Date: Thu, 18 Feb 2010 17:24:05 +0100 From: Harald Schmalzbauer <h.schmalzbauer@omnilan.de> To: Stephen Hurd <shurd@sasktel.net> Cc: freebsd-stable@freebsd.org, Patrick Mahan <mahan@mahan.org> Subject: Re: RELENG_8 ignoring TCP window size? [Was: Re: Help for TCP understanding wanted, ACK-MSS-Window [Was: Re: best practice to watch TCP parms of established sockets]] Message-ID: <4B7D69A5.4010506@omnilan.de> In-Reply-To: <4B7D6635.20605@sasktel.net> References: <4B7C1365.9070806@omnilan.de> <70CD649D-7659-4CE2-A16C-49B8C891CB5B@mac.com> <4B7C4066.5040006@omnilan.de> <4B7D3938.1000309@omnilan.de> <4B7D5AC4.9020509@mahan.org> <4B7D61DE.2020906@omnilan.de> <4B7D6635.20605@sasktel.net>
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[-- Attachment #1 --] Stephen Hurd schrieb am 18.02.2010 17:09 (localtime): ... > A TCP SHOULD implement a delayed ACK, but an ACK should not be > excessively delayed; in particular, the delay MUST be less than 0.5 > seconds, and in a stream of full-sized segments there SHOULD be an ACK > for at least every second segment. That's why I asked for help understandig TCP. I'm surely wrong then. I thought the ACK segment gets sent after the transfer of n segments equals windows-size. I don't undesrtand that window size yet... I'm back into my books > The idea of delayed ACKs is to allow an ACK to be sent with data if > there will be data sent right away, not to combine ACKs... leaving out > ACKs makes calculation of RTT problematical which causes performance > problems all over the place... maybe the dearth of ACKs from the windows > system is causing the problem? The problem is not with the windows box, these transfer rates are sensible. The problem is with two RELENG_8 machines. I'm doing this whole thing because I observed slowdowns under 20MB/s and I try to reproduce and investigate this. But first I have to get the idea right... If I don't understamd things going on when transfers make sense, I won't be able to determine what happens when transfers are slowed down... Thanks, -Harry [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.13 (FreeBSD) iEYEARECAAYFAkt9aaYACgkQLDqVQ9VXb8gYpQCfeJSz+CmIPUe47T+IEdKL+Rtf SqoAn1DOzDMZ4aIRgIE+wSg3v9fv4Gcp =GF9X -----END PGP SIGNATURE-----
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