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I am doing troubleshooting in my network.

I found some re-transmission by using wireshark.

The segment 1400 bytes are well transmitted but

The segment 800 bytes are lost and re-transmitted.

I know RTO value is controlled by RTT and its variance.

My question is Are RTO value and RTT different with the segment size?

In my intuition, The large segment, the longer RTT and the longer RTO.

Is it right? Could you help me a little? Thanks!

nimdrak
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1 Answers1

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EDITED.

Short answer: No.

RTT is the time from when a packet is sent to when it is acknowledged, and approximates the propagation delay of the logical connection.

TCP uses SRTT or "smoothed RTT" that continually averages the RTT. So the effect of packet size is averaged out (assuming a variety of packet sizes).

RTO is based on RTT, but it is rounded up to 1 second (see RFC 6298, para 2.4). So except for extremely slow connections, RTO is 1 second.

If small packets are getting lost, it could be a buffer problem on one of your routers.

Ron Trunk
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  • Thank you so much! But could you explain it in detail? RTT = Time from [when a packet is sent] to [when its ack is received]. Then is a RTT influenced by its link bandwidth and its packet size? Because small packet and large bandwidth make the time consumed for transmission small. And you mean RTO is at least larger than 1 seconds? I appreciate you again! – nimdrak Aug 30 '19 at 14:59
  • RTT is definitely influenced by BW. TCP averages RTT to get SRTT. RTO starts at 1 second, but can be smaller. RFC 6298 suggests 1 second as a minimum, but it depends on the OS implementation – Ron Trunk Aug 30 '19 at 16:46
  • @nimdrak https://tools.ietf.org/html/rfc6349 – c4f4t0r Aug 30 '19 at 17:03
  • @RonTrunk@c4f4t0r I really totally understand. I appreciate you! :) – nimdrak Aug 31 '19 at 02:54