XB7 replacement modem speed issues (10% of subscription speed)

So, 10% of the subscription speed, if your device cant negotiate the correct speed it defaults to the next lowest one, which would be 100 Mbps, eerily similar to what your getting, there can be several reasons why this is happening, look on the back of the Xb7, where your ethernet cable is connected, the light next to it should be green, if its amber its not negotiating the faster speed, but defaulting to 100Mbps, so remove the ethernet cable, reinstall it, paying close attention that the ends are completely seated in the ports, this sometimes corrects the problem, if its still amber, i would replace the cable with a known good one...     

Well it isn't just one device. I have tried my desktop PC with a wifi adapter, my phone (both devices on 5ghz), and my NUC upstairs connected directly to the modem. I have also used Xfinity's "test speed to gateway" test without involving any devices. I have included a screenshot. as well. As you can see my upload speed still remains 3mbps above my 800/20 subscription.

thanks!

I'd like to add that regarding the "cable tightening" that it was doing this before I switched out the coax and then after I installed the brand new one (both were tightened on each side.

i didn't say coax cable, i specifically said ethernet cable, two different items, the connecting cable between your computer and the gateway, did you look at the light? 

I know you didn't say coax cable. But what i'm telling you is that without ANY devices involved. The speed to the gateway is where it's slow (coax to modem only). It isn't just slow at the device level. That is why I included that screenshot. That is the gateway test. not the device speed test.

Don't  know if this applies, I just upgraded from 100 to 800mps, with same upgrade from 6 to Xb7 modem. On both ethernet and WiFi my speeds were around 110 130mps. reboots didn't help, green lights on. I didn't switch cable because it worked fine for me on my Xb6. What finally worked for me was forget WiFi network on all my devices,  unplugging and powering down  all ethernet connected and WiFi devices.  Powered on modem then devices, steady 800 to 900 now. 

sorry i don't see any screenshot, i am curious as how you did that test, when you need a device to connect to the gateway to do that test ....

Hello everyone,

It is really awesome to see the community reaching out to help. @Ohio18616 has been working with us to figure out why the new gateway is getting perfect speeds after a reboot and then dropping to ~10%. Having another set of eyes on the problem never hurts though!

I am having the same issue with my XB7 Technicolor gateway.  After any reboot I get the full plan speed of 1.2 to 1.4 Gigs but a few hours later the speed drops to 800 to 900.  I had a Xfinity tech come out and check the signal levels and everything was good.  There's something up with this gateway.  In the first month of use I did not have this issue.  I suspect it's a gateway software issue.  I'm just gonna live with it and see if a later software update returns the modem to full speed.

@smarthur This my take on this subject, the fact that some sometime you get the 1.4 gig speeds tells me that line from the pole outside is delivering the correct speeds to your Xb7, you don't specify your setup, so i am going to assume a few things for sake of a spirited discussion, the fact that you achieve the 1.4 gig speed at all,  tells me you probably have a 2.5 gig adapter on your computer, that is a common, i have one myself, it gives me 3 speed link tiers on the network adapter, 2500 Mbps, 1000 Mbps and 100 Mbps, so when you connect your computer to the Xb7, it negotiates the link speed, ideally it should connect at 2500 Mbps, that does not mean you are going to get that speed, but your going to see speeds over 1000 Mbps, depending on certain variables it could possibly  only connect at 1000 Mbps, even tho the Xb7 can deliver 1400 Mbps, it can possibly only connect at 100 Mbps even tho the Xb7 once again can deliver 1400 Mbps, for a example my speed dropped from 1400 Mbps to just under 100 Mbps, so the math indicated to me it was probably a link negotiating issue, any other number above 101 Mbps i wouldn't have thought that, so to me there a variable why it wasn't connecting at the maximum speed, so i always inspect the easy options first, the first thing i checked was the back of my Xb7, the initiator light next to the ethernet port was amber and not green, so with a 5 second visual check i was able to determine there was a connection issue between my computer and the Xb7, so easy things first, i removed the ethernet cable, reinstalled it making sure the ends were securely seated all the way into ports, checked indicator light again, green, did a speed test 1400 Mbps, success, i could have easily just blamed Xb7, but my Xb7 performs flawlessly so i didn't go that route, also some network cards sometimes have a problem negotiating the correct speeds when set to "auto" , on my network card i can set the speed manually, so in the drop down menu i select the speed i want to connect at, i can only assume that they even offer this option is to easily correct a link speed negotiating problem, I have found also rebooting the gateway will cause the renegotiating the link speeds, it can fix them, but only "temporary" if there is some other issue,  Just my thoughts

Ok, for what its worth, i have had Comcast internet since about 2006 or so when it first was offered in my area, i have never had the speed fluctuate from the advertised speed, its usually more, i read on a post where a guy had his fluctuate, but it was do to a squirrel chewing on his feed coax, i get a steady roughly 1500 Mbps, if it deviates from that, its always something other then the feed to the gateway, the Xb7 performs flawlessly for me, I use 5 different operating systems, all perform stellar, but Microsoft Windows is the worst out of all of them, one reason i believe is the plug and play drivers, they work very well, but i don't seem to remember a device advertised as "Plug and Play with Optimum/Performance" in fact i have drivers on my windows 10 computer, dated 2006, when i try to update them, i am told its the best driver, even tho that driver was dated 7 years before my computer was build....

