CISCO CCNA 200-301 Q192

Which statement is TRUE of the CSMA/CD Ethernet media access method?

A. It requires centralized monitoring and control.
B. It is ideal for a switched network environment.
C. It uses a back-off algorithm to calculate a random time value.
D. Each station is allotted a time slot in which they can transmit data.

Correct Answer: C

The Carrier Sense Multiple Access – Collision Detection (CSMA/CD) Ethernet Media Access Control (MAC) method uses a back-off algorithm to calculate random times to transmit packets across a channel. When two stations start transmitting at same time, their signals will collide. The CSMA/CD method detects the collision and causes both stations to hold the retransmission for an amount of time determined by the back-off algorithm. This is done in an effort to ensure that the retransmitted frames do not collide.

CSMA/CD does not require centralized monitoring and control nor does it assign time slots to stations. Moreover, the CSMA/CD method is designed to work in non- switched environment. It is an alternative to a token-passing topology, in which each station waits in turn to receive a token that allows it to transmit data. With CSMA/CD, each station is capable of making the decision regarding when to transmit the data.