Re: daily restart of modem

Question

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!

EG · Accepted Answer

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 · Answer

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

bluesrhythm · Answer

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:

Index

33

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

34

35

36

37

38

39

40

159

Lock Status

Locked

Frequency

651 MHz

507 MHz

513 MHz

519 MHz

525 MHz

531 MHz

537 MHz

543 MHz

549 MHz

555 MHz

561 MHz

567 MHz

573 MHz

579 MHz

585 MHz

591 MHz

597 MHz

603 MHz

609 MHz

615 MHz

621 MHz

627 MHz

633 MHz

639 MHz

645 MHz

657 MHz

663 MHz

669 MHz

675 MHz

681 MHz

687 MHz

693 MHz

702 MHz

620600000

SNR

38.3 dB

39.2 dB

39.4 dB

39.7 dB

39.8 dB

39.6 dB

39.5 dB

39.4 dB

39.1 dB

39.2 dB

39.3 dB

39.7 dB

39.8 dB

39.7 dB

39.6 dB

39.5 dB

39.3 dB

39.1 dB

39.3 dB

39.0 dB

38.7 dB

38.4 dB

38.6 dB

38.4 dB

38.6 dB

39.0 dB

38.9 dB

39.9 dB

39.7 dB

39.5 dB

NA

Power Level

-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

-3.1 dBmV

-3.2 dBmV

-3.1 dBmV

-2.8 dBmV

-3.4 dBmV

-4.2 dBmV

-4.6 dBmV

-4.4 dBmV

-3.9 dBmV

-3.0 dBmV

-2.0 dBmV

0.8 dBmV

0.0 dBmV

0.8 dBmV

-4.3 dBmV

NA

Modulation

256 QAM

OFDM

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

bluesrhythm · Answer

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 · Answer

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.

bluesrhythm · Answer

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

bluesrhythm · Answer

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 · Answer

@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 Ratio	35dB	-
Upstream Power Level	+35dBmV	+50dBmV
Upstream Signal to Noise Ratio	31dB	-
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.

bluesrhythm · Answer

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.

bluesrhythm · Answer

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 · Answer

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

bluesrhythm · Answer

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

Procedure	Status	Comment
Acquire Downstream Channel	579000000 Hz	Locked
Connectivity State	OK	Operational
Boot State	OK	Operational
Security	Enabled	BPI+
IP Provisioning Mode	Honor MDD	honorMdd(4)

Downstream Bonded Channels

Channel	Lock Status	Modulation	Channel ID	Frequency	Power	SNR	Correctables	Uncorrectables
1	Locked	QAM256	21	579000000 Hz	0.1 dBmV	40.2 dB	0	0
2	Locked	QAM256	1	453000000 Hz	0 dBmV	40 dB	0	0
3	Locked	QAM256	2	459000000 Hz	-0.4 dBmV	39.8 dB	0	0
4	Locked	QAM256	3	465000000 Hz	-0.6 dBmV	39.8 dB	0	0
5	Locked	QAM256	4	471000000 Hz	-0.9 dBmV	39.6 dB	0	0
6	Locked	QAM256	5	477000000 Hz	-0.8 dBmV	39.7 dB	0	0
7	Locked	QAM256	6	483000000 Hz	-0.9 dBmV	39.6 dB	0	0
8	Locked	QAM256	7	489000000 Hz	-1 dBmV	39.5 dB	0	0
9	Locked	QAM256	8	495000000 Hz	-0.5 dBmV	39.8 dB	0	0
10	Locked	QAM256	9	507000000 Hz	-0.1 dBmV	40 dB	0	0
11	Locked	QAM256	10	513000000 Hz	-0.2 dBmV	40 dB	2	0
12	Locked	QAM256	11	519000000 Hz	-0.3 dBmV	40 dB	1	0
13	Locked	QAM256	12	525000000 Hz	-0.6 dBmV	40 dB	3	0
14	Locked	QAM256	13	531000000 Hz	-1.1 dBmV	39.8 dB	3	0
15	Locked	QAM256	14	537000000 Hz	-1.5 dBmV	39.5 dB	2	0
16	Locked	QAM256	15	543000000 Hz	-1.9 dBmV	39.4 dB	2	0
17	Locked	QAM256	16	549000000 Hz	-1.7 dBmV	39.5 dB	2	0
18	Locked	QAM256	17	555000000 Hz	-1.8 dBmV	39.4 dB	1	0
19	Locked	QAM256	18	561000000 Hz	-1.5 dBmV	39.5 dB	1	0
20	Locked	QAM256	19	567000000 Hz	-1.3 dBmV	39.6 dB	0	0
21	Locked	QAM256	20	573000000 Hz	-0.7 dBmV	39.9 dB	0	0
22	Locked	QAM256	22	585000000 Hz	0.3 dBmV	40.2 dB	0	0
23	Locked	QAM256	23	591000000 Hz	0.1 dBmV	40 dB	0	0
24	Locked	QAM256	24	597000000 Hz	-0.1 dBmV	39.8 dB	0	0
25	Locked	QAM256	25	603000000 Hz	-0.4 dBmV	39.7 dB	0	0
26	Locked	QAM256	26	609000000 Hz	-0.7 dBmV	39.5 dB	0	0
27	Locked	QAM256	27	615000000 Hz	-0.9 dBmV	39.2 dB	0	0
28	Locked	QAM256	28	621000000 Hz	-0.9 dBmV	39.3 dB	0	0
29	Locked	QAM256	29	627000000 Hz	-1.1 dBmV	39.2 dB	0	0
30	Locked	QAM256	30	633000000 Hz	-1.2 dBmV	39.1 dB	0	0
31	Locked	QAM256	31	639000000 Hz	-1.3 dBmV	39 dB	0	0
32	Locked	QAM256	32	645000000 Hz	-1.1 dBmV	39.1 dB	0	0

