bluesrhythm's profile

Contributor

 • 

15 Messages

Mon, Aug 3, 2020 10:00 AM

Re: daily restart of modem

I have a similar circumstance - started a few weeks ago when I upgraded to 1Gbps plan (our promotional plan expired and this was a nearly cost-equivilant switch) and a new Xfinity-owned XB6 gateway (hw details below).  After install we couldn't get anywhere near the plan speeds (we'd get about 30Mbps down, 40Mbps up), had many chats with tech support, and eventually after they pushed a refresh started getting 300Mbps down consistently, and up to 700Mbps down (all speeds measured via direct ethernet connection to the gateway).  But at that point, started seeing intermittent disconnects throughout the day. 

 

Tech came out, verified in-house wiring, modem install itself, and the wire to the pole are all fine, and was going to have line techs examine further (I don't know if that has happend).  Of course the day he was here we were pretty stable and fast.  🙂  After that though, it's a bit random - if I'm getting high speed, I get drops.  If I reboot, I may get high speed (and continue drops), or back to 30Mbps but fairly stable.  And when very I'm lucky, I'll get both (right now I'm at 293Mbps down and no connection errors for 4 hours), but it'll last a day at most before starting to drop intermittently again.  A reboot (or 2 or 3) gets me back in business for about another day.

 

I've taken to monitoring the connection status from a Linux box that's directly connected to the gateway and also connected to my internal wireless (so I can get to it even if the gateway is down/rebooting).  "ping -i 10 -f -n -4 www.google.com" does a nice job - just leave it in a window, it'll ping Google every 10 seconds and print a dot, and then erase that dot as soon as the response comes in.  Ideally you get nothing but a blank screen - when the intermittent connection drops hit, it leaves a dot on the screen for every dropped ping.  No timestamping with this, but it does a nice job of showing when things have gone downhill, and I can correlate that it's not just google having an issue (when dots start appearing, all internet traffic is pretty much deceased).

 

The XB6 doesn't have nearly the detailed log folks are showing above (only seeing radio harvester thread start notices and my admin signons).  I can try posting downstream/upstream/CM error info if helpful although it doesn't grab as nicely as above.

 

HW details on the XB6:  under the hood it's a Technicolor XB6 version 2.2, BOOT Version:S1TC-3.49.18.14, Core Version:1.0, Model:CGM4140COM, Product Type:XB6, Download Version:Prod_18.1_d31 & Prod_18.1

 

Any hints, suggestions, or help would be very much appreciated!  

Responses

Accepted Solution

EG

Expert

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88.1K Messages

1 y ago

Even though the signal stats looked o/k at that snapshot in time, the error log entries confirm that something is going on. Perhaps there is noise ingress into the line(s) somewhere.

 

There are other signal stat figures that can't be read by the modem. They are the "Upstream Rx Power" (Upstream Receive Power Level), the "Upstream SNR Ch." (Upstream Signal To Noise Ratio), and the "Upstream ICFR" (In Channel Frequency Response). These are as equally important in diagnosing connectivity issues as are the modem's stats.


I'm going to escalate your issue to the Comcast corporate employees that are available to these boards. They can check the CMTS (Cable Modem Termination System) for any real time degradation and / or error reports, see your node / cable plant and modem health, and see whether or not everything is in the green zone. They can also see a history plot for the modem and poll for those upstream receive signal stats.

You should get a reply here in your topic. Good luck !

EG

Expert

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88.1K Messages

1 y ago

Please post the *Downstream Power Level*, the *Upstream Power Level*, and the *SNR* (Signal to Noise Ratio) numbers.


Contributor

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15 Messages

1 y ago

Here's the latest set - hopefully timely, I've just started seeing connectivity glitches after my last reboot about 6 hours ago.  I also checked the logs for messages but they only show my admin login and the startup of the radio & device data harvesting.

