GATE CSE 2016 Set 2 | Question: 24

Question

In an Ethernet local area network, which one of the following statements is TRUE?

• A. A station stops to sense the channel once it starts transmitting a frame.
• B. The purpose of the jamming signal is to pad the frames that are smaller than the minimum frame size.
• C. A station continues to transmit the packet even after the collision is detected.
• D. The exponential back off mechanism reduces the probability of collision on retransmissions.

Answer 1

Option D is correct .... exponential back off algo reduces probability of collision on retransmission

Answer 2

The question is asking for the true statement among the given options related to an Ethernet local area network.

Let's look at each option:

1. A station stops to sense the channel once it starts transmitting a frame. This statement is false. In the Carrier Sense Multiple Access/Collision Detection (CSMA/CD) protocol used by Ethernet, a station continues to sense the channel even when it is transmitting a frame. This is to detect any possible collisions.

2. The purpose of the jamming signal is to pad the frames that are smaller than the minimum frame size. This statement is false. The purpose of the jamming signal in Ethernet is not to pad smaller frames, but rather to ensure that all stations recognize that a collision has occurred.

3. A station continues to transmit the packet even after the collision is detected. This statement is false. After a collision is detected, stations stop transmitting and initiate a backoff algorithm.

4. The exponential back off mechanism reduces the probability of collision on retransmissions. This statement is true. After a collision is detected, the Ethernet stations use an exponential backoff algorithm to randomize their retransmission times in order to reduce the probability of a collision happening again.

Therefore, the correct answer is option 4

Answer 3

A - False (Station continues to sense the channel till Transmission time)

B - False (To indicate collision as occurred)

C - False (As Jam Signal indicates if Collison as occurred in the network, it will help to stop the transmission of packet those who are transmitting at that time and that station stops its transmission)

D - True (Backoff wait time is calculated for re-transmission which helps to reduce the Collison of packet)