On Thu, 2011-03-17 at 23:50 +0200, Jonathan Morton wrote: > On 17 Mar, 2011, at 8:22 pm, Rick Jones wrote: > > So initialRTO is specced currently to be 3 seconds, with a small but > > non-trivial effort under way to reduce that, but once established > > connections have a minimum RTO of less than or equal to a second don't > > they? > > If the RTT they measure is low enough, then yes. If the queues > lengthen, the measured RTT goes up and so does the RTO, once the > connection is established.
Right. I should have been more explicit about "You know it won't retransmit any sooner than N." (for some, changing value of N :) > But the *initial* RTO is the important one for unmanaged queue sizing, > because that determines whether a new connection can be started > without retransmissions, all else functioning correctly of course. > There is no way to auto-tune that. > > Note also that with AQM that can re-order packets, the length of the > bulk queue starts to matter much less, because the SYN/ACK packets can > bypass most of the traffic. In that case the RTT measured by the > existing bulk flows will be higher than the latency seen by new and > interactive flows. I would think that unless the rest of the segments of the connection will also bypass most of the traffic, the SYN or SYN|ACK should not bypass - to do so will give the TCP connection a low, unrealistic initial estimate of the RTT. Given the recent change in Linux upstream to go to cwnd_init of 10 segments, and the prospect of other stacks following that lead in implementing the draft RFC, if there is a big slow queue of traffic that the data segments will not bypass, it would seem better to have the SYN or SYN|ACK get delayed and retransmitted to get the cwnd down. SYN and SYN|ACK segments should not receive special treatment beyond what data segments for the same connection would get. rick _______________________________________________ Bloat mailing list [email protected] https://lists.bufferbloat.net/listinfo/bloat
