Qam16/qpsk
 

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.

Re: Qam16/qpsk
 

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

Re: Qam16/qpsk
 

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

Re: Qam16/qpsk
 

It's automatic.

Re: Qam16/qpsk
 

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.

Re: Qam16/qpsk
 

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

Re: Qam16/qpsk
 

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

Re: Qam16/qpsk
 

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

ATDMA = QAM16
TDMA = QPSK?

Re: Qam16/qpsk
 

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

Re: Qam16/qpsk
 

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

Re: Qam16/qpsk
 

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.

Re: Qam16/qpsk
 

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

Re: Qam16/qpsk
 

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.

Re: Qam16/qpsk
 

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

Re: Qam16/qpsk
 

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

Re: Qam16/qpsk
 

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.

Re: Qam16/qpsk
 

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

Re: Qam16/qpsk
 

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

Re: Qam16/qpsk
 

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

Re: Qam16/qpsk
 

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

Re: Qam16/qpsk
 

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 may assist you to understand better.

Re: Qam16/qpsk
 

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.

Re: Qam16/qpsk
 

Yes as long as it is not massive jumps.

Re: Qam16/qpsk
 

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

Re: Qam16/qpsk
 

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 .:)

Re: Qam16/qpsk
 

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.

Re: Qam16/qpsk
 

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

Re: Qam16/qpsk
 

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

Re: Qam16/qpsk
 

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

Re: Qam16/qpsk
 

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

Re: Qam16/qpsk
 

care to explain?

Re: Qam16/qpsk
 

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

Re: Qam16/qpsk
 

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

Re: Qam16/qpsk
 

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

Re: Qam16/qpsk
 

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

Re: Qam16/qpsk
 

Ask VM?