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LocalMaximum
join:2014-09-16
USA

LocalMaximum

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[Connectivity] New to Cable. High uncorrectable codewords

I just got cable internet a few days ago. Before this I have only had DSL, so I don't really know what I'm doing. I checked the status page on my modem, and shows over a thousand uncorrectable codewords, and it's only been on for an hour and a half. I've also noticed that my upstream power is high. If I constantly refresh the status page, I can observe the downstream power levels fluctuating by 0.1 or 0.2. Is this normal?

Here is my status page:



My connection details are as follows: The main line to my house goes through a ground block, which connects to a 1ft quad shielded RG6. This is connected to an Antronix 3-way unbalanced splitter. The cable modem is plugged into the -3.5dB port, and a 30ft RG6 runs through a window (for now) upstairs to the modem. Two televisions are plugged into the -7dB ports. They use the indoor wiring that came with my 21 year old house.

Do I need to get a Comcast technician out here or are these stats acceptable?

NetFixer
From My Cold Dead Hands
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NetFixer

Premium Member

[Connectivity] Re: New to Cable. High uncorrectable codewords

Your upstream power levels are indeed marginal, but if you are not getting a large number of T3 timeouts or T4 timeouts that result in losing upstream channels or modem reboots, it is unlikely that Comcast will do anything but charge you for a service call. I had to install my own active return adjustable amp to compensate for high upstream power levels that were causing my modem to get T4 errors and reboot during warm weather.

As for the excessive uncorrectable errors, what I see is not that unusual unless what you see continues to increase by a large amount hourly/daily.

Here is a snapshot I just took of my modem stats, and my errors are somewhat comparable to your (this is for a 23 day period):




And FWIW, without the amp, my upstream power levels would be ~51-52 dBmv at this time if I were not using the amp.

andyross
MVM
join:2003-05-04
Aurora, IL

andyross to LocalMaximum

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The error counts are for the downstream. Keep an eye on them for a few days and see how fast they change. Personally, mine can be near static for several days, then suddenly jump. I just had that happen today with one of the frequencies that are in the 700's (interference from smartphones data frquencies.)
LocalMaximum
join:2014-09-16
USA

1 edit

LocalMaximum

Member

Thank you very much for the fast and helpful responses. They are much appreciated. I have a few followup questions.

So as long as I don't lose modem upstream channels or have modem reboots, my upstream power level is fine? How do I know if I've incurred a T3/T4 timeout?

Also, I was under the impression that any uncorrectable codewords were a problem. Is this not the case? And what causes these errors in the first place?

Are there any potential downsides to using the kind of amp you recommend?

What could a Comcast tech feasibly do to improve my upstream power stats?

andyross
MVM
join:2003-05-04
Aurora, IL

andyross

MVM

To access the log on the Zoom, log into the connection screen, then use this link: »192.168.100.1/RgEventLog.asp

I would still worry about those upstream signals. They are right at the edge and it won't take much for it to drop out. You should have better signals, both downstream and upstream, if you are only at -3.5dB loss. I have a feeling the cable between the pole or post to your house may be old and deteriorated.
LocalMaximum
join:2014-09-16
USA

LocalMaximum

Member

Re: [Connectivity] New to Cable. High uncorrectable codewords

If that's the case how much would Comcast charge to run a new cable?

NetFixer
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Re: New to Cable. High uncorrectable codewords

said by LocalMaximum:

So as long as I don't lose modem upstream channels or have modem reboots, my upstream power level is fine? How do I know if I've incurred a T3/T4 timeout?

You can see the T3 and T4 errors in the modem's log. Also, the T4 errors may be accompanied by a loss of upstream channels and/or modem reboots.
said by LocalMaximum:

Also, I was under the impression that any uncorrectable codewords were a problem. Is this not the case? And what causes these errors in the first place?

