CODEWITHSUNDEEP
network-programmingtcpgo-back-n
miketsui3a
miketsui3a

Reputation: 301

What is the ACK number using Go-Back-N?

In my lecture notes, the example of go back n shows that when reciever recieved a packet number n, reciever will send a ACK number n to the sender.

But when i search on the web, some of the website said that reciever will send the n+1 ACK to the sender in order to request next packet.

Which one is the correct one about go back n?

Upvotes: 0

Views: 2065

Answers (1)

Banghua Zhao
Banghua Zhao

Reputation: 1556

For Go-Back-N, the receiver uses cumulative acknowledgment, which sends the sequence number of largest correctly received in order packet. Two example to help you understand. 1. The receiver has correctly received packet n and sent ACK=n. Later the receiver received packet n+1, then it will send ACK=n+1. 2. The receiver has correctly received packet n and sent ACK=n. Later the receiver received packet n+2, then it will send ACK=n.

Now, what you have searched on the web is talking about TCP not Go-Back-N. For TCP, ACK is different from Go-Back-N. Although TCP still uses cumulative acknowledgment, but acknowledgment number is the sequence number of the next byte the receiver is expecting from the sender, i.e., n+1.

Upvotes: 0

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