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Troubleshooting Slow Internet Speeds. Chat wasn't helpful

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Troubleshooting Slow Internet Speeds. Chat wasn't helpful

Hello, let me start off by saying I have a degree in computer network systems and networking has been a hobby of mine for a long time. I try to self-troubleshoot as much as I can before requesting help. I tried working with chat and not only were none of my questions answered, but when I tried to get detailed and move the troubleshooting forward I was disconnected. I work from home most days and rely on a VPN connection to my office to share files constantly, and with the amount of data being sent I require a fast internet connection.

 

My equipment: Netgear CM1150V Modem, Asus RT-AC68P router, X1 4k DVR Box, X1 non-HDR cable box

 

The problem: Since at least 3:30 PM EST today all of my devices in my network have been capped at 37 mbps.

 

What I have done: I run speed tests at least weekly because I am crazy, and I consistently get between 350-450 mbps on my 5Ghz wireless, and wired connections in my network. I have manually restarted the router and modem mutiple times, as well as use Xfinity Assistant to troubleshoot the connection, as well as having a chat representative send refresh signals. Still getting 37 mbps max speed.

 

2 things that I'm curious if it could be causing issues:

1) While Xfinity outage map nor My Xfinity tell me I don't have any service outages, the 2 areas directly to the right of my area on the map, as well as the zip codes in my same town do have outages. Could their outages be affecting my speed even if I don't have a complete outage? The chat rep said no but I don't necessarily buy it.

2) I checked the cable connection page of my modem and noticed a couple of channels don't seem to be right. Would this be a hardware issue with the modem or potentially a wiring issue, or an xfinity signal issue? I will post the information from the modem page.

 

Downstream Bonded Channels
Channel Lock Status Modulation Channel ID Frequency Power SNR Correctables Uncorrectables
1 Locked QAM256 29 675000000 Hz -5.1 dBmV 40.7 dB 0 0
2 Not Locked Unknown 0 0 Hz 0.0 dBmV 0.0 dB 0 0
3 Locked QAM256 2 513000000 Hz -6.2 dBmV 31.3 dB 1114569 120
4 Locked QAM256 3 519000000 Hz -5.8 dBmV 41 dB 0 0
5 Locked QAM256 4 525000000 Hz -5.6 dBmV 41 dB 0 0
6 Locked QAM256 5 531000000 Hz -5 dBmV 41.3 dB 0 0
7 Locked QAM256 6 537000000 Hz -5.5 dBmV 41.1 dB 0 0
8 Locked QAM256 7 543000000 Hz -5.2 dBmV 41.2 dB 0 0
9 Locked QAM256 8 549000000 Hz -5.3 dBmV 39.2 dB 0 0
10 Locked QAM256 9 555000000 Hz -4.7 dBmV 40.3 dB 0 0
11 Locked QAM256 10 561000000 Hz -4.3 dBmV 39.6 dB 0 0
12 Locked QAM256 11 567000000 Hz -4 dBmV 35.7 dB 0 0
13 Locked QAM256 12 573000000 Hz -3.9 dBmV 33.1 dB 0 0
14 Locked QAM256 13 579000000 Hz -4.1 dBmV 33.8 dB 0 0
15 Locked QAM256 14 585000000 Hz -4.7 dBmV 38.1 dB 0 0
16 Locked QAM256 15 591000000 Hz -5.1 dBmV 41.2 dB 0 0
17 Locked QAM256 16 597000000 Hz -6.1 dBmV 40.8 dB 0 0
18 Locked QAM256 17 603000000 Hz -6.1 dBmV 40.9 dB 0 0
19 Locked QAM256 18 609000000 Hz -6.7 dBmV 40.6 dB 0 0
20 Locked QAM256 19 615000000 Hz -6.8 dBmV 40.5 dB 0 0
21 Locked QAM256 20 621000000 Hz -6.4 dBmV 36.8 dB 0 0
22 Locked QAM256 21 627000000 Hz -6.3 dBmV 39.6 dB 0 0
23 Locked QAM256 22 633000000 Hz -6.1 dBmV 40.8 dB 0 0
24 Locked QAM256 23 639000000 Hz -6.3 dBmV 31.2 dB 0 0
25 Locked QAM256 24 645000000 Hz -6.8 dBmV 31 dB 8 0
26 Locked QAM256 25 651000000 Hz -6.5 dBmV 37.6 dB 0 0
27 Locked QAM256 26 657000000 Hz -6.7 dBmV 40.5 dB 0 0
28 Locked QAM256 27 663000000 Hz -6.1 dBmV 40.5 dB 0 0
29 Locked QAM256 28 669000000 Hz -5.7 dBmV 40.8 dB 0 0
30 Locked QAM256 30 681000000 Hz -4.8 dBmV 41.3 dB 0 0
31 Locked QAM256 31 687000000 Hz -4.7 dBmV 41.2 dB 0 0
32 Locked QAM256 32 693000000 Hz -5 dBmV 41.1 dB 0 0
 