Uncorrectable codewords are undesirable, but not necessarily a problem unless there are a very large number of them (as in hundreds of thousands, not just a few hundred or a few thousand) and the count continuously increases. They are usually caused by noise on the line such as interference from cell phone activity -- or anything that can produce wide band EMI or RFI noise. Whenever I am assigned channels in the 700 mhz range that correspond to LTE frequencies, I have noticed that those channels will usually have a noticeably higher number of both correctable and uncorrectable codewords.
said by LocalMaximum:

Are there any potential downsides to using the kind of amp you recommend?

An amp can potentially add noise (it will amplify both incoming noise and incoming signal) which can lower your SNR and also increase the codeword error rates. I did not notice that happening in my case, but it is a possibility. Also, if it is an adjustable amp, you will need to actually adjust the gain in both directions to achieve optimum results for all attached devices (you may have to compromise between too much gain for some devices and not enough for other devices). And if it is a fixed gain amp, you may need to insert attenuators to compensate for too much gain for some devices. If your modem/router/PC are on a UPS, you will also need to put the amp on a UPS (possibly its own UPS depending on where the AMP is physically located), or you will lose service during a local power outage. Plus, you will be responsible for taking into consideration the possibility that the amp may eventually start causing problems that are not seen immediately after it was installed (and Comcast will certainly bill you if a site visit is required because of a failure in your amp). Life is a series of compromises.
said by LocalMaximum:

What could a Comcast tech feasibly do to improve my upstream power stats?

Possibly replace defective cable runs and/or connectors (especially the outside cables/connectors that Comcast is responsible for maintaining), and also make adjustments in Comcast's amps.
LocalMaximum
join:2014-09-16
USA

LocalMaximum

Member

Re: [Connectivity] New to Cable. High uncorrectable codewords

Thanks, guys, for all the great info! Really appreciated.

A few more questions:

As I said before, I have a 3-way splitter which connects the modem and two TVs. Can the quality of the cables connecting to the TVs affect the signal of the cable running to the modem? I ask because they're quite old and I doubt they're quad-shielded.

Also, is there any way to determine if the line running to my house is RG6 or RG59?

And why are some downstream channels more prone to codeword errors than others? It seems like the first and last get the majority of errors.
LocalMaximum

LocalMaximum

Member

Click for full size
Here are my modem stats after 27 hours of uptime.

[att=2]

My understanding is that this is an acceptable number of codeword errors?

And although my upstream power is high, I checked the modem log, and I have not had any T3 or T4 timeouts.

It seems to be working alright. Still trying to decide if I should call Comcast or not. What do you guys think?

NetFixer
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NetFixer

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My own experience with contacting Comcast support is that if you are not experiencing any adverse effects from marginal or questionable modem stats (and sometimes even if you are actually having problems), you are not likely to get any help from them. Keep an eye on the codeword errors, and if they start to climb by tens of thousands per day, then that might indicate a problem -- but even then, I would probably reboot the modem to see if I got a better selection of channel frequencies if the increase was only on one (or a couple) of channels, before I would consider calling Comcast support.

Your upstream levels (while higher than I would like to see) may or may not cause you problems next year during the hotter summer months if you live in an area where the mid summer temperatures are significantly higher than early fall temperatures (this is because hot weather increases the resistance of the conducting wire in the cable and the modem must push a higher signal to compensate). Until/unless you actually start to see adverse effects from the high upstream power levels, Comcast is not likely to consider it a problem.

Have I mentioned that I would rather schedule a root canal than call Comcast support for anything?
LocalMaximum
join:2014-09-16
USA

LocalMaximum

Member

said by NetFixer:

Have I mentioned that I would rather schedule a root canal than call Comcast support for anything?

Yes, I'm starting to realize this. I just spent two hours on the phone because Comcast decided to deactivate my cable TV boxes for some reason. And now I'm getting channels which aren't included in my package, but the two women I spoke to assured me that I would not be charged for them. I have my fingers crossed.

Devious
Premium Member
join:2002-08-22
Seattle, WA

Devious

Premium Member

This may help you understand codewords.

