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Thread: Help for TCP Window configuration

  1. #1
    Junior Member
    Join Date
    Jan 2023

    Help for TCP Window configuration

    Good morning

    I have a 1 Gb fiber connection, win 7 and Chrome 109 and I set TCP Optimizer with these data:

    Chose settings: Optimal
    Connection speed = 100+Mbps
    MTU = 1500
    Autotuning TCP = Normal

    I checked with SG TCP/IP Analyzer, with these results:
    « TCP Analyzer Results »
    Tested on: 2023.01.20 11:59
    IP address:
    Client OS/browser: Windows 7 (Chrome

    TCP options string: 020405b401010402
    MSS: 1460
    MTU: 1500
    TCP Window: 64240 (multiple of MSS)
    RWIN Scaling: 0 bits
    Unscaled RWIN : 64240
    Recommended RWINs: 64240, 128480, 256960, 513920, 1027840
    BDP limit (200ms): 2570 kbps (257 Kilobytes/s)
    BDP limit (500ms): 1028 kbps (103 Kilobytes/s)
    MTU Discovery: ON
    TTL: 119
    Timestamps: OFF
    SACKs: ON
    IP ToS: 00000000 (0)
    I noticed the TCP Window value at 64240, when it should be with BPD calculator with 1Gbit fiber and 5ms average latency, at least 625000.

    I ask for your help to understand what this value depends on and how to raise it.
    NB: Before the fiber i had a 7 Mbps ADSL.

    Thanks to whoever can help me.

  2. #2
    Administrator Philip's Avatar
    Join Date
    May 1999
    Jacksonville, Florida
    Blog Entries
    Newer Windows variants only show the "current" RWIN value, rather than the maximum, and then the autotuning algorithm scales it up as necessary depending on line conditions. I wouldn't worry about the Analyzer showing a smaller value.
    Linux is user friendly, it's just picky about its friends...
    Disclaimer: Please use caution when opening messages, my grasp on reality may have shaken loose during transmission (going on rusty memory circuits). I also eat whatever crayons are put in front of me.

  3. #3
    Junior Member
    Join Date
    Jan 2023
    Thanks Philip. For information, I set TCP autotuning to Experimental, but I encountered some problems: sometimes the download speed drops considerably and then rises again and also the Ookla app from PC doesn't work.

    Thanks again for the reply.

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