Formats, Encrypts, Compresses Data (like Translation).
5 Session Layer Manages Sessions (like Login Sessions).
4 Transport Layer Ensures Reliable Data Delivery (TCP/UDP Protocols).
3 Network Layer Handles Routing & Addressing (IP Addresses).
2 Data Link Layer Handles Data Frames, MAC Addresses, Error Detection.
1 Physical Layer Transmits Raw Bits Via Cables, Wi-Fi, Etc.

Detailed Explanation Of Each Layer:

1. Physical Layer (Layer 1)

  • Transfers raw Bits Over Physical Medium.

  • Includes: Cables, Switches, Hubs, Wi-Fi Signals.

  • Example: Ethernet Cables, Fiber Optics.

2. Data Link Layer (Layer 2)

  • Converts Bits Into frames.

  • Adds MAC Addresses (hardware Address).

  • Responsible For error Detection And flow Control.

  • Example: Ethernet, Wi-Fi (IEEE 802.11).

3. Network Layer (Layer 3)

  • Handles IP Addresses And Routing Of Packets Between Devices.

  • Breaks Data Into packets And Decides best Route.

  • Example: Internet Protocol (IP), Routers.

4. Transport Layer (Layer 4)

  • Responsible For end-to-end Communication.

  • Ensures reliable Data Transfer Using Protocols Like:

    • TCP (Transmission Control Protocol) → Reliable.

    • UDP (User Datagram Protocol) → Fast But Unreliable.

  • Splits Data Into segments.

5. Session Layer (Layer 5)

  • Manages sessions (like Logging In & Maintaining Connections).

  • Handles Opening, Managing, And Closing Sessions.

  • Example: Remote Procedure Calls (RPC), NetBIOS.

6. Presentation Layer (Layer 6)

  • Ensures Data Is In A readable Format.

  • Handles data Encryption, Compression, Translation.

  • Example: SSL/TLS (encryption), JPEG (compression).

7. Application Layer (Layer 7)

  • Closest To The User.

  • Provides network Services Directly To Applications.

  • Example: Web Browsers, Email Clients, FTP Apps.

  • Protocols: HTTP, FTP, SMTP, DNS.

Simple Analogy:

Imagine sending A Parcel Via Courier:

  1. Application Layer: You Write The Letter.

  2. Presentation Layer: You Translate It If Needed.

  3. Session Layer: You Decide When To Send/receive.

  4. Transport Layer: You Ensure It’s Securely Packed.

  5. Network Layer: You Find The Best Route To Send It.

  6. Data Link Layer: You Tag It With The Address & Tracking ID.

  7. Physical Layer: Truck Physically Transports It.

Key Points:

  • OSI Model Is A theoretical Model; Not All Real Networks Follow It Exactly.

  • It Helps In network Troubleshooting (e.g., "Is It A Physical Problem Or A Transport Problem?").

  • TCP/IP Model (used In The Internet) Is Simpler With 4 Layers, Derived From OSI.

Common Exam Question:

Q: Why Is The OSI Model Important?
A: It Provides A Standard Way To Design And Troubleshoot Networks By Dividing Communication Into 7 Logical Layers.

1. How Many Layers Are There In The OSI Model?

a) 5
b) 6
c) 7
d) 8
Answer: C) 7

2. Which Layer Is Responsible For End-to-end Communication And Error Recovery?

a) Network
b) Transport
c) Data Link
d) Session
Answer: B) Transport

3. In OSI Model, Encryption And Compression Are Functions Of:

a) Application Layer
b) Presentation Layer
c) Session Layer
d) Network Layer
Answer: B) Presentation Layer

