---
title: "Multiple access protocols"
subject: "Computer Networks and Security"
chapter: 3
key: "semester_7/computer_networks_and_security:multiple-access-protocols"
source: https://www.bctengineer.com/q/semester_7/computer_networks_and_security/multiple-access-protocols
site: BCT Engineering
---

# Multiple access protocols

Computer Networks and Security · Chapter 3: Data Link Layer

- Asked in: 2071 Chaitra, 2 marks; 2070 Asar, 3 marks (asked 2 times)
- Video: [Multiple Access Protocols](https://www.youtube.com/watch?v=YAjfUc7Tt24) — Neso Academy
- 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/multiple-access-protocols
- Whole chapter: https://www.bctengineer.com/md/semester_7/computer_networks_and_security/chapter-3

## Question

What are multiple access protocols? How can a multi-access channel be shared by different nodes?

## Short answer

Multiple access protocols are MAC rules for sharing a channel: random access (ALOHA, CSMA/CD) with collision handling, controlled access (polling, token passing) with turns, and channelization (FDMA, TDMA, CDMA) dividing the medium.

## Answer

#### Multiple access protocols
When many nodes share a single broadcast channel, collisions can occur if two nodes transmit at the same time. **Multiple access protocols** are the rules in the MAC sublayer that decide which node may use the shared channel and when, so that the channel is used efficiently with few or no collisions.

#### How a multi-access channel is shared
```text
 Multiple access protocols
 |- Random access : ALOHA (pure, slotted), CSMA, CSMA/CD, CSMA/CA
 |- Controlled access : Reservation, Polling, Token passing
 |- Channelization : FDMA, TDMA, CDMA
```

1. **Random access:** no station is in control; each sends when it has data and resolves collisions by retransmitting after a random wait. Examples: ALOHA, CSMA/CD (Ethernet), CSMA/CA (Wi-Fi).
2. **Controlled access:** stations take turns, so no collision. Methods: **reservation** (reserve a slot before sending), **polling** (a master asks each station) and **token passing** (the station holding the token sends).
3. **Channelization:** the channel is split by frequency (FDMA), time (TDMA) or code (CDMA) and each station gets a fixed share.

## Check yourself

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

1. What do multiple access protocols decide?
   A. Which route a packet takes
   B. Which node may use the shared channel and when
   C. How IP addresses are assigned
   D. How data is encrypted
   Answer: B. They are MAC sublayer rules that control access to a shared broadcast channel to reduce collisions. (Key point: Purpose of MAC protocols)

2. Which group contains only controlled-access methods?
   A. ALOHA, CSMA, CSMA/CD
   B. Reservation, polling, token passing
   C. FDMA, TDMA, CDMA
   D. CSMA/CA, TDMA, polling
   Answer: B. Controlled access has stations take turns: reservation, polling and token passing. (Key point: Controlled access)

3. How does channelization share a channel?
   A. Stations transmit at random and retransmit after collisions
   B. A master polls each station
   C. The channel is split by frequency, time or code with a fixed share per station
   D. A token is passed around
   Answer: C. FDMA, TDMA and CDMA give each station a fixed share by frequency, time or code. (Key point: Channelization)

## Related in Computer Networks and Security

- [Multiple access in IEEE 802.5](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Aieee-802-5-access) — Computer Networks and Security, chapter 3
- [Static channel assignment and CSMA/CD](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Astatic-channel-csmacd) — Computer Networks and Security, chapter 3

## Related in other subjects

- [Frequency hopped multiple access (FHMA)](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Afhma-operation) — Wireless Communication, chapter 7, asked 5×
- [Multiplexing vs multiple access](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Amux-vs-multiple-access) — Data Communication, chapter 6
- [CDMA vs TDMA; FHSS multiple access](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Acdma-advantages-fhss-types) — Wireless Communication, chapter 7
- [Hybrid multiple access techniques](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Ahybrid-multiple-access) — Wireless Communication, chapter 7