Date: Thu, 17 Sep 1998 08:59:32 +0200 From: "Kevin Kyeong-il CHOI" <kevin.choi@cnes.fr> To: "FreeBSD Question" <freebsd-questions@FreeBSD.ORG>, "FreeBSD Net" <freebsd-net@FreeBSD.ORG>, <tcp-over-satellite@achtung.sp.trw.com> Subject: Why FreeBSD (or Solaris as well) get stuck in case of long delay ? Message-ID: <006801bde208$b8e51ac0$52099584@pc-kichoi.cst.cnes.fr>
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Hi,
I'd like to have some expertized opinions.
I have a ATM network (25 Mbps) as follows;
[FreeBSD Box]---+---[Delay generator]---+---[SUN Solaris]
| |
[Windows 98]----+ +---[Windows NT]
| |
[Windows NT]----+ +---[FreeBSD 2]
The delay generator can introduce the packet delays upto
couple of seconds for TCP or UDP packets.
When there is no delay, the whole link between left and right
side shows the maximum performance which is about 20 Mbps.
BUT, once the delay is introduced, the famous rule
Capacity = RTT x Bandwidth.
and the capacity would be limited by the window size.
Here, I used 64K for Window size (65536), so the Bandwidth
should be
Bandwidth = Capacity (65536) / RTT
I made the delay in one way as 200 ms, and RTT becomes 400 ms, so
the nominal Bandwidth becomes 1310720 bps = 1.3 Mbps.
Curiously enough, between two Windows boxes, the maximum bandwidth
is obtained, which is about 1.0 ~ 1.1 Mbps.
BUT, for FreeBSD, or for Solaris, I obtain only 200 ~ 300 kbps.
(precisely 200 kbps for Solaris, and 300 kbps for FreeBSD).
I don't understand what happened, but guess that the UNIX machines
may evaluate the RTT in a wrong way or what ...
Can anyone have a similar experience, please give me an e-mail.
-------------------------------------
Kevin Kyeong-il CHOI
~'/ (o\)
^
\___/o
Doctoral Research Engineer
Service DEE/IR/TSI/TN
Centre National d'Etudes Spatiales
18 Avenue Edouard-Belin
31401 Toulouse cedex 4
France
(Tel) +33-561 28 15 31
(Fax) +33-561 28 29 13
(Email) kevin.choi@cnes.fr
(www) http://www.chez.com/kichoi/
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