Unstable internet

[JMy1]

Hello .  For the past 2 weeks my internet has been going from 116 down to 9 down then up and down between the two.   One or 2 days ok but now it is over 2 weeks .  You call customer support they want to restart your modem , which i have done more than once.  I have also put in place a router between the modem and the internet that did nothing same results.   What;s going on with comcast ?  

[EG]

Start here;

https://forums.xfinity.com/t5/Your-Home-Network/Connection-Troubleshooting-Tips/m-p/1253575#M94474

Post the requested info from here;

https://forums.xfinity.com/t5/Your-Home-Network/Information-Requested-for-Connection-Related-Posts/m...

[JMy1]

I have the same problem if directly connected to the modem or using the router.  The same conditions occur almost exactly.

Router is nighthawk AC1900 - R7000

Again it does the same thing with the router attached or no router attached just the modem.

[EG]

Can't see your pics. Since you are a new poster, they need to be approved by a Forum Admin. That could take some time. In the interim, you could try hosting them at one of those free third-party pic hosting sites like Imgur or Photobucket and post the link to them here.

[JMy1]

I have had this service for about 6 months now.  The bottom light of the modem is always blinking very fast when directly connected to pc.  It seems to slow down when the router in included.  Dslreports speed test is 9.29 megabit/s Down and 5.69 megabit/s up,  Xfinity gives the following -

9.29 megabit/s Down and 5.69 megabit/s up

Xfinity is showing 80.1 Mbps Down and 5.8mbps up , 26ms , IPv4 , Detroit MI

When I am watching a youtube video the video stops playing and the buffering symbol in middle of video keeps going for about 1 minute then starts playing again.

I also get the freeze on other web pages.  Firefox freezes and will not connect to internet , check event viewer there will be some kind of dns server error.

[JMy1]

I have turned off modem and router for about an hour then turned on only the modem no router , the same contions start all over.  The same even with the router connected.

[EG]

I'll repeat;

Can't see your pics. Since you are a new poster, they need to be approved by a Forum Admin. That could take some time. In the interim, you could try hosting them at one of those free third-party pic hosting sites like Imgur or Photobucket and post the link to them here.

[JMy1]

here is a cut and paste

Channel Lock Status Modulation Channel ID Frequency Power SNR Correctables Uncorrectables
1                Locked       QAM256   17 573000000 Hz             5.7 dBmV     35.4 dB    21     0
2 Locked QAM256 1 471000000 Hz 7.5 dBmV 37.7 dB 0 0
3 Locked QAM256 2 477000000 Hz 6.8 dBmV 37.4 dB 0 0
4 Locked QAM256 3 483000000 Hz 6.5 dBmV 37.3 dB 0 0
5 Locked QAM256 4 489000000 Hz 6.2 dBmV 37.2 dB 0 0
6 Locked QAM256 5 495000000 Hz 6.6 dBmV 37.2 dB 0 0
7 Locked QAM256 6 507000000 Hz 5.7 dBmV 35.2 dB 0 0
8 Locked QAM256 7 513000000 Hz 5.1 dBmV 36.7 dB 2 0
9 Locked QAM256 8 519000000 Hz 5.5 dBmV 36.8 dB 0 0
10 Locked QAM256 9 525000000 Hz 6.0 dBmV 36.9 dB 2 0
11 Locked QAM256 10 531000000 Hz 6.2 dBmV 37.0 dB 3 0
12 Locked QAM256 11 537000000 Hz 6.0 dBmV 36.9 dB 3 0
13 Locked QAM256 12 543000000 Hz 5.9 dBmV 36.9 dB 1 0
14 Locked QAM256 13 549000000 Hz 6.0 dBmV 36.9 dB 2 0
15 Locked QAM256 14 555000000 Hz 6.0 dBmV 36.8 dB 3 0
16 Locked QAM256 15 561000000 Hz 6.1 dBmV 36.8 dB 8 0
17 Locked QAM256 16 567000000 Hz 5.8 dBmV 35.6 dB 0 0
18 Locked QAM256 18 579000000 Hz 5.8 dBmV 36.5 dB 0 0
19 Locked QAM256 19 585000000 Hz 5.7 dBmV 36.5 dB 0 0
20 Locked QAM256 20 591000000 Hz 5.8 dBmV 36.3 dB 0 0
21 Locked QAM256 21 597000000 Hz 5.6 dBmV 36.3 dB 0 0
22 Locked QAM256 22 603000000 Hz 5.3 dBmV 36.0 dB 0 0
23 Locked QAM256 23 609000000 Hz 5.4 dBmV 35.8 dB 0 0
24 Locked QAM256 24 615000000 Hz 5.8 dBmV 36.1 dB 0 0

