Sparklight → Slow Down and Uncorrectables

I have a fairly new SBG6580 modem. I have been experiencing a dropoff in speed over time. Within 48 hours after a reboot, I will be down from 52mb to around 10mb or less. A reboot brings it back to 52mb instantly.

I talked to CableOne support, and they made some checks, and asked me to get another modem from their office and try it. The second modem did exactly the same thing. It's not the modem.

I can watch the slow-down happening. By the time the downstream correctables get up to a half-million or so, and the uncorrectables get into the hundreds, the downstream speed will be 10mb or less. I have seen it as low as 5mb. A reboot always fixes the problem. This is a very repeatable problem. I have to reboot at least every 48hours.

Another point worth mentioning. When discussing this with a Motorola CSR, he told me that my typical upstream bonded channel power of 30dbMv is too low for the Motorola SBG6580. He said it should be over 40dbMv.

Low upload power is usually an issue only C1 can handle. It usually means the CMTS and/or amps need some fine tuning in your area.

Then again, I've had low upload power for years with no problems.

Frequency 549000000 Hz
Signal To Noise Ratio 40.5 dB
Power Level 12.8 dBmV

Channel ID 1
Frequency 30669000 Hz
Power 30.7 dBmV

Of course, this is just D2. You're on D3 and it's much more sensitive to power levels and line noise.

Thanks for the explanation for upload power. I would still like to know what the relationship is between uncorrectables and up/down speed. And why does a reboot of the modem make them disappear.

Are these cumulative over time, which causes them to continually build up and never decrease? Is it possible that the modem justs gets to the point that it can't handle any more correctables and uncorrectables, and throughput slows down? The CableOne CSR I talked to pretty much ignored my asking about them.

Uncorrectables are pieces of corrupt data the modem receives due to noise, interference, or a weak signal. It's like a number of errors. They disappear after a reboot because the modem doesn't permanently store that data in its memory. It basically resets its counters to zero.

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Are these cumulative over time, which causes them to continually build up and never decrease? Is it possible that the modem justs gets to the point that it can't handle any more correctables and uncorrectables, and throughput slows down? The CableOne CSR I talked to pretty much ignored my asking about them.

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An error count will never decrease except with a reboot; no copper internet connections are immune to an error or two, but your error rate shouldn't dramatically increase either. (1 error a day vs. 10,000 per day)

As the error rate increases, things start to slow down and in some cases, the modem may reboot itself or reinitialize the connection to straighten things out if it gets bad enough.

I'd like to know the rest of your modem stats, preferably a snapshot of everything that's going on (SNR, upstream/downstream power of each channel, unerrored, uncorrectable, & correctable codewords) It might further help us on what's going on.

Here is a print screen of my modem status today. It took about 3 days to get to this level of correctables and uncorrectables. I have found that by checking the "Block Fragmented IP Packets" in the Firewall menu, I can greatly reduce the effect of the correctables and uncorrectables.

Right now, I am getting a download speed of about 40MB. Normal is 52MB after a reboot. Without checking the "Block Fragmented IP Packets" my speed would be around 10MB now.

It's pretty odd that the modem doesn't provide the unerrored reading. What really matters is the ratio of problem codewords to the total, not the absolute number. This was from when I was using a Moto 6220:

»/r0/do ··· 1253.jpg

You can see that the uncorrectables were high on an absolute basis, but not as a proportion of total. Note that I am not one CableOne, but that shouldn't matter.