Speed issue, modem log shows high number of uncorrected errors

Thank you @flatlander3

Hello @JG5881 we are very sorry you've encountered issues with your internet speeds, having the Gig plan but only getting around 500-600 mbps, our team would like to provide some assistance.

In addition, I see flatlander3 suggested a few tips, were these tips able to assist you at this time?

I will try out their suggestion of bypassing the splitter and see if that accomplishes anything. Will be back in a few days to update my findings.

@flatlander3​ Thank you for the detailed reply. I actually do use MoCA to get Ethernet backhaul to a mesh system at opposite ends of the house. It works very well and I'd like to keep it if at all possible. But you do raise a good point - I should try to bypass that splitter altogether and see if that changes anything. Will do so when I get a moment and report back my findings. 

I can confirm the modem is coming off the H1 port for the least possible attenuation. I had originally hoped that was just in the wrong port as that might be an easy fix, but nope it's all good. 

@JG5881​ Those ODFM PLC correctables are fine and are just part of the protocol, it's the uncorrectables that are not a good thing.  You got uncorrectables on the channels too, so not so great either.  Might not be the signal power levels at all.  They're still in range, it was just something to look at.  The 16/24's are noise or not locking.  T3 timeout errors on the channels are a similar thing.

This one might be a tech visit to check the line going to your house unless someone's got a better idea.  If you did a clean run and got the same or worse, it might not be your end at all and something upstream.

Remember also, if you are using a 1Gbps port on a MB8600, the best you will see is 860-940ish Mbps -- test speed directly at the modem to remove other gear from the mix (reboot the modem when you hook something up directly to it).  That's just the top end for the 1Gpbs port with driver overhead, but it should be higher than 500Mbps with 1.2G service assuming good Ethernet cables and no link speed bouncing (watch the Ethernet light color on the font panel, that could be happening too but doesn't impact modem signal errors).   If you want faster and have the service, you'll have to pop the hidden cover to expose more Ethernet ports and hook them to something that can bond two Ethernet ports (LAGG).  I'd post the motorola FAQ to remove the cover, but the bot ate it.

That isn't going to help with the current signal issue though.  Fix that first.

Thank you, will have to get a tech out when I find the time, as I'm really out of options to try on my end. The funny thing is I was considering bumping up to the 1.2Gbps plan just to get the corresponding boost on the upload side from 20 to 35. I suspect that would probably be fine as I currently get the full upload speed plus overprovisioning. But now I don't want to change anything until we figure this out first. 

My router only has 1Gbps ports anyway so that's a project for another day.

@JG5881​ I remain largely unimpressed with marketing speak, especially when it comes to "speed".  What is that?  That's a theoretical  calculation based on a spec and number of bonded channels, if the sun is in the correct position and shines just right on the back side of a dog.

1G vs 1.2G?  Well, if you have a lot of users all pulling high bandwidth at the same time, perhaps you'll notice.  I'm not so sure it matters otherwise or if a "speed test" from an unthrottled server on a decent backbone that is close to you is really all that important.

What are you talking to usually?  A leased cloud server somewhere in the world.  Could be anywhere.  What matters for speed in that case?  Everything between you and them, the content, how it's delivered, the service they pay for, and what kind of load balancing they do themselves and your own hardware and OS. 

Example?  Maybe you like to watch a bunch of 4K TVs all pulling UHD streams at 26MB/s or larger at the same time.  Then perhaps you could benefit from a slightly larger pipe -- provided the services aren't throttled per location or you are pulling from different locations for all of the streams. If I am pulling that kind of load, or running a multi-user office, fiber might be the way to go in that case.  You'll be better off on the latency, and it's pretty consistent if you really need that.

Folks may disagree with me and that's fine.  I'm not the one paying for it, so it doesn't matter to me.  As for supported vs unsupported DOCSIS 3.1?  I don't know.  I've never tested it with a protocol analyzer, but that's what you'd need. It's the spec or it isn't, but maybe Xfinity's plant does something different and a firmware tweak matters.  Unknown.

Well the purpose of upgrading to the 1.2Gbps plan would really be more about the upload side, which is currently 20Mbps on my "Gigabit" plan but moves up to 35Mbps on the 1.2 plan. That's pretty significant. I've read about some big upload increase but that isn't coming to folks who use our own modems until who knows when. 

Back to download speeds though, various people here who have the same plan as me tend to get 1100-1200Mbps under ideal conditions (speed test site on the fastest/closest server). If I'm getting only 2/3 that speed at best, and sometimes less than 1/2, also under those same ideal conditions, it strikes me that I am in fact missing out. Will I notice a big difference in day to day use? Probably not. But I'm paying for it and I'd like to get what I'm paying for regardless. If nothing else it's a matter of principal. Frankly if I could get the higher upload speeds on a lower download tier I'd be content to downgrade to a ~500Mbps plan, assuming it actually delivered that amount. That's all the download speed I'm getting most of the time as it is. 

@BruceW​ Yeah the MB8600 was on the list when I purchased it a few years back, and only recently did they change it. Which is obnoxious because 940something Mbps is realistically what a "1Gbps" plan should do. It's not like there's some magic distinction that allows for the remaining Mbps. Granted with overprovisioning their 1Gbps plan could realistically be more like 1100Mbps but still. Also, the MB8600 allows for link aggregation which can exceed that speed, but Comcast won't support that either. 

But for the record, I did upgrade from my old SB6141 to the MB8600 when it was fully supported for Gigabit speeds.

@Jlavaseur​ How did you get your MB8600 to function properly with link aggregation enabled? I enabled mine and would only get ~600MBp on a 1.2 GBps plan. Note I have the Asus RT-AX88U which is capable of accepting link aggregation from modems such as the MB8600 and have configured it correctly. The MB8600 is showing the ethernet port light in the front blue but I am not able to get the GB speed levels.