Upstream Bonded Channels
Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power
1 Locked ATDMA 5 5120 Ksym/sec 36500000 Hz 50 dBmV
2 Locked ATDMA 6 5120 Ksym/sec 30100000 Hz 56.5 dBmV
3 Locked ATDMA 7 5120 Ksym/sec 23700000 Hz 54.5 dBmV
4 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 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

 

 

While I'm not exactly sure what the levels should be, it seems to me there is something wrong with channels 2 and 3 on the downstream side.

 

Could anybody help? I should be logged in to work right now but as I said, the current speed isn't sufficient for what I need to do.

 
Expert

Re: Troubleshooting Slow Internet Speeds. Chat wasn't helpful

The upstream power is too high and it may be intermittently fluctuating even higher to out of spec levels. The downstream power is a bit weak. And the SNR is too low / out of spec on some channels. That can cause random disconnects, spontaneous re-booting of the modem, and speed and latency problems.

In a self troubleshooting effort to try to obtain better connectivity / more wiggle room, 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.



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Diamond Problem Solver

Re: Troubleshooting Slow Internet Speeds. Chat wasn't helpful

Adding to EG
EG gave great troubleshooting ideas. All of your upstream channels are too high and channel 2 on the downstream has bad SNR. It’s possible your signal levels are related to neighboring issues, your modem is connected and online that’s why you aren’t considered an outage.

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Frequent Visitor

Re: Troubleshooting Slow Internet Speeds. Chat wasn't helpful

Thank you for your reply.

 

Do you have a recommended brand of model of splitters I should order? I was also under the impression that the fewer splitters in your overall connection, the better. I guess thats an old theory or I misunderstood.

 

Currently there is a single 4-way splitter where the line comes into the house. It is an Antronix CMC2004H 4-way splitter 5-1002Mhz. each line is a -7 db drop. I have the modem and my 2 boxes connected to it and the 4th is open.

 

I may have another splitter lying around the house from an xfinity install kit. Could I use the 2-way and the 4-way and just cap the ends I don't use, or should I use (2) 2-way splitters since I only have 3 pieces of equipment in the house?

Diamond Problem Solver

Re: Troubleshooting Slow Internet Speeds. Chat wasn't helpful

You should use a 3 way splitter but there would be only 1.5 dB difference, not enough to be noticeable and make a difference. It’s possible your upstream is too high from the tap if you’ve only got a 4 way splitter. Get a tech out

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Frequent Visitor

Re: Troubleshooting Slow Internet Speeds. Chat wasn't helpful

I have reconfigured my wiring to the following:

 

Line from pole into Extreme Broadband Engineering BDS102H 2 way splitter. Line out to modem, line out to Antronix 4 way splitter. 2 X1 Cable boxes coming off of the 4 way splitter.

 

All channels are now locked, and my speed has increased slightly to a max of 120 mbps and average of 70 mbps, but this still isn't anywhere near where it should be or what I was getting. I'm a little suspicious to think that it is something on my end, unless the wires and signal can degrade over a period of 6 months, as I have had 0 issues up until today and have no made any changes to the wiring in my house since I switched to all comcast services in November.

 

Below is the updated cable modem status page:

 

