TCP and WAN issue

Wed Mar 28 09:12:45 UTC 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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> 
> 
> 
> 