Comcast XFINITY → [Connectivity] Modem keeps losing upstream channel bonding

3 channel upstream bonding was enabled in my area a while ago and for a long time it worked great. It allows me to get over 10 Mbps upstream speeds.

For the past two days, when I've looked at my Zoom Technology 5341's status screens, I've noticed that my modem is only locked on one upstream channel and worse that channel is only 3.2 MHz in width. The other two 6.4 MHz channels aren't there. With only one channel I can get at most 8 Mbps up.

If I reset my modem, it locks on to all 3 channels again.

I looked in the log files and I noticed that past few days there was a T4 error at night. I'm presuming that was when it switched from bonded to one channel. I'm not sure why it's not switching back.

Any ideas on how to fix this?

Here are the current signals:

Channel Frequency: 	663002075 Hz	668998901 Hz	675000122 Hz	692999390 Hz
Modulation: 	256 QAM	256 QAM	256 QAM	256 QAM
Signal strength: 	-3.5300 dBmV	-3.1544 dBmV	-3.7413 dBmV	-5.3016 dBmV
Signal noise ratio: 	36.175 dB	36.387 dB	36.844 dB	36.175 dB

Upstream
Channel Id: 			9			7		8
Upstream Frequency: 	22000144 Hz		36200059 Hz	29400326 Hz
Upstream bandwidth: 	3200000 Hz		6400000 Hz	6400000 Hz
Transmission signal strength: 	52.0000 dBmV		51.0000 dBmV	51.0000 dBmV

That's really interesting. There's a bunch of threads here and on the Comcast site that have been filled with folks seeing a similar problem with their SB612X modems after a recent firmware push. This is the first I've read where a no SB modem is exhibiting a similar symptom.

It's probably because your upstream signal is really high. You need to schedule a tech to come out and see if he can adjust it any.

Or if you have excess splitters, you need to remove one or two.

Now I'm getting packet loss (about 5 to 10% depending on test). It does look like an upstream problem.

Edit:

Called into Comcast and was told my signals are "bad". Upstream SNR is 27.1 and receiving power level at the headend is -0.9 (I was told this was the biggest issue).

As mentioned, your upstream levels are too high. With 3-channel (or more) bonding, the limit is 51dB for 64 and 32QAM, and 52dB for 16QAM. It's 54/55 for 2-channel, and 57/58 for single.

Well that explains why I'm dropping down to a single channel. I had massive packet loss this morning.

I'm back on one channel and my upstream power is now 55.2500 dBmV.

Ironically, my connection is working a lot better now with one one channel which I guess is based on the above.

That SNR of 27dB is WAYY low. You want to see about 35-37dB. The scale is logarithmic so 37dB is like 10x as much as 27dB.

Comcast tech came out and he was seeing upstream power levels about 4 dB too high at the tap so he put it in to the line techs.

In the mean time he swapped legs on the 3-way splitter so that my modem has the 3.5db leg. That brought the upstream power levels down from about 51/52 to 47/48.

The downside is that the 3.5dB leg had been feeding a 4-way splitter near my TV (don't ask), so now the downstream signals at my TV are barely enough to get a picture.

When things get fixed, I'll probably swap the legs back.

You may be confusing that with the downstream SNR and not the upstream ?

Seeing as high as 35-37 dB on the uSNR as read at the CMTS would be quite rare, if not impossible.

Being for TV, you could consider an amp for that leg. Just make certain it is 'digital' or 'broadband' compatible and will pass the upstream if you have any full cable boxes on that leg. Any TV's directly connected, or using DTA, don't send a return signal, and could be OK with a cheaper amp (but I still wouldn't waste money on one.) Use a quality amp like the Motorola series, and not some cheap Radio Shack or WalMart thing.

As for some ideas for an amp to use on the TV side, see: »[DVR] Which AMP to use

Wouldn't an amp just introduce noise into the signal? Part of the problem is that certain frequencies are pretty strong, despite the 4-way splitters, while some are borderline. I wouldn't want to overload my boxes on the "good" channels, simply to boost the "bad" ones.

I do have another option. I have a NetGear MoCA bridge currently hooked up off the 4 way splitter. The MoCA bridge has an amplified passthru which I could then feed into a 3 way splitter. That wouldn't help 2 of the devices, but the 3rd would get a slight boost.

The downside to that is that if the bridge loses power, the signal strength goes down the toilet. I have a few DVRs connected to a UPS so they can keep recording during a brief power outage. I'd have to connect the bridge to that as well.

In case anyone is curious I have 2 TiVos, a Comcast Cable box and the MoCA bridge off the 4-way splitter. Supposedly On-Demand is coming to the TiVo sometime in the future (it's already available in some areas). Once that happens I can get rid of the box and simply use a 2-way splitter.

If you place the (good quality) amp before the losses (splitters and cabling) then any extra noise introduced should be minimal.

See the "Cable Modem Setup #1" case at the end of this webpage: »www.cabletvamps.com/educ ··· Splitter

Well my signals have gotten a lot worse.

