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[jelv]

If you were a very early user on the cabinet it's not unusual to see a slow down as more users are added due to cross talk. If there's no reason to suspect there is an issue with the line causing slower speeds it would be pointless upgrading to Extra as any increase you might see would be minimal (if any).

[spotter]

That would make sense, I was probably one of the first to get fibre as it was only a week after it went live that i was connected. Would the line profile drop as more users are connected though ?

[jelv]

That is my understanding: as cross talk increases the errors the DLM will reduce the sync speed to compensate. Perhaps someone with more knowledge could confirm?

[Dray]

DLM may increase interleaving or error-correction but I don't think it will reduce sync speed. My understanding is that cross-talk increases the noise meaning less SNR margin is available so a resync will sync at a lower speed.

[Chrysalis]

jelv its the crosstalk itself that creates noise on the line which in turn reduces snr.

The line can hold on with reduced snrm if the crosstalk isnt severe enough in which case is no immediate speed loss but would be speed loss the next time the line resyncs, or if the crosstalk is severe enough the reduced snr will cause the line to resync immediatly at a lower speed.

DLM would only intervene if the crosstalk also decreases stability in the form of either excessive resyncs or error rates.

I do have my own personal theory that the dslam in addition also adjusts power levels as more lines are enabled which would reduce sync speeds even further, but noone here or elsewhere agrees with me on that one :p

[kitz]

As Chrys says, its the reduction in SNRm that causes the loss of speed.

When a new line gets attached, the crosstalk generates more noise on the line which causes the SNRm to decrease and that in turn causes the reduction in sync speed.

-----------------------

If you are using DSLstats, then you can spot the signs of a cross-talker coming online.  You can sometimes even see when one of your crosstalkers has a resync or reboots their router.

For example heres my DSLstats SNRm graph and you can see that at about 1:20am one of my crosstalkers had a resync.   
Note how my SNRm momentarily goes up to 7.8 dB when he's not using his connection.
Then look what effect it has on my connection speed and how the max attainable jumps up.  This particular crosstalker 'costs me' 5Mbps of sync speed.   

[kitz]

I do have my own personal theory that the dslam adjusts power levels as more lines are enabled which would reduce sync speeds, but noone here or elsewhere agrees with me on that one :p

Its not anything that Ive ever seen and it would go against the rules why we have such things as PSD masks and PCB.   
There is one time when it may perhaps affect your Tx power and thats if an addition to the cab somehow affected your attention. The theory says this shouldnt happen, but its possible that a line may be disturbed when the engineer adds a line.   

If theres a change in attenuation then this could take you in to another bracket of the PSD masks as which PSD mask gets applied depends upon your line-length (measured using the atten).

Ive never seen my power change when a new line is applied.   For example Ive just gone back to the first set of DSLstats figures that I have to hand on this drive and when I first started using the Zyxel just over a year ago

These are the relevant figures from 31-03-2014

Code: [Select]

Attainable Net Data Rate:           30843 kbps              90039 kbps
Actual Aggregate Tx Power:             5.6 dBm               14.3 dBm

Line Attenuation(dB): 10.7 23.4 36.9
SNR Margin(dB): N/A 8.4 8.4
TX Power(dBm): 11.9 7.3 7.4

and from now

Code: [Select]

Attainable Net Data Rate:           30173 kbps              82456 kbps
Actual Aggregate Tx Power:             6.1 dBm               14.3 dBm

Line Attenuation(dB): 10.6 23.3 36.6
SNR Margin(dB): 6.5 6.6 6.6
TX Power(dBm): 11.9 7.4 7.4

From this you can see over the past year that :

-  Ive lost a total of 7.5 Mbps of headline sync (Im now in year 2 and most of the loss was during the first year)
-  My Tx power has stayed the same despite more users being added to the cab - in fact my upstream has gone up slightly, which is reverse of your theory.
-  The SNRm has gone down (as expected) which has caused the attainable to go down. 

[spotter]

Regarding the latest firmware, do i download from  the Zyxel site download library?

[clonc]

Regarding the latest firmware, do i download from  the Zyxel site download library?

Try this link


ftp://certified:zyxel@ftp.zyxel.it/firmware/VMG8924


and download 8C0,on zyxel site you will find only 7C0.....

[Bald_Eagle1]

I do have my own personal theory that the dslam adjusts power levels as more lines are enabled which would reduce sync speeds, but noone here or elsewhere agrees with me on that one :p

Its not anything that Ive ever seen and it would go against the rules why we have such things as PSD masks and PCB.   
There is one time when it may perhaps affect your Tx power and thats if an addition to the cab somehow affected your attention. The theory says this shouldnt happen, but its possible that a line may be disturbed when the engineer adds a line.   

If theres a change in attenuation then this could take you in to another bracket of the PSD masks as which PSD mask gets applied depends upon your line-length (measured using the atten).

Ive never seen my power change when a new line is applied.   For example Ive just gone back to the first set of DSLstats figures that I have to hand on this drive and when I first started using the Zyxel just over a year ago

FWIW, see the attached montage from my connection, starting January 2015.

Various stats have waxed & waned.

Over the years I have had my FTTC service, although not particularly highlighted in the 4 months of stats used for the montage, Line & Signal attenuation do gradually increase during summer & decrease in winter. That does have some effect on other stats/attainable rates etc.
August tends to be the period with the highest Line & Signal attenuation & lowest SNRM etc.
 

[spotter]

Regarding the latest firmware, do i download from  the Zyxel site download library?

Try this link


ftp://certified:zyxel@ftp.zyxel.it/firmware/VMG8924


and download 8C0,on zyxel site you will find only 7C0.....

thanks, i have been linked to that page a few times but when i click on one of the file names i just get this webpage is unavailable , what am i doing wrong ?

[broadstairs]

Regarding the latest firmware, do i download from  the Zyxel site download library?

Try this link


ftp://certified:zyxel@ftp.zyxel.it/firmware/VMG8924


and download 8C0,on zyxel site you will find only 7C0.....

thanks, i have been linked to that page a few times but when i click on one of the file names i just get this webpage is unavailable , what am i doing wrong ?

I have no idea because I just clicked on that link and tried to download the latest version which worked. Try clearing your browser cache.

Stuart

[spotter]

All i get if i click any of the links is ERR_FTP_FAILED in chromw and this webpage cannot be displayed in IE?

[kitz]

link  working fine here in FF and IE 

[kitz]

All i get if i click any of the links is ERR_FTP_FAILED in chromw and this webpage cannot be displayed in IE?

I get that same message in chrome if I use a C&P of the url rather than a direct click of the link.