Downstream Bonded Channels
Channel Lock Status Modulation Channel ID Frequency Power SNR Correctables Uncorrectables
1 Locked QAM256 29 675000000 Hz -0.1 dBmV 41.5 dB 0 0
2 Locked QAM256 1 507000000 Hz -2 dBmV 26.4 dB 7452733 900508
3 Locked QAM256 2 513000000 Hz -1.6 dBmV 32.2 dB 1283 0
4 Locked QAM256 3 519000000 Hz -1.3 dBmV 41.9 dB 0 0
5 Locked QAM256 4 525000000 Hz -1.2 dBmV 41.9 dB 0 0
6 Locked QAM256 5 531000000 Hz -1.2 dBmV 42 dB 0 0
7 Locked QAM256 6 537000000 Hz -1.3 dBmV 41.9 dB 0 0
8 Locked QAM256 7 543000000 Hz -1 dBmV 42 dB 0 0
9 Locked QAM256 8 549000000 Hz -0.4 dBmV 40.4 dB 0 0
10 Locked QAM256 9 555000000 Hz 0.5 dBmV 41.5 dB 0 0
11 Locked QAM256 10 561000000 Hz 1.1 dBmV 40.8 dB 0 0
12 Locked QAM256 11 567000000 Hz 0.7 dBmV 33.2 dB 0 0
13 Locked QAM256 12 573000000 Hz 0.2 dBmV 32.5 dB 0 0
14 Locked QAM256 13 579000000 Hz -0.1 dBmV 33.4 dB 0 0
15 Locked QAM256 14 585000000 Hz -0.2 dBmV 37.9 dB 0 0
16 Locked QAM256 15 591000000 Hz -0.3 dBmV 42 dB 0 0
17 Locked QAM256 16 597000000 Hz -0.4 dBmV 42 dB 0 0
18 Locked QAM256 17 603000000 Hz -0.5 dBmV 42.1 dB 0 0
19 Locked QAM256 18 609000000 Hz -1.5 dBmV 41.9 dB 0 0
20 Locked QAM256 19 615000000 Hz -2.1 dBmV 41.6 dB 0 0
21 Locked QAM256 20 621000000 Hz -1.9 dBmV 37.1 dB 0 0
22 Locked QAM256 21 627000000 Hz -1.8 dBmV 40.5 dB 0 0
23 Locked QAM256 22 633000000 Hz -1.3 dBmV 41.8 dB 0 0
24 Locked QAM256 23 639000000 Hz -1 dBmV 32 dB 0 0
25 Locked QAM256 24 645000000 Hz -1.4 dBmV 32.9 dB 0 0
26 Locked QAM256 25 651000000 Hz -1.6 dBmV 39.3 dB 0 0
27 Locked QAM256 26 657000000 Hz -1.8 dBmV 41.6 dB 0 0
28 Locked QAM256 27 663000000 Hz -1.3 dBmV 41.6 dB 0 0
29 Locked QAM256 28 669000000 Hz -1 dBmV 41.8 dB 0 0
30 Locked QAM256 30 681000000 Hz 0 dBmV 42.1 dB 0 0
31 Locked QAM256 31 687000000 Hz -0.5 dBmV 41.8 dB 0 0
32 Locked QAM256 32 693000000 Hz -1.3 dBmV 41.6 dB 0 0
 
Upstream Bonded Channels
Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power
1 Locked ATDMA 5 5120 Ksym/sec 36500000 Hz 45.5 dBmV
2 Locked ATDMA 6 5120 Ksym/sec 30100000 Hz 50 dBmV
3 Locked ATDMA 7 5120 Ksym/sec 23700000 Hz 53 dBmV
4 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 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
 
Downstream OFDM Channels
Channel Lock
Status
Modulation /
Profile ID
Channel
ID
Frequency Power SNR /
MER
Active Subcarrier
Number Range
Unerrored
Codewords
Correctable
Codewords
Uncorrectable
Codewords
1 Locked 0 159 702000000 Hz -1.9 dBmV 38.6 dB 1126 ~ 2969 25527625 20274204 0
2 Not Locked 0 0 0 Hz 0 dBmV 0.0 dB 0 ~ 4095 0 0 0
 
Upstream OFDMA Channels
Channel Lock Status Modulation / Profile ID Channel ID Frequency Power
1 Not Locked 0 0 0 Hz 0 dBmV
2 Not Locked 0 0 0 Hz 0 dBmV
Diamond Problem Solver

Re: Troubleshooting Slow Internet Speeds. Chat wasn't helpful

You overall improved your downstream, your upstream still needs improvement and the SNR is still bad on multiple downstream channels. Remember, how you just improved your modem’s signal you degraded the signal to your cable box (if you see the picture breaking up).

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Frequent Visitor

Re: Troubleshooting Slow Internet Speeds. Chat wasn't helpful

Technician came today (extremely quick turnaround between schedule and arrival, very impressed!) and replaced the line from the pole to the house, as well as gave me a balanced 3 way splitter (I can return the unbalanced 3 way i ordered from amazon yesterday).

 

He said since all of my devices are docsis and I'm not on the end of the signal line that a balanced splitter is better for my situation. All of my modem levels look great and my download speeds are now running just around 400 mbps.

 

I will post the current modem status page, but consider this issue resolved. Thank you for all that contibuted to resolving my issue, I appreciate it!

