a) Why, despite the carrier sense functionality, collisions may still occur in t

Question

a) Why, despite the carrier sense functionality, collisions may still occur in the CSMA/CD
Medium Access Control? Answer (give a cause of collisions) in one short sentence. [2]
b) How does an Ethernet switch know where to forward a frame with a given destination MAC
address? Name and briefly (in 1-2 sentences) describe the applicable protocol. [2]
c) If you disconnect a host from one port on the switch and connect it to another port, how does
the switch know that the host is no longer connected to the old port? Name and briefly describe
the mechanism responsible for “dropping” MAC addresses from port forwarding tables. [2]

Explanation / Answer

a) Two nodes listen to the Ethernet wire and sense that no carrier is present. When both nodes decided to transmit simultaneously, this cause a collision. b) The switch have a CAM table which list down the which port is connected to which MAC address. CAM table is updated through the use of Address Resolution Protocol(ARP). c) When the host is disconnect from the old port, the port status is change from up to down as there is nothing connected to it. When the host is connected to a new port, the status of the port is change from down to up, the MAC address is updated to the switch CAM table. The CAM table will remove the MAC address tagged to the old port and updated it to the new port.

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