Upstream Bonded Channels

Channel	Lock Status	US Channel Type	Channel ID	Symbol Rate	Frequency	Power
1	Locked	ATDMA	1	5120 Ksym/sec	36500000 Hz	46.3 dBmV
2	Locked	ATDMA	2	5120 Ksym/sec	30100000 Hz	46.8 dBmV
3	Locked	ATDMA	3	5120 Ksym/sec	23700000 Hz	47.8 dBmV
4	Locked	ATDMA	4	5120 Ksym/sec	17300000 Hz	46.8 dBmV
5	Not Locked	Unknown	0	0 Ksym/sec	0 Hz	0.0 dBmV
6	Not Locked	Unknown	0	0 Ksym/sec	0 Hz	0.0 dBmV
7	Not Locked	Unknown	0	0 Ksym/sec	0 Hz	0.0 dBmV
8	Not Locked	Unknown	0	0 Ksym/sec	0 Hz	0.0 dBmV

Downstream OFDM Channels

Channel	Lock Status	Modulation / Profile ID	Channel ID	Frequency	Power	SNR / MER	Active Subcarrier Number Range	Unerrored Codewords	Correctable Codewords	Uncorrectable Codewords
1	Locked	0	159	702000000 Hz	-2.1 dBmV	40.4 dB	1546 ~ 2549	58081722	3611	13
2	Not Locked	0	0	0 Hz	0 dBmV	0.0 dB	0 ~ 4095	0	0	0

Upstream OFDMA Channels

Channel	Lock Status	Modulation / Profile ID	Channel ID	Frequency	Power
1	Not Locked	0	0	0 Hz	0 dBmV
2	Not Locked	0	0	0 Hz	0 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).

bluesrhythm · Answer

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.

Time	Priority	Description
Mon Aug 17 12:26:22 2020	Critical (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 2020	Warning (5)	Dynamic Range Window violation
Mon Aug 17 12:14:15 2020	Warning (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 2020	Warning (5)	Dynamic Range Window violation
Mon Aug 17 12:14:15 2020	Warning (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 2020	Notice (6)	TLV-11 - unrecognized OID;CM-MAC=[redacted];CMTS-MAC=[redacted];CM-QOS=1.1;CM-VER=3.1;
Time Not Established	Notice (6)	Honoring MDD; IP provisioning mode = IPv6
Time Not Established	Critical (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;

bluesrhythm · Answer

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

Channel	Lock Status	US Channel Type	Channel ID	Symbol Rate	Frequency	Power
1	Locked	ATDMA	1	5120 Ksym/sec	36500000 Hz	43.3 dBmV
2	Locked	ATDMA	2	5120 Ksym/sec	30100000 Hz	44.8 dBmV
3	Locked	ATDMA	3	5120 Ksym/sec	23700000 Hz	45.8 dBmV
4	Locked	ATDMA	4	5120 Ksym/sec	17300000 Hz	45.3 dBmV

bluesrhythm · Answer

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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bluesrhythm

Re: daily restart of modem

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