Modem configuration has changed - help!

[WarnersEnd]

Ooops, That was Modem! configuration has changed.

Hi there, Recently my connection speed has reduced drastically. It was 10mb per pc, limited I think by my ancient router. It is now optimistically 1mb!

I had a replacement modem 4 years ago. At that time I recorded this configuration: Notice taps 32 increment 4, amongst others.

Cable Modem Upstream
Upstream Lock : Locked
Upstream Channel ID : 3
Upstream Frequency : 29200000 Hz
Upstream Modulation : QPSK
Upstream Symbol Rate : 2560 Ksym/sec
Upstream transmit Power Level : 42.5 dBmV
Upstream Mini-Slot Size : 2



Cable Modem Downstream
Downstream Lock : Locked
Downstream Channel Id : 4
Downstream Frequency : 402750000 Hz
Downstream Modulation : QAM256
Downstream Symbol Rate : 5360.537 Ksym/sec
Downstream Interleave Depth : taps32Increment4
Downstream Receive Power Level : 0.5 dBmV
Downstream SNR : 41.9 dB

It is now:

Cable Modem Downstream
Downstream Lock : Locked
Downstream Channel Id : 64
Downstream Frequency : 435000000 Hz
Downstream Modulation : QAM256
Downstream Symbol Rate : 6952 Ksym/sec
Downstream Interleave Depth : taps12Increment17
Downstream Receive Power Level : -2.7 dBmV
Downstream SNR : 38.0 dB



Cable Modem Upstream
Upstream Lock : Locked
Upstream Channel ID : 11
Upstream Frequency : 32600000 Hz
Upstream Modulation : QPSK
Upstream Symbol Rate : 5120 Ksym/sec
Upstream transmit Power Level : 38.4 dBmV
Upstream Mini-Slot Size : 4


Notice the taps and increment have changed. I didn't do it! is this why it's going slow? Or is there another underlying issue. I'm in Hemel Hempstead, HP1. Other web sites have indicated this is a "slow area". But 1mb? Help!

[General Maximus]

I going to make this super quick dude because I am already late for work. I'll provide further explanation later if somebody doesn't beat me too it. Long story short is that the modem you are using is ancient and rather than having a debate at what could be wrong, the first thing you need to do is ring up tech support, tell them it is faulty and they'll send somebody round with a shub. You aren't getting 10mbits per PC because the "modem" can only handle ~25mbits max and it is a modem and not a router. Your upstream is also on qpsk which is wrong as well.

More to come late........

[Sephiroth]

The General has it absolutely right. You should have been/be eligible for a free upgrade to the current lowest tier (it was 30 meg now 50 meg). When you've got this sorted out after calling Customer Services (put the phone down on India and try again till you get a UK agent, you will receive a gateway modem/router. This will provide 8 downstream and 2 upstream channels.

Now the potentially awkward bit. Your upstream modulates at 2 bits per symbol (QPSK) whereas the current modulation is 4 bits per symbol - 16QAM (and now being further augmented by infrastructure improvements to 6 bits per symbol - 64QAM).

The QPSK modulation may be due to the legacy nature of your upstream as connected at the VM end or it may be a noisy upstream circuit which can seriously reduce downstream speeds, So the install technician when you upgrade needs to ensure that you are not left on QPSK upstream modulation.

Let us know if you need further guidance here and how you get on with VM.

[qasdfdsaq]

Originally Posted by General Maximus

I going to make this super quick dude because I am already late for work.

I'm impressed you find CableForum more important than turning up for work on time.

[Ignitionnet]

The configuration change doesn't affect you, it's part of a change that supplied more capacity. You were moved from the USA DOCSIS standard to EuroDOCSIS which meant adjustments to the downstream interleave depth amongst other things.

The QPSK on the upstream is not actually the case, your ancient modem misreports things.

Call into the nice people at customer services and get yourself a new Superhub first off.

[WarnersEnd]

Well that's interesting. Just spoke to support, apparently it's over-utilisation of the cable. (Our cables were installed by Telecential decades ago). We will suffer low speed connection in Warners End, Hemel Hempstead until August! Got a refund for non delivery of the promised broadband performance plus a free superhub is on it's way, but presumably that won't deliver much in the way of benefits until August.

[Sephiroth]

Originally Posted by Ignitionnet

The configuration change doesn't affect you, it's part of a change that supplied more capacity. You were moved from the USA DOCSIS standard to EuroDOCSIS which meant adjustments to the downstream interleave depth amongst other things.

The QPSK on the upstream is not actually the case, your ancient modem misreports things.

Call into the nice people at customer services and get yourself a new Superhub first off.

Ah - if it were really QPSK then it would have shown half the symbol rate? Right?

[Ignitionnet]

Originally Posted by Sephiroth

Ah - if it were really QPSK then it would have shown half the symbol rate? Right?

Sadly not. Symbol rate is a function of channel width not of modulation. 2560kSym/s for 3.2MHz, 5120kSym/s for 6.4MHz.

Just the bits per symbol modulation changes, not the symbol rate.

[WarnersEnd]

I've just checked the Virgin media service status for my postcode - says good broadband service. Bit of a porky there then! Why does it not mention there are speed problems due to be addressed by August? I guess it's a case of sell the service and fix the problems once people are committed to a contract. A bit shabby.

[Sephiroth]

Only hard outages are posted on the service status page. Overutilisation issues are not in that class.

[General Maximus]

Originally Posted by WarnersEnd

but presumably that won't deliver much in the way of benefits until August.

I am pretty sure the shub will fix all your problems dude. Utilisation and fix dates seems to the de facto excuse these days. You sit there waiting till August for this magical transformation and when things don't get better you ring up to find out what is going on only to be told there wasn't an issue to start off with. Anyways, I digress...

The thing which I wanted to explain this morning and didn't have time to is why you need a shub. You have got to think of your internet connection (to VM) as a motorway with lots of lanes (channels) . Each lane can only handle so much speed so the faster you want to go (like 152mbits) the more lanes you need to use. The problem you have got is that the modem you are currently using can only use one of these lanes and if there is a problem with that lane you are screwed. The shub can use 8 channels simultaneously (varies by area but you will have at least 6 available to you) to which your traffic will be load balanced across. The means that if there is a problem with one or two of channels, you hopefully won't notice it too much because your traffic will still go across the other 4 or so.

Having a shub requires you to consider a few things though. The shub is a combi modem/router so not only is it going to be connected to the coax cable for your internet connection, your pc/whatever else is also going to plug into the back. At the moment you have either got one pc you connect straight to your modem or you have got your own router which you are using separately. If you have got your own router you can put the shub in modem mode which will basically allow you to retain your current setup, or if your current router is quite old (especially for wireless), you might want to think about ditching it if they send you a shub2 and using that instead.

Come back and let us know when it arrives and how things go. Click on this link and scroll down to the 5th post. There are some screen shots there of what the shub gui looks like. All the info is exactly the same apart from there is more of it because you will be using more downstream and upstream channels. My power levels are pretty much perfect so use them as a guide for yours. Any concerns come back and post yours for analysis.