 

Downstream:

Index339101112131415161718192021222324252627282930313234353637383940159 
Lock StatusLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLocked
Frequency651 MHz507 MHz513 MHz519 MHz525 MHz531 MHz537 MHz543 MHz549 MHz555 MHz561 MHz567 MHz573 MHz579 MHz585 MHz591 MHz597 MHz603 MHz609 MHz615 MHz621 MHz627 MHz633 MHz639 MHz645 MHz657 MHz663 MHz669 MHz675 MHz681 MHz687 MHz693 MHz702 MHz620600000
SNR38.3 dB39.2 dB39.4 dB39.7 dB39.8 dB39.8 dB39.8 dB39.6 dB39.5 dB39.4 dB39.1 dB39.2 dB39.3 dB39.7 dB39.8 dB39.7 dB39.6 dB39.5 dB39.3 dB39.1 dB39.3 dB39.0 dB38.7 dB38.4 dB38.6 dB38.4 dB38.6 dB39.0 dB38.9 dB39.9 dB39.9 dB39.7 dB39.5 dBNA
Power Level-4.5 dBmV-4.5 dBmV-4.2 dBmV-3.8 dBmV-3.2 dBmV-3.1 dBmV-3.2 dBmV-3.6 dBmV-3.9 dBmV-4.4 dBmV-4.6 dBmV-4.8 dBmV-4.3 dBmV-3.3 dBmV-2.9 dBmV-2.9 dBmV-2.9 dBmV-3.1 dBmV-3.2 dBmV-3.1 dBmV-2.8 dBmV-3.4 dBmV-4.2 dBmV-4.6 dBmV-4.4 dBmV-4.4 dBmV-3.9 dBmV-3.0 dBmV-2.0 dBmV0.8 dBmV0.0 dBmV0.8 dBmV-4.3 dBmVNA
Modulation256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAMOFDMOFDM

 

Upstream:

IndexLock StatusFrequencySymbol RatePower LevelModulationChannel Type

1
2
3
4
Locked
Locked
Locked
Locked
36 MHz
30 MHz
23 MHz
17 MHz
5120
5120
5120
5120
48.3 dBmV
48.3 dBmV
48.8 dBmV
48.3 dBmV
QAM
QAM
QAM
QAM
ATDMA
ATDMA
ATDMA
ATDMA

 

CM Error Codewords:

Index
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
Unerrored Codewords
392971927
949458298
949463365
949467626
949473986
949477908
949483935
949488746
949497708
949502021
949507527
949511738
949517762
949522755
949528778
949533711
949545458
949550306
949555209
949560705
949565170
949570441
949575725
949581194
949585865
949591372
949597226
949600949
949605820
949609849
949612169
949614448
392971927
Correctable Codewords
2762
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
2762
Uncorrectable Codewords
113
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
113

Contributor

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15 Messages

1 y ago

Lost a few days of connectivity due to tropical storm Isaias - but we're back up, and although it seems a little more stable the pattern still seems to hold that at least once per day we'll start seeing drops and degradation of the connection, and a reboot of the modem gets us reset and working fine for many hours after that.

 

I've been considering purchasing my own modem (likely a Netgear CM1150V since we use the voice service) - figure that might solve the probelm if the modem itself is degrading the connection over time.  But I'm pretty reluctant to make the switch as it seems that would just add another layer of complication to solving the issue if it's not the modem (i.e. I don't want to get into a spiral of "Your third-party modem must be the problem, things look fine") - I'd rather get this resolved while all the problems are on Comcast gear + wire, then think about a modem shift.

EG

Expert

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88.1K Messages

1 y ago

The upstream power is on the high side and it may be intermittently fluctuating even higher to out of spec levels. That can cause random disconnects, spontaneous re-booting of the modem, speed, packet loss, latency problems, and the un-bonding of channels.

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.

Contributor

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15 Messages

1 y ago

Quick update - I just removed the 3-way and replaced with a straight coupler so only the gateway is on the line.  Upstream power levels dropped by about 6dBmV from my prior post.  I'll report back on stability in a couple days, or when my family starts getting really irritated that the TVs are offline, whichever occurs first.  😉

 

IndexLock StatusFrequencySymbol RatePower LevelModulationChannel Type

1
2
3
4
Locked
Locked
Locked
Locked
36 MHz
30 MHz
23 MHz
17 MHz
5120
5120
5120
5120
42.3 dBmV
42.8 dBmV
43.3 dBmV
42.8 dBmV
QAM
QAM
QAM
QAM
ATDMA
ATDMA
ATDMA
ATDMA

Contributor

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15 Messages

1 y ago

Thanks EG, that's very helpful.  There's a coax coupler outside the house in the junction box connecting the line from the street to the line in the house (not a splitter, but I'll inspect the connections for corrosion), and just one splitter in the house but that is a three-way (Comcast-installed) feeding the modem, DVR, and a TV extension all off the line in.  I'll pull that three-way for now (sorry kids, no TV today!) and see if things stabilize.  Either way I'll report back.

