What causes duplicate ACK packets?

Related questions

1. How TCP connection is terminated?
2. Why do TCP retransmissions occur?
3. How is TCP checksum calculated?
4. Why is TCP Reliable?
5. What are the three phases of the TCP three way handshake?
6. Why TCP uses 3 way handshake?
7. What is TCP ACK?
8. Why is TCP needed?
9. What is SLE and SRE in Wireshark?
10. How does TCP detect duplicate packets?

Tags

1. #segment
2. #small
3. #reordering
4. #waits
5. #sequence
6. #receiver
7. #since
8. #received
9. #number
10. #whether
11. #caused
12. #acknowledgment
13. #packets
14. #segments
15. #order
16. #receives
17. #duplicate