In reply to a post by ukhardy07:

they pushed your line down to 3db probably (something most ISPs only give to really really massively, living next to the phone exchange stable lines).

Such my 26 dB attenuation, 2km line?

Still maintains 3dB NM after switching off/on!

In reply to a post by XRaySpeX:

Such my 26 dB attenuation, 2km line?

Not many lines can anymore, so you're very lucky. Must have not much cross talk in your cable bundle from other people on ADSL2+.

Problem being I have had over 5Mb sync speed for the last 4 years so lowering it is a pain as I use my internet not just for surfing but downloading via MSDN. The extra 1Mb would speed things up slightly. Will wait on the 10 days see what happens.

BTW I have a billion 7800N would I be able to install that again instead of the Sky router and tweak that?

I may be lucky but I can't believe I'm in some exclusive minority. I live in a town and all my neighbours have BB, mostly BT judging by their SSIDs (I don't advertise my ISP ), so I expect my cable bundle is dense.

When you say ADSL2+, you are including FTTC cuz they also run down the same "last mile" bundle from the cab?

It'd probably just make things worse as DLM wont like that.

Sky DLM now sets a max sync. I will dig out an old post I've written elsewhere explaining DLM.
Essentially sky set a hard max speed which you will be syncing at. You can't manually lower the SNR anymore it doesn't work.

Firstly lets just say again that for your line stats you are getting the right speed.

BE was just being extra nice to you. Every ISP sets a speed based on different criteria so it varies ISP to ISP. On the whole though Sky goes for stability not speed (as do plenty of other mainstream ISPs).

You have to think of it like this. Generally those on BE had an idea what they were doing. BE users were not the average Joe looking for the cheapest deal (on the whole).

People on BE had correct broadband setups and knew what they were doing. Due to this BE could be more leanient.

Now here's a typical sky customer.

1) Lets get the best deal
2) lets plug the router into the extension socket and then plug in a 30m £1.99 DIY extension and connect the internet here.
3) Lets not filter the sky box.

To compensate for all of the above DLM is very strict. It needs to ensure that the users who do everything wrong get a stable connection.

Now here's a DLM post I wrote a while back. It's long but it explains things quite well... SKY DLM is so very different to anything you will be used to on BE. It's very unique but on the whole it works far better (I feel). DLM does ensure stability in every situation.

For the average Joe DLM is good as it requires no intervention and it just works. For the technical wizard it can be a nightmare to get the line how YOU want it. You have to let it go sometimes and accept it...

"Do not get me wrong DLM is quite harsh. It chooses absolute stability over speed. You will see plenty of Sky lines with well over 2000 hours uptime without a single drop out. My friend in Sky was checking uptime on lines and some had over 1 year without a drop out. It's quite staggering how stable and reliable a sky connection is. I have yet to find any ISP out there which is quite as stable.

The Sky routers also NEVER and I mean NEVER crash. I have over 20 devices going into my sky hub and I have never rebooted the router not once. It's a fighter.

Now the way that Sky works is they set a sync rather than a noise margin.
There does exist noise margin figures for lines (but I'll go into that in a minute).

Basically DLM runs for 10 days. During this time it tries out lots of different sync speeds. If the line drops it reduces the sync slightly etc.

DLM aims to find a speed that will mean that the line will never ever drop out. It finds the maximum speed that will not drop out.
DLM then fixes this speed.
In the sky broadband account in MySky you will see this speed.

DLM may set a speed of 10,000Kbps download and 900Kbps upload.

This means that every single time the router is rebooted you sync at 10,000Kbps download and 900Kbps upload. Give or take 1 or 2 Kbps each way.

Now this is the maximum speed that DLM will allow you to go.
Most people (99.99999% of people) sync at this speed whenever they reboot their router.

Here's the complicated part.

Sky set this download speed of 10,000 Kbps.
If you reboot the router at 10am a sync of 10,000 Kbps may give a noise margin of 8db.
If you reboot at 7pm, you also get a sync of 10,000Kbps but the noise margin may only be 4db now.

So noise margin works entirely different on Sky. It's not a case of you sync at the fixed noise margin every time.
On o2, BE and BT. The noise margin is set to say 6db. You sync at 6db every router reboot and the sync changes every reboot.

On Sky.
The sync remains the same every router reboot. It is whatever value DLM sets.
The noise margin can fluctuate each reboot.

Now it gets more confusing.
DLM basically does set a noise margin target as well.
So DLM sets a sync speed of 10,000Kbps.
It also sets a noise margin of 3db.

I sync at 10am and get a sync of 10,000Kbps. My noise margin comes in at say 5db. This is fine.