 

What sort of upstream power levels should I be seeing typically?  I can take a look right when I'm having issues and see if they look out of line.

EG

Expert

 • 

88.1K Messages

1 y ago


@bluesrhythm wrote:

 

What sort of upstream power levels should I be seeing typically?  I can take a look right when I'm having issues and see if they look out of line.


Here are the ranges;

 

Check your signal levels

To view your modem’s status page go to http://192.168.100.1 or http://10.0.0.1

 

Specification      Min             Max

Downstream Power Level  
Cable Modems-10dBmV+10dBmV
Gateways and EMTAs-7dBmV+7dBmV
Downstream Signal to Noise Ratio35dB-
Upstream Power Level+35dBmV+50dBmV
Upstream Signal to Noise Ratio31dB-
Upstream Receive Power-2dBmV+2dBmV

 

Note: Not all modems will allow you to view the status page and some will have different URLs to access this info. If you are unable to access your modem’s status page, you can contact Comcast Customer Support and ask the support representative for these values.

Contributor

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15 Messages

1 y ago

Stability was a little better but still pretty spotty yesterday even after removing the splitter (which dropped the upstream power by about 6dBmV as posted above), and was positively terrible this morning even after a couple reboots.  BUT - I had noticed yesterday when temporarily removing the splitter that the connector on the coax line in had a plastic shield on it that made it rather difficult to connect the line to the coupler.  I replaced that (didn't make a difference either way).  Late this morning I paid a visit to the outside drop box and the line into the house had the same type of connector, so I replaced that as well and reconnected the line to the ground block.  It's pretty soon to make a call, but it's been nearly an hour since replacing that connector and I haven't had a single drop yet - I'll keep an eye on it and update this thread shortly.

Contributor

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15 Messages

1 y ago

Turns out my optimism was misplaced - I hadn't checked speed after I removed the splitter and replaced the cable ends, turns out we were error-free but at 30Mbps.  Once I rebooted we came backup up at 300Mbps+ but started getting drops again.  That's been a typical pattern - on any given reboot we'll occasionally hit low speed but fairly solid connection, or back closer to plan speeds but unstable.

 

Line techs are due out tomorrow to check the node at the street - it's the next link in the chain and hasn't been looked at yet as far as I know.  Given the connection sensitivity to weather/temperature I'm hopeful that'll nail it down - will keep the thread posted!

EG

Expert

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88.1K Messages

1 y ago

FWIW, the timestamp is normal. Modems don't do DST.

Contributor

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15 Messages

1 y ago

Update on status - I got Comcast to commit to send out a line technician to check the node and the pole.  I don't know if they actually did that or not, but I do know that a Comcast tech visited the house (totally unseen, like The Shadow!) because when I went out yesterday to put a better compression fitting on the cable line into the house (wasn't confident in my prior replacement), the ground block/surge protector in the box had been replaced and the old one was left loose in the box.  However, connectivity was still dodgy at best, and downright miserable at times although it appears work may have been being performed nearby. 

 

This morning, back to low speed and/or intermittent connectivity - so I took the plunge and bought a Netgear CM1150V to replace the Technicolor XB6 Comcast had supplied, since the modem is the only thing on-prem that hasn't been replaced, and our issues began at roughly the same time we upgraded to it.  Activated fine, but still getting the intermittent connectivity errors.  Here are the new signal tables from the CM1150V:

 

Startup Procedure
ProcedureStatusComment
Acquire Downstream Channel579000000 HzLocked
Connectivity StateOKOperational
Boot StateOKOperational
SecurityEnabledBPI+
IP Provisioning ModeHonor MDDhonorMdd(4)
 
