noise margin values?

Hi Guys,

I have BT infinity, and I've read people's comments about ''noise margin'. But never really understood the low and high values lol.

My current noise margin is "Noise margin "14.8 / 12.3". And I use to use a Cat 6 RJ11 cable which had a margin of 18. This is a custom cable from eBay.

Out of curiosity, is it a good thing to have a lower margin?

The noise margin is a trade off with sync speed and stability.
A high noise margin is associated with a lower sync speed but higher stability.
A low noise margin is associated with higher sync speed but lower stability.
The target noise margin is usually 6.

If you�re connecting at the maximum for your service, eg 55Mbps or 80Mbps then a higher noise margin is good as it indicates your line can support faster speeds if and when they become available.

If you�re not connecting at the maximum, it suggests your line speed has been reduced to improve stability.

Showing all the stats from the router will allow more informed opinion .

The high noise margin suggests you already get the maximum your current package offers, or DLM has capped the line to try stabilise it.
As mentioned above the target margin is 6dB, anything above that is "spare noise margin", the more the better.
So the cable with the 18dB SNRM is the better of the 2 cables.

Having 6dB as the target margin is no longer the case since the introduction of the new lower 3dB target margin.

That's being a bit picky, and is irrelevant to the OP.
In fact you've worded that like is no longer 6dB, and is now 3dB.
The default is still 6dB. Only specific lines on Huawei cabinets have lower targets, and it's 5, 4, then 3dB, providing the line remains stable at each stage.

Not being picky at all, just giving out the correct information. As 3dB is the new default that is being rolled out to all cabinets including eci ones and the rollout should be completed by the end of August.

I'm on a eci cabinet and have the new 3dB target margin.

Do you have a link to the article saying 3db is the new default target SNR on FTTC please ?

I'm not sure why you've all lost your memories on the subject as it was talked about in length on this forum last year

http://forums.thinkbroadband.com/fibre/4514857-openr...

Nope.

3db isn't the target margin by default.

6db still is, but DLM has the option now to reduce to 5, 4 or 3db if it thinks a line can handle it.

Lee beat me too it ...

If you read through your linked thread again, you'll see that *if* a line is stable DLM will attempt to lower SNR in 1db increments from the default 6, ensuring at each stage that the service stays stable.

Nowhere does it say that 3db is the new default.

In reply to a post by lee111s:

Nope.

3db isn't the target margin by default.

6db still is, but DLM has the option now to reduce to 5, 4 or 3db if it thinks a line can handle it.

the 6dB is not the default anymore as noted by Openreach's SIN document 498 which states that:

1.2.2 VDSL2 noise margins

Currently the default target downstream noise margin is set to 6dB. From March 2017 the target downstream noise margin shall be set to either 3, 4, 5 or 6dB

As you can see it says clearly that from March 2017 the default 6dB will change so that 6dB will no longer be the default.

I work on this stuff every day, 6 is the default, if it weren't, how come when I do a reset it reverts to 6 ??

In reply to a post by Zarjaz:

I work on this stuff every day, 6 is the default, if it weren't, how come when I do a reset it reverts to 6 ??

One of my neighbours had an issue last week and their line was reset and it went straight to 3, so I guess some areas haven't been fully updated yet as I believe the full the rollout will be done by the end of August.

If their line was reset and went straight to 3db, then either the reset didn't go through, or the issue causing the low SNR wasn't resolved.

Any how, us bickering isn't helpful to the OP at all.

I'm not bickering, just giving out up to date information regarding noise margin values, which is the topic of this thread and I wasn't the first person to mention about the 6dB.

Would everyone like some ice cream?

In reply to a post by robertcrowther:

I'm not bickering, just giving out up to date information regarding noise margin values, which is the topic of this thread and I wasn't the first person to mention about the 6dB.

Would everyone like some ice cream?

Zarjaz is an OR engineer. I think he knows what he's on about.

As he's rightly said, the DEFAULT is 6db.

When a circuit is first enabled, the target noise margin is 6db by default. IF DLM believes the line can handle a lower TARGET margin (by looking at error rates, retrains etc, it will attempt to reduce the target margin in 1db increments. That does not mean the default margin for VDSL2 circuits is 3db.

In reply to a post by lee111s:

Zarjaz is an OR engineer. I think he knows what he's on about.

As he's rightly said, the DEFAULT is 6db.

When a circuit is first enabled, the target noise margin is 6db by default. IF DLM believes the line can handle a lower TARGET margin (by looking at error rates, retrains etc, it will attempt to reduce the target margin in 1db increments. That does not mean the default margin for VDSL2 circuits is 3db

From what I've seen out in the field and by what other OR engineers have said is that existing connections will be going through the 5dB, then 4dB and finally 3dB steps, but new connections will be going straight to 3dB and if that's unstable then it will try a higher dB rate.

That's not my experience of it.

The lower target margins are simply an additional tool to DLM's belt in the battle between speed and stability.

3db is not the default target.

Edited by deleted (Mon 10-Jul-17 11:22:58)

In reply to a post by lee111s:

That's not my experience of it.

The lower target margins are simply an additional tool to DLM's belt in the battle between speed and stability.

3db is not the default target.

