General Discussion
  >> Fibre Broadband


Register (or login) on our website and you will not see this ad.


Pages in this thread: 1 | 2 | (show all)   Print Thread
Standard User xreyuk123
(learned) Thu 18-Sep-14 16:59:53
Print Post

SNRM big change.


[link to this post]
 
Hi guys,

I've had a couple of power cuts and some massive interference from some new power line adapters in the past few days.

My connection was capable of ~43Mbps with an SNRM of 6.5dB, however I used the --maxDataRate command on my unlocked modem to limit the connection to 38.7Mbps with an SNRM of 7.9dB (in an attempt to get interleaving taken off - bit of an experiment).

As a result of the power cuts and interference, DLM put me on a banded profile of 34.9Mbps, with an SNRM of 9.6dB. Two days later, it has taken me off the banded profile.

I am now connected at 37.8Mbps again, however I now only have an SNRM of 6.4dB, when I previously had 7.9dB. My max attainable has dropped by about 1.5Mbps.

Can anyone explain why that might be the case?

I've been logging my connection with DSLStats 24/7 if that will help, and I've ran the --pbParams command on my modem and cannot see any changes in attenuation.

Thanks for the help.

Edited by xreyuk123 (Thu 18-Sep-14 17:01:22)

Standard User WWWombat
(fountain of knowledge) Fri 19-Sep-14 16:58:15
Print Post

Re: SNRM big change.


[re: xreyuk123] [link to this post]
 
Possibly crosstalk from a new subscriber to FTTC. You can never discount the addition of more subscribers at any time.

Good idea with limiting the rate though. You probably want to set it so that the ES value stays very low.
Standard User xreyuk123
(learned) Sun 21-Sep-14 01:26:27
Print Post

Re: SNRM big change.


[re: WWWombat] [link to this post]
 
In reply to a post by WWWombat:
Possibly crosstalk from a new subscriber to FTTC. You can never discount the addition of more subscribers at any time.

Good idea with limiting the rate though. You probably want to set it so that the ES value stays very low.


Thanks. I've an unlocked HG612, are there any stats in there that could indicate cross talk? I've been keeping logs so can look for changes.


Register (or login) on our website and you will not see this ad.

Standard User Chrysalis
(legend) Sun 21-Sep-14 02:44:13
Print Post

Re: SNRM big change.


[re: xreyuk123] [link to this post]
 
an increase of QLN I think is an indicator. It only refreshes on a new sync event. So e.g. if your modem stayed synced when the snrm reduced, your QLN will not have updated.

Standard User xreyuk123
(learned) Sun 21-Sep-14 09:10:54
Print Post

Re: SNRM big change.


[re: Chrysalis] [link to this post]
 
Thanks.

The SNRM change occurred immediately after a DLM resync. I was connected at 34999Kbps (because DLM put me on banded profile) with an SNRM of 9.6dB.

DLM then resynced my line to 38796Kbps with an SNRM of ~6.5dB (I know from previous logging that this should be around 7.9dB SNRM).

Looking at the QLN logs, you can see a bit of a difference towards the end of the graph, any idea what this indicates?

Before: http://cl.ly/XeUD
After: http://cl.ly/Xf6q

My max attainable rate is currently higher than it was on the 5th September. Here are the stats from 5th Sept, Today and what I usually see with this sync with the example taken from 7th Sept after applying --maxDataRate.

5th Sept: Max: 50888Kbps, Sync: 41490Kbps, SNRM: 6.6dB
7th Sept: Max: 51180Kbps, Sync: 38690Kbps, SNRM: 7.8dB
Today: Max: 51164Kbps, Sync: 38696Kbps, SNRM: 6.7dB

So I've got a slightly higher max attainable today compared to the 5th, and pretty much exactly the same stats as the 7th, except my SNRM is the lower than the 7th.

I've never looked at QLN so please forgive my ignorance, but a quick Google shows it's a measure of noise on the line? Any help in interpreting the graphs? laugh

Your help is much appreciated smile

Edited by xreyuk123 (Sun 21-Sep-14 09:13:14)

Standard User WWWombat
(fountain of knowledge) Sun 21-Sep-14 15:35:46
Print Post

Re: SNRM big change.


