Final answer:
The Go-Back-N protocol retransmits all subsequent packets when an ACK is not received, while the Selective Repeat protocol only retransmits the individual lost or damaged packet.
Step-by-step explanation:
In the Go-Back-N protocol, if a sender does not receive an ACK (acknowledgment) for a sent packet within a specified time, it assumes the packet was lost or damaged. It then goes back to the last unacknowledged packet and retransmits all subsequent packets in the send window. This process continues until the sender receives the expected ACK.
In contrast, the Selective Repeat protocol only retransmits the individual lost or damaged packet, not all the subsequent ones. The receiver buffers out-of-order packets, and upon receiving the missing packet, it acknowledges all packets up to and including the received packet.