verywhitenoise's profile

Frequent Visitor

 • 

19 Messages

Thu, Jan 7, 2021 3:00 PM

Very bad latency and packet loss to Comcast CMTS Gateway (wired directly)

As the title states, I have been having very bad issues with latency and packet loss to my comcast gateway at the CMTS. I have connected directly to my router and also directly to my modem via cat6 to eliminate those as issues. I have replaced (now TWICE) my cable modem with approved comcast devices. I have had technicians come to my house (now FOUR times) and they have FULLY replaced all wiring from the POLE to my modem. I am ONLY using 1 modem, zero other devices (no tv, phone, etc). There are no splitters involved. Every wires is brand new and installed by comcast technician from the utility pole to my modem. This is pure RG6 quad shielded with zero splitters in the mix.

 

This has been going on for nearly 2 months now, and I'm at wits end. I have called support nearly 10 times, and they are completely and utterly useless. They keep trying to send more technicians, who come and then tell me to 'never have them send another technician, all your cables are brand new and test fine, the issue likely lies at the headend or CMTS."

 

This image is a typical day for me. Pings directly to my Comcast gateway at the CMTS will spike to 500ms or higher, and packet loss hovers in the 5-10% range. This is a single hop from my router, which shows ZERO packet loss and and avg latency of 3ms. I also have my modem disconnect and need a power cycle multiple times a week. This happens on ALL of my 3 modems (one older Motorola and 2 brand new devices - one Netgear and the other Arris).

 

Please see the linked image as evidence of this. This makes things like gaming, working, video chat and simple streaming from netflix/youtube nearly impossible. This issue occurs at all hours of the day.

 

https://imgur.com/a/arSvq93

 

Any help would be GREATLY appreciated as I am stuck with Comcast (no other service in my area). When it works, it works fine - up to 2 months ago I had zero issues and nothing changed at my location.  

 

Tech support is very useless and often runs a single "your modem is online" test and then asks me to perform a speed test, which works fine. Speed tests do NOT count for latency or packet loss, they simply try to get as fast as possible and that typically shows 800-900Mbps on my 1Gb plan. My issue is EXTENSIVE latency and packet loss which makes actual usage very hard to live with.

 

Thank you very much for reading this and please, please dear god, help me 🙂

 

https://imgur.com/a/arSvq93

 

@ComcastTambrey @ComcastEva 

Responses

Frequent Visitor

 • 

19 Messages

5 m ago

Even as I typed this message, my connection went to pot again. Completely unreliable.

 

verywhitenoise_0-1610067253339.png

 

Frequent Visitor

 • 

19 Messages

5 m ago

From my Netgear:

 

 

 

 

Cable Connection
 
 
Apply             Cancel    
Frequency start Value
This field below allows you to modify the frequency the cable modem start with its scan during initialization and registration. Enter the new start frequency and restart the cable modem for it to take effect.
Starting Frequency

Startup Procedure
ProcedureStatusComment
Acquire Downstream Channel669000000 HzLocked
Connectivity StateOKOperational
Boot StateOKOperational
SecurityEnableBPI+
IP Provisioning ModeHonor MDDIPv6 only

Downstream Bonded Channels
ChannelLock StatusModulationChannel IDFrequencyPowerSNR / MERUnerrored CodewordsCorrectable CodewordsUncorrectable Codewords
1LockedQAM25641669000000 Hz16.8 dBmV37.7 dB7620733910
2LockedQAM25613495000000 Hz11.7 dBmV37.5 dB75050885320
3LockedQAM25614507000000 Hz13.2 dBmV38.2 dB7505484280
4LockedQAM25615513000000 Hz14.3 dBmV38.4 dB75057908120
5LockedQAM25616519000000 Hz14.7 dBmV38.4 dB75061316210
6LockedQAM25617525000000 Hz14.9 dBmV38.3 dB75065709250
7LockedQAM25618531000000 Hz14.9 dBmV38.3 dB75069264290
8LockedQAM25619537000000 Hz15.2 dBmV38.4 dB75072788300
9LockedQAM25620543000000 Hz15.0 dBmV38.2 dB75076815150
10LockedQAM25621549000000 Hz15.1 dBmV38.1 dB7508019800
11LockedQAM25622555000000 Hz15.3 dBmV38.2 dB7508453210
12LockedQAM25623561000000 Hz15.6 dBmV38.0 dB7508814600
13LockedQAM25624567000000 Hz15.7 dBmV38.2 dB7509186220
14LockedQAM25625573000000 Hz15.9 dBmV38.1 dB7509551720
15LockedQAM25626579000000 Hz16.1 dBmV38.2 dB7509939900
16LockedQAM25627585000000 Hz16.4 dBmV38.3 dB7510321600
17LockedQAM25628591000000 Hz16.5 dBmV38.2 dB7510682300
18LockedQAM25629597000000 Hz16.7 dBmV38.4 dB7511026630
19LockedQAM25630603000000 Hz16.8 dBmV38.4 dB7511428500
20LockedQAM25631609000000 Hz16.9 dBmV38.1 dB7511792900
21LockedQAM25632615000000 Hz17.0 dBmV38.2 dB7512135500
22LockedQAM25633621000000 Hz17.1 dBmV38.1 dB7512522800
23LockedQAM25634627000000 Hz17.0 dBmV38.0 dB7512918410
24LockedQAM25635633000000 Hz16.9 dBmV38.1 dB7513258820
25LockedQAM25636639000000 Hz17.0 dBmV38.0 dB7513663500
26LockedQAM25637645000000 Hz16.9 dBmV38.0 dB7514019200
27LockedQAM25638651000000 Hz16.8 dBmV37.9 dB7514354600
28LockedQAM25639657000000 Hz16.9 dBmV37.9 dB7514756000
29LockedQAM25640663000000 Hz17.0 dBmV37.6 dB7515078510
30LockedQAM25642675000000 Hz16.8 dBmV37.3 dB7515517110
31LockedQAM25643681000000 Hz16.6 dBmV37.4 dB7515746110
32LockedQAM25644687000000 Hz17.0 dBmV37.4 dB7515822800

