Tema 1.1 - Ethernet

With CSMA/CD, the first time a station attempts to transmit a packet:

• It is transmitted immediately, independently of channel occupation.

• It is transmitted immediately if the channel is free.

• Waits for a backoff period, and then transmits immediately.

• Waits for a backoff period, and then transmits if the channel is free.

In Ethernet, the maximum number of times a frame can be retransmitted if collisions are detected is:

• 10

• 16

• 2^10

• None of the former.

The transmission time of the largest possible Ethernet frame using Gigabit Ethernet is:

• 12 microseconds

• 12,144 microseconds

• 1,500 microseconds

• 1,518 microseconds

The minimum size of an Ethernet frame is:

• 64 bits

• 512 bits

• 512 bytes

• None of the former.

The end-to-end signal propagation time for a fiber-optic Ethernet link of 2 km in length is:

• 1000 microseconds

• 100 microseconds

• 10 microseconds

• 1 microseconds

In Ethernet, if two stations collide for the 2nd time when transmitting a frame, then these stations, before attempting to transmit again, they wait:

• For a time always greater than the wait time after the 1st crash.

• For a time probably longer than the initial one, but it could be equal to or lower than the wait time after the 1st crash.

• The same time as in the 1st collision.

• Twice the wait time associated to the 1st collision.

When an Ethernet link is used in Full-Duplex mode, it is still necessary to use:

• The CARRIER SENSING mechanism.

• The COLLISION DETECTION mechanism.

• The LOOPBACK mechanism.

• None of the former.

In a switch, HOL blocking refers to:

• Blocking an input queue due to the switch’s lack of power to process all incoming data.

• Blocking the input queue because an occupied output causes a frame at the input queue to be retained.

• Blocking the output queue because the input data rate is greater than the output bandwidth.

• All previous cases are applicable.

A switch that does not achieve wirespeed performance:

• Should have output queues mandatorily.

• Should have input queues mandatorily.

• Can have either input or output queues.

• Should have both input and output queues.

In Ethernet's auto-negotiation mechanism, the order of priority to select the optimal configuration is:

• Duplex mode, then speed, then flow control support.

• Speed, then duplex mode, then flow control support.

• Duplex mode, then flow control support, then speed.

• Speed, then flow control support, then duplex mode.