Final answer:
A timeout event occurs when a sender does not receive an acknowledgment, while a three-duplicate-ACKs event occurs when the receiver receives the same duplicate packet multiple times.
Step-by-step explanation:
The correct answer is option C: A timeout event is when a sender does not receive an acknowledgment from the receiver within a specified time period. This usually indicates that the packet or message that was sent got lost or dropped somewhere in the network. On the other hand, three-duplicate-ACKs event occurs when the receiver receives the same duplicate packet multiple times, indicating that the sender's previous packet was lost and needs to be resent.
Of the two events, three-duplicate-ACKs is a stronger sign of congestion in the network. This is because when packets are lost or dropped, the receiver will send duplicate ACKs to inform the sender that one or more packets are missing. Receiving multiple duplicate ACKs suggests that there is congestion in the network, as multiple packets are being lost or dropped. Three-duplicate-ACKs is a stronger sign of congestion in the network.
Ultimately, both timeout events and three-duplicate-ACKs events are indicators of network congestion, but the latter is generally considered a stronger sign.