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sarmitage
join:2012-09-20
North York, ON

1 edit

sarmitage

Member

[Cable] Huge bit error rates on DCM475

Hi everyone, I've recently been seeing numerous disconnects (usually around two per day, once in morning once in evening, but tonight it's been cutting out every 30 minutes or so) on my DCM475. Usually the "Online" light starts blinking and I'm unable to use the internet or connect to the modem's diagnostics page.

Channel Frequency   Power     SNR      BER      Modulation
1       651.0 MHz   8.4 dBmV  38.3 dB  2.034 %  256 QAM
2       615.0 MHz   8.0 dBmV  39.5 dB  2.126 %  256 QAM
3       621.0 MHz   8.0 dBmV  38.7 dB  1.957 %  256 QAM
4       633.0 MHz   8.5 dBmV  38.2 dB  2.020 %  256 QAM
5       639.0 MHz   8.6 dBmV  37.1 dB  2.049 %  256 QAM
6       645.0 MHz   8.6 dBmV  38.3 dB  2.181 %  256 QAM
7       657.0 MHz   8.8 dBmV  36.8 dB  2.327 %  256 QAM
8       663.0 MHz   8.8 dBmV  38.1 dB  2.350 %  256 QAM
 

This is causing all sorts of badness -- terribly slow speeds for pretty much everything, can't play online video games at all (too many packet drops), can't stream video, etc..

Is this indicative of a problem with my modem, or a problem with the service? I'm not sure what the proper levels are for Rx power and SNR, but I know that my bit error rate was 0% when I first set up the modem 10 months ago, and it's been working perfectly until last Sunday when these disconnects started happening.

If I open a ticket, am I on the hook if it's a problem with the modem? I purchased the modem as part of the TekSavvy package.

Cheers,
-S

Edit: this is what a speed test looks like right now with ~2% bit error rate; should be 28/1 =(



Oinktastic
Let them use fibre
join:2005-08-24
Scarborough

Oinktastic

Member

Your incoming power level seems a little high. You might need to "crapify" it a little bit to let the modem connect more comfortably. Try adding a splitter or some crappy wire between the outlet and your modem to attenuate the signal.

What do your upstream channels look like?
sarmitage
join:2012-09-20
North York, ON

sarmitage

Member

Upstream channels have been fairly consistent throughout all of this..

ID  Frequency  Power  Modulation
4   38.6 MHz   41.8 dBmV  64 QAM
1   31.3 MHz   42.5 dBmV  64 QAM
2   25.3 MHz   43.3 dBmV  64 QAM
3   22.1 MHz   41.8 dBmV  64 QAM
 

At the moment I am getting decent (but not great) connection, bit error rates are down around 0.25% at the moment, with downstream power down around 7.5 to 7.9 dBmV. "Too strong a signal" is not something I've ever heard of outside of blowing out the receiver =S

Edit: Although even as I say that, while the upstream diagnostics page looks fine (to me), the "US" light is blinking slowly on my modem. All other lights (including the "Online") light are on solid, and internet connection is working finish.
nbinont
join:2011-03-13

nbinont to Oinktastic

Member

to Oinktastic
said by Oinktastic:

Your incoming power level seems a little high.

High, but not unreasonably so. DOCSIS 3.0 is required to work between -15 and +15 dBmv. +8 is within that range.

I seem to recall my last place had +7, and my current place now has +5.

I have the DCM475 as well and only saw this problem once. I believe a factory reset of the modem (with a paperclip on the back) solved it for me.
sarmitage
join:2012-09-20
North York, ON

sarmitage

Member

said by nbinont:

said by Oinktastic:

Your incoming power level seems a little high.

High, but not unreasonably so. DOCSIS 3.0 is required to work between -15 and +15 dBmv. +8 is within that range.

TBH, I would be surprised if it were an input power issue at ~+8 dBmV; I would generally be more concerned about the SNR -- what's a reasonable range for that with this modem?

If I were going to reduce the input power I would use an attenuator (between 2 and 5 dB, DC to 1 GHz), not a crappy cable -- that would likely reduce the SNR and increase the BER.
nbinont
join:2011-03-13

1 edit

nbinont

Member

said by sarmitage:

I would generally be more concerned about the SNR -- what's a reasonable range for that with this modem?

