TCP uses an estimated RTT plus estimated deviation when determining the timeout value for segments. Why does TCP include the deviation value? What would be more likely to occur if the deviation value were not included?
Try an answer before revealing the guidance below.
Key Concepts
- EstimatedRTT
- DevRTT
- TimeoutInterval
- RTT variation
- Spurious retransmission
Answer Approach
- Explain why an average alone misses variability.
- Describe the safety margin the deviation term adds.
- Describe the effect of a timeout that expires too early.
Full Answer
Answer status: Verified against study notes. Revision notes, not an official marking scheme.
Round-trip times fluctuate as queuing and routes change. TCP adds a margin based on RTT deviation so ordinary longer samples do not immediately trigger a timeout. Without the deviation term, the timeout would more often expire before a valid ACK arrived, causing unnecessary retransmissions and possibly unnecessary congestion responses.
TimeoutInterval = EstimatedRTT + 4 × DevRTTShortcuts: K concepts · A approach · F answer · R reviewed · B bookmark · ← / → previous / next