Downstream Bonded Channels
ChannelLock StatusModulationChannel IDFrequencyPowerSNRCorrectablesUncorrectables
1LockedQAM25621579000000 Hz0.1 dBmV40.2 dB00
2LockedQAM2561453000000 Hz0 dBmV40 dB00
3LockedQAM2562459000000 Hz-0.4 dBmV39.8 dB00
4LockedQAM2563465000000 Hz-0.6 dBmV39.8 dB00
5LockedQAM2564471000000 Hz-0.9 dBmV39.6 dB00
6LockedQAM2565477000000 Hz-0.8 dBmV39.7 dB00
7LockedQAM2566483000000 Hz-0.9 dBmV39.6 dB00
8LockedQAM2567489000000 Hz-1 dBmV39.5 dB00
9LockedQAM2568495000000 Hz-0.5 dBmV39.8 dB00
10LockedQAM2569507000000 Hz-0.1 dBmV40 dB00
11LockedQAM25610513000000 Hz-0.2 dBmV40 dB20
12LockedQAM25611519000000 Hz-0.3 dBmV40 dB10
13LockedQAM25612525000000 Hz-0.6 dBmV40 dB30
14LockedQAM25613531000000 Hz-1.1 dBmV39.8 dB30
15LockedQAM25614537000000 Hz-1.5 dBmV39.5 dB20
16LockedQAM25615543000000 Hz-1.9 dBmV39.4 dB20
17LockedQAM25616549000000 Hz-1.7 dBmV39.5 dB20
18LockedQAM25617555000000 Hz-1.8 dBmV39.4 dB10
19LockedQAM25618561000000 Hz-1.5 dBmV39.5 dB10
20LockedQAM25619567000000 Hz-1.3 dBmV39.6 dB00
21LockedQAM25620573000000 Hz-0.7 dBmV39.9 dB00
22LockedQAM25622585000000 Hz0.3 dBmV40.2 dB00
23LockedQAM25623591000000 Hz0.1 dBmV40 dB00
24LockedQAM25624597000000 Hz-0.1 dBmV39.8 dB00
25LockedQAM25625603000000 Hz-0.4 dBmV39.7 dB00
26LockedQAM25626609000000 Hz-0.7 dBmV39.5 dB00
27LockedQAM25627615000000 Hz-0.9 dBmV39.2 dB00
28LockedQAM25628621000000 Hz-0.9 dBmV39.3 dB00
29LockedQAM25629627000000 Hz-1.1 dBmV39.2 dB00
30LockedQAM25630633000000 Hz-1.2 dBmV39.1 dB00
31LockedQAM25631639000000 Hz-1.3 dBmV39 dB00
32LockedQAM25632645000000 Hz-1.1 dBmV39.1 dB00
 
Upstream Bonded Channels
ChannelLock StatusUS Channel TypeChannel IDSymbol RateFrequencyPower
1LockedATDMA15120 Ksym/sec36500000 Hz46.3 dBmV
2LockedATDMA25120 Ksym/sec30100000 Hz46.8 dBmV
3LockedATDMA35120 Ksym/sec23700000 Hz47.8 dBmV
4LockedATDMA45120 Ksym/sec17300000 Hz46.8 dBmV
5Not LockedUnknown00 Ksym/sec0 Hz0.0 dBmV
6Not LockedUnknown00 Ksym/sec0 Hz0.0 dBmV
7Not LockedUnknown00 Ksym/sec0 Hz0.0 dBmV
8Not LockedUnknown00 Ksym/sec0 Hz0.0 dBmV
 
Downstream OFDM Channels
ChannelLock
Status
Modulation /
Profile ID
Channel
ID
FrequencyPowerSNR /
MER
Active Subcarrier
Number Range
Unerrored
Codewords
Correctable
Codewords
Uncorrectable
Codewords
1Locked0159702000000 Hz-2.1 dBmV40.4 dB1546 ~ 254958081722361113
2Not Locked000 Hz0 dBmV0.0 dB0 ~ 4095000
 
Upstream OFDMA Channels
ChannelLock StatusModulation / Profile IDChannel IDFrequencyPower
1Not Locked000 Hz0 dBmV
2Not Locked000 Hz0 dBmV
 
Current System Time:Mon Aug 17 13:17:46 2020
System Up Time:01:04:36

 

A few things of note:  I know upstream is bit toward the high side, I'm currently back to Comcast's supplied 3-way splitter that feeds the modem, DVR, and an additional TV box.  New splitters arriving today so I can split line-in to 1) modem and 2) next splitter, with the DVR+TV box on that second splitter (should drop that signal about 3dBmV).  And - the system time is wrong, it's off by an hour, apparently whatever's transmitting it on the upstream side isn't aware of daylight savings time (there's no config option on my side to fix that).