According to: »www.speedguide.net/artic ··· ide-1686 , +30dB SNR should be fine, though I'm not sure if they are referring to a lower modulation. Anything around +35dB and above is generally preferred (Mine is about +34 or +35 if I recall - also with 256QAM). Your SNR seems fine and shouldn't be causing that high of a BER.

Did you try that factory reset on the modem?

EDIT: (From »forum.dvdtalk.com/tech-t ··· ers.html )
QPSK: 12 dB minimum. 15 dB or higher recommended.
16 QAM: 18 dB minimum. 21 dB or higher recommended.
64 QAM: 24 dB minimum. 27 dB or higher recommended.
256 QAM: 30 dB minimum. 33 dB or higher recommended.
said by sarmitage:

If I were going to reduce the input power I would use an attenuator (between 2 and 5 dB, DC to 1 GHz), not a crappy cable -- that would likely reduce the SNR and increase the BER.

Yah, assuming no clipping or saturation is happening (unlikely at 7dB below max levels)
sarmitage
join:2012-09-20
North York, ON

sarmitage

Member

said by nbinont:

Did you try that factory reset on the modem?

I haven't yet, but I've mentioned it in the TekSavvy Direct thread that I have open (just get faster responses here, and trying to suss out anything I can work on while waiting for responses from them). It's up next on my list though.

Will this return it to STAC.02.08? (I believe this modem originally shipped with that and got updated by Rogers' network some time after that..).
HKPolice
join:2002-08-09
Scarborough, ON

HKPolice to sarmitage

Member

to sarmitage
Are you sure no one else is using the connection when you're doing the speed tests? What if someone hacked your wifi and is leeching off your network?
sarmitage
join:2012-09-20
North York, ON

sarmitage

Member

said by HKPolice:

Are you sure no one else is using the connection when you're doing the speed tests? What if someone hacked your wifi and is leeching off your network?

Short answer is that yes, I am sure. The performance hits are also directly correlated with spikes in the downstream channel bit error rate. When working properly, I can max out my connection and I'll still see ~0% BER.
nbinont
join:2011-03-13

nbinont to sarmitage

Member

to sarmitage
said by sarmitage:

Will this return it to STAC.02.08? (I believe this modem originally shipped with that and got updated by Rogers' network some time after that..).

I have STAC.02.08 myself, and am pretty sure Rogers doesn't upgrade the firmware for you (this has been a sticky point in some threads).
sarmitage
join:2012-09-20
North York, ON

sarmitage

Member

said by nbinont:

I have STAC.02.08 myself, and am pretty sure Rogers doesn't upgrade the firmware for you (this has been a sticky point in some threads).

I could be wrong about it originally being STAC.02.08.
nbinont
join:2011-03-13

nbinont

Member

I don't think a factory reset will revert the firmware - you'd need to reload the old firmware to do that. Simply put - if you didn't manually upgrade the firmware yourself, there's no way for a factory reset to change the firmware version.
sarmitage
join:2012-09-20
North York, ON

sarmitage

Member

said by nbinont:

I don't think a factory reset will revert the firmware - you'd need to reload the old firmware to do that. Simply put - if you didn't manually upgrade the firmware yourself, there's no way for a factory reset to change the firmware version.

Cool. I've got a script set up now to log the diagnostics stats to a CSV file periodically; I'll let that run for a day or so and see if I can get any correlations, then I'll do a factory reset and let it run again.
nbinont
join:2011-03-13

1 edit

nbinont

Member

Have fun and good luck!

If you're really ambitious, run a day's tests with a -3dB splitter in front of the modem as Oinktastic suggests see if that has an impact. (Nothing like a little hard data to examine whether the DCM475 actually follows the spec!)

EDIT: Someone else has a DCM475 and was achieving 0BER with +12/13 dBmv downlink power: »[Cable] Modem Stats
sarmitage
join:2012-09-20
North York, ON

sarmitage

Member

said by nbinont:

If you're really ambitious, run a day's tests with a -3dB splitter in front of the modem as Oinktastic suggests see if that has an impact. (Nothing like a little hard data to examine whether the DCM475 actually follows the spec!)

I may; I was taking a look at DigiKey but I couldn't find any F-type attenuators.
mlord
join:2006-11-05
Kanata, ON

mlord

Member

said by sarmitage:

I was taking a look at DigiKey but I couldn't find any F-type attenuators.