»volpefirm.com/docsis-cod ··· -errors/

The problem with the Zoom is it does not show you how many good codewords there were like the Motorola does. The Zoom only shows how many it could correct and how many it could not correct.

Look at Netfixers attachment pic and you see unerrored (good) processed in the billions compared to only 100's corrected/uncorrected which is fine.

THZNDUP
Deorum Offensa Diis Curae
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join:2003-09-18
Lard

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said by LocalMaximum:

...
And why are some downstream channels more prone to codeword errors than others? It seems like the first and last get the majority of errors.

Some places maybe yes, other places maybe no.

The following are my modem stats for 28 days and about 450GB of data. They're somewhat spaced out pretty evenly. Any differences between channels are minimal and have little/no impact.




Certainly not going to call Comcast about ch 5 having over 400 uncorrectables.............
LocalMaximum
join:2014-09-16
USA

1 edit

LocalMaximum

Member

Here are my stats connecting directly to the line to my house: (is that called a drop?)



Would running a new line improve my upstream power?

Also, can uncorrectable errors cause packet loss?

NetFixer
From My Cold Dead Hands
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NetFixer

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said by LocalMaximum:

Here are my stats connecting directly to the line to my house: (is that called a drop?)
[image of good stats]

Would running a new line improve my upstream power?

Also, can uncorrectable errors cause packet loss?

I assume that you mean that you connected to the first coax outlet (or perhaps to a barrel connector depending on how your connection is wired) before the splitter, not that you connected to the tap in the pedestal. If you actually connected to the tap in the pedestal, that could possibly point a finger to Comcast's "drop" line to your dmarc as possibly allowing noise to be injected (in other words, anything after the point where you were connected to make this post could be allowing/causing noise injection).

Part of the improvement you see is simply because you have eliminated the 3.5 db loss in the splitter. If you could actually get Comcast to run a separate drop to your modem (eliminating the need for a splitter), that would certainly put your upstream power in a better place. However, getting Comcast to do that would not be an easy task. I tried to get Comcast to run a separate drop for my business class Internet service so that I would not have to use a splitter to my Xfinity residential TV service -- but I was told that was not going to happen (and that is the primary reason I had to install my own active return adjustable amp).

OTOH, since you don't see any downstream errors when you bypassed the splitter, that might imply that you have a defective splitter, or that something attached to that splitter is allowing/causing noise to be injected. That would be something that I would look into by trying a new splitter. Next (if the new splitter didn't help) I would use the splitter, but remove the coax cable going to the STB/TV(s), and/or remove the STB/TV(s) to see if that brought the error count down. Even the first coax patch cable from the dmarc to the splitter might be allowing noise to be injected.

An uncorrectable error is information loss; whether it is packet loss depends on the kind of traffic involved. For TCP traffic, it would be detected as an error, and the packet would need to be retransmitted. For most UDP traffic (especially streaming traffic), the information in the error cell would simply be lost -- which does not necessarily mean that an entire packet was lost (for streaming voice, think of it as one syllable in a sentence being lost or garbled). The error could have also occurred in the background noise ARP and DHCP traffic which constantly bombards your cable modem simply because it is on a common connection with other Comcast customers in your area (think of it as when a tree falls in the forest, and no one is near enough to hear it -- does it make a sound?).
LocalMaximum
join:2014-09-16
USA

LocalMaximum

Member

I connected it to the ground block attached to my house. The reason there are no errors is that it was only active for about 30 seconds before I took the screen shot. I just wanted to see what the signal levels would be without being split. I'll try going splitter-less for a longer period of time and see how the error count adds up, and then try addings TVs.

I guess what I'm wondering is if the 21 year old cable running to the back of my house might be getting a tad decrepit, and if replacing it would give me better stats. It might even be RG59 - is there any way to tell? Is replacing it something Comcast would be willing to do, and if so what do you think they'd charge?

Thanks for the help.

