|
[Connectivity] Is this a sign of a bad modem?I have a Motorola SB5100 that's been on 24/7 for about 8 years now.
Last week my download speed, as measured by speedtest.net, dropped to about 0.2 Mbps. I called in to Comcast and the CSR sent a refresh to my modem. It fixed the issue and I was back up to about 22Mbps.
A week later, the same thing happened - download was at 0.1 Mbps - so I called in again and asked them to send the refresh. This time nothing changed.
They scheduled a tech but I thought in the meantime I'd try the "reset all defaults" and "restart" from the modems configuration page. This got me working and up to 30Mbps.
Now it's happening every other day and 4 times out of 4 the "reset all defaults" works when a regular reboot does nothing.
When the speed is low, my ping response time is not out of control (around 20ms) and the signal levels look decent. There are no unusual messages in the log file and I never fully lose connectivity. My upload speed always remains between 5 and 10Mbps regardless of download
Does this sound like a modem going bad? What else could it be?
My signals right now are (and they don't really deviate when download speed is slow):
Frequency 681000000 Hz Locked Signal to Noise Ratio 37 dB Power Level -8 dBmV
Channel ID 3 Frequency 36400000 Hz Ranged Power Level 47 dBmV |
|
palmer_j_rCongenital Optimist Premium Member join:2000-06-08 Chicago, IL ARRIS SB6190 Ubiquiti EdgeRouter X Ubiquiti UAP-AC-M
|
this is also my issue and I've posted a topic here in this forum and on the comcast direct forum.. this yo yo effect is a major pain in the ass and frustrating because comcast can't seem to "fix it" .. although I have a feeling it's going to cost a lot of time and money to fix as it seems to be affecting my block. Noisy lines, and nothing to do with my newly installed drop from the pole. |
|
|
The funny thing is, the problem hasn't resurfaced after I posted this. I have no idea what the root cause was and whether it will come back |
|
beachintechThere's sand in my tool bag Premium Member join:2008-01-06 |
Your downstream power level is borderline out of spec. You may have a wiring problem causing you intermittant issues. |
|
|
|
-8 dBmV is borderline out of spec? I thought it could go as low as -14 or so. I've not noticed any problems until it reached -15/-16 one time due to an extra splitter |
|
nerdburg Premium Member join:2009-08-20 Schuylkill Haven, PA |
nerdburg
Premium Member
2011-Oct-27 9:02 am
Generally, an acceptable signal range for a modem is:
Downstream (forward path): -7 to +7 dBmV. (-10 to +10 dBmV are the officially accepted levels, but signal levels fluctuate so you don't want to be at the edge of the range.)
Upstream: (return path): >40 dBmV but <50 dBmV. Some systems tolerate levels as low as 35 dBmV though.
Signal to Noise Ratio (SNR): >33 dB (higher is better)
The operational range of modems is generally much greater than the desired range, so it's not unusual to have a modem operating just fine outside of the specified range. |
|
CableToolPoorly Representing MYSELF. Premium Member join:2004-11-12 |
said by nerdburg:The operational range of modems is generally much greater than the desired range, so it's not unusual to have a modem operating just fine outside of the specified range. Agreed- Operation Range is what the manufacturers state it will work at. However- Your operational range isnt -16.. its -15. So if the signal fluctuates 1db your offline or close to it. That is why all MSOs have a much tighter operational range. This allows for swings in signal without affecting performance. I dont know if the -8 would be of much concern. Loosing downstream speed like that does sound like a modem issue however, Palmers issues aside. Never conclude an issue a few states away is in any way related to what you are seeing. One could be fixed with a new config file, one with a loose connector and one with modem swap. All exhibiting the same issue. Because really- The modem is two channels ( in theory, bonding aside) up and down. There is a 50/50 chance you will have one issue or the other. I hate to see people lump all of their issues together then sit back and wait for it to be fixed, all the time increasing their frustration and patience. |
|
|
YeahWhat to nerdburg
Anon
2011-Oct-28 10:51 am
to nerdburg
Downstream (forward path): -5 to +5 dBmV. I don't think -10 or +10 are acceptable levels. Certainly -8 your having issues. Check for lose connections or bad splitters. Call for a technician. Could be the cable modem also.
