Modulation 64QAM and not 256QAM reason why 50MbXXL NEVER been over 12Mbps

[andrew513210]

Hi all, Have had 50Mb virgin since last summer and have only just looked at broadband speed tests. On average the speed is between 6Mbps and 9Mbps, but can quite often be about 4Mbps. Highest ive ever seen is about 12Mbps. Anyways, after a lot of internet reading, I logged onto my modem and found that the only thing different from mine in that on all DS-1,DS-2 and DS-3, the modulation is at 64QAM, whereas EVERY other 50Mb connection has theirs at 256QAM. Could this be the reason for a slow (1/5 speed) connection?! Much thanks.

DS-1    DS-2    DS-3    DS-4
Frequency     435000000    443000000    451000000    N/A
Lock Status
(QAM Lock/FEC Sync/MPEG Lock)     Y/Y/Y    Y/Y/Y    Y/Y/Y    N/N/N
Channel Id     54    55    56    N/A
Modulation     64QAM    64QAM    64QAM    N/A
Symbol Rate
(Msym/sec)     6.952    6.952    6.952    N/A
Interleave Depth     I=12
J=17    I=12
J=17    I=12
J=17    N/A
Power Level
(dBmV)     -1.88    -2.12    -2.20    N/A
RxMER
(dB)     37.30    37.88    38.21    N/A
Correctable
Codewords     0    0    0    N/A
Uncorrectable
Codewords     241    238    791    N/A

US-1    US-2    US-3    US-4
Channel Type     1.0    N/A    N/A    N/A
Channel ID     2    N/A    N/A    N/A
Frequency
(Hz)     45800000    N/A    N/A    N/A
Ranging Status     Success    N/A    N/A    N/A
Modulation     16QAM    N/A    N/A    N/A
Symbol Rate
(KSym/sec)     2560    N/A    N/A    N/A
Mini-Slot Size     2    N/A    N/A    N/A
Power Level
(dBmV)     44.75    N/A    N/A    N/A
T1 Timeouts    0
T2 Timeouts    0    0    0    0
T3 Timeouts    52    0    0    0
T4 Timeouts    3    0    0    0

 Item      Status      Comments
Acquired Downstream Channel         435.000122 MHz         Primary Downstream Locked
Ranged Upstream Channel         45.799999 MHz         Success
Provisioning State         OK         Operational
Ethernet Link Status         Up         100 Mbps/Full duplex

General Configuration
Network Access :     Allowed
Maximum Number of CPEs :     1
Baseline Privacy :     Enabled
DOCSIS Mode :     DOCSIS 3.0
Config File :     vca69834ncxv9873254k
Primary Downstream Service Flow
SFID :     20
Max Traffic Rate :     53000000 bps
Max Traffic Burst :     3044 bytes
Min Traffic Rate :     0 bps
Primary Upstream Service Flow
SFID :     19
Max Traffic Rate :     1750000 bps
Max Traffic Burst :     3044 bytes
Min Traffic Rate :     0 bps
Max Concatenated Burst :     1522 bytes
Scheduling Type :     Best Effort

[chaos1986]

I've never gotten above 8MB before, my avarage download speed when downloading large files is 30 - 80kb/s. (I'm supposed to be on 50MB)

The boss although very nice couldn't find a problem and said my connection looks fine. So i have come to the conclusion that 50MB is actually 8MB in reality, and obviously we don't get full speeds most of the time so mine lingers around 2 - 6

I might move to another (faster) ISP

[canveyboy]

As far as im aware it should be 256QAM and you should expect average speeds of 45Mb/s and upwards. you also have a lot a T3 errors.

Phone them tell them you are not getting what you are paying for and have never had the speeds you should have been getting, ask them for refunds for every month you have never had what you were intitled to, get the persons name you speak to and if you dont get anywhere send me a PM and I will give you the email for the CEO,s office, you can also insist on a reply from the CEO himself !

[cabsandy]

There is nothing to worry about if your downstreams are at 256QAM or 64QAM-some parts of the country have this difference, for various technical reasons.

Unless there is a general contention issue on your CMTS caused by 64QAM (256 QAM can provide more bandwidth through the modulation techniques it employs-see here  for more details), then this wont be the cause of your issues. I wouldn't get too hung up on it, honestly

[Sephiroth]

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cabsandy wrote:

There is nothing to worry about if your downstreams are at 256QAM or 64QAM-some parts of the country have this difference, for various technical reasons.

........

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What are those technical reasons?

[cabsandy]

Not at liberty to to say, sorry.

[Sephiroth]

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cabsandy wrote:

Not at liberty to to say, sorry.

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What's VM got to hide then? 

[Ignition]

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cabsandy wrote:

Not at liberty to to say, sorry.

---

For the curious:

Downstream laser loading - 256QAM puts more 'stress' on the downstream optics than 64QAM. Overstressing the lasers by pushing too much power at them causes them to 'clip' which has some really quite unpleasant effects.

The other issue is signal quality. 256QAM requires 3dB better CNR than 64QAM so marginal networks for either power or quality will run 64QAM.

The only effect that having 64QAM running instead of 256QAM will have is that each downstream is good for 38Mbps not 50Mbps - if this is the issue it will show as slower speeds at peak times but be absolutely fine off-peak.

I'd be more interested in the T3 / T4 timeouts to be honest.

[cabsandy]

Agree

[andrew513210]

Thank you all for your help. I just got off the phone to virgin and was told that the technical team would take over it and call me about the problem *soon*. I will make sure I tell them about the high T3 error rate im experiencing and see if they can change the QAM issue too.

Andrew