AP CSP Day 48: Distributed Computing
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Practice Question
A 1 MB file is divided into 100 packets and sent over the Internet. During transmission, 3 packets are lost. Which of the following best describes what happens next?
TCP uses sequence numbers and acknowledgments to detect missing packets. When 3 packets are not acknowledged, only those 3 are retransmitted. The destination holds the 97 received packets and reassembles the complete file once the 3 retransmissions arrive.
A) Resending the entire file would be wasteful. TCP retransmits only the specific missing packets. C) TCP ensures reliable delivery — missing packets are retransmitted, not permanently lost. B) Lost packet data cannot be reconstructed from other packets; it must be retransmitted from the source.
Students think either the whole file needs resending or that missing data is lost forever. TCP's selective retransmission is a key feature of reliable data delivery.
TCP provides reliable delivery through acknowledgments and retransmission. Missing packets trigger retransmission of only the missing packets, not the entire message.
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