Massive error spike on my 24Meg connection - Help

[chris6273]

Hi guys,

On February 21st I was switched over to 21CN and have maintained a roughly steady ~24000Kbps sync, however tonight something very weird (and worrying) has happened.

About 45 minutes ago, I noticed things started to get a bit slower, so I took a look at my router, and tried doing a speedtest.

It was reporting around 400 CRC errors every two minutes!!!

By chance, I had left the DMT tool recording my noise margin and therefore the error counts on my connection. The image of the screen is below:

As you can see, around an hour ago I was getting the normal 20 CRC errors, however they have skyrocketed suddenly! 

What could have caused this? I have never seen in excess of 400 errors being reported every 2 minutes.

Speedtests are fluctuating probably because of the number of errors which are occuring.

Line stats are below:

             Down Up
SNR (dB): 0.1 6.4
Attn(dB): 16.5 6.5
Pwr(dBm): 0.0 12.4
Max(Kbps): 25636 1212
Rate (Kbps): 23896 1219

The downstream Noise Margin is very low because I have tweaked my line to get a higher sync, however earlier it was holding at a steady 0.7dB :S.

I haven't seen it that low since I was testing at around 1am a few weeks back, but it crawled back up afterwards to around 0.4dB.

I've been holding ~24000 sync speeds mostly since I was switched over to 21CN, but this is the first time I have seen this on my connection.

Any ideas as to what could be causing it?

[Keith_Beddoe]

See Noise margins

See my hint at the end.

[chris6273]

I know about noise margins, and my router has kept my line synced at around ~24000Kbps since a week after I was switched over (And I usually have a higher noise margin) - This is the first time this problem has occured.

Any more ideas as to what could be causing it?

[Webby]

Most likely a spike of noise interference. With your SNR being so low it's not going to take much to put errors on the circuit.

[Keith_Beddoe]

Your noise margin is too low, try what I have suggested and see if you can raise it to at least 4dB. You will lose a bit of speed, but your line will be more stable.

[john46]

with that connection you could still have very good speed an a 9db margin with a lot less errors

[chris6273]

I tried the line by resetting my SNR slider to 100% (Where I had a ~19900Kbps sync with a 6.3dB SNR), so I increased it a bit to see how well it plays out.

I have taken the line down to:

           Down Up
SNR (dB): 1.4 6.1
Attn(dB): 16.5 6.5
Pwr(dBm): 0.0 12.6
Max(Kbps): 25440 1220
Rate (Kbps): 22654 1219

Speedtests seem to be completely stable now, so I will see how well it goes. If it still gets worse, I'll reset it again and see if it still is bad.

Thanks for your answers

[john46]

Glad to help Chris it has gone low again from your latest stats

[chris6273]

🙂 , Yeah I did set the SNR slider to 10% from 1% and it has synced slower with a 1.4dB SNR Margin but it has much more stable throughput now. I'm still very confused as to why that error problem happened tonight, when I've been running higher syncs on the line without nearly as many errors as that (I've gone up to a 24,184Kbps sync with around 8500 CRC errors in a 50 hour period).

Here are the stats from another post I made earlier this month showing what it usually performs like:

             Down Up
SNR (dB): 0.5 5.2
Attn(dB): 16.5 6.4
Pwr(dBm): 0.0 12.2
Max(Kbps): 17556 1212
Rate (Kbps): 24184 1211

SFErr(CRCErr): 8496 0

Connection Time 49:39:17

That was on the 2nd of March. 

[john46]

With that low a noise margin any noise would cause that to be honest I am surprised the connection is holding and your throughput could be affected by the errors a minimum 3db is ok but to safe preferably 6db