Down Signal to Noise Ratio: >3535 dBmV 32 with 32 being optimal. |
|
your moderator at work
hidden :
|
EGThe wings of love Premium Member join:2006-11-18 Union, NJ
1 recommendation |
EG to YeahWhat
Premium Member
2011-Oct-28 11:07 am
to YeahWhat
Re: [Connectivity] Is this a sign of a bad modem?said by YeahWhat :Downstream (forward path): -5 to +5 dBmV. I don't think -10 or +10 are acceptable levels. Certainly -8 your having issues. Down Signal to Noise Ratio: >3535 dBmV 32 with 32 being optimal. Opinion ? There are no cookie cutter standard figure/s. Individual system specs vary. Plant hardware, CPE hardware/environmental conditions vary.. |
|
CableToolPoorly Representing MYSELF. Premium Member join:2004-11-12
1 recommendation |
to YeahWhat
said by YeahWhat :Downstream (forward path): -5 to +5 dBmV. I don't think -10 or +10 are acceptable levels. Certainly -8 your having issues. Check for lose connections or bad splitters. Call for a technician. Could be the cable modem also.
Down Signal to Noise Ratio: >3535 dBmV 32 with 32 being optimal. I would say 32 is unacceptable. It would be a good UPSNR however. And I agree again, those are thresholds that we would like to see to allow for headroom. Will -8 cause a modem to loose synch? Never Will -8 cause a modem to have intermittent issues? Never Will -8 fluctuating down to -12 cause an issue, probably. Will -8 which is caused by a bad configuration using sub par passives cause an issue? Yes. -5 to +5 just gives you more room to fluctuate and play with. Signal strength and quality wise, all things being equal, -8 is just as good as -5. Either reading would have no effect on your service. My opinion. |
|
|
YeahWhat to EG
Anon
2011-Oct-28 3:07 pm
to EG
Please don't flame, don't understand why my opinion is being questioned. Sorry are only certain people allowed to respond on this board? |
|
ats join:2008-11-14 Vallejo, CA |
ats
Member
2011-Oct-28 3:28 pm
its not that your opinion is being questioned, nerdburg,beach and cabletool were once or is still with comcast and works in the field thats why their opinion carries weight and i agree with them too. |
|
EGThe wings of love Premium Member join:2006-11-18 Union, NJ |
to YeahWhat
said by YeahWhat :Please don't flame, don't understand why my opinion is being questioned. Sorry are only certain people allowed to respond on this board? It wasn't meant to be a "Flame". Sorry if you took it that way. Opinions and "facts" are two different things and we all know what opinions are like don't we ! You made an absolute statement here; "Certainly -8 your having issues." |
|
|
YeahWhat
Anon
2011-Oct-28 11:16 pm
For the original poster, my opinion coincides with points in several CableTool opinion posts. It also agrees with beachintech's opinion "Your downstream power level is borderline out of spec. You may have a wiring problem causing you intermittant issues. . In response to the poster which the information below is directed, the operating range of the modem is -15 to +15 but doesn't mean it will operate properly at that range or that there won't be issues. Also there needs to be enough for drift or other conditions "That is why all MSOs have a much tighter operational range" . Being -8 and having issues would be one thing to look and if there is opportunity to eliminate potential simple issues "One could be fixed with a new config file, one with a loose connector and one with modem swap. All exhibiting the same issue." . No one here has access to see your modem in the network regardless of the who's who list here. There is a Direct Support forum I noted. I was noted a range that somehow the format was garbled when I submitted the post. One part of that I was noting that and upstream signal noise level (uSNR) of 32 being optimal with recommendation to contact your service provider since no one here can obtain that information. Recommended ranges can vary by manufacturer, plant equipment, or engineer claimed or otherwise. I narrow that gap because these are the extremes even if "some" equipment may be able to operate at those ranges it is not a rule and there are many other conditions. I noted there is a FAQ here which you can follow: » Comcast High Speed Internet FAQ » What should my Signal Levels be?For all others, please note forum policy 10. |
|
EGThe wings of love Premium Member join:2006-11-18 Union, NJ
1 recommendation |
EG
Premium Member
2011-Oct-29 12:34 am
Why not sign up here instead of being an anon ? |
|