[re: xreyuk123] [link to this post]
 
Those QLN graphs don't help much, as they only cover the ADSL tones (tone 300 is around 1.3MHz) rather than the full set needed for VDSL2 (up to 17MHz, or around 4000 tones).

I can't tell you what to do with DSLstats - I monitor mine using the other package (HG612 Modem Stats) from the same forum, and have recently started using mydslwebstats too: http://forum.kitz.co.uk/index.php?board=46.0

QLN does indeed show you the "Quiet Line Noise" - which is the amount of "noise" measured on your line prior to the modem squawking at each other to synchronise.

A level of -140 would appear to be the base for a very quiet line at all frequencies. I have seen this *once* on my line, while the rest of the time I see a regular pattern with values between -120 and -140. For the one "odd" time, the best guess is that the DSLAM restarted that time, so the QLN measurement was made with no neighbouring VDSL2 modems running.

Other ways to look at what has happened on your line:
- HLog graph: shows the quality of your line. A non-"smooth curve" to the line might suggest problems with the wiring topology, such as a bridge tap, while significant changes from sync to sync might suggest an intermittent problem in some joints.

- SNR per tone: big changes (drops) here might suggest an increase in noise - which could be plain interference, or crosstalk.

- Bits per tone: should reflect the SNR per tone graph.

Over a year ago, I made a post on a simiar vein, where I animated my 18-month history of these graphs. You can see the post & animations here:
http://forums.thinkbroadband.com/fibre/4241788-attai...

Result: There may have been issues with the modem, and what it was reporting at the time. The behaviour I saw disappeared when the modem firmware was updated in October 2013.

I now run at a speed of 79Mbps, and an SNRM of 6dB; the bottom line is that you *will* get gradually-reducing SNRM values over time. You will also get a gradually-increasing rate of errors, until DLM is triggered; I am now in the region where this can happen, and has happened (I get around 72Mbps during DLM intervention).

Personally, I think that a drop of ~1.5dB is not actually that much, and you can expect much more. In Ireland, where they have turned on vectoring (to counter crosstalk), people have seen increases in SNRM of 10dB or more.
Standard User xreyuk123
(learned) Mon 22-Sep-14 16:51:32
Print Post

Re: SNRM big change.


[re: WWWombat] [link to this post]
 
Thanks, I'll have a look at all that and post back if needed.

It was more the fact that the 1.5dB SNR drop was instant.

I'd synced the day before at the same speeds, with the correct SNRM, but then the next morning there is a sudden 1.5dB difference in SNRM.

Standard User WWWombat
(fountain of knowledge) Mon 22-Sep-14 19:00:03
Print Post

Re: SNRM big change.


[re: xreyuk123] [link to this post]
 
Expect to see crosstalk arrive in steps, when each new customer is activated & connected, rather than a gradually-sloping reduction.

The steps themselves can vary in height, depending on how close the wires are to yours within the cable bundle. Some of these steps could be a lot higher than 1.5dB, but most are probably lower.

The lesson is to never recommend the service to your neighbours wink
Standard User Bald_Eagle1
(experienced) Mon 22-Sep-14 20:57:40
Print Post

Re: SNRM big change.


[re: xreyuk123] [link to this post]
 
If the stepped reduction in SNRM happened during normal working hours, there's every chance it was a new user being connected.

I have described my own experience of gradually increasing crosstalk here:-

Crosstalk Effects



You would need to be logged in to see the attached montage.
Standard User xreyuk123
(learned) Sat 27-Sep-14 11:28:49
Print Post

Re: SNRM big change.


[re: Bald_Eagle1] [link to this post]
 
Well DLM resynced me this morning and the SNRM is now reading 7.8dB again. Maybe it was a new subscriber being installed when the resync happened (it was within 9-5) and it messed up the stats temporarily.

Standard User adslmax
(knowledge is power) Sat 27-Sep-14 11:51:28
Print Post

Re: SNRM big change.