Home Hardware, College & Spadina, in the electronic components section (downstairs).
mlord

mlord to sarmitage

Member

to sarmitage
Line stats look fine (apart from the BER figures, which should all be zeros). What firmware version is running on it (same screen that you pulled the line stats from)?
sarmitage
join:2012-09-20
North York, ON

sarmitage

Member

said by mlord:

Line stats look fine (apart from the BER figures, which should all be zeros). What firmware version is running on it (same screen that you pulled the line stats from)?

Software Version : STAC.02.16
Software Model : a81a
Bootloader : 2.3.0

I've got some interesting-looking data that I will put up when I get home today; it looks like the BER moves in unison between all 8 channels. Anything below ~0.5% and I don't notice it too much in my regular browsing, but above that, internet slows to a crawl as packet drop rate skyrockets.

TSILiz
Premium Member
join:2012-08-20

TSILiz

Premium Member

Hi There,

What does your event log say within your modem? What are some of the reoccuring reasons you see 3 criticals appear?
sarmitage
join:2012-09-20
North York, ON

1 edit

sarmitage

Member

This is a fairly representative event log:

Time Priority Description
Sun Sep 23 20:16:34 2012 Notice (6) Bad CMTS DBC-ACK: msg syntax error;CM-MAC=00:26:24:e6:41:98;C...
Sun Sep 23 19:39:28 2012 Warning (5) Dynamic Range Window violation
Time Not Established Warning (5) DHCP WARNING - Non-critical field invalid in response ;CM-MAC...
Sun Sep 23 19:03:13 2012 Critical (3) Unicast Ranging Received Abort Response - Re-initializing MAC...
Sun Sep 23 03:44:24 2012 Critical (3) No UCDs Received - Timeout;;CM-MAC=00:26:24:e6:41:98;CMTS-MAC...
Time Not Established Critical (3) TFTP failed - Request sent - No Response;CM-MAC=00:26:24:e6:4...
Sun Sep 23 19:09:56 2012 Critical (3) No Ranging Response received - T3 time-out;CM-MAC=00:26:24:e6...
Sun Sep 23 20:24:31 2012 Critical (3) UCD invalid or channel unusable;CM-MAC=00:26:24:e6:41:98;CMTS...
Time Not Established Critical (3) Started Unicast Maintenance Ranging - No Response received - ...
Time Not Established Critical (3) UCD invalid or channel unusable;CM-MAC=00:26:24:e6:41:98;CMTS...
Sun Sep 23 12:28:59 2012 Critical (3) No UCDs Received - Timeout;;CM-MAC=00:26:24:e6:41:98;CMTS-MAC...
Sun Sep 23 05:21:46 2012 Critical (3) 16 consecutive T3 timeouts while trying to range on upstream ...
Sun Sep 23 05:21:26 2012 Critical (3) 16 consecutive T3 timeouts while trying to range on upstream ...
Sun Sep 23 05:20:46 2012 Critical (3) 16 consecutive T3 timeouts while trying to range on upstream ...
Sun Sep 23 05:21:06 2012 Critical (3) 16 consecutive T3 timeouts while trying to range on upstream ...
Sun Sep 23 05:44:36 2012 Critical (3) Unicast Maintenance Ranging attempted - No response - Retries...
Sun Sep 23 21:41:16 2012 Critical (3) Started Unicast Maintenance Ranging - No Response received - ...
Sun Sep 23 04:16:55 2012 Critical (3) Received Response to Broadcast Maintenance Request, But no Un...
Sun Sep 23 01:40:51 2012 Critical (3) REG RSP not received;CM-MAC=00:26:24:e6:41:98;CMTS-MAC=00:1b:...
Time Not Established Critical (3) DHCP FAILED - Request sent, No response;CM-MAC=00:26:24:e6:41...
Time Not Established Critical (3) DHCP FAILED - Discover sent, no offer received;CM-MAC=00:26:2...
Time Not Established Critical (3) No Ranging Response received - T3 time-out;CM-MAC=00:26:24:e6...
Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/Q...
Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire FEC f...

