Upgrade to 20M all gone to pot

[robgosty]

Hi all, upgraded to 20m last week bad mistake i think, prior to upgrade speeds were fairly stable but now speeds have all gone mad, one minute going like the clappers the next down to bugger all, pasted below modem info and speeds on speedtest .net, anyone help before it all goes out the window :mad: sorry for long post but wanted to give as much info as poss
Cable Modem : Euro-DOCSIS 1.0/1.1/2.0 Compliant
MAC Address : *********
Serial Number : *********
Boot Code Version : 3.1.6d
Software Version : 2.94.1015
Hardware Version : 1.19
Acquire a Downstream Channel 586750000 Hz Locked
Connectivity State OK Operational
Boot State OK Operational
Cable Modem Downstream
Downstream Lock : Locked
Downstream Channel Id : 4
Downstream Frequency : 586750000 Hz
Downstream Modulation : QAM64
Downstream Symbol Rate : 6952 Ksym/sec
Downstream Interleave Depth : taps12Increment17
Downstream Receive Power Level : 13.6 dBmV
Downstream SNR : 38.6 dB

Cable Modem Upstream
Upstream Lock : Locked
Upstream Channel ID : 4
Upstream Frequency : 29200000 Hz
Upstream Modulation : QPSK
Upstream Symbol Rate : 2560 Ksym/sec
Upstream transmit Power Level : 38.0 dBmV
Upstream Mini-Slot Size : 2
Cable Modem Upstream Burst
Req Init Maint Per Maint Short Data Long Data
(1) (3) (4) (5) (6)


Modulation Type QPSK QPSK QPSK QPSK QPSK
Differential Encoding Off Off Off Off Off
Preamble Length 64 128 128 100 80
Preamble Value Offset 396 6 6 396 396
FEC Error Correction (T) 0 5 5 3 9
FEC Codeword Information Bytes (k) 16 34 34 78 232
Scrambler Seed 338 338 338 338 338
Maximum Burst Size 0 0 0 35 0
Guard Time Size 8 48 48 25 137
Last Codeword Length Fixed Fixed Fixed Short Short
Scrambler on/off On On On On On
Cable Modem Operation Configuration
Network Access : Allowed
Maximum Downstream Data Rate : 20480000
Maximum Upstream Data Rate : 768000
Maximum Upstream Channel Burst : 1600
Maximum Number of CPEs : 1
Modem Capability : Concatenation Enabled, Fragametation Enabled, PHS Disabled

speedtest results
https://www.cableforum.co.uk/images/local/2010/01/60.png (http://www.speedtest.net)
https://www.cableforum.co.uk/images/local/2010/01/61.png (http://www.speedtest.net)

[Sephiroth]

The speedtest.net results are unrealistic (certainly the first). It would be better to download 3 files simultaneously from the Virgin Media ganes site and stop them after a minute. noting the KB/sec and posting them here. We'd add them up, multiply by 10 to get kb/sec.

On your modem stats, there is something wrong that could account for the problem..

Downstream Receive Power Level : 13.6 dBmV

Your downstream power level is unhealthy and should not really be greater than 5 dBmv without risiking instability.

[Peter_]

As Seph says your downstream may be the issue and you may need a engineer so you need to call Tech Support which is open 24/7 on 151 from your Virgin Media Phone.

It's absolutely free.

Or call 0845 454 1111 from any other phone line.

[robgosty]

Hi all thanks for quick reply, not to sure if this is right or not but worked for cobra a few years ago so had a few bits and bobs knocking about, popped two 6db attenuators on modem,

Downstream Receive Power Level : was 13.6 dBmV now
Downstream Receive Power Level : 1.9 dBmV
Downstream SNR : 38.6 dB

No idea if this is correct but seems to have made everything a lot more stable

[Peter_]

Downstream Receive Power Level : was 13.6 dBmV now
Downstream Receive Power Level : 1.9 dBmV
Downstream SNR : 38.6 dB

No idea if this is correct but seems to have made everything a lot more stable
A massive improvement and you should see a big difference in performance.;)

[Sephiroth]

Just to add to Moldova's advice - check that your upstream power hasn't fallen below, say, 33 dBmv.

You didn't mention whether the attenuator you put on was a forward path one, which it should be and minimises negative effect on upstream.

[robgosty]

Hi, all seems to be looking good
Upstream transmit Power Level : 44.0 dBmV

saved someone a call out lol

[Sephiroth]

Hi, all seems to be looking good
Upstream transmit Power Level : 44.0 dBmV

saved someone a call out lol

Actually you've proved that it all works. The CMTS determines the upstream power used by the modem. It's "seen" the attenuation and called for more power. 44 dBmv is fine.

Doesn't look as if you deployed a forward path attenuator and any engineer you might eventually call would have to turn a blind eye to this piece of homework!

Keep us posted.

[robgosty]

Mant thanks to the both of you for advice & quick replys, problem had been really bugging me & i really did not want to give my money to Sky :Yikes:

Once again, Thanks for the help
Rob

[Ignitionnet]

Your downstream power level is unhealthy and should not really be greater than 5 dBmv without risiking instability.

Woah. It can go considerably above 5dBmV without any trace of issues, and if analogue has been switched off in the area 10dBmV is quite workable especially when using 64QAM.

[Sephiroth]

Woah. It can go considerably above 5dBmV without any trace of issues, and if analogue has been switched off in the area 10dBmV is quite workable especially when using 64QAM.
No woah on this occasion, my friend. He had more than a trace of issue which he says he fixed.

[Ignitionnet]

No woah on this occasion, my friend. He had more than a trace of issue which he says he fixed.

For sure, however I was pointing to your suggestion that 5dBmV is marginal - it's not.

Your downstream power level is unhealthy and should not really be greater than 5 dBmv without risiking instability.

On a network that isn't hosed with other issues a power level of 5dBmV presents no risk at all. Networks should be coping with 8-9 or more even with the rubbish modems.

5-8dBmV should be quite satisfactory for 1024QAM EuroDOCSIS to be honest with you let alone the 64QAM the OP is on or the 256QAM used on most overlay networks. There are other impediments downstream such as slope, micro-reflections and group delay which are far more of an 'issue' than a nice flat channel coming in slightly warm.