[95472] in North American Network Operators' Group
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daemon@ATHENA.MIT.EDU (Jim Shankland)
Tue Mar 27 18:44:23 2007
From: Jim Shankland <nanog@shankland.org>
To: <nanog@merit.edu>
Cc: <michael.dillon@bt.com>
In-Reply-To: <D03E4899F2FB3D4C8464E8C76B3B68B01AAC58@E03MVC4-UKBR.domain1.systemhost.net>
Date: Tue, 27 Mar 2007 15:32:34 -0700
Errors-To: owner-nanog@merit.edu
<michael.dillon@bt.com> writes:
> Use GigE cards on the servers with a jumbo MTU and only buy IP network
> access from a service provider who supports jumbo MTUs end-to-end
> through their network.
I'm not sure that I see how jumbo frames help (very much). The
principal issue here is the relatively large bandwidth-delay
product, right? So you need large TCP send buffers on the sending
side, a large (scaled) receive window on the receiver side, and
turn on selective acknowledgement (so that you don't have to
resend the whole send buffer if a packet gets dropped).
At 45 Mb/s and 120 ms RTT, you need to be able to have ca. 700 KBytes
of data "in flight"; round up and call it a megabyte.
Having said that, I too have tried to configure Windows to use
a large send buffer, and failed. (In my case, it was Windows
machines at a remote location sending to Linux machines.)
I'm not a Windows person; maybe I didn't try hard enough. In
the event, I threw up my hands and installed a Linux proxy server
at the remote site, appropriately configured, and went home happy.
Jim Shankland
