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Motorola Arris SB6121 very slow download but good upload speed...

Frequent Visitor

Motorola Arris SB6121 very slow download but good upload speed...

Just got new service of 60/5 mbps and at times, the download gets horribly slow.

I got over 60 mbps download and after around an hour, it was 1.1 mbps down but upload was still at 6mbps.

I have a Netgear N300 router that connects to my laptop via ethernet cable.

 

I'll test directly without the router and see if it's modem or the router but how can the upload be great all the time but only download drops to a crawl?

Is there something I can do like upgrade firmware of the modem?

Expert

Re: Motorola Arris SB6121 very slow download but good upload speed...

The firmware will be pushed by Comcast so nothing for you to do there. Try your speeds after directly connecting to the modem via ethernet.

 

See: troubleshooting guide. If you still need help, please post your equipment details (make/model of your modem/gateway/router) and a screenshot of your signal levels and your error/event log. Thank you!

 

 


I am not a Comcast employee, just a moderator. Pls observe Wheaton's Law.
Frequent Visitor

Re: Motorola Arris SB6121 very slow download but good upload speed...

I'll try that.

BTW, is there a web address to access the modem to see it's status/connection etc?

Routers have that but what about modem?

Expert

Re: Motorola Arris SB6121 very slow download but good upload speed...


@Mystery132 wrote:

I'll try that.

BTW, is there a web address to access the modem to see it's status/connection etc?

Routers have that but what about modem?


http://192.168.100.1/


I am not a Comcast employee, just a moderator. Pls observe Wheaton's Law.
Frequent Visitor

Re: Motorola Arris SB6121 very slow download but good upload speed...

The issue persists.

It looks like after few hours of regular download speeds, it goes to very slow downloads.

Upload is more consistent and speed is still 5-6mpbs even when download is around 2mbps.

It usually works when I power cycle the modem.

Is my modem messed up?
I'll buy another and try.

BTW, I talked with support and the agent said my modem status is showing up red.

She sent reset signal but that didn't resolve the red status.

 

Here is the signal for this modem: snr is around 30 and power level is -17, too low?

 

DownstreamBonding Channel ValueChannel ID29 22 28 31 Frequency651000000 Hz 615000000 Hz 645000000 Hz 669000000 Hz Signal to Noise Ratio30 dB 29 dB 30 dB 31 dB Downstream ModulationQAM256 QAM256 QAM256 QAM256 Power Level

The Downstream Power Level reading is a snapshot taken at the time this page was requested. Please Reload/Refresh this Page for a new reading

-17 dBmV  -17 dBmV  -16 dBmV  -16 dBmV  

Motorola Arris SB6121 xfinity signal 20180324.jpg
Diamond Problem Solver

Re: Motorola Arris SB6121 very slow download but good upload speed...

Your signal stats are horrible !! A new modem won't help a line / connectivity issue.

 

In a self troubleshooting effort to try to obtain better connectivity, check to see if there are there any excess/unneeded coax cable splitters in the line leading to the modem that can be eliminated/re-configured. Any splitters that remain should be high quality and cable rated for 5-1002 MHz, bi-directional, and no gold colored garbage types like GE, RadioShack, RCA, Philips, Leviton, Magnavox, and Rocketfish from big box stores like Home Depot, Lowes, Target, Wal-Mart etc. Splitters should be swapped with known to be good / new ones to test

If there aren't any unneeded splitters that can be eliminated and if your coax wiring setup can't be reconfigured so that there is a single two way splitter connected directly off of the drop from the street/pole with one port feeding the modem and the other port feeding the rest of the house/equipment with additional splits as needed, and you've checked all the wiring and fittings for integrity and tightness and refresh them by taking them apart then check for and clean off any corrosion / oxidation on the center wire and put them back together again, then perhaps it's best to book a tech visit to investigate and correct.


Frequent Visitor

Re: Motorola Arris SB6121 very slow download but good upload speed...

No splitters as we don't have TV cable service.
Modem is hooked up to the wall directly using the coax cable Comcast sent.

 

I have another coax wall plate in upstairs room but not sure if that's the same as this one.

I'll see if that is active.

Frequent Visitor

Re: Motorola Arris SB6121 very slow download but good upload speed...


Tried the outlet upstairs and it has slightly better signals.

Here's the screenshot.

I'll plug the router and check if download is consistent here as I can't just have one computer hooked up in the house.

Motorola Arris SB6121 signal upstairs - 20180324.JPG
Diamond Problem Solver

Re: Motorola Arris SB6121 very slow download but good upload speed...

Still bad. Perhaps there is a problem with the coax cable drop / main feed from the pole / pedestal. Perhaps you should consider getting a tech out to investigate / correct. Good luck !

Frequent Visitor

Re: Motorola Arris SB6121 very slow download but good upload speed...

My new mode/router combo Arris SBG6400 got here today and here are the signals.

It has better SNR than what I had with SB6121 but I see power levels are still pretty low at aroun -17.

This is in the living room.

I'll leave it for a day or two to see if speed is consistent during the day followed by testing upstairs where it should get slightly better signals.

 

 

Arris SBG6400 signal 20180328.jpg
Diamond Problem Solver

Re: Motorola Arris SB6121 very slow download but good upload speed...

Still no good..............

