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I have been using Xfinity’s 1.2 Gigabit plan for about 5 months. I was using this with a Netgear C7100V, but as it maxes out at 800Mbps and I no longer get voice service from Xfinity I upgraded to a Arris G36 about a month ago.

My office PC is connected to the G36 via a unmanaged gigabit switch. When I ran speed tests with my Netgear gateway I used to consistently get download speeds around 800Mbps. (My history shows 795-817 Mbps).  Since upgrading I’ve consistently been getting under 500 Mbps. (My history shows I once got 641, but on average it’s 450-460mbps).  Since I’m going through a gigabit switch connected to one of the gigabit ports on the G36 I’m expecting to get closer to 950Gbps. 

Based on similar posts I’ve checked a number of different settings but can’t seem to find anything wrong. Can anyone tell me why I’m not getting the expected speed?  It seems odd that I purchased a newer, faster gateway to only get slower service.

  • I’m using the same cables and hardware that I used with the Netgear gateway, so that is not likely the issue.
  • The Ethernet port is set to Auto Configuration and connected at 1,000 Mbps

  • When I switched the Gateways I worked with Xfinity to have them properly update their system as the old Gateway was DOCSIS 3.0 and the G36 is 3.1.  The G36 is correctly reporting DOCSIS Operating Mode:3.1.

  • Download power level and SNR seem to be within range.

  • I’m not sure how to interpret Error Codewords, but this is what is reported. 

     

a couple things 

  1. test with a directly connected pc and test on xifnity’s speedtest site. 
  2. you have some errors in the line. Start with removing any amplifiers, signal attenuators, or splitters from the coax.
    From there check the line for kinks, damage, moisture in the line.
    Check the connectors for improperly made ends, foil touching the copper coax line, loose connections, bad/old/cheap connectors, or corroded connections. Replace them if you do.
    If you can, simply connect the modem right where the coax comes into the home. This prevents wiring in the home from being the issue. And some ISP’s charge if the wiring issue is in the home. So this helps prevent this.

OK. Now I’m even more confused than before.

I checked the Xfinity box outside and the connection is tight. There was a splitter, but I disconnected that a few months ago when I dropped Cable TV and no longer needed it. The run from the box goes into the house and strait to the modem with nothing else in between and this has not changed between this modem or the previous modem. I also verified the cable connection to the modem was tight.

Before playing with anything I ran a speed test from Xfinity (305.8 Mbps) and Speedtest.net (455Mbps)

Bypassing the switch made no significant difference. (488.31Mbps on Speedtest.net)

I also tried using the 2.5G port instead of one of the 1G ports and that made no significant difference (471.85 Mbps on Speedtest.net)

FYI, the Xfinity speedtest seemed to be inconsistent and varied from 300-600 between tests without even making any changes.

To make things even more puzzling, I ran a speed test over WiFi from my tablet and got 955 Mbps. I also did a speed test on my tablet using my office router (configured as a WAP) and got 871 Mbps.  I also tried switching to the second Ethernet port on my PC and got similar results as before (477 Mbps)

I’ll need to run some more tests. It doesn’t make sense that a speed test over WiFi via a WAP would be faster than using the Ethernet connection the WAP uses.

that does seem very strange. 

Looks like something else is at play here that I can’t figure out that will take some more research to figure out. I tried a different Ethernet cable and was able to get 948 Mbps, so I swapped out the old cable and run the new one behind my desk, ran another test and got 458 Mbps. Thinking maybe there’s some interference I then tried using a Cat7 cable which has better shielding but is a longer cable and got 457 Mbps. I have a couple more things to try included a different computer.

This makes no sense. Using a new Dell laptop with a new docking station that supports gigabit Ethernet. I connected the docking station directly to the G36 using a new 3’ Cat 5e cable. I ran a speed test using speedtest.net and set the server to the local Comcast server. I ran the same test on the two different kinds of Ethernet ports on the G36 as well as WiFi. I really don’t understand why the Ethernet performance is so poor.

  • 1 Gigabit port - 377 Mbps
  • 2.5 Gigabit port - 321 Mbps
  • 5G Wi-Fi - 878Mbps

Just to add yet more confusion. I ran a speed test from my desktop while connected to my office VPN and got 935 Mbps. I then disconnected from the VPN and ran the same test and got 460 Mbps. I would think the VPN would be slower, not faster.

I still haven’t figured this out, but I’m convinced there’s something odd with ethernet on this gateway. I consistently get 450-500Mbps on ethernet despite having 1.2Gb service and all hardware being able to support at least 1Gb. The few occasions where I’ve gotten faster have been a fluke and have not been repeatable.

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