Which of the following are controlled-access protocols?
A. Reservation
B. Polling
C. TDMA
D. Token Passing
E. CSMA/CA
Choose the correct answer from the options given below:

Correct option is B

In controlled-access protocols, the right to transmit is governed through coordination among stations, which helps avoid data collisions on the communication medium. Among the given options, Reservation, Polling, and Token Passing are all categorized as controlled-access protocols. They ensure that stations get permission to send data in an organized and conflict-free manner. These methods use different mechanisms—like reservation slots, master polling, or token circulation—to manage access control. Hence, only A, B and D correctly represent controlled-access protocols.
Information Booster:
1. Reservation: This protocol divides the channel into time slots and allows stations to reserve a slot in advance to avoid collisions. It works well in networks requiring predictable transmission.
2. Polling: In this technique, a master device polls each connected device in a round-robin or priority fashion to check if it wants to transmit. Only the polled device can send data, reducing conflict.
3. Token Passing: A logical token circulates in the network. A device can only transmit when it has the token, ensuring a collision-free and orderly communication system.
Additional Knowledge:
· TDMA (Time Division Multiple Access): TDMA is a multiplexing technique, not a controlled-access protocol. It allocates fixed time slots to users in a periodic manner, not based on real-time coordination among stations.
· CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance): This is a random-access protocol, where stations transmit based on carrier sensing and use techniques to avoid, but not fully prevent, collisions. It does not involve centralized control or coordinated access like controlled-access protocols.