4. Which Layer Is Called The “network Layer”?

a) Layer 2
b) Layer 3
c) Layer 4
d) Layer 5
Answer: B) Layer 3

5. HTTP, FTP, SMTP Operate At Which OSI Layer?

a) Transport
b) Network
c) Application
d) Session
Answer: C) Application

6. Which Layer Breaks Data Into Packets And Handles Routing?

a) Data Link
b) Transport
c) Network
d) Session
Answer: C) Network

7. MAC Address Is Used In Which Layer?

a) Data Link
b) Network
c) Physical
d) Application
Answer: A) Data Link

8. The Physical Layer Is Mainly Concerned With:

a) Logical Addressing
b) Encryption
c) Transmission Of Raw Bits
d) Routing
Answer: C) Transmission Of Raw Bits

9. Which Layer Provides Services Directly To User Applications?

a) Network
b) Session
c) Presentation
d) Application
Answer: D) Application

10. TCP And UDP Operate At Which OSI Layer?

a) Application
b) Transport
c) Network
d) Data Link
Answer: B) Transport

11. Which Layer Handles Session Establishment And Termination?

a) Application
b) Session
c) Presentation
d) Transport
Answer: B) Session

12. Which Layer Performs Data Translation And Formatting?

a) Presentation
b) Network
c) Session
d) Application
Answer: A) Presentation

13. What Does The Data Link Layer Provide?

a) Logical Addressing
b) Reliable Transmission Between Two Devices
c) Packet Switching
d) Data Compression
Answer: B) Reliable Transmission Between Two Devices

14. Which Of The Following Is NOT A Function Of The OSI Transport Layer?

a) Flow Control
b) Error Detection
c) Routing
d) Segmentation
Answer: C) Routing

15. The Lowest Layer Of OSI Model Is:

a) Data Link
b) Network
c) Physical
d) Session
Answer: C) Physical

16. Which Of The Following Layers Is Responsible For Path Determination And Logical Addressing?

a) Application
b) Network
c) Presentation
d) Physical
Answer: B) Network

17. Which Layer Converts Data Into Signals For Transmission?

a) Transport
b) Data Link
c) Physical
d) Network
Answer: C) Physical

18. Which Layer Ensures Reliable Data Transfer Using Acknowledgments?

a) Data Link
b) Network
c) Transport
d) Application
Answer: C) Transport

19. Ethernet Operates Mainly At Which Layers?

a) Physical & Data Link
b) Data Link & Network
c) Network & Transport
d) Application & Presentation
Answer: A) Physical & Data Link

20. IP Operates At Which OSI Layer?

a) Network
b) Data Link
c) Transport
d) Application
Answer: A) Network

21. Flow Control Is Mainly A Function Of:

a) Transport Layer
b) Physical Layer
c) Network Layer
d) Session Layer
Answer: A) Transport Layer

22. Which Layer Creates Frames From Packets?

a) Data Link
b) Network
c) Transport
d) Application
Answer: A) Data Link

23. SSL/TLS Security Protocols Work At Which OSI Layer?

a) Transport
b) Session
c) Presentation
d) Application
Answer: C) Presentation

24. Which Layer Is Responsible For Media Access Control?

a) Transport
b) Data Link
c) Network
d) Application
Answer: B) Data Link

25. DNS (Domain Name System) Works At Which Layer?

a) Application
b) Network
c) Data Link
d) Transport
Answer: A) Application

26. Which Layer Identifies Devices Using MAC Addresses?

a) Network
b) Physical
c) Data Link
d) Transport
Answer: C) Data Link

27. In Which Layer Do We Perform Packet Forwarding And Routing?

a) Data Link
b) Network
c) Transport
d) Session
Answer: B) Network

28. Which Layer Is Concerned With Establishing, Maintaining, And Ending Connections?

a) Session
b) Application
c) Data Link
d) Network
Answer: A) Session

29. Compression Is Performed At Which OSI Layer?

a) Session
b) Presentation
c) Application
d) Transport
Answer: B) Presentation

30. Which Layer Handles Dialog Control Between Devices?

a) Network
b) Session
c) Presentation
d) Data Link
Answer: B) Session

Tags:
Open Systems Interconnection Model, OSI Reference Model, MCQ

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