I sync at 8pm. A sync of 10,000Kbps would give me a noise margin of say 2.5db.
DLM would not allow this. WHY?
It does not allow it as the noise margin is below the 3db that it has set.
In this case you will sync at whatever speed a 3db noise margin would yield. Say 9500 Kbps.

This only occurs on very few lines.
It is usually the lines which DLM pushes to their limits.

Usually the target sync speed is set well above the noise margin.
So if Sky sets a noise margin of 3db.
Usually the sync speed is set to one that never results in a noise margin below say 3.5db.

So everytime the user gets the same sync speed.

So it's a very different approach and hard to get your head around as it's different to every ISP out there.

It does work very well however and it ensures stable speeds 24/7.

Every line will have a different target sync speed. Every line will have a different interleaving depth dependant on how stable it is. A very stable line gets pings of 10ms or less, it works its way upwards from there.

DLM is so specific on each line and every line is configured differently.
There is not this attitude of everyone gets a 7db noise margin.
Pre-DLM when Sky first setup it did give everyone a 7db noise margin and there was none of this fixed sync speed.

It has completely changed in the last few years.

What the fixed sync speed does mean is that if you use DMT or customised router firmware to try and manually lower the noise margin it will not work.

DLM sets a line to a sync of 10,000 Kbps.
If you try to manually lower the noise margin (like you can on BE and o2) nothing will happen. This is because your sync is fixed to 10,000 kbps. DLM makes it physically impossible to go over this fixed speed. If you try to set the SNR to the lowest level manually it'll keep coming back with a 10,000 Kbps sync.

Plenty of lines get speeds set which yield SNRs of 3db - 5db at most resyncs. It's not a case of most lines are 7db or above.

DLM works well in that customers coming from other ISPs often find that FINALLY their broadband connection is stable. Most people don't mind so much loosing a tiny bit of speed if it's stable. Most people get fuming when it's constantly dropping however.

DLM also ensures stability for people with incorrect setups. People using extension sockets, with long poundland extensions etc still get a stable connection."

Long but it explains a lot.

In reply to a post by XRaySpeX:

I may be lucky but I can't believe I'm in some exclusive minority. I live in a town and all my neighbours have BB, mostly BT judging by their SSIDs (I don't advertise my ISP ), so I expect my cable bundle is dense. When you say ADSL2+, you are including FTTC cuz they also run down the same "last mile" bundle from the cab?

Yes, I would now be including FTTCVDSL2 but that wasn't around when I had my personal experience.

In 2010 I was still with BE, and my connection which had been solid for 2 years on 3db margin with 24db attenuation, wouldn't stay connected. I logged for months with RouterStats and with discussions in the BE members forum (and on tbb) the conclusion was cross talk.

In the same time frame BTwholesale had started pushing ISPs to shift customers from IPstream to WBC and regrade to ADSL2+ services. More locally Sky LLU was being heavily marketed to a very extensive VM area - so much that a lot of dishes and a lot of Sky broadband SSID's appeared.

The route my cable takes (and yes I've seen the line plant diagrams on an Openreach eng's laptop) is all through my housing estate, the other end is the exchange. The only "industry" is goes past is a school and a church.

In reply to a post by colinjh:

Problem being I have had over 5Mb sync speed for the last 4 years so lowering it is a pain as I use my internet not just for surfing but downloading via MSDN. The extra 1Mb would speed things up slightly. Will wait on the 10 days see what happens.

In my 12 years of DSL I have never seen sync speeds rise in the first few weeks. In fact Sky was set to 4mbps and it never changed in the 18 months I had it. Whereas my Be connection would fluctuate one or twice in as many months - only marginally mind you.

Sky start you at 4Mbps and work up from there. This is for everyone.

So if you live next to the phone exchange, day one, first ever sync is at 4Mbps. Over the 10 days these customers usually get increased to the full 20+ Mbps. It does work its way up slowly.

One reboot of the router / reset etc is enough to stop DLM increasing the line speed for numerous days though I have found.

What you are suggesting is that everyone gets left on 4Mbps with Sky. Totally untrue. You only stay at 4Mbps if the line can't really handle anymore.

Some lines start off even slower than 4Mbps (the lines which can't handle 4Mbps usually).

Edited by ukhardy07 (Sun 31-Mar-13 16:58:23)

In reply to a post by drummerjohn:

In my 12 years of DSL I have never seen sync speeds rise in the first few weeks.

As Andrew (MrSaffron) has said before, Sky is the only ISP that works this way. They change the sync speed whereas other ISPs and BTwholesale change the SNR margin.