---
title: "Multiple access in IEEE 802.5"
subject: "Computer Networks and Security"
chapter: 3
key: "semester_7/computer_networks_and_security:ieee-802-5-access"
source: https://www.bctengineer.com/q/semester_7/computer_networks_and_security/ieee-802-5-access
site: BCT Engineering
---

# Multiple access in IEEE 802.5

Computer Networks and Security · Chapter 3: Data Link Layer

- Asked in: 2071 Chaitra, 6 marks
- 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/ieee-802-5-access
- Whole chapter: https://www.bctengineer.com/md/semester_7/computer_networks_and_security/chapter-3

## Question

Explain how multiple access is achieved in IEEE 802.5.

## Short answer

IEEE 802.5 uses token passing: a free token circulates on a logical ring. A station needing to send captures the token, marks it busy, and appends its data. The frame goes around; the destination copies it. The sender removes the returning frame and releases a new free token, avoiding collisions and providing deterministic access.

## Answer

**IEEE 802.5 (Token Ring)** uses **token passing**, a controlled-access method, on a ring topology. No collisions occur because only the station holding the token may transmit.

#### Operation
1. A special 3-byte frame called a **token** circulates continuously around the ring when all stations are idle. A free token has the token bit set to 0.
2. A station with data waits for the free token, captures it by changing a bit (making it busy, 1) and adds the data to make a data frame with source and destination address.
3. The frame circulates around the ring. Each station regenerates (repeats) it and passes it on. Only the destination station copies the data, and it sets the **address recognised** and **frame copied** bits.
4. The sender removes the frame when it returns, checks the status bits for success, and releases a **new free token**.
5. Token holding time is limited, so every station gets a turn.

```text
     +---[A]---[B]---+
     |               |
    [D]-------------[C]    token -->
```

#### Features
- Speeds 4 or 16 Mbps (maximum 100 Mbps in later versions).
- A **monitor station** (active monitor) removes lost or duplicate tokens and keeps the ring healthy.
- **Priority and reservation bits** in the token let high-priority frames go first.
- Deterministic access time, so good under heavy load and for real-time traffic.
- Drawback: waiting for the token even at low load, and a ring break affects everything unless a wiring concentrator (MAU) is used.

## Check yourself

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

1. How does IEEE 802.5 avoid collisions?
   A. Carrier sensing and backoff
   B. Only the station holding the token may transmit
   C. Time slots for each station
   D. Random polling
   Answer: B. Token passing is controlled access; only the token holder sends. (Key point: Access method)

2. How does a station start sending in Token Ring?
   A. Waits for a free token and changes a bit to make it busy, then adds data
   B. Sends right away and waits for an ACK
   C. Sends a request to a master
   D. Broadcasts a jam signal
   Answer: A. The free token (bit 0) is captured by setting it to busy (1) and attaching the data frame. (Key point: Capturing the token)

3. Who removes the frame from the ring?
   A. The destination
   B. The active monitor always
   C. The sender, when it returns, and then it releases a new free token
   D. The next station after the destination
   Answer: C. The sender checks the status bits for success, removes its frame and issues a new free token. (Key point: Frame removal)

4. What is the role of the active monitor?
   A. Assigns addresses
   B. Removes lost or duplicate tokens and keeps the ring healthy
   C. Sets priority bits
   D. Encrypts frames
   Answer: B. The monitor station handles lost or duplicate tokens and ring maintenance. (Key point: Monitor station)

## Related in Computer Networks and Security

- [Multiple access protocols](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Amultiple-access-protocols) — Computer Networks and Security, chapter 3, asked 2×

## 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