Upstream Bonded Channels
Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power
1 Locked ATDMA 4 5120 Ksym/sec 16600000 Hz 40.3 dBmV
2 Locked ATDMA 1 5120 Ksym/sec 35800000 Hz 38.8 dBmV
3 Locked ATDMA 2 5120 Ksym/sec 29400000 Hz 40.3 dBmV
4 Locked ATDMA 3 5120 Ksym/sec 23000000 Hz 40.3 dBmV
5 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 dBmV
6 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 dBmV
7 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 dBmV
8 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 dBmV

I spaced out the first line.

[EG]

What is the exact make and model number of your cable modem ? 

The SNR is a bit on the low side and it may be intermittently fluctuating even lower to out of spec levels. Perhaps there is some noise ingress into the line(s) somewhere. That can cause random disconnects, spontaneous re-booting of the modem, speed, packet loss, and latency problems.

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.

[JMy1]

Oh and when this happens firefox is still working , bookmarks still work , file open still works , dim function still works , relad page just gets the buffering symbol , just no movement with the internet when this happens , also i don't  know f it pretains , but my cable box the remote selections from menu , to on demand viewing get a lag of about 45 to 60 seconds between any movement to next selection.

[JMy1]

Modem is Netgear CM600 , I bought this just for this  account same for the router.

[EG]

Have you tried any of those tips I supplied ??

[JMy1]

I just replied it is an Modem is Netgear CM600

[JMy1]

I just did another dslreports speed test and it shows 68.3 down and 6.12 up. It also shows comcast all green in the middle circle which is good.

Xfinity speed test is 83.6 down and 5.8 up

I expect there to be some difference between the the two , but earlier it was a huge gap not so much now.

[JMy1]

Speakeasy speed test 71.3 down and 6 up to chicago. Earlier it was 12.6 down and new york was only 9. So these three are pretty much agreeing right now. Dslreports , xfinity , and speakeasy.

[JMy1]

There is one line from the wall to splitter then from splitter to cable tv box and modem which are near each other .  All connections are tight and no kniks in lines.

[JMy1]

I have blast internet this is the speeds i have been getting.  Goes from this to 118 download.  Xfinity Speed Test included and Dslreports Speed Test.

[JMy1]

Time 8:33am new test this is after the previous post by about 10-12 minutes 

[EG]

Download and test using this app;

https://www.speedtest.net/apps/desktop

It does not use any browser. What do you get with it ?

[JMy1]

Here we go again.  Goes from 115-117 to less than 60 down on xfinity and less than 50 down on dslreports speed test.

[JMy1]

Here it is going down further.   This seems like a re acuring problem with comcast internet.

[JMy1]

EG

Expert

‎01-23-2020 12:48 PM

Re: Internet speed goes up and down again

Download and test using this app;

https://www.speedtest.net/apps/desktop

I do not have an microsoft account.  So that does not work for me.   The internet goes up and down like a yo yo , as I have post in other posts on this forum.   My friends and I believe it is with all the people hooking up to comcast's unsecured serivce.   I live in an 11 story apartment building.

[JMy1]

Download and test using this app;

https://www.speedtest.net/apps/desktop

I do not have an microsoft account.  So that does not work for me.   The internet goes up and down like a yo yo , as I have post in other posts on this forum.   My friends and I believe it is with all the people hooking up to comcast's unsecured serivce.   I live in an 11 story apartment building.

[JMy1]

Also if I just run the modem by itself the internet just stops for 5 to 16 minutes.  Using the router I get the posted speeds.  And the speeds are the same with or without the router.  There is nothing in the modem's log to give a clue.

[JMy1]

Oh another interesting fact , when I have the cable tv box plugged in and running I hear lots of tv noise from several apartments.  When I unplug the box no more tv from the apartments.

[EG]

You don't need to have a Microsoft account in order to download that app. Just click on the appropriate blue-colored link for your particular O/S.

[JMy1]

It will not let me get to the download button unless I enter my microsoft account information which i do not have an microsoft account.