My modem lost the two upstream channels again despite now being on the 3.5 dB leg of the splitter and the one channel is now reporting 53 dB power.

In addition my downstream signals dropped by about 3 dB. They were positive and now they are negative.

My TV is actually worse. The SNR for channels now ranges from 29 to 32. To the TiVo's benefit, it's still working with these lousy signals. It is having to do a lot of error correction though.

Whatever Comcast did, it's not getting better.

Here's what my modem is reporting now:

Channel Frequency: 651000854 Hz	657002075 Hz	669000244 Hz	686999390 Hz
Modulation: 256 QAM256 QAM256 QAM256 QAM
Signal strength: -1.0664 dBmV	-0.9207 dBmV	-0.9617 dBmV	-2.1725 dBmV
Signal noise ratio: 36.610 dB	37.093 dB	37.093 dB	36.844 dB

Upstream
Channel Id: 9
Upstream Frequency: 22000134 Hz
Upstream bandwidth: 3200000 Hz
Transmission signal strength: 53.0000 dBmV

I wish SmokePing was working as I'm very curious as to what that looks like.

The TV signals got better, but I noticed my Zoom 5341 still reported fairly poor signals and the one locked upstream channel reported a upstream signal strength of 51 dbmv.

I removed the coax cable and waited for the modem to lose sync and then reconnected the coax cable. When it locked, the signals looked a lot better and all three upstream channels locked with an upstream power of 47 dbmv.

I can only conclude that once the Zoom 5341 decides that it's lost channel bonding it won't try to re-establish until it completely loses sync. That seems like a fatal flaw in the mode.

In any case, signals are bad during the day and okay at night. Here's the current signals reported by the modem:

Downstream
Channel Frequency: 	651000854 Hz	669000244 Hz	675001465 Hz	680998169 Hz
Modulation: 	256 QAM	256 QAM	256 QAM	256 QAM
Signal strength: 	2.4982 dBmV	2.2278 dBmV	1.6749 dBmV	0.9289 dBmV
Signal noise ratio: 	37.356 dB	37.936 dB	37.356 dB	37.936 dB

Upstream
Channel Id: 		9			7		8
Upstream Frequency: 	22000158 Hz		36200258 Hz	29400249 Hz
Upstream bandwidth: 	3200000 Hz		6400000 Hz	6400000 Hz
Transmission signal strength: 	46.5000 dBmV	47.2500 dBmV	47.5000 dBmV

While not enough to cause problems, things are bad again. Of course yesterday, the day I had my appointment for, things were okay.

Channel Frequency:	669000732 Hz	675001953 Hz	680998779 Hz	693001343 Hz
Modulation:	256 QAM	256 QAM	256 QAM	256 QAM
Signal strength:	0.2058 dBmV	-0.1346 dBmV	-0.3019 dBmV	-1.3562 dBmV
Signal noise ratio:	36.610 dB	36.844 dB	36.844 dB	36.844 dB

Upstream
Channel Id:	9		7	8
Upstream Frequency:	22000175 Hz		36200123 Hz	29400182 Hz
Upstream bandwidth:	3200000 Hz		6400000 Hz	6400000 Hz
Transmission signal strength:	52.0000 dBmV		51.0000 dBmV	51.0000 dBmV

When I had high upstream signals like yours with reasonably good download stats, like yours, the tech first measured ingress at the modem and said I had bad wiring in the house. He went outside, disconnected the inside from the drop at the ground block, found that from there to the modem, ingress was not a problem but measuring from the ground block to the pedestal through the 30 year old buried line he found incredible ingress. He replaced the drop and everything was just fine.

Has a tech measured ingress from your ground block to the pedestal or the pole connection? It's possible ingress on the drop cable is the cause of your problems. YMMV, of course.

I have a Zoom 5341J, and when upstream sig got to ~ 51 dBmv, and probably higher, Internet connection was intermittent.

The high levels were actually at the tap, so they are upstream from me.

Now my upstream levels increased by about 4 dB and my downstream ones decreased 4dB. Note the signals I posted last night are with my modem now off the 3.5 dB level of my outside split. Originaly it was off the 7 dB, so even though the signals are "the same" they're actually much worse.

Every time I schedule a tech to come out, the signals suddenly go back to normal (47 dB power up, 35/36 SNR down) since they seem to cycle every 2 days or so. Two days of borderline poor signals and two days of okay signals.

What I have now is actually usable as my my TiVo and modem are reporting errors are being corrected, but the signals shouldn't be that bad as there is very little wiggle room. When the signals drop a bit I start getting packet loss and TV picture blocking.