Contributor

 • 

15 Messages

1 y ago

Also, I have a better event log now than the XB6 provided (yay!) - here's the content since power-up.  The momentary internet drops don't seem to be generating an error or warning here in the log, as I'm watching pings fail to multiple addresses (including the gateway address for my IP) nothing is getting added here.

 

TimePriorityDescription
Mon Aug 17 12:26:22 2020Critical (3)SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=[redacted];CMTS-MAC=[redacted];CM-QOS=1.1;CM-VER=3.1;
Mon Aug 17 12:14:15 2020Warning (5)Dynamic Range Window violation
Mon Aug 17 12:14:15 2020Warning (5)RNG-RSP CCAP Commanded Power Exceeds Value Corresponding to the Top of the DRW;CM-MAC=[redacted];CMTS-MAC=[redacted];CM-QOS=1.1;CM-VER=3.1;
Mon Aug 17 12:14:15 2020Warning (5)Dynamic Range Window violation
Mon Aug 17 12:14:15 2020Warning (5)RNG-RSP CCAP Commanded Power Exceeds Value Corresponding to the Top of the DRW;CM-MAC=[redacted];CMTS-MAC=[redacted];CM-QOS=1.1;CM-VER=3.1;
Mon Aug 17 12:14:05 2020Notice (6)TLV-11 - unrecognized OID;CM-MAC=[redacted];CMTS-MAC=[redacted];CM-QOS=1.1;CM-VER=3.1;
Time Not EstablishedNotice (6)Honoring MDD; IP provisioning mode = IPv6
Time Not EstablishedCritical (3)SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=[redacted];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;

Contributor

 • 

15 Messages

1 y ago

Thanks EG, that makes sense.

 

Redid my splitters and as expected the upstream power level dropped 2-3dBmV on each channel.  Will see how it does from here!

Upstream Bonded Channels
ChannelLock StatusUS Channel TypeChannel IDSymbol RateFrequencyPower
1LockedATDMA15120 Ksym/sec36500000 Hz43.3 dBmV
2LockedATDMA25120 Ksym/sec30100000 Hz44.8 dBmV
3LockedATDMA35120 Ksym/sec23700000 Hz45.8 dBmV
4LockedATDMA45120 Ksym/sec17300000 Hz45.3 dBmV

Contributor

 • 

15 Messages

1 y ago

Although it seems a bit better, still getting quite a few intermittent drops, and as before it seems to be morning that triggers it - we ran completely error/drop free last night from 9pm until about 2am, then at some point between 2am and 8am collected a bunch of failed pings, thousands of correctable and hundreds of uncorrectable codewords, and lost the lock on OFDM channel 1 so we were down to 30Mbps.  Rebooted the CM1150V and came back up at close to 300Mbps (nowhere near the 1Gbps plan we're on), with still a number of drops from then until now (about noon).

 

Somewhat random item, but I'm clutching at straws here:  last tech here replaced the ground/surge block in the demarc box, and grounded to our house electrical ground (which is right there).  All cable & compute gear is grounded to that same point, so there shouldn't be any ground loops.  BUT ... I recently mounted an antenna on our chimney at the other end of the house for a cell booster, and pounded in a brand new ground over there.  The booster lives in the same closet that the Comcast cable line comes into.  I disconnected the antenna-in coax from the booster, and measured voltage from it's shield to the Comcast line-in shield (i.e. basically measuring voltage from old house ground to a brand new ground on the other side of the house), and I'm reading about 500mV AC.  Not sure if that's normal (line-of-sight distance between the two stakes is about 50', with the house basement in between), or a sign of a dodgy ground on one side or the other.  Would it be worth putting in a new ground for the house to see if it mitigates the drops, or is it all moot since all of the cable gear and the line already share a common ground?  (Thinking probably moot since house ground is also bonded to neutral and up to the utility transformer - a new stake & wire at the house isn't going to budge it if it's wired right).

 

Problems did NOT start when I put in the cell booster, they predate it - it just gave me a handy measurement opportunity to flail around with.  😀

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