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Thread: MTU, Rwin and TCP Window Help

  1. #1
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    Exclamation MTU, Rwin and TCP Window Help

    Hi,

    I am trying to optimize my 50Mbps fiber internet.
    When I use TCP-IP Analyzer I get the report below.

    So I want to ask some questions to better understand some options. I don't have much experience about networking tweaking. I made some searches but I couldn't find satisfying answers.

    1) It says that I must change MTU to 1500. Though I did so by using TCP Optimizer, analyzer page still shows MTU 1452. Somewhere is written that if you are using PPPoE, it is ok to have 1492. Though I changed it to 1492, this analyzer page still shows it 1452. And since it makes all calculations according to 1500, I don't know what numbers shall I use for other options like Rwin. I also tried to change MTU from modem interface but there is no option for it and I can't also change PPPoE connection type. So what MTU shall I use now or how can I change MTU to 1500?

    2) I can't see the Rwin value in my computer by using TCP Optimizer. Do I miss something? How can I see and change Rwin value? And what Rwin value shall I use? I tried Ashampoo Winoptimizer internet tuner to change rwin and mtu but I am not sure, if it made that changes correctly. Some says 65K is enough but below it suggest over 1 millions some even suggest 2 millions. What shall I exactly use for 50Mbps fiber internet and how will change that value?

    3)It writes in this report that "Your TCP Window limits you to: 2598 kbps (325 KBytes/s) @ 200ms" and "Your TCP Window limits you to: 1039 kbps (130 KBytes/s) @ 500ms" And when I use my hosting firm's FTP I exactly stuck with around 300KB/s. Though they said there is no cap in their side I can't go up. At some other ftps I can go up to 2MB/s. How can I increase this limit? Is it something to do with Rwin?

    Thanks. I appreciate any help...

    ----------------------------------------------

    TCP options string = 0204058401010402

    MTU = 1452
    MTU is not fully optimized for broadband. Consider increasing your MTU to 1500 for better throughput. If you are using a router, it could be limiting your MTU regardless of Registry settings.

    MSS = 1412
    MSS is not optimized for broadband. Consider increasing your MTU value.

    Default TCP Receive Window (RWIN) = 64952
    RWIN Scaling (RFC1323) = 0 bits
    Unscaled TCP Receive Window = 64952

    In Windows 7, unless "TCP/IP Auto-Tuning" is disabled, only the Current TCP Window is displayed. Use the latest TCP Optimizer for tweaking.
    RWIN is a multiple of MSS
    Other RWIN values that might work well with your current MTU/MSS:
    64952 (up to 2 Mbit lines, depending on latency. MSS * 46) <-- current value
    129904 (1-5 Mbit lines, depending on latency. MSS * 46 * 2)
    259808 (2-14 Mbit lines, depending on latency. MSS * 46 * 2^2)
    519616 (8-30 Mbit lines, depending on latency. MSS * 46 * 2^3)
    1039232 (25-60 Mbit lines depending on latency. MSS * 46 * 2^4)

    bandwidth * delay product (Note this is not a speed test):

    Your TCP Window limits you to: 2598 kbps (325 KBytes/s) @ 200ms
    Your TCP Window limits you to: 1039 kbps (130 KBytes/s) @ 500ms

    MTU Discovery (RFC1191) = ON

    Time to live left = 117 hops
    TTL value is ok.

    Timestamps (RFC1323) = OFF
    Selective Acknowledgements (RFC2018) = ON

    IP type of service field (RFC1349) = 00000000 (0)

  2. #2
    Regular Member KEiGHT's Avatar
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    Hi there,

    Open Command Prompt with Run As Administrator (meaning right click and choose Run As...)
    And copy/paste these commands one by one and press ENTER until you see OK !

    netsh int tcp set global autotuninglevel=restricted
    netsh int tcp set heuristics wsh=disabled
    netsh int tcp set global congestionprovider=ctcp

    Restart PC , then try again speed test !
    Last edited by KEiGHT; 11-23-14 at 01:29 AM.
    Every man has his destiny.

  3. #3
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    Thanks for the response. It worked once but didn't work at all afterwards. I didn't understand why. First time I tried; MTU still didn't change but RWIN was showing 1 million and limits were increased. But afterwards the values returned back to previous settings. I tried some different combinations for these settings but didn't help.

  4. #4
    Regular Member KEiGHT's Avatar
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    Open Command Prompt(cmd.exe) with Run As Administrator (meaning right click and choose Run As Administrator)
    Every man has his destiny.