I called Comcast this morning and at the start of the call, my signals were as above. Over the course of 20 minutes, they changed to:

Downstream
Frequency to tune to:	 Hz
Scanning start frequency:	 999000000 Hz
Channel Frequency:	669000732 Hz	675001953 Hz	680998779 Hz	693001343 Hz
Modulation:	256 QAM	256 QAM	256 QAM	256 QAM
Signal strength:	2.0167 dBmV	1.3366 dBmV	1.0503 dBmV	0.3865 dBmV
Signal noise ratio:	37.093 dB	37.093 dB	37.093 dB	37.093 dB

Upstream
Channel Id:	9		7	8
Upstream Frequency:	22000113 Hz		36200233 Hz	29400101 Hz
Upstream bandwidth:	3200000 Hz		6400000 Hz	6400000 Hz
Transmission signal strength:	49.7500 dBmV		50.5000 dBmV	50.5000 dBmV

My TV downstream SNR on a channel at 211000 KHz went from 30 to 35. That's a significant jump.

The guy on the phone actually commented on this. I still made an appointment since the signals are fluctuating up and down. The phone guy recommended having a monitor put on my line.

It sure looks like you have intermittent ingress at 22 MHz to 30 MHz and even at the TV frequencies - ~200 MHz. This is occurring in Comcast's system at or beyond your pedestal or pole tap. Could be a neighbor's system or quite further away. Then again, the contents of the pedestal may have to be swapped out. This will probably take a line tech or higher kind of maintenance person to fix.

It would also seem that your neighbors or others further on would also be having the same problem depending on where the ingress occurs.

I'm beginning to wonder if this may be at least partially caused by something on my end.

I have a pair of Netgear MoCa bridges: one between my modem and the wall outlet and the other off a splitter near my TV.

Today my upstream signals took a major dive and my modem lost sync and got stuck trying to find an upstream channel. At the same time my TV signals crapped out and I had a SNR of 29 on one my lower frequency channels (not enough to lose picture, but I was getting a lot of corrected errors).

I called into Comcast and they told me all my neighbors were online so I tried disconnecting my modem and hooking up an old DOCSIS 2.0 modem. That wouldn't lock either. I then bypassed my Netgear MoCA bridge and the modem locked and actually got a 44 dB upstream power level. I then placed the Netgear MoCA bridge back in and the modem still locked with the upstream power level about 45 dB. I checked my TV downstairs and the signal levels looked good there too after this.

So it looked like the MoCA bridge was somehow corrupting the upstream and low frequency signals a lot and the higher frequencies a little, but that makes no sense since the MoCA bridge is supposed to operate at frequencies greater than 1 GHz and has worked fine for a few years now. What's odd is that on October 9th, when I first started having problems, the Comcast tech measured the signals before and after the MoCA bridge and they were basically the same. Also I don't know why a MoCA bridge upstairs would cause problem with the TV downstairs

I suppose that it could be a coincidence that the signals got better when I disconnected and reconnected the MoCA bridge, as the time it got better was around the same time it got better yesterday, but that seems suspect. I also have 3 other MoCA devices, none of which I disconnected to get things working, though the one I disconnected is the "Master/Controller".

Currently my modem signals (going through the MoCA bridge) have been steady for the last 3 hours at:

Downstream
Channel Frequency: 	657001587 Hz	651000244 Hz	662998413 Hz	675000977 Hz
Modulation: 	256 QAM	256 QAM	256 QAM	256 QAM
Signal strength: 	2.8401 dBmV	2.7655 dBmV	2.7906 dBmV	1.9403 dBmV
Signal noise ratio: 	37.936 dB	37.356 dB	37.936 dB	37.356 dB

Upstream
Channel Id: 	9		7	8
Upstream Frequency: 	22000200 Hz		36200144 Hz	29400296 Hz
Upstream bandwidth: 	3200000 Hz		6400000 Hz	6400000 Hz
Transmission signal strength: 	45.5000 dBmV		46.5000 dBmV	46.7500 dBmV

The downstream signals are what they were yesterday, but the upstream power levels are lower.

My Zoom 5341J had this happen moments ago! It lost upstream bonding & wouldn't re-lock. Pulling the coax of the back fixed it. Hooked it back up & all is well again. Thanks to all of you that figured this out!

Things were still good this morning, but I kept my appointment because I wanted to know the status of the maintenance and the phone support no longer has access to that info.

Any way the tech noticed that I was off a splitter inside the tap itself. There are 4 houses off my tap and one of my neighbors has two drops. The tap only has 4 ports and I ended up being off a splitter connected to one of those ports. Switching me gave me the following great signals:

Downstream
Channel Frequency:	657001587 Hz	651000244 Hz	662998413 Hz	681002197 Hz
Modulation:	256 QAM	256 QAM	256 QAM	256 QAM
Signal strength:	6.0627 dBmV	6.1458 dBmV	5.9716 dBmV	4.6478 dBmV
Signal noise ratio:	37.936 dB	37.356 dB	37.936 dB	37.936 dB

Upstream
Channel Id:	9		7	8
Upstream Frequency:	22000131 Hz		36200117 Hz	29400258 Hz
Upstream bandwidth:	3200000 Hz		6400000 Hz	6400000 Hz
Transmission signal strength:	42.2500 dBmV		43.2500 dBmV	43.2500 dBmV

What a major difference. Now my downstream signals are a bit hot, but the SNR on my TiVo and modem is now 37. I'll need to watch it when it gets cold out as that will increase signals and might make it too hot, but for now it's good.