NetFixer
From My Cold Dead Hands
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NetFixer

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said by LocalMaximum:

I guess what I'm wondering is if the 21 year old cable running to the back of my house might be getting a tad decrepit, and if replacing it would give me better stats. It might even be RG59 - is there any way to tell? Is replacing it something Comcast would be willing to do, and if so what do you think they'd charge?

One way to tell if a cable is RG6 or RG59 is to look for manufacturer's markings on the outside of the cable, and then look-up that information (assuming that the markings have not worn off, or were ever even there). Also, RG59 usually has a smaller diameter (both the overall diameter of the cable and the diameter of the inner conductor) than RG6, and is also usually much more flexible.

The cable running from the pedestal to the ground block on your house is Comcast's responsibility, and they should replace it at no charge if they conclude that it is defective and is causing connectivity problems.

As for what Comcast charges for customer requested maintenance, that will likely vary in each franchise area. You can see (and probably get a copy of) the current price list for all Comcast products and services in your franchise area at a local Comcast office. FWIW, I get billed a minimum $99.95 for any maintenance that Comcast deems was outside their area of responsibility (and in my experience, you can count on Comcast to deny responsibility for almost everything).
LocalMaximum
join:2014-09-16
USA

LocalMaximum

Member

$100? Yikes. Let's hope the problem is their responsibility then.

Anyway, here are my stats after 29 hours of uptime with the splitter.


Is this acceptable? Seems like an awful lot to me.

EG
The wings of love
Premium Member
join:2006-11-18
Union, NJ

EG

Premium Member

The "uncorrectables" are low FWIW. The up time since the modem was last rebooted needs to be taken in to consideration in order to truly be able to evaluate the amount of errors. The upstream power is borderline. There is no wiggle room for any potential higher fluctuations.

andyross
MVM
join:2003-05-04
Aurora, IL

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If you notice, the highest uncorrectables are for the frequencies closest to 700MHz. For me, I've noticed the one channel at 705MHz has had several big jumps lately. The total counts are over 2 weeks (had long power outage that outlasted the UPS on Sept 12.)

telcodad
MVM
join:2011-09-16
Lincroft, NJ

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telcodad to LocalMaximum

MVM

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said by andyross:

The error counts are for the downstream. Keep an eye on them for a few days and see how fast they change. Personally, mine can be near static for several days, then suddenly jump. I just had that happen today with one of the frequencies that are in the 700's (interference from smartphones data frquencies.)

said by andyross:

If you notice, the highest uncorrectables are for the frequencies closest to 700MHz. For me, I've noticed the one channel at 705MHz has had several big jumps lately. The total counts are over 2 weeks (had long power outage that outlasted the UPS on Sept 12.)

Yes, here's a chart of some 4G LTE cellular frequency bands from a post (»Re: [Connection] Bad node / outside line again... ) from a previous thread about interference.

So in the near 700 MHz area, the interfering signals are from cellphone to tower transmissions. Anyone in your home have a (AT&T?) 4G LTE cellphone?
LocalMaximum
join:2014-09-16
USA

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LocalMaximum

Member

No one here has a smartphone. Would my neighbor's phones reach far enough to interfere with the signal? They're pretty close by.

Also, could wireless routers cause interference as well? And is the frequency range you get when you connect just luck of the draw?

Edit: wow, they really increased overnight.


Another thing: these codewords seem to increase the most when I'm not using the computer. Strange. I would think you'd only get them when transmitting or receiving data...

NetFixer
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NetFixer

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said by LocalMaximum:

No one here has a smartphone. Would my neighbor's phones reach far enough to interfere with the signal? They're pretty close by.

Also, could wireless routers cause interference as well? And is the frequency range you get when you connect just luck of the draw?

Edit: wow, they really increased overnight.

