Qam16/qpsk

[chambohambo]

Hi all, am normally on QAM16, noticed today though am on QPSK done several reboots and still on QPSK anyone kno why this could be? am not facing any problems.

[pip08456]

Noise on your upstream. QPSK is more noise tolerant. They should be aware of it.

[chambohambo]

So would they have turned off QAM16 until fixed and put everyone on QPSK?

[Ignitionnet]

It's automatic.

[General Maximus]

I noticed by accident that I was on qpsk for over a week back in February and truth be told, I didnt notice any performance degradation. I still got full upload speed and I think my download speed maxed out at 4.5mbit instead of 6 but it wasnt anything to moan about.

[craigj2k12]

it happened to me the other bank holiday, upload speeds slowed to about 2 to 3 meg and pings were all over the place

[pip08456]

You need a tech out to adjust your power level. That is the whole reason it is happening in your case.

[Neo-Tech]

And if you're on the Dud I'm guessing:

ATDMA = QAM16
TDMA = QPSK?

[Ignitionnet]

Nah. ATDMA = 6.4MHz channel width, TDMA = 3.2MHz channel width.

[Neo-Tech]

So if you're switched to TDMA there's noise issues, or is this a completely different thing altogether?

[Chrysalis]

What I say is subject to been wrong.

But generally interpret ATDMA as been docsis2, if there is a noise issue it will drop back to QPSK, on the superhub that will appear as ATDMA 10240kbit/sec. Still be the equivelent to QAM16 on docsis1 in terms of capacity. If no noise issue you should be seeing ATDMA 20480kbit/sec.

Docsis1 would show as TDMA 10240kb/src if no noise issue or TDMA 5120kbit/sec if a noise issue, the latter been QPSK on docsis1.

I have never heard of someone been rolled back to docsis1 due to noise it would just go to QPSK but stay on docsis2.

[craigj2k12]

What I say is subject to been wrong.

But generally interpret ATDMA as been docsis2, if there is a noise issue it will drop back to QPSK, on the superhub that will appear as ATDMA 10240kbit/sec. Still be the equivelent to QAM16 on docsis1 in terms of capacity. If no noise issue you should be seeing ATDMA 20480kbit/sec.

Docsis1 would show as TDMA 10240kb/src if no noise issue or TDMA 5120kbit/sec if a noise issue, the latter been QPSK on docsis1.

I have never heard of someone been rolled back to docsis1 due to noise it would just go to QPSK but stay on docsis2.

he wont be put back to docsis 1, his area wont have the upload increase, and will be on docsis 1 in the first place

[Ignitionnet]

What I say is subject to been wrong.

But generally interpret ATDMA as been docsis2, if there is a noise issue it will drop back to QPSK, on the superhub that will appear as ATDMA 10240kbit/sec. Still be the equivelent to QAM16 on docsis1 in terms of capacity. If no noise issue you should be seeing ATDMA 20480kbit/sec.

Docsis1 would show as TDMA 10240kb/src if no noise issue or TDMA 5120kbit/sec if a noise issue, the latter been QPSK on docsis1.

I have never heard of someone been rolled back to docsis1 due to noise it would just go to QPSK but stay on docsis2.

Correct. The secondary / fallback profile is still a 6.4MHz wide DOCSIS 2 channel, just the modulation changes.

They could actually have 3 profiles, 64QAM, 16QAM and QPSK for example, perhaps one to think about once plant upgrades are done.

[chambohambo]

I am still on QPSK.

Cable Modem Downstream
Downstream Lock : Locked
Downstream Channel Id : 166
Downstream Frequency : 307000000 Hz
Downstream Modulation : QAM256
Downstream Symbol Rate : 6952 Ksym/sec
Downstream Interleave Depth : taps12Increment17
Downstream Receive Power Level : 7.5 dBmV
Downstream SNR : 37.4 dB

Cable Modem Upstream
Upstream Lock : Locked
Upstream Channel ID : 1
Upstream Frequency : 35800000 Hz
Upstream Modulation : QPSK
Upstream Symbol Rate : 5120 Ksym/sec
Upstream transmit Power Level : 49.7 dBmV
Upstream Mini-Slot Size : 4

[Efour]

Would this explain why my PL is shocking for the past 3 days
im also on the QPSK crap now

20 mbit at POPLAR ubr London..

Its unplayable peak hours

[pip08456]

QPSK is not necessarily crap. It is an only indication of an upstream noise problem, the modulation has been automatically adjusted to take account of this.

It does not mitigate any other problem on your area of the network, eg over utilisation etc.

[Ignitionnet]

Would this explain why my PL is shocking for the past 3 days
im also on the QPSK crap now

20 mbit at POPLAR ubr London..

Its unplayable peak hours

Yes that could well be it, chops the available bandwidth in half.

[chambohambo]

Checked modem today and noticed the downstream has dropped from 7.5 DBMV what would cause this to happen? and I am still on QPSK upstream.

Cable Modem Downstream
Downstream Lock : Locked
Downstream Channel Id : 168
Downstream Frequency : 323000000 Hz
Downstream Modulation : QAM256
Downstream Symbol Rate : 6952 Ksym/sec
Downstream Interleave Depth : taps12Increment17
Downstream Receive Power Level : 0.9 dBmV
Downstream SNR : 37.0 dB

Cable Modem Upstream
Upstream Lock : Locked
Upstream Channel ID : 1
Upstream Frequency : 35800000 Hz
Upstream Modulation : QPSK
Upstream Symbol Rate : 5120 Ksym/sec
Upstream transmit Power Level : 49.7 dBmV
Upstream Mini-Slot Size : 4

[craigj2k12]

Checked modem today and noticed the downstream has dropped from 7.5 DBMV what would cause this to happen? and I am still on QPSK upstream.

