Cell Relay Archive

["Scott D. Weberg" <sweberg@wes.army.mil>]

I keep reading that the TCP window size has a lot to do with how
fast you can push data thru a unix socket over ATM.  So I went
snooping around, trying to figure out how to set the TCP window
size.  Well, I am assuming that it is configured in the kernel, or
something like that.  I found out how to set the send/receive
buffer sizes, using setsockopt().  I also found out about the 
maximum TCP segment size, which cannot be set by the application,
but is set by the hardware at the time a connection is made.

But I still don't know what the "TCP window size" is - and how it is
set.  There seems to be no socket routines that allow you to set
the TCP window size.  Can someone tell me how you set it?  Is it
something the sys admin has to do?

My next question is about cell-level pacing.  I read a paper
(TCP/ATM Experiences in the MAGIC Testbed) that suggested that cell-
level pacing dramatically improves throughput over an ATM WAN.
What is cell-level pacing?  How do you go about implementing it?
Does it apply at the unix socket level, or at the ATM level?

And finally, I was able to get a little more throughput by setting
the NODELAY flag with setsockopt().  But this was on our LAN.  
What effect will the NODELAY flag have when pushing info over an
ATM WAN?  Will it potentially cause problems?

Thanks for any and all help, suggestions, and pointers to info!

Scott D. Weberg
Computer Scientist
U.S. Army Corps of Engineers