---
title: "Tasks done at OSI layers (set 1)"
subject: "Computer Networks and Security"
chapter: 1
key: "semester_7/computer_networks_and_security:osi-layer-task-mapping-1"
source: https://www.bctengineer.com/q/semester_7/computer_networks_and_security/osi-layer-task-mapping-1
site: BCT Engineering
---

# Tasks done at OSI layers (set 1)

Computer Networks and Security · Chapter 1: Introduction to Computer Network

- Asked in: 2072 Chaitra, 3 marks
- Video: [OSI Model Explained | OSI Animation | Open System Interconnection Model | OSI 7 layers | TechTerms](https://www.youtube.com/watch?v=vv4y_uOneC0) — TechTerms
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/computer_networks_and_security/osi-layer-task-mapping-1
- Whole chapter: https://www.bctengineer.com/md/semester_7/computer_networks_and_security/chapter-1

## Question

Explain in which level of the OSI layer the following tasks are done: i) Error detection and correction ii) Encryption and decryption of data iii) Logical identification of computer iv) Point-to-point connection of socket v) Dialogue control vi) Physical identification of computer.

## Short answer

Error detection and correction are done at the data link layer, encryption and decryption at the presentation layer, logical identification at the network layer, point-to-point socket connection at the transport layer, dialogue control at the session layer, and physical identification at the data link layer.

## Answer

| Task | OSI layer |
|---|---|
| i) Error detection and correction | **Data link layer** (CRC, checksum; also done end-to-end at the transport layer) |
| ii) Encryption and decryption of data | **Presentation layer** |
| iii) Logical identification of computer | **Network layer** (IP address) |
| iv) Point-to-point (process-to-process) connection of socket | **Transport layer** (port number and socket address) |
| v) Dialogue control | **Session layer** |
| vi) Physical identification of computer | **Data link layer** (MAC address) |

The data link layer handles both error control for each hop and the MAC (physical) address. The network layer uses a logical address such as an IPv4 address so that a host can be located on any network.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. At which OSI layer are encryption and decryption done?
   A. Session
   B. Application
   C. Presentation
   D. Transport
   Answer: C. Encryption/decryption, translation and compression are presentation layer functions. (Key point: Encryption layer)

2. Which pair is correct?
   A. IP address: data link; MAC address: network
   B. IP address: network; MAC address: data link
   C. IP address: transport; MAC address: network
   D. Both at the physical layer
   Answer: B. Logical (IP) addresses belong to the network layer; physical (MAC) addresses belong to the data link layer. (Key point: Logical vs physical identification)

3. Which layer performs dialogue control?
   A. Session layer
   B. Transport layer
   C. Presentation layer
   D. Physical layer
   Answer: A. The session layer controls who transmits when (dialog control) and synchronization. (Key point: Dialogue control)

## Related in Computer Networks and Security

- [Tasks done at OSI layers (set 2)](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Aosi-layer-task-mapping-2) — Computer Networks and Security, chapter 1