Cable Modem Downstream
Downstream Lock : Locked
Downstream Channel Id : 168
Downstream Frequency : 323000000 Hz
Downstream Modulation : QAM256
Downstream Symbol Rate : 6952 Ksym/sec
Downstream Interleave Depth : taps12Increment17
Downstream Receive Power Level : 0.9 dBmV
Downstream SNR : 37.0 dB

Cable Modem Upstream
Upstream Lock : Locked
Upstream Channel ID : 1
Upstream Frequency : 35800000 Hz
Upstream Modulation : QPSK
Upstream Symbol Rate : 5120 Ksym/sec
Upstream transmit Power Level : 49.7 dBmV
Upstream Mini-Slot Size : 4

they will be making changes at the network end, which could possible affect your power levels, however your levels awere out of spec before, and are now well in

[chambohambo]

Oh I thought power levels and stuff was all to do with the green cabinet. So do you mean at the UBR?

[pip08456]

Oh I thought power levels and stuff was all to do with the green cabinet. So do you mean at the UBR?

It's a little more complex than that as a problem could be at the cabinet or the UBR or anywhere inbetween.

A read of this (http://community.virginmedia.com/t5/Up-to-50Mb-broadband/POWER-LEVELS-amp-SNR-A-TECHNICAL-PRIMER/td-p/148072) may assist you to understand better.

[chambohambo]

Is it normal for the downstream power level and snr to be bouncing around slightly? just noticed when I keep clicking refresh but then when I keep hitting refresh on upstream power level it just stays stuck on what it is.

[pip08456]

Yes as long as it is not massive jumps.

[chambohambo]

How come the upstream doesn't bounce around but downstream does?

[Nedkelly]

The downstream can be affected by heat in the main cabs with amps .In the summer you can loose 3db and in the winter gain 3 db .what also could be happening is that the network has been reset due to the maitanence that is going on .Here we visit every cab with a amp in once a year and check all forward and reverse levels 1000+ cabs done every year its like painting the forth rail bridge once you finish you start again .:)

[Ignitionnet]

How come the upstream doesn't bounce around but downstream does?

Upstream is a transmit power and only changes when the power arriving at the other end goes outside a certain range, it is only adjusted when needed. What you're seeing on the downstream is the receiving power at your modem.

[Peter_]

they will be making changes at the network end, which could possible affect your power levels, however your levels awere out of spec before, and are now well in
Actually both sets of power levels are well within spec.;)

[craigj2k12]

Actually both sets of power levels are well within spec.;)

i said they were out, look at post 15 (they were slightly high)

[Peter_]

i said they were out, look at post 15 (they were slightly high)
I did say both sets of power levels and neither are over 11.;)

[pip08456]

I wouldn't be happy if downstream was over 7dBmv. But that's just me.

[craigj2k12]

I did say both sets of power levels and neither are over 11.;)

care to explain?

[chambohambo]

Still on QPSK wonder when I will go back to QAM16.

Cable Modem Downstream
Downstream Lock : Locked
Downstream Channel Id : 168
Downstream Frequency : 323000000 Hz
Downstream Modulation : QAM256
Downstream Symbol Rate : 6952 Ksym/sec
Downstream Interleave Depth : taps12Increment17
Downstream Receive Power Level : 1.1 dBmV
Downstream SNR : 36.1 dB

Cable Modem Upstream
Upstream Lock : Locked
Upstream Channel ID : 1
Upstream Frequency : 35800000 Hz
Upstream Modulation : QPSK
Upstream Symbol Rate : 5120 Ksym/sec
Upstream transmit Power Level : 49.7 dBmV
Upstream Mini-Slot Size : 4

[craigj2k12]

they will be aware of using QPSK, and will be in the process of sorting the problem out

[chambohambo]

Hi all, just to let you all know I am still on QPSK, I would of thought I would of been put back on QAM16 by now.

Cable Modem Downstream
Downstream Lock : Locked
Downstream Channel Id : 166
Downstream Frequency : 307000000 Hz
Downstream Modulation : QAM256
Downstream Symbol Rate : 6952 Ksym/sec
Downstream Interleave Depth : taps12Increment17
Downstream Receive Power Level : 1.6 dBmV
Downstream SNR : 37.2 dB

Cable Modem Upstream
Upstream Lock : Locked
Upstream Channel ID : 1
Upstream Frequency : 35800000 Hz
Upstream Modulation : QPSK
Upstream Symbol Rate : 5120 Ksym/sec
Upstream transmit Power Level : 49.4 dBmV
Upstream Mini-Slot Size : 4

[chambohambo]

Still on QPSK why?

Cable Modem Downstream
Downstream Lock : Locked
Downstream Channel Id : 168
Downstream Frequency : 323000000 Hz
Downstream Modulation : QAM256
Downstream Symbol Rate : 6952 Ksym/sec
Downstream Interleave Depth : taps12Increment17
Downstream Receive Power Level : 1.0 dBmV
Downstream SNR : 36.9 dB

Cable Modem Upstream
Upstream Lock : Locked
Upstream Channel ID : 1
Upstream Frequency : 35800000 Hz
Upstream Modulation : QPSK
Upstream Symbol Rate : 5120 Ksym/sec
Upstream transmit Power Level : 49.4 dBmV
Upstream Mini-Slot Size : 4

[qasdfdsaq]

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