  5. #5
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    I exactly did so. I saw OK message after every command. I even tried with TCP Optimizer but still the same.

  6. #6
    Administrator Philip's Avatar
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    Windows 7 advertises the current TCP Window in packets (it changes), that is why you can't see the maximum value in the Analyzer.
    PPPoE adds some more headers to packets, that is why the useful payload is smaller (i.e. you can't set MTU to 1500).

    If you used the TCP Optimizer that should give you some improvement. Other than that, you may want to look at your modem signal levels.

  7. #7
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    I see, thank you very much...

  8. #8
    Regular Member KEiGHT's Avatar
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    [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Afd\Parameters]
    DefaultReceiveWindow = 1024000
    DefaultSendWindow = 1024000

    set it to decimal
    Every man has his destiny.

  9. #9
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    Thanks for trying to help, but it didn't work either. I couldn't manage to change RWIN whatever I did...

  10. #10
    Administrator Philip's Avatar
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    Hakey, like I mentioned, in Windows 7 you can only adjust how aggressively the RWIN value is allocated, you can't change the actual number.

    As for the MTU value - it is dependent on the type of your connection as well. DSL PPPoE is limited to 1492 or 1480 because it adds PPPoE headers to each packet. Some routers/ISPs may limit it to 1452 as well, I wouldn't worry too much, just be aware of the limitation. You just may want to make sure the limit is not in your client PC or router.

    The Analyzer report is partially correct in that "Your TCP Window limits you to: 2598 kbps (325 KBytes/s) @ 200ms"... With Windows 7 and newer OSes, only the "current" RWIN value is reported by your end, not the maximum RWIN value. Your OS supposedly adjusts this with each packet depending on network conditions.

    If you're stuck at ~300Kbytes/sec that is about 2.5 Megabits connection (upstream limit if you're serving files via FTP). You may have better luck checking your modem signal levels, latency etc. if you have already tried the TCP Optimizer.

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    Thanks for the reply Philip. I got what you mean. I am just trying to find a reason for my low ftp download speed. So just desperately trying any option to solve the problem. I just gave a try KEiGHT's message because I am out of solutions here. But thanks for making it clear for me again

  12. #12
    R.I.P. Nov 2015 RaisinCain's Avatar
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    Your download speed is mainly dependent on the source you are getting the file(s) from- especially during an FTP transfer.

  13. #13
    Regular Member KEiGHT's Avatar
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    In that case, my advise is to dld a fresh copy of Windows 7 Ultimate from digital media, untouched ! maybe your windows has an issue with autotuninglevel...
    Every man has his destiny.

  14. #14
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    Quote Originally Posted by RaisinCain View Post
    Your download speed is mainly dependent on the source you are getting the file(s) from- especially during an FTP transfer.
    Yeah I know, but I am talking about the ftp server of a big hosting company and they say they have no limit in their side and they can easily go up to 1.2MB/s easily with single connection. I had also some speed issues and TCP optimizer solved pretty much all of them, yet this problem is persistent.

    Quote Originally Posted by KEiGHT View Post
    In that case, my advise is to dld a fresh copy of Windows 7 Ultimate from digital media, untouched ! maybe your windows has an issue with autotuninglevel...
    I don't have that option yet but I'll give it a try when I have

  15. #15
    Administrator Philip's Avatar
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    If you can download up to 2MB/s from other FTPs as you mention in your first post, it must have something to do with this particular one, or the route to it.
    Is it more distant than other FTPs ?
    Are the other/fast FTPs on your ISP, or different ones ? (sometimes your throughput to your ISP is higher than that to distant servers)

  16. #16
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    Yeah I think so too. But though I created several tickets they insist they have no problem on their side. I can go up to 2MB/s on some FTPs but not for all and also it is not stable at also. It is constantly moving between 300KB and 2MB. Though I should be able to go up to stable 3 MB/s if not 5 MB/s. So I thought it is something to do with my settings of connection. FTPs are usually in USA in different companies. I connect from Turkey. So in short I can't get the peak potential I can reach in FTP servers mostly and when I saw 300KB/s on the analyzer I thought it is something to do with RWIN but I think this is not the case.

    When I do speedtest to the cities closest to the servers in USA I can get up to 30 Mb/s. But when I connect to FTPs I see an unstable 2MB/s at most. And I can only see 300KB/s with my current hosting.

  17. #17
    Regular Member KEiGHT's Avatar
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    that's because of your RWIN autotuninglevel = disabled ! dld untouched win 7 from the site mentioned above !
    Every man has his destiny.

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