[JMy1]

I just finished an malware scan on windows 10 nothing found.

[JMy1]

I just did another speed scan and this is what I got;

[JMy1]

Oh and it does not matter if I am running windows or linux the same thing happens , just not as often on linux.

[JMy1]

the send and recieve lights on the modem just blinked for about 2 minutes during power up. Never done that before. Power light was solid green and internet connection solid green.

[JMy1]

Went from all zero correctable errors to this

[JMy1]

System up time 7 hours

[JMy1]

Notice the correctable errors have gone up since last post.

[JMy1]

Now this is with linux

[dazinger]

looks like I can't bump or anything here (sorry, I guess?) my topic seems to be very much related to yours though.

@JMy1 JMy1, does my thread look like anything you might have mentioned here?  if any of my data helps your problem, feel free to use it.  but, I don't have any pictures or anything just a copy-paste of what it says on my modem.  Any similarities, differences in computer specs?

[JMy1]

These are all dell workstations with 24gig ram etc.  I you live in an apartment building then they might be similiar , i live in an 11 story apartment building.

[dazinger]

Hah, I hope it's not the same 11 story apartment building I'm in! 

[cxrider]

@dazinger @JMy1  you folks need to determine whether or not you're seeing congestion vs errors on the network.    The modem is not the only place you could be seeing errors.     There could be packet errors between the modem and the router or the router and your end device.    Interfaces only know when they *receive* a packet that contains an error, it can not tell whether or not it sent a bad packet or if the packet was corrupted between endpoints.

Devices on the network maintain error counters.   You need to figure out how to monitor the error packets on your router WAN port, your router LAN ports, and the end devices (PC).      Error counters are generally cumulative counters.   Some counters will stop adding counts once they hit their limit other counters will 'roll over' or wrap so you have to pay attention to how they behave.  

Once you figure out how to monitor your error counters you can then see if there is a correlation between counter changes and poor throughput.    If there is no correlation, and more importantly, if the error counters that you can monitor do not increase, you'll want to take the next step which is monitoring for retransmission problems.   If error counters increase then address the connection and ports on both ends; the place where the counters increase is the downstream end.

A retransmission occurs when a system does not get a response to a packet it sent.    Packets sent to remote servers generally expect something back; either an acknowledgement that the packet was received or data.   Machines do not like to wait forever for an expected response and will set a timer for how long it will wait for the response.   If the timer expires before the response is received it will retransmit the original packet.    

To observe this you need to run a tool called tcpdump (unix) or wireshark (unix, windoze).    Retransmission packets have a header in the packet identifying them as a retransmission and they stand out like a sore thumb in wireshark.       A few retransmissions are not abnormal on a busy network.     By a few I mean a dozen in say 10,000 packets captured.     The higher the ratio of retransmits to total packets the worse things are.     

There's a place to start.   Good luck and I'd be interested in seeing what you discover.  

[JMy1]

Hello it seems i have the same problem that i have posted on this forum more than once.  Went from 119 down to the following only have modem no router.

[JMy1]

Here's the modem stuff

[JMy1]

The previous post was under windows 10 now running linux here's what i get

[cxrider]

Let me make sure I have your testing methodology correct.

- You plug your windoze box directly into the modem using the only port available on the modem.

- You run the download speed test from http://www.dslreports.com/speedtest and observe 34.4 Mb/s

- You run the download speed test from http://speedtest.xfinity.com and observe 58.5 Mb/s

- You unplug the windoze box from the modem and plug in the linux box using the same ethernet cable.

- You run the download speed test from http://www.dslreports.com/speedtest and observe 121.5 Mb/s

- You run the download speed test from http://speedtest.xfinity.com and observe 117.3 Mb/s

Your modem report shows nothing wrong *on the coax cable side* of the connection, i.e., between the modem and the CMTS.   It says nothing of conditions between your PC and the modem.    I doubt you have access to interface error counter on the modem but did you check your counters on the PC?   What about tcpdump/wireshark?   Any captures there?  

[JMy1]

I posted the speed tests right above your post closest one to your post is linux nesxt two are windows 10.  Iam using windows 10 now and have the same problem since 8am.   

[cxrider]

And what are the error counters *on your PC while you are experiencing the slow download*?     I do not know whether or not this info is readily available in windoze but this link might help:  http://techgenix.com/DisplayErrorStatisticsontheNetworkConnectionStatusWindow/