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Can F-RTO be harmful? NO! If RTO is not spurious (or F-RTO fails to detect) F-RTO reverts back to traditional RTO recovery Exactly same amount of segments get transmitted Hidden losses when F-RTO declares RTO spurious A few known scenarios Loss of the unnecessary RTO retransmission Severe reordering retransmitted segment bypasses the full window of original segments Malicious receiver Delays ACKs until RTO expires and retransmitted segment arrives ACKs data it has not received 1 & 2 considered as rare corner cases; won’t harm TCP flow With 3 benefit is questonable; concealing losses harms TCP flow None of these can harm the network, if conservative response is taken F-RTO sender is recommended to take the spurious RTO as a congestion signal |