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Thread: TcpWindowSize is limited

  1. #1
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    TcpWindowSize is limited

    (Sorry for my bad English)
    Hello!

    My TcpWindowSize in registry is 496400.
    I downloaded a WireShark to make sure that all okey.
    And i noticed that my TcpWindowSize is 262144
    Help me, what`s wrong?
    Windows 10, WindowsScalingOption=256
    P.S And TcpAnalyzer say the same

  2. #2
    Administrator Philip's Avatar
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    Windows 10 uses an "auto tuning" algorithm to determine what size RWIN is needed at the moment depending on network conditions. You can control how aggressively this algorithm allocates the RWIN value, however, you can't control it directly, it does not follow the registry value. The relevant settings that are editable in Windows 10 are covered by the TCP Optimizer.
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  3. #3
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    Quote Originally Posted by Philip View Post
    Windows 10 uses an "auto tuning" algorithm to determine what size RWIN is needed at the moment depending on network conditions. You can control how aggressively this algorithm allocates the RWIN value, however, you can't control it directly, it does not follow the registry value. The relevant settings that are editable in Windows 10 are covered by the TCP Optimizer.
    OK but can you please say what parameters are controlling how aggressively this algorithm allocates the RWIN value in Win7\Win10
    As I understood there are: CongestionProvider, autotuninglevel, Tcp1323Opts?

  4. #4
    Administrator Philip's Avatar
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    Autotuninglvl is the one that controls the algorithm, i.e. how much memory is assigned for the TCP Window buffer per connection. it considers the current speed and latency, and assigns a maximum RWIN value based on those parameters.

    Tcp1323Opts only determines if TCP Options are turned on, as defined in RFC1323. This allows for RWIN values of over 65535. The only other thing it controls is timestamps.

    CongestionProvider deals with what the TCP/IP stack does when it encounters packet loss, those are congestion avoidance algorithms. Those algorithms also control how fast the speed scales up in the beginning of a transfer.

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