Puzzling problem with intermittent Internet outage

[TacTican]

Dear Computer-Savvy Netizens of MMO:

Apologies if this is in the wrong forum. I thought I'd get some advice from people who know more about networks than I do for a bewildering problem that I've had with our home's Internet connection.

Background: This is a high-speed cable residential connection shared between three computers in the house. Our ISP is Charter, but we get VOIP from Vonage as well. The usual setup is that the cable from the wall runs to a Motorola SB 6120 modem, which is then serially connected to a Vonage VOIP modem (VDV21-VD), which in turn is serially connected to the D-LK DIR655 router. The router supports the individual computers. Our location is outside Atlanta, GA.

Problem: High packet loss starting as of about two weeks ago (when Atlanta and most of the South in general had some devastating storms). Pingtest reported 40-50% packet loss on the extremely rare occasions that it was able to complete at all. This means that our connection is down to a glacial crawl. Attempting to direct download or upload anything more than a few dozen kilobytes usually results in a timeout error. Torrents generally fare better, but right now I'm staring at a torrent that has averaged 1.3 kb/s for the past few hours.

Diagnostics and attempted fixes:
- It's not the router. Plugging the computers (I tested with more than one computer, both a laptop and a desktop) directly into the modem still gives the same high packet loss and intermittent Internet. I am writing this post with the Surfboard connected directly to the computer.
- It's not the CAT5 cables. I've tried half a dozen different cables, including some brand new ones.
- It's not the network cables. See above.
- It's probably not the modems. I replaced an old SB5120 with the current brand new SB6120. No change.
- It's not the NICs. Obviously if it were a network card problem, only one of the three computers connected to the router should be experiencing any problems.
- It's not the outside cables. Today a Charter tech came and replaced the outdoor cable, which was damaged, with a new one. No difference.

The new Surfboard 6120, when plugged in, usually shows a green light for Online, a blue light for Receive, a green light for Send and Online, and a blinking orange light for Link. I'm guessing it's not supposed to flash regularly for Link, but I'm not sure why it would do that.

Regrettably, the Charter tech was not able to tell me much besides that the outside cable was damaged (and replaced). He did say something about the SNR to the modem being too high (it's about 35-37 dB, he said it should be no higher than 26-30 dB), but that doesn't really make sense to me (shouldn't a higher signal-to-noise ratio be better?). The tech recommended either a new UBee or Netgear modem, however, the Surfboard 6120 is a Charter-recommended modem per http://www.myaccount.charter.com/Cus...tabeugd#brand2 .

Modem diagnostics:

Downstream Bonding Channel Value
Channel ID 216 213 214 215
Frequency 585000000 Hz 567000000 Hz 573000000 Hz 579000000 Hz
Signal to Noise Ratio 36 dB 36 dB 37 dB 37 dB
Downstream Modulation QAM256 QAM256 QAM256 QAM256
Power Level The Downstream Power Level reading is a snapshot taken at the time this page was requested. Please Reload/Refresh this Page for a new reading
3 dBmV 0 dBmV 2 dBmV 2 dBmV

Upstream Bonding Channel Value
Channel ID 2
Frequency 32000000 Hz
Ranging Service ID 3819
Symbol Rate 2.560 Msym/sec
Power Level 47 dBmV
Upstream Modulation [3] 16QAM
[3] 64QAM

Ranging Status Success

Signal Stats (Codewords) Bonding Channel Value
Channel ID 216 213 214 215
Total Unerrored Codewords 305561005 305561300 305561394 305561460
Total Correctable Codewords 53 47 43 65
Total Uncorrectable Codewords 1499 1337 1378 1422 <-- These values typically spike on a modem reset and then stay constant until reset again.

Some additional comments:
- The upstream power level MAY be too high. 47 dBmV is the typically reported value, although I did once see it escalate to 56 dBmV randomly.
- Downstream power levels would be about 6-7 dB higher but I have a 4-way attenuator attached to the cable coming out of the wall. One of the cables then plugs into the modem and the other three are not attached.
- Tracert usually shows request timeouts starting from the very first node.
- A Charter representative confirmed that the company could trace all the way to the modem, although I wasn't able to glean details about whether they could actually ping the modem.

So ... I'm clueless. Any thoughts? Charter tech support wasn't able to help and I'm more mystified than ever. If you need more information, let me know and I'll try to see what I can do. Responses will necessarily be slow due to said aforementioned Internet problem.

EDIT: Problem resolved, after some more diagnosis.

[tmarshal61]

I am experiencing the exact same issue it sounds like. I am also have Charter, live in the Atlanta area (McDonough), and have a SB6120 modem. I have had technicians out no less than 10 times, and they have yet to be able to fix the problem although it has gotten much better than it originally was.

What was you resolution?

My symptoms, like yours, are that I am dropping packets. For me, it is sporadic, and seems to always happen at night around 9:00 - 10:00 pm. I will get anywhere from 1% to 50% packet los when it is acting up. The Charter techs put my modem on a watch list found that I am getting a CMTS Rx SNR below the spec of 22 about 2% of the time (Thats upstream indicating its the cable company, not my modem). Their monitor can only be set to take a reading at minimum intervals of 15 minutes, so most of the time, it looks good at the instant that the snapshot is taken. My Modem Tx Power is also sporadic. It fluctuates both above and below the spec (54 - 44.8, the spec is 37.3 - 35.4). From what I understand, a signal is supposed to be sent to constantly adjust the modem power.

I would be curious to know what solved your issue.

[TacTican]

My issue was that the outside cable connected to a signal amplifier which had all the other cables of the house connected to it (it's a 1-to-8 way signal outlet). The voltage source, which had been installed by a previous Charter tech, is 120 V, but the amplifier can't take that much voltage - it degrades the resistors which are in it. The Charter tech was able to diagnose this problem and install a new amplifier, as well as attached an attenuator to the voltage source.

I'm going to hazard a guess, however, that if your packet loss is sporadic - not constant like mine - it probably isn't the amplifier or the cable.

[ispano]

The new Surfboard 6120, when plugged in, usually shows a green light for Online, a blue light for Receive, a green light for Send and Online, and a blinking orange light for Link. I'm guessing it's not supposed to flash regularly for Link, but I'm not sure why it would do that.

Actually it is, anything being moved makes it blink, even normal stuff that you never even know is happening.