Scenario: From a non-windows-device data is streamed to a windows 2008 server over two TCP-Connections at a continous data rate of x Mbit/s. the link is 1Gbit. Every almost excatly 21 minutes the data rate breaks down to almost zero. Things changed with no effects: datrate, link rate, server hardware, data source, auto-tuning , receiving software, Service packs , server edition Things changed with effects: OS. Changing to windows 2003 does not show this effect with the same binaries. Conclusion: Problem seems to be in Windows 2008 maybe the new TCP stack. Further Analysis: After taking a wireshark record I discovered that a normal function the Tcp window size stayed all the time at 64kb (autotuning disabled). When the data rate starts droping the windows size seems to be reset very unregularly until it drops to zero. The question is why is the windows size not reset. Seems like the data hangs in the stack but is not treated. Is there any parameter to speed this up. Or does anybody have a idea what could happen each 21 minutes an has to be disabled? Look at the two last acks. The data is acknowledged right after receiving the packet ( 14 nanoseconds later) but the windows update takes 2.7 milliseconds after the last packet received. I am happy about any suggestions.

Hi, Have you configure NIC teaming on this server? If so, please try to disable it. And also temporary disable TCP Offloading, RSS and TCP Chimney, to see if the issue still persist. Information about the TCP Chimney Offload, Receive Side Scaling, and Network Direct Memory Access features in Windows Server 2008 http://support.microsoft.com/kb/951037 New Networking Features in Windows Server 2008 and Windows Vista http://technet.microsoft.com/en-us/library/bb726965.aspx Best Regards, AidenAiden Cao TechNet Community Support

Hi, Have you configure NIC teaming on this server? If so, please try to disable it. And also temporary disable TCP Offloading, RSS and TCP Chimney, to see if the issue still persist. Information about the TCP Chimney Offload, Receive Side Scaling, and Network Direct Memory Access features in Windows Server 2008 http://support.microsoft.com/kb/951037 New Networking Features in Windows Server 2008 and Windows Vista http://technet.microsoft.com/en-us/library/bb726965.aspx Best Regards, AidenAiden Cao TechNet Community Support