Upstream Bonded Channels
ChannelLock StatusModulationChannel IDFrequencyPower
1LockedATDMA116200000 Hz43.5 dBmV
2LockedATDMA222700000 Hz43.5 dBmV
3LockedATDMA329200000 Hz43.5 dBmV
4LockedATDMA435700000 Hz43.5 dBmV
5LockedATDMA541200000 Hz42.0 dBmV
6Not LockedUnknown00 Hz0.0 dBmV
7Not LockedUnknown00 Hz0.0 dBmV
8Not LockedUnknown00 Hz0.0 dBmV

Downstream OFDM Channels
ChannelLock StatusModulation / Profile IDChannel IDFrequencyPowerSNR / MERActive Subcarrier Number RangeUnerrored CodewordsCorrectable CodewordsUncorrectable Codewords
1Locked0159722000000 Hz17.5 dBmV36.0 dB1246 ~ 28495538619727960
2Not Locked000 Hz8.9 dBmV0.0 dB0 ~ 4095000

Upstream OFDMA Channels
ChannelLock StatusModulation / Profile IDChannel IDFrequencyPower
1Not LockedUnknown00 Hz0 dBmV
2Not LockedUnknown00 Hz0 dBmV

Current System Time: Thu Jan 07 16:59:54 2021
System Up Time: 0:28:18

 

 

 

 

 

Help Center
 

 

Show/Hide Help Center

Frequent Visitor

 • 

19 Messages

5 m ago

Another day - more insanely high packet loss: 15% avg with an average ping of 77 to my first hop gateway in comcasts network.

 

https://imgur.com/a/Be7ppHZ

EG

Expert

 • 

87.1K Messages

5 m ago

The downstream power is very high / out of spec. Is there a drop amplifier on the coax line that leads to the modem ? If so, try bypassing it and see.

Frequent Visitor

 • 

19 Messages

5 m ago

Thanks EG. There is nothing between the runs, just a barrel connector and it has no dB markings on it. This is all 100% fresh cable that a technician just ran, from pole to modem, including all connectors and cables. No splitters, etc.

jlavaseur

Valued Contributor

 • 

432 Messages

5 m ago

Just a thought, check and see if your modem/gateway has the puma 6 chipset, it has issues with latency 

EG

Expert

 • 

87.1K Messages

5 m ago

What is the exact model number of your Netgear modem ?

 

The downstream power should be addressed regardless of anything else. It may be saturating / overdriving the front-end receiver of the modem which can cause packet loss / waveform distortion.

 

Perhaps it would be best to get a tech out to properly balance the line. Good luck !

Frequent Visitor

 • 

19 Messages

5 m ago

@EG Thank you for the information. It's the CM1000, and I also have an Arris SB8200 that I bought to rule out the modem itself. Is reducing the downstream power as simple as buying an attenuator and plopping it inline? As I said, I've had 5 technicians out and not a single one of them identified this issue. I have lost nearly all faith in the guys they send out. 

 

Now that you've pointed me to a problem, I'll work on getting that sorted and report back if there is any improvement. Thank you again, I really appreciate the help!

EG

Expert

 • 

87.1K Messages

5 m ago

As a P.S. Please be advised that this may or may not be the root cause of the problem (YMMV). But it should be addressed regardless. This problem can also be being caused by a local cable segment / node traffic capacity / congestion problem.

Good luck with it !

EG

Expert

 • 

87.1K Messages

5 m ago

For that large amount of reduction needed, you would have to use a Forward Path Only attenuator so that it only knocks down the downstream power without affecting the upstream power, which happens to be good / in spec. If you used a 10 dB (or more) overall signal attenuator pad it would push the upstream power higher to out of spec levels and cause the very problems that you are trying to cure.

 

In regards to overall line attenuation, the upstream and the downstream power levels work in equal but opposite ways. It makes the downstream power go lower while it simultaneously makes the upstream power go higher.

 

You could try using two of these coupled together for a total of 12 dB downstream power reduction;

 

https://www.amazon.com/line-Signal-Forward-Attenuator-FPA6-54/dp/B07882H96R

New Poster

 • 

1 Message

5 m ago

@verywhitenoise I've read some of your posts about this issue since I'm experiencing the same thing at my apartment complex in Clackamas, OR. It's been going on for months and I've recently had my 2nd tech out with no resolution saying they've done all they can. I have a variety of ideas about possible culprits, but in the end there's nothing that I could do besides try and convince comcast that it is something on their end because I've exhausted all troubleshooting unless I want to learn how to install a new 8-way trap and wiring to my entire building(I do have access to the box, so the thought has crossed my mind) I noticed on one of your pingplotter screenshots your first hop was Beaverton, are you in the Portland metro area also?
ComcastChe

Official Employee

 • 

6.1K Messages

5 m ago

Hi @verywhitenoise! I hope all is well. I just wanted to check in with you to see if you've had any luck with the suggestions that our awesome expert @EG provided? 

ComcastChe

Official Employee

 • 

6.1K Messages

5 m ago

Hi @Highpingity! Thank you for sharing your experience here on the Xfinity Forum! I'm sorry for the issues you're having as I know how important it is to have reliable services. I wanted to see if there is anyway me and my team can help. I want to review your account, your premise signal levels and check your local node to see if I can find a culprit. Can you send a private message with your first and last name and the numbers associated with your address? To send a message, click on my name, "ComcastChe," then click send a message. 

New to the Community?

Start Here