 

 

Downstream Bonded Channels
Channel Lock Status Modulation Channel ID Frequency Power SNR Correctables Uncorrectables
1 Locked QAM256 21 627000000 Hz -2.4 dBmV 40.2 dB 0 0
2 Locked QAM256 1 507000000 Hz -2.4 dBmV 40.3 dB 0 0
3 Locked QAM256 2 513000000 Hz -2.2 dBmV 40.4 dB 0 0
4 Locked QAM256 3 519000000 Hz -2.1 dBmV 40.4 dB 0 0
5 Locked QAM256 4 525000000 Hz -1.8 dBmV 40.5 dB 0 0
6 Locked QAM256 5 531000000 Hz -1.4 dBmV 40.7 dB 0 0
7 Locked QAM256 6 537000000 Hz -0.9 dBmV 40.9 dB 0 0
8 Locked QAM256 7 543000000 Hz -0.9 dBmV 41 dB 0 0
9 Locked QAM256 8 549000000 Hz -0.3 dBmV 41.1 dB 0 0
10 Locked QAM256 9 555000000 Hz 0.3 dBmV 41.3 dB 0 0
11 Locked QAM256 10 561000000 Hz 0.3 dBmV 41.4 dB 0 0
12 Locked QAM256 11 567000000 Hz 0.5 dBmV 41.4 dB 0 0
13 Locked QAM256 12 573000000 Hz 0.1 dBmV 41.2 dB 0 0
14 Locked QAM256 13 579000000 Hz -0.2 dBmV 41.2 dB 0 0
15 Locked QAM256 14 585000000 Hz -0.6 dBmV 41 dB 0 0
16 Locked QAM256 15 591000000 Hz -0.9 dBmV 40.9 dB 0 0
17 Locked QAM256 16 597000000 Hz -1.3 dBmV 40.7 dB 0 0
18 Locked QAM256 17 603000000 Hz -1.4 dBmV 40.9 dB 0 0
19 Locked QAM256 18 609000000 Hz -1.8 dBmV 40.6 dB 0 0
20 Locked QAM256 19 615000000 Hz -1.9 dBmV 40.4 dB 0 0
21 Locked QAM256 20 621000000 Hz -2.3 dBmV 40.3 dB 0 0
22 Locked QAM256 22 633000000 Hz -2.3 dBmV 40.3 dB 0 0
23 Locked QAM256 23 639000000 Hz -2.5 dBmV 40.2 dB 0 0
24 Locked QAM256 24 645000000 Hz -2.2 dBmV 40.3 dB 0 0
25 Locked QAM256 25 651000000 Hz -1.8 dBmV 40.5 dB 0 0
26 Locked QAM256 26 657000000 Hz -1.9 dBmV 40.5 dB 0 0
27 Locked QAM256 27 663000000 Hz -1.7 dBmV 40.5 dB 0 0
28 Locked QAM256 28 669000000 Hz -1.6 dBmV 40.5 dB 0 0
29 Locked QAM256 29 675000000 Hz -1.8 dBmV 40.1 dB 0 0
30 Locked QAM256 30 681000000 Hz -2.4 dBmV 40.2 dB 0 0
31 Locked QAM256 31 687000000 Hz -3.3 dBmV 39.7 dB 0 0
32 Locked QAM256 32 693000000 Hz -2.9 dBmV 39.8 dB 0 0
 
Upstream Bonded Channels
Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power
1 Locked ATDMA 5 5120 Ksym/sec 36500000 Hz 38.5 dBmV
2 Locked ATDMA 6 5120 Ksym/sec 30100000 Hz 40.5 dBmV
3 Locked ATDMA 7 5120 Ksym/sec 23700000 Hz 40.5 dBmV
4 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 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
 
Downstream OFDM Channels
Channel Lock
Status
Modulation /
Profile ID
Channel
ID
Frequency Power SNR /
MER
Active Subcarrier
Number Range
Unerrored
Codewords
Correctable
Codewords
Uncorrectable
Codewords
1 Locked 0 159 702000000 Hz -0.7 dBmV 40.4 dB 1126 ~ 2969 22714394 5413 0
2 Not Locked 0 0 0 Hz 0 dBmV 0.0 dB 0 ~ 4095 0 0 0
 
Upstream OFDMA Channels
Channel Lock Status Modulation / Profile ID Channel ID Frequency Power
1 Not Locked 0 0 0 Hz 0 dBmV
2 Not Locked 0 0 0 Hz 0 dBmV
Expert

Re: Troubleshooting Slow Internet Speeds. Chat wasn't helpful

Glad you got it squared away !



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Official Employee

Re: Troubleshooting Slow Internet Speeds. Chat wasn't helpful

It was a pleasure working with you, MayoTheGreat. Have a good one! 


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