US Cable Support > Comcast HSI > [Connectivity] Modem keeps losing upstream channel bonding

reply to Morac

Re: [Connectivity] Modem keeps losing upstream channel bonding

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.
--
There is nothing more deceptive than an obvious fact.

Sherlock Holmes in
The Boscombe Valley Mystery
A. C. Doyle
Strand Magazine, October 1891

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.
--
The Comcast Disney Avatar has been retired.

reply to Morac
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

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.
--
There is nothing more deceptive than an obvious fact.

Sherlock Holmes in
The Boscombe Valley Mystery
A. C. Doyle
Strand Magazine, October 1891

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

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