• Yes it could be, excellent point, but if you look at his numbers he posted, it drops from 1.4 gig to roughly 800 - 900 Mbps, he don’t specify exactly, but those numbers are reminiscent of what I get if my link speed connects at 1000 Mbps, I don’t know exactly how the node thing works, but it seems odd to me that a simple reboot somehow fixes a congested node, I guess it’s possible, I question it tho because I dealt with a similar issue when I got my first Xb7, I know I come across rather eccentric, but let me briefly state my diagnostic practice, so I have had Comcast internet sense roughly 2006, so my block has competitors come canvas us to change to their internet service, they have a list of all the Comcast subscribers and what tier service they have, so I guess it’s against protocol to share that info with you, but they are desperate to make a sale, so if you finesse the questions you ask them, they eventually cave and tell me the info I was fishing for, so I now know 2 neighbors, one on either side of me with the gigabit service, not exactly but close, so anytime I experienced a speed slow down I would consult with them if they experienced the same thing, I figured we probably were on the same node, it was odd that they weren’t experiencing also, so I learned very early with my Comcast service that it was rock solid, I always enjoyed optimum performance, but if happen to a glitch and my speed fluctuates, I don’t even entertain the thought that it could possibly be Comcast, so consequently I can find the issue and remedy it in very short time, I have never failed at this, I read these posts and see similar patterns, every one immediately blames Comcast, some have many customer service phone calls, tech visits only to tell them everything looks good, i by passed all that because I took that as a given, I run multiple operating systems, they all work flawlessly with the Xb7 and the Comcast internet service, so if I suddenly get a issue, it’s mostly likely with windows 10, so let’s say it’s speed issue or conductivity issue, so I boot into another operating system, most of time Linux as it works extremely well, so I do a speed test and analyze the results, so if on a completely different operating system I get the correct speeds, it immediately tells me that there is no issue with Comcast, no issue with any of my hardware because it’s all same computer and same connection, so that pin points to me where the issue is, I have never had a tech come to house, no need to, I am sure where for some depending on their environment where it be a issue, this approach works extremely well for me and my neighbors I consult with, for their cooperation with me I fix any issues that they have, we all enjoy maximum performance and superior conductivity, of course if there is area wide issue, I can’t control that, there are a couple of settings I change on all my computers, I can’t prove it, but it seems to fix issues I was having, I got this information directly from the Microsoft website, I have shared it on here, but it’s so simple it couldn’t work I am told, anyway I believe I am leaving these forum, @eg thanks for the valuable insight you have given me, it has given me a different approaches to solving issues, we have different styles, but combining the best aspects of both into a hybrid system that never fails me …

Just a follow up to this. I was researching on what else I could try to at least narrow down my issue. I looked at using another coax drop from somewhere in my house but as i read  internet is not enabled on just any drop. So I went outside, looked where the one coax cable was going from my modem to the outside of the house, and then traced it to the back of my house. I removed some vines that had grown so the tech could get to them easier (they grow on the side of my house). I noticed that that single cable connects into a sort of barrel connector and then that single cable goes up to my roof and then out towards the telephone pole. 

I inspected this cable by moving it around a bit. Nothing looked loose and it was even grounded to our gas meter. I then decided to just run another speed test about 30min after I was outside just because i was curious. My speed jumped to 900mbps+ out of the 800mbps i am paying for. So basically what it had been running for a few months before I had issues.

For the next week and a half I'd run a few tests a day and the problem didn't seem to occur again. Then today, I was watching a stream while working. I noticed that it kept buffering over and over. I went and did another test. Again the speed to the gateway was now 50-60mbps. I went upstairs and discovered it was POURING down rain. I mean the hardest i've seen it rain all year. 

Cooincidence? Maybe.....but i'm feeling like we are possibly dealing with an outside line issue. Either way my service call is still scheduled for tomorrow. 

Well very astute observation, as one poster in the past had squirrels chewing on his coax, chewed coax, rain, I can see maybe a correlation there

FWIW. Seen it a million times ! It's quite common !

@Scrigface Be sure to point that out to the tech ! Good luck !