Maybe that part hasn't rolled out to your area yet, but as far as I know the rollout should be complete by the end of August, so you should see changes by then

https://www.thinkbroadband.com/news/7668-openreach-a...

I know this refers to the original trial ... but nothing has changed.

Changes will only be seen if DLM thinks a line can handle a reduction in target margin. That doesn't mean the default is changing from 6db

You don't seem to get that.

I've said my bit. Adios.

In reply to a post by lee111s:

Changes will only be seen if DLM thinks a line can handle a reduction in target margin. That doesn't mean the default is changing from 6db

You don't seem to get that.

I've said my bit. Adios.

Nice to see that you didn't read the link that Zarjaz posted about the trial. It states that during the trial: The trial involved the Openreach DLM system identifying lines that were stable at a 6dB target noise margin, and then lowering the target noise margin in 1dB steps over an extended period and monitoring the error rates and connection speeds.

Note the words "lowering the target noise margin"

This applies to existing connections with the full rollout and new connections will be placed on 3db to start and raised if the DLM sees that it's not stable.

As yet I've not seen any of the broadband forums post any of the details of the rollout and it's changes from the trial, but I have seen a couple of people post of the BT forum in particular about it now working on eci cabinets like the ones in my area. This does prove that changes have been made since the trial and maybe not everyone is aware of them yet.

The target noise margin and the default target noise margin are two seperate things. No one has denied that lower target margins can be and indeed are being implemented by DLM.

I read the article when it was published, and did again when Z posted the link.

Nowhere does it state the default is 3db for new connections. You're adding 2 and 2 together and coming out with 3

In reply to a post by lee111s:

The target noise margin and the default target noise margin are two seperate things. No one has denied that lower target margins can be and indeed are being implemented by DLM.

I read the article when it was published, and did again when Z posted the link.

Nowhere does it state the default is 3db for new connections. You're adding 2 and 2 together and coming out with 3

As stated in my post, that link refers "ONLY" to the trial and not to the rollout. As I'm sure you are aware changes do happen from a trial to full rollout and I'm only going by what I've seen in the field (with the full rollout) and what I've been told is happening

As nothing has been published, we can only assume (and go from engineers who work on the products ona daily basis) that nothing has changed.

In reply to a post by lee111s:

As nothing has been published, we can only assume (and go from engineers who work on the products ona daily basis) that nothing has changed.

A good lesson for if you're ever in a business meeting. Don't assume anything, always go in with either facts or observations, otherwise you won't be taken seriously and you will end up looking stupid (or even fired)

Why did you not paste that complete paragraph from SIN 498. You conveniently picked the part that suits you.

" the actual value shall be determined by the Dynamic Line Management (DLM) algorithm based on line stability. "

The default is still 6dB. It will remain 6dB.
ECI cabinets are not part of the current lower dB rollout until retransmission is fixed.
Even in areas where this has been rolled out to the Huawei estate, the majority of lines remain on 6dB.
New lines stay on 6dB, and reset lines return to 6dB.

We have dozens of lines uploading stats every minute to here:
https://www.mydslwebstats.co.uk/Container.htm
Find me a single line that started on 3dB, because I can name you 10 that started at 6dB, and have since dropped to 5, 4, then 3, and a few that have stayed at 5, or 4.
The majority remain on 6dB.

Nuff said.

Edited by j0hn83 (Mon 10-Jul-17 13:58:47)

sorry jOhn83 but your information regarding ECI cabinets is incorrect.

I post an image of a screenshot of a connection on a ECI cabinet clearly showing a 3dB

https://postimg.org/image/o68zsvzpj/

Too many people are assuming things

What evidence do you have to show that's not due to a power cut and that user being one of the first to sync?

The current SNRM being 3dB can be caused by many various factors, and does not mean it's a target SNR.

I would politely suggest you are the one assuming things
I can see I'm peeing into the wind here...

In reply to a post by lee111s:

What evidence do you have to show that's not due to a power cut and that user being one of the first to sync?

because with that connection the smarthub reboots every 14 days and it's gone through 2 re-boot cycles already and in a few days it will go through another one and I'm 100% sure it will still be at 3dB

So what did it sync at prior to the 3 db target ? If at 80,000 Kbps already then DLM will do diddly

DSL uptime:
14 Days, 9 Hours 21 Minutes 13 Seconds
Data rate:
20.00 kbps / 80.00 kbps
Maximum data rate:
19999 / 104159
Noise margin:
22.8 / 12.8
Line attenuation:
10
Signal attenuation:
VPI / VCI:
0/38
Modulation:
G_993_2_ANNEX_B
Latency type:
Fast Path
Data sent / received:

This is on an ECI cab also.

prior to the change to 3db this was the line stats for that line and as you can see it has made a difference to the sync speed

https://postimg.org/image/bbcmkzaob/

73 meg at 14db attenuation ?

Heavy cross talk, a fault on the pair, or everyones favourite, a duff set up.







[edit for typo]

Edited by Zarjaz (Mon 10-Jul-17 17:28:57)

heavy cross talk as it was a perfect 80meg connection when the cabinet was new, but as lines got connected to the cabinet the connection speed dropped, but it's good that it's back to full speed again