Edit: Note that timestamps appear to be UTC.
mlord
join:2006-11-05
Kanata, ON

mlord to sarmitage

Member

to sarmitage
said by sarmitage:

Software Version : STAC.02.16

Good. The modem is up-to-date, so the firmware is not the issue.
That leaves two things, really:

(1) line issues --> try your modem at a friends house (not next door) to see if it behaves fine on a different line.

(2) faulty modem --> see (1) above.

Cheers
sarmitage
join:2012-09-20
North York, ON

sarmitage

Member

said by mlord:

(1) line issues --> try your modem at a friends house (not next door) to see if it behaves fine on a different line.

Would it even be able to get on the network? I was under the impression that Rogers provisions the modems based on their MAC address, and that any given network node will not bond with an unrecognized MAC.

Teddy Boom
k kudos Received
Premium Member
join:2007-01-29
Toronto, ON

Teddy Boom

Premium Member

said by sarmitage:

said by mlord:

(1) line issues --> try your modem at a friends house (not next door) to see if it behaves fine on a different line.

Would it even be able to get on the network? I was under the impression that Rogers provisions the modems based on their MAC address, and that any given network node will not bond with an unrecognized MAC.

Not at all. Just give it a try, will work perfectly (or it won't, but that's kind of the point ). If you can't think of anybody, I offer this as a service, but I have to charge a nominal fee.
sarmitage
join:2012-09-20
North York, ON

sarmitage

Member

said by Teddy Boom:

Not at all. Just give it a try, will work perfectly (or it won't, but that's kind of the point ). If you can't think of anybody, I offer this as a service, but I have to charge a nominal fee.

Thanks, but I know a bunch of people around town that would let me try =) If it will work perfectly at some other location, why does Teksavvy have a $65 "cable move" fee?

Teddy Boom
k kudos Received
Premium Member
join:2007-01-29
Toronto, ON

Teddy Boom

Premium Member

Of course the cable line has to be active, so that is number one.

The topic is being discussed over here:
»[Cable] Toronto - Cable - Moving modem but staying on same POI...
mlord
join:2006-11-05
Kanata, ON

mlord to sarmitage

Member

to sarmitage
said by sarmitage:

said by mlord:

(1) line issues --> try your modem at a friends house (not next door) to see if it behaves fine on a different line.

Would it even be able to get on the network? I was under the impression that Rogers provisions the modems based on their MAC address, and that any given network node will not bond with an unrecognized MAC.

Absolutely true. Except the MAC is inside the modem, so it goes whereever you take the modem, and therefore the modem will work on any live cable connection on the same POI.

That's where it could get tricky -- if you take it to a different city, it is unlikely to work (the cable system there won't recognize the MAC). I don't know if it will work on a different POI in the same city (unlikely), so best not to go too far from home with it.

Cheers
mlord

mlord

Member

said by mlord:

That leaves two things, really:

(1) line issues --> try your modem at a friends house (not next door) to see if it behaves fine on a different line.

(2) faulty modem --> see (1) above.

Oh, there's a third possibility too:

(3) faulty power supply --> it's a pretty standard item, at least, so any 12VDC regulated adapter will likely work with it. eg. the PSU from a Linksys WRT54G router.
sarmitage
join:2012-09-20
North York, ON

sarmitage to mlord

Member

to mlord
said by mlord:

Absolutely true. Except the MAC is inside the modem, so it goes whereever you take the modem, and therefore the modem will work on any live cable connection on the same POI.

Ah, OK; for some reason I thought the provisioning happened at the local node, not the POI. The latter would make sense though.
mlord
join:2006-11-05
Kanata, ON

mlord

Member

The modem gets DHCP from the CMTS at the POI. So the local nodes normally don't care, they just pass things along in either direction.

There are more complex scenarios where the local nodes might route things in a less straightforward manner than this, but so long as they're routing your modem to the same POI as you normally connect with, it should all work.

The $65 change fee is likely what Rogers charges Teksavvy to update their databases. Accurate info there is essential when "node splitting" happens to increase capacity in the future.

Teddy Boom
k kudos Received
Premium Member
join:2007-01-29
Toronto, ON

Teddy Boom to mlord

Premium Member

to mlord
said by mlord:

the modem will work on any live cable connection on the same POI.

POI is not a limiting factor. I don't know what is, I doubt a Toronto modem would work in Ottawa, but...