Frequent Visitor

Re: Motorola Arris SB6121 very slow download but good upload speed...

Thanks for reply EG.

I'll monitor it for few days for speed drops.

If it doesn't and consistently gives 70/6 speeds, I don't mind low signal levels as my service is only 60/5 and that won't get any better regardless of signal levels.

 

BTW, I also bought a Netgear C3700 modem/router that has dual band wifi.

I'll try that next and see how it goes.

Comcast tech visit may cost me so I'm trying to make sure it's not the modem. 

Haha... I have now 3 modems to play with.

Diamond Problem Solver

Re: Motorola Arris SB6121 very slow download but good upload speed...


@Mystery132 wrote:

 

If it doesn't and consistently gives 70/6 speeds, I don't mind low signal levels as my service is only 60/5 and that won't get any better regardless of signal levels.

 

It's not just about speeds. It's also about reliabilitiy.

 

BTW, I also bought a Netgear C3700 modem/router that has dual band wifi.

I'll try that next and see how it goes.

Comcast tech visit may cost me so I'm trying to make sure it's not the modem. 

Haha... I have now 3 modems to play with.

 

It's not the hardware. It's in the line somewhere...


 

Frequent Visitor

Re: Motorola Arris SB6121 very slow download but good upload speed...

In this case, will the tech visit cost me or will it be on their side if it's the line that has issue?
I see coax cable on the side of house that splits into 3 and goes inside.
Should I test signal there before the split??
Btw, I tested speed in phone from upstairs room and Wi-Fi speed is 12/26.
How is it possible ro get 26 mbps upload from 5mbps service?
Screenshot_2018-03-29-07-46-57.png
Expert

Re: Motorola Arris SB6121 very slow download but good upload speed...

Typically the signal issues you are experiencing are related to wiring. You own the inside wiring, so typically yes, Comcast will bill you to get that fixed. 

 

Tip: sign up for the Service Protection Plan (SPP). It's around $6 a month and you must keep it for at least 60 days after your service call. If you have SPP, you won't incur a service charge. You can sign up when you schedule an appointment.


I am not a Comcast employee, just a moderator. Pls observe Wheaton's Law.
Frequent Visitor

Re: Motorola Arris SB6121 very slow download but good upload speed...

Hmm... is the SPP fee associated with monthly fees?

If I start now, after a week of service, does that mean I have to have it at least for 3 months?

Silver Problem Solver

Re: Motorola Arris SB6121 very slow download but good upload speed...

Yeah, the service plan is a good idea if you don't know if the problem is inside or out. can save you a bit, if you need a few tech visits to sort your inside wiring. Don't cancel until 60 days after the last visit as Nerd says.

https://www.xfinity.com/support/articles/service-protection-plan

 

Frequent Visitor

Re: Motorola Arris SB6121 very slow download but good upload speed...

Here's the signal levels on my last modem, Netgear C3700.

Not sure what 551 uncorrectables mean.

 

It's so far working great but if internet speed is inconsistent, I'll have a tech come out.

thanks

 

Netgear c3700 modem status-20180330.PNG
Diamond Problem Solver

Re: Motorola Arris SB6121 very slow download but good upload speed...


@Mystery132 wrote:

Here's the signal levels on my last modem, Netgear C3700.

 

They were terrible as well.

 

Not sure what 551 uncorrectables mean.

 

Notice that on that channel that the SNR is even lower than others. That channel has even more noise on it, hence there are more correctable and uncorrectable bit errors.

 

It's so far working great but if internet speed is inconsistent, I'll have a tech come out.

 

It's a problem just waiting to become worse. Get a tech !! 


 

Frequent Visitor

Re: Motorola Arris SB6121 very slow download but good upload speed...

Thanks EG.

So I moved this c3700 to upstairs outlet and the uncorrectables are completely gone now.

It had bunch of correctables like 2, 951013, 959, 174 on channels 22, 16, 17, 18 and one uncorrectables  of 551 on channel 16.

Connected to upstairs, correctables are only 23 and 1 on channels 24 and 27 with no uncorrectables.

Also SNR are all more than before.

Does this mean, downstairs cable is worse than upstairs?

 

I'm using 5G mode on and wireless speeds are 71mbps/7mbps.

That's much better than my service level agreement.

I'll keep tech visit in mind but if it works like this, I'm happy.

Netgear c3700 modem status-20180330-upstairs.PNG
Diamond Problem Solver

Re: Motorola Arris SB6121 very slow download but good upload speed...


@Mystery132 wrote:

Thanks EG.

So I moved this c3700 to upstairs outlet and the uncorrectables are completely gone now.

It had bunch of correctables like 2, 951013, 959, 174 on channels 22, 16, 17, 18 and one uncorrectables  of 551 on channel 16.

Connected to upstairs, correctables are only 23 and 1 on channels 24 and 27 with no uncorrectables.

Also SNR are all more than before.

 

It's a bit better but it's still lousy.

 

Does this mean, downstairs cable is worse than upstairs?

 

So it would seem but not much.

 

I'm using 5G mode on and wireless speeds are 71mbps/7mbps.

That's much better than my service level agreement.

I'll keep tech visit in mind but if it works like this, I'm happy.

 

As I commented earlier, it's not just about speeds. It's also about reliabilitiy. Good luck !!