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Standard User WWWombat
(knowledge is power) Sat 14-Jan-17 21:42:18
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Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: adslmax] [link to this post]
 
In reply to a post by adslmax:
Why can't BT Wholesale Broadband Diagnostic Test or Availability Checker to show how many % of the lines take up of the cabinet?


As the others said, it's useless to you.

But also because, quite frankly, it would be extraordinarily useful market intelligence data for all of their competitors.
Standard User ukhardy07
(knowledge is power) Sat 14-Jan-17 23:49:55
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Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: Zarjaz] [link to this post]
 
In reply to a post by Zarjaz:
I wonder why the remote system would lower the SNR if the line in question already achieves max sync ?
Surely it would be better to have a little built in stability ?
Not sure how fibre works but if we look at sky ADSL, there is a power management module used to reduce output power which lowers the noise margin, reduces DSLAM energy and thereby lower costs.

Here's the one sky uses as far as I know:

http://www.assia-inc.com/products-services/pdf/Brief...

Savings equate to around 3KWh per line which is 30 to 50p a year per customer, multiplied by several million customers, you have your answer.

Edited by ukhardy07 (Sat 14-Jan-17 23:53:32)

Standard User WWWombat
(knowledge is power) Sun 15-Jan-17 00:31:16
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Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: ukhardy07] [link to this post]
 
BT uses their own home-brew DLM equivalent to Assia's.

Lowering the power will reduce the received signal strength, so reduce the SNR. That will tend to reduce the sync speed.

If you want to maintain speed, then you can only reduce the transmit power on those lines already syncing at full speed. That might be 20% of lines at 80Mbps, or 30% of lines at 40-55Mbps.

However, crosstalk can cut in at any point, as new subscribers join. If you are on a reduced power, and they reduce your working SNRM you will need to increase power to get back your error-free margins. And other neighbouring lines will do the same.

As each of you increase your power, you'll start interfering with all your neighbouring lines a little more ... so they all have to react.

It can be a vicious circle...


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Standard User Chrysalis
(legend) Sun 15-Jan-17 21:06:13
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Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: WWWombat] [link to this post]
 
I have always wondered if DLM cuts power on lines with excessive snrm, user thinks its crosstalk, then if the sync falls below max power is never increased again.

Sky Fibre Pro BQM - IPv4 BQM - IPv6
Standard User WWWombat
(knowledge is power) Mon 16-Jan-17 14:35:13
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Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: Chrysalis] [link to this post]
 
You could be right, but that would make DLM rather dumb. Unfortunately, as time goes by, DLM seems to elevate its dumbness.

One problem I have with "power" is that it is a tricky concept to deal with, and one that many people (including me) cannot handle properly.

For example, we are very used to seeing the idea that profile 17a is listed with a maximum power of 14.5dBm, and seeing modems report power - anywhere from -10dBm to 13+dBm.

But those numbers are aggregate power, accumulated from the individual power on each tone. And there is another limitation that affects the individual power on tones: the PSD (power spectral density), measured in dBm per Hertz.

So, when we see a modem report a lower-than-expected (aggregate) power value, it might be because
- there are fewer tones than expected
- the PSD mask has limited power of many tones
- "something" has reduced the power of individual tones (eg UPBO or DPBO). (*)

There's also the gotcha that we're counting in log scales. Doubling power is +3dBm. Or, when calculating aggregate power, doubling the number of tones at the same power is also +3dBm.

LR-VDSL has a change that allows aggregate power to be +20.5dBm instead of 14.5dBm. A 6dBm difference means quadruple power ... but aggregated over (roughly) only half as many tones ... so could mean octuple power per tone. Wow.

Except it has to fit inside the broad parameters of the existing PSD mask (power per hertz), but benefitting from removal of the DPBO shaping that would otherwise allow coexistence with ADSL.

Who can tell, off the top of their heads, whether +6dBm in aggregate amounts to more or less than the change in shape of the PSD mask?



(*) - The UPBO article is interesting. It shows that the settings can be tuned to a "preferred distance", above which the upstream speeds fall away considerably.
Standard User RobertoS
(elder) Mon 16-Jan-17 14:50:25
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Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: WWWombat] [link to this post]
 
In reply to a post by WWWombat:
You could be right, but that would make DLM rather dumb. Unfortunately, as time goes by, DLM seems to elevate its dumbness.
I believe there is also a form of "conflict of interest" on the specification of requirements from Openreach DLM.

The idea of a lower default margin, or simply its availability as happened with the ADSLx BT Wholesale one, is a great idea for most customers at little cost to Openreach. Also conferring on "BT" the bonus of higher average rates to put against Virgin Media.

The conflict comes in that it has been clear from the early days that the BT Wholesale estimate table for any given line, which has to be culled from the Openreach one for VDSL2, has aggressively revised downwards as soon as actuals fall. Again we know the BTW ADSLx ones always tracked actual over time, but the underlying emphasis seems to have changed for VDSL2.

The BT Wholesale and probably the Openreach attitude now seems to be strongly on holding that lines can degrade for a number of reasons, so they aren't going to spend money sorting out even significant degradation.

It's a "Shrug the shoulders - that's what happens" sort of approach. "The user still has a service so what the heck?"

Kindness isn't going to cure the world of all its awfulness but it's a good place to begin. Daisy Ridley.
My broadband basic info/help site - www.robertos.me.uk. Domains, site and mail hosting - Tsohost.
Connection - AAISP Home::1 80/20. Sync 54999/14466Kbps @ 600m. BQMs - IPv4 & IPv6

Edited by RobertoS (Mon 16-Jan-17 14:51:16)

Standard User philippercival
(knowledge is power) Mon 16-Jan-17 17:12:14
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Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: RobertoS] [link to this post]
 
In reply to a post by RobertoS:
The BT Wholesale and probably the Openreach attitude now seems to be strongly on holding that lines can degrade for a number of reasons, so they aren't going to spend money sorting out even significant degradation.

It's a "Shrug the shoulders - that's what happens" sort of approach. "The user still has a service so what the heck?"


Agreed, though I have no proof, other than various ISPs telling me that if they report a fault BT will do nothing as it is still above the acceptable level.

BT will have to be a little careful in the future though I suspect. Many countries are switching to their mobile phone networks and I am very impressed with what 4G can do ( though admittedly not where I currently live). I know a lot of people in the UK have already given up their land lines and as 4G becomes more widely available I suspect this will accelerate. Unfortunately thanks to Plusnet switching it off I can not see my recent usage, but if I was to take all the money I pay for phone and broadband, that would buy me a fair whack from a mobile network.

Standard User AndyHCZ
(committed) Mon 16-Jan-17 17:23:33
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Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: philippercival] [link to this post]
 
There has to be some threshold for fault investigation though.

I've seen some people (with low cost ISPs) requesting an engineer just because their sync rate has dropped from 80Mbps to 75Mbps.
Standard User adslmax
(knowledge is power) Mon 16-Jan-17 17:35:21
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Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: AndyHCZ] [link to this post]
 
In reply to a post by AndyHCZ:
There has to be some threshold for fault investigation though.

I've seen some people (with low cost ISPs) requesting an engineer just because their sync rate has dropped from 80Mbps to 75Mbps.


I probably do the same if my sync rate has dropped to below 74999k from 79999k to ask my isp to get engineer out to reset DLM.
Standard User AndyHCZ
(committed) Mon 16-Jan-17 17:36:05
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Re: Openreach to rollout 3dB target SNRm for FTTC next year


[re: adslmax] [link to this post]
 
And that is one of the reasons why we have a fault threshold.
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