Downstream Frequency Change, Connection Suffering

[Agent Dread]

Hi guys first post. Virgin must have carried out some work in my area (SW7) around 1am on Tuesday 29 March. I notice in my modem stats my downstream frequency has changed from 586750000 Hz to 330750000 Hz and my downstream receive power has gone up by 6db.

I assume this is part of upgrade work, but since it happened the connection has gone to the dogs, especially peak times yesterday evening and tonight. Have tried rebooting modem to get a different upstream, no joy. Here's my TBB graph:

https://www.cableforum.co.uk/images/local/2011/03/6.png

Any ideas what might have happened? I have posted on official forums also. Here's current modem stats which I believe to be within spec:


Cable Modem Downstream
Downstream Lock : Locked
Downstream Channel Id : 5
Downstream Frequency : 330750000 Hz
Downstream Modulation : QAM256
Downstream Symbol Rate : 6952 Ksym/sec
Downstream Interleave Depth : taps12Increment17
Downstream Receive Power Level : 5.8 dBmV
Downstream SNR : 39.6 dB


Cable Modem Upstream
Upstream Lock : Locked
Upstream Channel ID : 2
Upstream Frequency : 29200000 Hz
Upstream Modulation : QAM16
Upstream Symbol Rate : 2560 Ksym/sec
Upstream transmit Power Level : 45.0 dBmV
Upstream Mini-Slot Size : 2

Thanks in advance.

[Ignitionnet]

Your modem stats are all fine. Your area has two downstream frequencies now I suspect and it could be that you've congestion on the upstream side of things as they may have also moved some modems onto that new downstream that weren't on yours before, and while they've plenty of capacity downstream there are issues upstream :(

The downstreams are both 50Mbps, so 100Mbps is available downstream, but that's only serving at most 36Mbps of upload.

[Chrysalis]

it looks like a typical over subscription issue VM's side.

[pip08456]

I think that's what Igni was saying but he does tend to use engineer speak!:D

[Chrysalis]

we posted pretty much at same time, his reply wasnt there when I read it. :) but yeah his is engineer style.

[Agent Dread]

Thanks for the replies guys, much appreciated. I forgot to add that I have a 6db attenuator fitted, so if i took that off my downstream power level would hit 12db? Does that suggest an underlying issue at the cabinet or elsewhere? Thanks again for your help.

[pip08456]

No, the whole point of the attenuator is to bring the downstream power down before it hits your modem/hub. The amp you are connected to in the cab may be supplying the higher downstream power purely to make sure your upstream hits the UBR at the correct level, hence the attenuator on the downstream.

Both your up and down levels are within spec and should not be causing a problem.

As said it looks like a utilisation problem.

[Agent Dread]

Thanks for all your replies guys, looks like it is a downstream utilisation issue and has been passed to the network team.

http://community.virginmedia.com/t5/Fibre-optic-broadband-cable/High-Jitter-Poor-Gaming-SW7/m-p/431625#M72708

[craigj2k12]

wow, your minimum latency on the ttb graph looks like its below 5ms! (the green bit)