TCP and WAN issue

Marshall Eubanks tme at multicasttech.com
Wed Mar 28 12:34:04 UTC 2007


On Mar 28, 2007, at 5:12 AM, Andre Oppermann wrote:

>
> 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
>

And, of course, if you have Ethernet duplex or other mismatch issues  
anywhere along the
path, performance will be bad.

Regards
Marshall


> -- 
> 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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