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If another request with the same Token arrives before the set time interval expires, the server classifies it as spurious (a consequence of delayed ACK rather than a true loss) and responds only with an Empty ACK
This decision prevents retransmission of the payload while still confirming that the server is active and aware of the transaction.
When no ACK is received within the current waiting interval, the server concludes that either the response or its ACK has been lost. In this case, the response must be retransmitted to ensure reliability.
To avoid congestion caused by frequent retries, the timer is exponentially increased with some pre-set formular – (some upper-threshold adaptation to guarantee that the retransmission interval grows conservatively, limiting network load while maintaining delivery assurance).
If an ACK finally arrives after a retransmission has occurred, the server infers that the loss was transient and the channel condition has improved, hence it calibrates its timer downwards.
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IEEE/ICACT20260196 Slide.29
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