North American Network Operators Group
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Re: TCP and WAN issue

  • From: Andre Oppermann
  • Date: Wed Mar 28 05:15:28 2007

Marshall Eubanks wrote:

You might want to look at this classic by Stanislav Shalunov

http://shlang.com/writing/tcp-perf.html

The description on this website is very good.

Disclaimer: I'm a FreeBSD TCP/IP network stack kernel hacker.

To quickly sum up the facts and to dispell some misinformation:

 - TCP is limited the delay bandwidth product and the socket buffer sizes.
 - for a T3 with 70ms your socket buffer on both endss should be 450-512KB.
 - TCP is also limited by the round trip time (RTT).
 - if your application is working in a request/reply model no amount of
   bandwidth will make a difference.  The performance is then entirely
   dominated by the RTT.  The only solution would be to run multiple
   sessions in parallel to fill the available bandwidth.
 - Jumbo Frames have definately zero impact on your case as they don't
   change any of the limiting parameters and don't make TCP go faster.
   There are certain very high-speed and LAN (<5ms) case where it may
   make a difference but not here.
 - Your problem is not machine or network speed, only tuning.

Change these settings on both ends and reboot once to get better throughput:

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters]
"SackOpts"=dword:0x1 (enable SACK)
"TcpWindowSize"=dword:0x7D000 (512000 Bytes)
"Tcp1323Opts"=dword:0x3 (enable window scaling and timestamps)
"GlobalMaxTcpWindowSize"=dword:0x7D000 (512000 Bytes)

http://www.microsoft.com/technet/network/deploy/depovg/tcpip2k.mspx

--
Andre

Marshall


On Mar 27, 2007, at 4:26 PM, Philip Lavine wrote:


To all,

I have an east coast and west coast data center connected with a DS3. I am running into issues with streaming data via TCP and was wondering besides hardware acceleration, is there any options at increasing throughput and maximizing the bandwidth? How can I overcome the TCP stack limitations inherent in Windows (registry tweaks seem to not functions too well)?

Philip






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