ndt-users list created

[Clarke Morledge <>]

On Wed, 23 Apr 2008, Richard Carlson wrote:

> The NDT sending process (C2S or S2C) runs in a tight 'do loop" dumping 8KB 
> buffers down to the kernel for delivery over the network.  I am currently 
> testing a change in the C2S test to move 64 KB blocks down to the kernel to 
> overcome a problem with Windows based hosts.  The kernel is responsible for 
> breaking these buffers into packets and TCP then delivers them across the 
> network.  All the data generated by the application should be sent to the 
> remote receiving host.  I would be interested in seeing network traces that 
> show some data blocks getting dropped by the kernel.

Rich,

Are you at liberty to discuss what the problem is with Windows based 
hosts?  We are seeing some cases where Windows XP does not have the same 
performance numbers when compared to hosts with other OSes.  But we 
haven't been able to make a good apples-to-apples comparison yet.

One thing we've been seeing is that in a high bandwidth, low latency 
environment that if a Windows host sees a number of TCP packets delivered 
to it out-of-order that the TCP/IP stack does not always handle that 
situation very well.  I do NOT have enough hard data available to stand on 
that observation, but it has come up frequently enough on our NDT tests 
that I was wondering if anyone has discovered something peculiar with the 
Windows TCP/IP stack.

This could just be a corner case due to some local architectural issues we 
have, but your comment drew my interest.

Thanks.

Clarke Morledge
College of William and Mary
Information Technology - Network Engineering
Jones Hall (Room 18)
Williamsburg VA 23187