Final answer:
TDMA and FDMA are multiple access protocols that are collision-free because they allocate distinct time slots and frequency bands to each user. Protocols like Aloha and CSMA do not guarantee collision-free operation, while polling can be collision-free if managed correctly by a central controller. Correct answer is a. TDMA and FDMA
Step-by-step explanation:
The question is asking which of the multiple access protocols are collision-free. In other words, in which protocols will collisions never happen. The options given are TDMA (Time Division Multiple Access), FDMA (Frequency Division Multiple Access), CSMA (Carrier Sense Multiple Access), Aloha, and polling. TDMA and FDMA are indeed collision-free because they allocate distinct time slots and frequency bands to each user, thereby preventing multiple nodes from transmitting simultaneously, which is a typical cause of collisions in networks. On the other hand, Aloha and its variant, Slotted Aloha, do not coordinate between nodes for access and can lead to collisions if two nodes transmit at the same time.
CSMA attempts to avoid collisions by sensing the medium before transmitting but is not guaranteed to be collision-free. Finally, polling is a control scheme where a central controller invites nodes to transmit in a managed sequence, which can effectively eliminate collisions if managed correctly. Based on this information, the correct answer to the question is TDMA and FDMA are the protocols that are collision-free. So, the correct answer is a. TDMA and FDMA.