While your 699 mhz channel is close to an AT&T LTE frequency, it should be far enough out of range that AT&T LTE activity should not bother it. Also, that is not the only channel that has the rather high error count. My guess (as we previously discussed) is that you are getting wide band EMI/RFI noise introduced into your connection. Unfortunately, I don't think that Comcast is going to pay any attention to you if you place a service call unless/until it actually causes noticeable connectivity problems (but who knows -- you may connect with a very responsive CSR, and your local Comcast management may actually take preemptive maintenance seriously).

It is highly unlikely that a wireless router would be causing such interference (unless it was really very badly defective) because its frequency range is much higher than the Comcast CATV frequencies. The noise could be coming from a flaky TV or radio, or florescent lamps, or even motor or lighting or HVAC controls -- but it could also be coming from outside your residence. You will probably need to try to isolate it youself by isolating your CATV wiring one section at a time to see if any improvement is noticed when certain parts of your coax network are taken out of the picture (as we previously discussed).

And yes, what channel assignments you get is mostly just the luck of the draw since they are determined by negotiation between your modem and the CMTS.

telcodad
MVM
join:2011-09-16
Lincroft, NJ

telcodad to LocalMaximum

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said by NetFixer:

said by LocalMaximum:

No one here has a smartphone. Would my neighbor's phones reach far enough to interfere with the signal? They're pretty close by.

Also, could wireless routers cause interference as well? And is the frequency range you get when you connect just luck of the draw?

Edit: wow, they really increased overnight.

While your 699 mhz channel is close to an AT&T LTE frequency, it should be far enough out of range that AT&T LTE activity should not bother it.

Well, if the LTE signal is strong enough (from someone using their AT&T LTE phone close to the cable line), isn't it possible that there could be some "adjacent channel" interference effects?

Also, the LTE interference can be getting into the cable line somewhere else in the neighborhood, not from just in the home.
said by LocalMaximum:

Another thing: these codewords seem to increase the most when I'm not using the computer. Strange. I would think you'd only get them when transmitting or receiving data...

The modem is always communicating with the CMTS and receiving and decoding all the data packets on each channel, even though they are not assigned to you and you're not using your computer. That's why the total (unerrorred) codewords count (shown by some other modems, like NetFixer See Profile 's) is always incrementing.
LocalMaximum
join:2014-09-16
USA

LocalMaximum

Member

I think I may have found the culprit:







Twist on connector horribly installed. Is there anyway to salvage this or do I need to purchase a stripper, compressor, and rg59 compression connectors?

Any cheaper way to fix this?

NetFixer
From My Cold Dead Hands
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join:2004-06-24
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NetFixer

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said by LocalMaximum:

I think I may have found the culprit:

[images of bad twist-on connector]

Twist on connector horribly installed. Is there anyway to salvage this or do I need to purchase a stripper, compressor, and rg59 compression connectors?

Any cheaper way to fix this?

That connector needs to be replaced (and any other crimped or twist-on connectors, even if they look mechanically sound). You can find moderately priced compression tools (you don't need a professional tool designed to be used every day for many years) at many retail DIY stores and on-line outlets. OTOH, depending on how the cable(s) are run, it may be cheaper to purchase prefabricated cable(s) with compression fittings already installed.
LocalMaximum
join:2014-09-16
USA

2 edits

LocalMaximum

Member

I just took the connector off. Whoever installed this didn't even strip the insulation before twisting it on; that's why it's not flush with the inner dielectric.

I'm really not comfortable with running a new line through the innards of the house, so I think I'll be going the new connector route.

EG
The wings of love
Premium Member
join:2006-11-18
Union, NJ

EG

Premium Member

FWIW, "twist on" and "crimp" type fittings should be banned !!
LocalMaximum
join:2014-09-16
USA

LocalMaximum

Member

I got a stripper, a compressor tool, and some RG59 connectors on sale at Lowes. My cables are now properly fitted. Hopefully this will reduce my error rate.
LocalMaximum

LocalMaximum

Member

My error rate is down significantly since re-terminating my cables with compression connectors. Thanks for all the help, everyone.