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300 Mbps service Speed Randomly Limited to 100 Mbps (Ethernet network)

RunLife Posts: 3 Spectator

2 Computers on Ethernet Connection to Router both loose speed at the same time. First 2 months of new service consistently getting at least 300 Mbps. For the last 3 days I have had 3 random speed drops to under 100 Mbps. Rebooting the router or modem returns speed to 300 Mbps on each computer, but only for a day. So this is not a wifi issue and not a computer setting issue since it happens on both computers at the same time.

Any ideas on what is causing this all of a sudden?


Spectrum Supplied Modem: Hitron E31N2V1 (2 months old)

Router TP-Link Deco x20 AX1800 Mesh (2 months old)




  • Renee_T
    Renee_T Posts: 698 ✅ Verified Employee Moderator

    Hello @RunLife!

    Welcome to our community! From what you're describing, it sounds like there may be a wireless interference issue. If your router is changing wireless channels, it can impact the speeds, even on wired devices. Do you notice if the issue happens around the same time every day or if there's anything that seems to be going on around the time the issue happens, such as a neighbor getting home from work or maybe a kid coming home from school?

  • HT_Greenfield
    HT_Greenfield Posts: 765 Contributor

    Those symptoms sound like cable modem thermal throttle mode which is unfortunately presumably not too uncommon. Try to maximize the ventilation and minimize the ambient heat around the modem and make sure it's standing upright as intended and see what happens.

  • RunLife
    RunLife Posts: 3 Spectator

    HT_Greenfield Thanks for your reply. The modem is standing upright and located in my basement. If anything the ambient temperature in my basement has been cooler since this started.

    I discussed location with the Spectrum Tech that installed it and he was fine with it.

  • RAIST5150
    RAIST5150 Posts: 918 Contributor
    edited November 2022

    May want to try resetting the TCP stack if it is a windows box... still prone to knackering the dynamic receive window during windows updates. Happened to me with the October cumulative update... laptop was throttling to around 180, but tests from the phone and the router itself were pegging 308+ downstream.

    Can run the TCPOptimizer tool (as admin) from to reset it to windows defaults (or try the optimized profile, as it may work better for some use cases).

    Otherwise... have you tried bypassing the TPLink when it happens? (IE: direct connecting to the modem) Or swapped in a different router?

    I ask b/c I once had issues with a TPlink throttling down like that and had to return it. Forget the specifics of it... think it was based around Archer C7 design... or was it C8?

    Never did figure out if it was maybe in the NAT acceleration features that could eventually be addressed via firmware, or something more hardware specific like with the screwy latency problems in the Intel Puma chipsets. All I knew was that when I went back to a much older Asus router (RTAC66U) it meant to replace, the problems went away. So I returned it to Office Depot and opted to spend the extra on a newer Asus model again.

    That AC86U upgrade is still running strong years later, so it appears it was a worthwhile investment.

    So it may be worth taking steps to rule out something with the TPLink router, just in case.

    Could simply be something with the QoS implementation that they need to address in firmware--if it becomes more stable with QoS disabled, that may well be it. QoS tends to disable some acceleration features often needed to sustain higher throughput levels. Will tend to see things like CPU load and thermals increase because of it. If you can isolate such a trend, may want to contact TPLink about it.

    If it turns out to be more of a chipset related issue though... may have to consider a replacement.

  • RunLife
    RunLife Posts: 3 Spectator

    RAIST5150 Thanks for the reply. I don't think it is a Windows PC setting issue, I changed the Network Device setting for Speed & Duplex from the default 'Auto Negotiate' to '1.0Gbps Full Duplex', but that didn't seem to help. I have 2 Win 10 PC's connected by ethernet and when the speed drops it hits both PC's simultaneously. They are not on the same Win 10 update version. I also have an iMac 27" connected by ethernet and that gets hit at the same time also.

    To add to the possibilities, I have a 5 port ethernet hub connected to the main Deco router that I use to connect the ethernet to the PC's. The Deco X20's only have 2 ethernet ports. I think I have ruled out the 5 port hub, as the iMac is ethernet connected to a satellite Deco X20 (bypassing the 5 port hub) and gets hit with the speed loss too.

    I was thinking of doing what you suggest by connecting the 5 port hub direct to the Spectrum modem, then ethernet to the main Deco X20 which would just feed my Wifi devices. This way the PC's will bypass the Deco X20 router and isolate the problem to either the Spectrum Router or the 5 port Hub.

    I will be bummed out if the problem is the TP-link Deco system as it is a vast improvement for Wifi throughout my home. I have the Main Deco in the office, one satellite in the living room and one upstairs in a bedroom. They aren't like range extenders, the bedroom unit is furthest away from the main unit and if I connect a PC to that satellite unit I get the same speed as I'm getting from the main unit.

    In the meantime, after rebooting the Spectrum Modem yesterday the speed drop hasn't happened again, so maybe it's the Modem. Thanks again.

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