CODEWITHSUNDEEP
network-programminggo-back-n
Jack
Jack

Reputation: 11

The retransmitted sequence number of Go-Back-N and Selective Repeat

Can you help me answer this question and explain it? Thank you.

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Upvotes: 0

Views: 567

Answers (1)

Banghua Zhao
Banghua Zhao

Reputation: 1556

Suppose other packets are correctly received and there is no premature timeout. Then the sequence numbers of the packets that are retransmitted are.

Go-Back-N: 2 and 3.

Selective Repeat: only 2.

Here is the reason.

Go-Back-N: Since sequence number 2 packet is lost, the receiver only cumulatively acknowledges sequence number up to 1. On the sender side, it only receives acknowledges number up to 1. When the timeout occurs, senders will retransmit all packets that have not yet been acknowledged. That is 2 and 3.

Selective Repeat: The receiver doesn't use cumulative acknowledgment. It will send acknowledges to correctly received packets. That is 0, 1, 3. On the sender side, only acknowledge for sequence number 2 is not received. When the timeout occurs, it only resends sequence number 2 packet.

Upvotes: 0

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