Date: Wed, 7 Oct 2015 12:54:45 -0700 From: hiren panchasara <hiren@strugglingcoder.info> To: transport@FreeBSD.org Subject: Setting congestion window on loss detection Message-ID: <20151007195445.GC42742@strugglingcoder.info>
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--0vzXIDBeUiKkjNJl Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Found this issue about a month ago and started a discussion on -net: https://lists.freebsd.org/pipermail/freebsd-net/2015-September/043249.html I feel this forum is a better place to discuss this further now. Problem: We set cwnd to 1mss when we detect loss via arrivals of 3 dupacks. That is wrong as we severely underutilizing network capacity by doing so. Next question is, what should we set cwnd to? RFC6675 (TCP SACK) suggests following on detecting loss: ssthresh = cwnd = (FlightSize / 2) RFC5681 (TCP Congestion control) suggest: ssthresh = max (FlightSize / 2, 2*SMSS) cwnd = (ssthresh + 3*SMSS) (Here, FlightSize is bytes in flight.) OR should we let whatever congestion control (CC) algo in control decide that value? Cheers, Hiren --0vzXIDBeUiKkjNJl Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQF8BAABCgBmBQJWFXiBXxSAAAAAAC4AKGlzc3Vlci1mcHJAbm90YXRpb25zLm9w ZW5wZ3AuZmlmdGhob3JzZW1hbi5uZXRBNEUyMEZBMUQ4Nzg4RjNGMTdFNjZGMDI4 QjkyNTBFMTU2M0VERkU1AAoJEIuSUOFWPt/lRAUH/2wsJssQ1BkEbbMERnVTQfLB SsM1+mJwu5BZDz39l+Z5HtxmNmN5Rz18oMkFxWFOEmbhxXAU3NWXwEyFiPZpwHvY r2SDrlNjUfy2d/D/uH4IHgLrq/zweD7w3zPrpn1j4zcm/g4rNl3HV+ATb8DUEzhg LXWMy1kSc2v/Qg6EcqCmO01EitBh7NI0xqgMB/BQF1y00enoi4UJAguDqLNEZPLV 9AlI6hkHI5txekm2BQTfLVXRcetSqd74bI99reTtqYiMUABj/c5Iz189LXPXQJq6 SBXsn+Dc67EWyWR3QKKP0hMIxZ31tCZwseeKj3uYrbzGDUqmNvcsqtaZSG4Kt/0= =lOoe -----END PGP SIGNATURE----- --0vzXIDBeUiKkjNJl--
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