JMy1's profile

Regular Contributor

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92 Messages

Fri, Dec 13, 2019 6:00 AM

Unstable internet

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 ?  

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JMy1

Regular Contributor

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92 Messages

1 y ago

System up time 7 hours

 

 

JMy1

Regular Contributor

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92 Messages

1 y ago

Notice the correctable errors have gone up since last post.

 

 

JMy1

Regular Contributor

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92 Messages

1 y ago

Now this is with linux

 

 

dazinger

New Poster

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16 Messages

1 y ago

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

Regular Contributor

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92 Messages

1 y ago

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

New Poster

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16 Messages

1 y ago

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

cxrider

Regular Contributor

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89 Messages

1 y ago

@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

Regular Contributor

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92 Messages

1 y ago

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

Regular Contributor

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92 Messages

1 y ago

Here's the modem stuff

JMy1

Regular Contributor

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92 Messages

1 y ago

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

cxrider

Regular Contributor

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89 Messages

1 y ago

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

Regular Contributor

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92 Messages

1 y ago

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

Regular Contributor

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89 Messages

1 y ago

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/

New Poster

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2 Messages

1 y ago

I have the same problem as you do. So frustrating.

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