IEEE 802.5 (Token Ring) implements a collision-prevention method at the media-access level. Which mechanism prevents collisions in this standard?

Introduction:
Local area network technologies differ primarily in how stations gain permission to transmit on a shared medium. IEEE 802.5 (Token Ring) was designed to avoid the need for contention by controlling access deterministically. This question asks which access mechanism prevents collisions in 802.5 networks.

Given Data / Assumptions:

• The standard in focus is IEEE 802.5 (Token Ring).
• The medium is logically a ring, often implemented physically as a star with a Multistation Access Unit (MAU).
• The goal is collision prevention, not merely detection after a collision occurs.

Concept / Approach:
Token Ring uses a special short frame called a token. Only the station holding the token may transmit data frames. After transmission (or if it has nothing to send), the station releases the token to the next station in the ring. Because only one token exists and only the token holder can transmit, two stations cannot transmit at the same time, thereby preventing collisions by design.

Step-by-Step Solution:

Verification / Alternative check:
Contrast with Ethernet's legacy CSMA/CD (Carrier Sense Multiple Access with Collision Detection), where collisions can occur and are handled probabilistically. Token Ring eliminates collisions by controlling access order with the token, often providing more deterministic latency under load.

Why Other Options Are Wrong:

• CSMA/CD: used by classic Ethernet (IEEE 802.3), not Token Ring.
• Collision detection: a behavior of CSMA/CD, not 802.5.
• Time sharing: vague concept; not the defined MAC for 802.5.
• Switched repeaters: a hardware concept; not the MAC algorithm.

Common Pitfalls:
Confusing Token Ring with Ethernet or assuming all LANs rely on contention. Another pitfall is thinking that a ring implies round-robin without a token—802.5 specifically uses a token frame to manage access.

Final Answer:
Token passing.