[re: xreyuk123] [link to this post]
 
Yep, it sadly as BT Openreach might not go ahead with vectoring now. As BT are eyeing G.fast instead.

I think BT should focus on vectoring as the higher priority first than the G.fast.

BT trial too much on vectoring and never release to nationwide (don't think it gonna to happen now)

Edited by adslmax (Sat 27-Sep-14 11:52:04)

Standard User WWWombat
(fountain of knowledge) Sat 27-Sep-14 12:15:37
Print Post

Re: SNRM big change.


[re: adslmax] [link to this post]
 
In reply to a post by adslmax:
Yep, it sadly as BT Openreach might not go ahead with vectoring now. As BT are eyeing G.fast instead.

How do you reach this conclusion?

Aren't BT allowed to look at both vectoring & G.fast at the same time? They're looking at plenty of things in their research divison.

Given where both schemes are in the ITU approval cycle, I'd say that G.fast is running about 5 years behind Vectoring. I wouldn't expect BT to even start to contemplate G.fast deployment for another 4-5 years - and that is only from a technical perspective.

If you consider things from a market, or demand, perspective, it might be even longer. They're getting a reasonably good uptake of NGA subscribers, but there aren't many of those that have already upgraded who *need* more, and are willing to pay more for the privilege. I'd guess at less than 10% of the current NGA subscribers - a group which is itself around 15% of the properties in the NGA coverage area.
Standard User Chrysalis
(legend) Sat 27-Sep-14 12:59:45
Print Post

Re: SNRM big change.


[re: WWWombat] [link to this post]
 
funny enough tho I cannot see BT deploying vectoring for 5 years either.

if it needs new ECI kit and its not economical to replace the kit for 7-8 years why bother just jump to g.fast.

Edited by Chrysalis (Sat 27-Sep-14 12:59:57)

Standard User pcoventry76
(knowledge is power) Sat 27-Sep-14 13:55:44
Print Post

Re: SNRM big change.


[re: adslmax] [link to this post]
 
In reply to a post by adslmax:
Yep, it sadly as BT Openreach might not go ahead with vectoring now. As BT are eyeing G.fast instead.

I think BT should focus on vectoring as the higher priority first than the G.fast.

BT trial too much on vectoring and never release to nationwide (don't think it gonna to happen now)


In this area they trialled FTTPoD with 3 engineers and then scrapped it - so let's be fair they have trouble releasing many things to help with the future.

g.fast or whatever it is called would be fantastic but there are so many poles to upgrade. on a side note I can see as I sit here a bird has left a poo on my DP. I hope it does not leak in lol
Standard User WWWombat
(fountain of knowledge) Sat 27-Sep-14 15:29:57
Print Post

Re: SNRM big change.


[re: Chrysalis] [link to this post]
 
In reply to a post by Chrysalis:
funny enough tho I cannot see BT deploying vectoring for 5 years either.

if it needs new ECI kit and its not economical to replace the kit for 7-8 years why bother just jump to g.fast.


Good point.

Vectoring only requires changes at the existing cabinet sites, while G.fast requires you to deploy nodes elsewhere, so there's a different momentum needed behind the two ideas before the board would say "Lets go".

Vectoring also (likely) allows services to be sold at 100Mbps, just, which ticks a box for the EU 2020 targets. That might add a political dimension behind vectoring's momentum.

But a failure to have an ECI solution could stop that. There is nothing wrong with deploying vectoring to Huawei sites alone, of course, but you can't really market the improved speeds until the solution is cross-platform.

BUT...

Your point raises an entirely different direction that BT could go.

If they're not going to bother with vectoring, and jump to G.fast, then they'll obviously have to deploy nodes in places deeper than the PCP. Why not start now?

Stop deploying FTTC cabinets, and start deploying FTTRN nodes instead, deeper in the network. Let them use VDSL2 for now (vectored or not), but make them plug-compatible with G.fast nodes in the future.

Kinda like the Swiss are doing with their FTTS deployment, except they are still deploying vectoring.
Pages in this thread: 1 | 2 | (show all)   Print Thread

Jump to