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BAF
Baffles
Premium
join:2004-02-22
Gansevoort, NY

1 edit

Strange Signal Issue

I'm still having continuing problems with my connection. Poor downstream speeds at times (upstream is fine), and randomly the connection cuts out. Modem doesn't lose sync, but I lose connectivity. This happened one time while I was on a voip call, and I could hear the person on the other end asking if I was still there, yet they couldn't hear me.

Earlier tonight when it cut out, I noticed the upstream power level fluctuating a ton. I had never noticed this before (and I checked when I had lost connectivity)...

Here's what my connection normally looks like, pretty damn good numbers unless I'm mistaken:

Downstream
Frequency 561000000 Hz Locked
Signal to Noise Ratio 37 dB
Power Level 2 dBmV

Upstream
Channel ID 17
Frequency 19000000 Hz Ranged
Power Level 33 dBmV

I was refreshing the signal page when the connection was acting up earlier, and upstream power level went up to 51 dBmV, and stayed there. Once my connection came back, it slowly worked its way back down to 33 over the course of 20 or 30 seconds. When the connection cuts out now, if I'm quick enough to start F5ing the signal page, I can watch it shoots from 32-33 dBmV upstream to 50-52 within several seconds.

Downstream power level and SNR stay the same while this is occurring. Downstream power level may fluctuate by 1 or 2 dBmV from day to day, and SNR sometimes drops to 36, but they change slowly and stay stable.

From the pole, I've got the drop coming in and directly to a two way splitter. One leg to modem, the other leg to another splitter for the televisions. I've bypassed the line between the splitter and the modem (run a new one temporarily), and I'm still seeing the signal level fluctuate wildly with intermittent connection lapses.

I'll check the box outside where the drop comes in from the pole tomorrow to make sure the connection is fine. (comes in underground, into a box with a grounding block/coupler outside, then into the house). DTV service is fine.

My best guess is that the modem is losing upstream signal intermittently. I say this based on the upstream power level shooting through the roof, and based on the one time it happened with VoIP and I could still hear the other person. The issue does seem to be getting worse day to day...

Has anyone seen anything like this before? Any ideas on what to check, aside from lines/splitters/connections? Is there any reason to suspect the modem (it's a ~10 year old SB5100)? If all my local wiring checks out fine, do I buy a new modem, or start collecting data on signal levels and connectivity drops to send to TW?

I have no problem upgrading old hardware... I wouldn't have any issues buying a SB6141 to replace my 5100. But if it's just an exercise in futility, then I'd rather get the connection stable first.

Also worth noting is that these issues seem to have begun back when they (presumably) began upgrading stuff to DOCSIS 3. I recall several waves of scheduled downtime for large areas (including one market-wide)... not sure if this relates to the problem at all.


kilrathi
Premium
join:2005-04-22
Rockaway Park, NY
33 to 51 db jump on power for upstream? well what modulation is that upstream channel on? Because for most 33 dbmv is actually too "quiet" or rather too low, you wanna have it at least 40 in most scenarios.

ddeerrff

join:2002-08-30
Brookfield, WI
reply to BAF
Normal downstream levels with a high upstream level can often be traced to a bad connector _shield_ connection. An upstream that is jumping around could very well be an intermittant crimp on one of the F connectors. Check these thoroughly.


BAF
Baffles
Premium
join:2004-02-22
Gansevoort, NY
reply to BAF
I don't know what modulation it is running upstream. This modem doesn't tell me, as far as I know.

All of the connections seem fine (there are only a couple between the drop and the modem). I moved the modem behind the 4-way splitter that's behind the 2-way, adding 7dB of attenuation, and things seem better. I'll give it a little time, but I haven't had any connection drops since doing that, and downstream speeds have been *way* better.

I'm still looking at a SNR of 37dB on the downstream, and now, a -6 dBmV downstream power level and a 40 dBmV upstream power level. I'll give it some more time, but like I said, over the past few hours the connection has been rock solid. I'm not sure how attenuating the signal would do that, as if it were a noise floor issue, I'd think it would still exist once the upstream signal was attenuated back down..


BAF
Baffles
Premium
join:2004-02-22
Gansevoort, NY
reply to BAF
I'm still having intermittent issues, though not nearly as often or as bad as before.

I did notice that the upstream and downstream channels changed though...

Downstream @ Frequency 543000000 Hz Locked
Upstream @ Frequency 23800000 Hz Ranged


BAF
Baffles
Premium
join:2004-02-22
Gansevoort, NY

2 edits
I set up some scripts to monitor what's up with the connection, and it happened to drop just now.

Downstream remained in-tact (as mentioned before, things like VoIP that aren't using TCP/requiring ACKs keep piping data, and I keep receiving it), but upstream crapped out.

Upstream frequency reported by the modem went from "23800000 Hz Ranged" to "23800000 Hz In Progress", then back to "23800000 Hz Ranged" when the connection came back up. And as I've observed before, upstream power level shot up while downstream remained relatively unaffected (it jumped around a little, but nothing too drastic).

Do these graphs help tell what's going on? I've checked all the connections and crimps, as suggested, and they're all good. Adding some attenuation before the modem to bump upstream power level some has helped stabilize the connection a LOT (it's much more stable now than it was before, and my speeds are better), the upstream drops are much more rare now. My moderately-educated guess tells me to suspect the modem (as any higher upstream power level is bled off by the attenuation I added, so if it were a noise issue, I'd think adding attenuation local to the modem wouldn't help), but I'm not totally sure.

»dl.dropbox.com/u/11015924/rr/dro···dex.html

If it helps, here are the logs surrounding the drop in the graph:

2012-08-27 22:33:00 3-Critical D003.0 DHCP WARNING - Non-critical field invalid in response.
2012-08-27 22:32:51 3-Critical R002.0 No Ranging Response received - T3 time-out
2012-08-27 22:32:45 3-Critical R004.0 Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 timeout
2012-08-27 22:32:12 3-Critical R005.0 Started Unicast Maintenance Ranging - No Response received - T3 time-out