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Thread: 1Gbps over Cable Modem issues

  1. #1
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    Unhappy 1Gbps over Cable Modem issues

    I am getting around 200 - 300 Mbps on Speedtest.net on my new Gigabit cable modem connection.

    I am wondering if this is due to the service or my Windows TCPIP settings.

    Here is some info to get the ball rolling.

    SpeedGuide.net TCP Analyzer Results
    Tested on: 2019.02.18 19:55
    IP address: 173.176.xxx.xx
    Client OS/browser: Windows 10 (Chrome 72.0.3626.109)

    TCP options string: 020405b40103030801010402
    MSS: 1460
    MTU: 1500
    TCP Window: 262656 (not multiple of MSS)
    RWIN Scaling: 8 bits (2^8=256)
    Unscaled RWIN : 1026
    Recommended RWINs: 64240, 128480, 256960, 513920, 1027840
    BDP limit (200ms): 10506kbps (1313KBytes/s)
    BDP limit (500ms): 4202kbps (525KBytes/s)
    MTU Discovery: ON
    TTL: 52
    Timestamps: OFF
    SACKs: ON
    IP ToS: 00000000 (0)


    I used TCP Optimizer to 'optimal' and used 'experimental' tuning.

    Any tips to troubleshoot this so I can see if it's my laptop or the service which is the isse?

    Thanks,

    M.

  2. #2
    Administrator Philip's Avatar
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    Considering you've already ran the Optimizer, here are some questions I'd ask before tweaking your settings further:

    Are you using a Wi-Fi connection between your cable modem and the laptop, or a Gigabit Ethernet cable?
    Is your local connection capable of handling higher-speed transfers?
    Do you have another wired client that you can test?
    Have you tried multiple simultaneous high-speed downloads at non-peak times?
    What is the CPU/Resource utilization on that laptop while that test is running?
    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).
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  3. #3
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    Hi and thanks.

    I am using an ethernet connection and tried cat 5e and 6 with same results. Same results on modem or using the router.
    My laptop is new and has a gigabit ethernet adapter.
    No other wired client but my new phone gets 600Mbps on the 5GHz wifi using the router.
    I'm using Speedtest.net with multiple option enabled if that can help.
    CPU does not change much before or during test, max 50% but I have tons of apps open.

  4. #4
    Administrator Philip's Avatar
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    It is possible that your laptop's ethernet adapter caps at that speed, some have a very lax definition of the term "gigabit". For example, even if the adapter is separate and its chipset supports gigabit speeds, it could be connected internally to the USB 2.0 bus with a max theoretical throughput of ~480Mbps. Most on-board host adapters also use and depend on the CPU (whatever slice of it is provided to them).

  5. #5
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    I got an Intel i219-LM onboard on my 2018 Dell business laptop and a RealTek GbE on the Tunderbolt docking station. CPU is fine. I think its the infamous 'last mile' of Cable Modem connection the issue. I got 900Mbps sometimes, but mostly around 300Mbps. I just looked at device manager and my ethernet adapters are connected to the PCI Express buss not USB.

  6. #6
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    regarding RealTek GbE LAN adapters, install the latest drivers for those from Realtek's web site.

    AND make sure Large Send Offload (LSO) is enabled for Realtek GBE as that is usually enabled by default when using those drivers from the Realtek web site (not the built-in Windows OS drivers for Realtek GBE) as I get faster data transfers when LSO is enabled for that realtek gbe lan adapter (actually LSO has two separate "LSO" settings for IPv4 & IPv6 protocols in the realtek adapters "advanced" settings in Device Manager)

  7. #7
    Administrator Philip's Avatar
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    Welcome to SG erpguy, this seems interesting. Have you tested with both LSO off and on? What is the transfer speed difference you get? What model adapter? A few years back many drivers had issues with offloads, just trying to narrow down which ones work well with them.

  8. #8
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    it's really hard to say what kind of transfer speeds I get with the recent Realtek GBE LAN drivers on different PCs, Philip.
    while my family's Dell Inspiron 620 desktop PC (and my custom built PC using a Gigabyte GA-78LMT-USB3 R2 motherboard) do have an onboard Realtek PCIe GbE LAN adapter and using the recent drivers, however the two computers are in different rooms and only my custom built PC can only be connected with a short blue CAT6 cable that I have in my bedroom and the Dell Inspiron PC is only connected thru WiFi and not by wired/ethernet - I would need a very long (maybe about a 100ft) CAT6 cable to test the ethernet connection on the Dell computer

    [GbE = Gigabit ethernet]

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