System Administrator 2026 — Test 23

Correct Answer: B. B. To avoid more collisions
Explanation: Collision includes two more stations, if those stations again re-transmit the frames at a time; it causes collision again. Back-off time is to avoid this collision by making the stations to wait for some random times.

Correct Answer: C. C. Restriction on the attempts for re-transmission
Explanation: If a station re-transmits a frame more than the times, that is defined by the pure aloha, then pure aloha will abort the process re-transmission of the particular frame. The station needs to try after sometime later to send the frames.

Correct Answer: A. A. 2*t
Explanation: Vulnerable time is time in which, there is a possibility for a collision. T(frame) is the time taken by a frame to be sent to destination. Vulnerable time will be 2 times the fixed length of frames.

Correct Answer: A. A. Polling
Explanation: Polling is the method for channel allocation where one station acts as a server and remaining stations acts according to the decision of master station. This master station also known as primary device, which uses two functions called poll function and select function to send and receive data within the network.

Correct Answer: B. B. Controlled access protocol
Explanation: In controlled access protocols, stations send frames only if they get the authorization from the other stations to use the channel. This authorization can be obtained using methods such as reservation, polling, token passing.

Correct Answer: B. B. Non persistent
Explanation: Unlike 1- persistent in non-persistent methods, stations wait for some random time even if it finds the channel idle. This random time reduces the collision at the same time it reduces the efficiency because random times may keep the channel unused even the stations have frames to send.

Correct Answer: A. A. T propagation
Explanation: In carrier sense multiple access, the stations sense the medium whether it is idle or not. This information is sent by the station which is using the medium, using propagation of a signal. The propagation delay in the signal causes the collision.

Correct Answer: A. A. True
Explanation: In slotted aloha, the time is divided into time slots, that are of T(frame) length. The stations are instructed to send the frames at the starting of the time slot. Still there is a chance for collision, if 2 frames are started at the same it. This is why vulnerable time is equal to the time taken by a frame to be sent to the destination.

Correct Answer: D. D. Bandwidth division multiple access
Explanation: The channelization protocols use frequency, time and code to divide the bandwidth of the channel. Bandwidth is divided into frequency bands in FDMA, same bandwidth is used by the stations in TDMA.

Correct Answer: A. A. Preamble bits
Explanation: Time division multiple access allocates the time slots for station to use the channel. These time slots are synchronized by preamble bits, which acts as guard time between two time slots.