Why DLM falls short of the mark ...

[snadge]

After noticing that DLM seems to land users sync rates slightly lower than what the line can truly perform (10-20%), I have been tooing and froing with Sky Support via email discussing the DLM process and also been talking to someone else who used to be a BTo engineer, after some discussion it appears that we may have found out why this happens, it also explains why users get the same 7db default Noise Margin on each sync rate, e.g. DLM ending on 16,000k / 7db on a 21db line capable of 20Mb - then when calling SKY to get line uncapped get 19,999k / 7db (same 7db NM but extra 4Mb in speed)... same happened to me, four of my friends and countless other new members (just for info: not all were 'complaining' customers either but many were users helped through the sign up and DLM process who ended up with same pattern of results, and ive not seen one of them get the correct speed for their line yet!).

It turns out that its probably the Power Management Module in the ASSIA software that controls DLM - this 'dynamically' tries to optimize energy consumption by keeping it as low as possible (but supposed to do so without sacrificing speed) and is probably set to use a low overall Power Output, we have witnessed this on one line already whereby the Power Output never went above 10dBm (10mW of energy) during the 10 days DLM - Power Output on the line it was witnessed on for ADSL2+ should have typically been 18dBm (64mW of energy), because the Output Power is less then the Signal-to-Noise Ratio is lower and attainable speeds are lower, so arriving at the default SNR Margin of 7db results in sync rate lower than what the line is capable of - however, when you call SKY to get it un-capped it must be switched to the proper/max Power Output for the line and therefore the SNR increases and when you arrive at 7db SNR Margin on the higher Power Output level the sync rate will be higher (the correct and max rate for the line).

Sky told me that DLM can set lower sync rates without raising the Noise Margin and this is how it does it, by dynamically adjusting Power Output on the line.

Output Power (in Decibels) / Energy Consumption
0dBm = 1mW (one thousandth of a watt)
3dBm = 2mW
6dBm = 4mW
9dBm = 8mW
10dBm = 10mW
12dBm = 16mW
15dBm = 32mW
18dBm = 64mW
26dBm = 400mW
you can see the trend here....

as you can see, using the line I mentioned above as an example, SKY would save a fortune in energy costs if DLM tightly managed lines energy consumption in this manner, the line above which hit a max of 13Mb sync rate once DLM finished would use about 5-6 times (just over 80%) less energy on that sync rate when using 10dBm as the output power instead of 18dBm - but, after calling SKY the user now has 17.7Mb with 18dBm Output Power on the line, increasing his speed to the proper speed for the line whilst still holding a 7db SNR Margin, but this means SKY are saving less money in the long run.

As you can see when Output Power increases by 3db it DOUBLES the amount of energy used, so its not surprising that SKY have chosen to keep this as minimal as possible, even if it means shaving a bit of the speed from the customers line, in example above a reduction of speed by roughly 20% (which 99% of customers will not notice) reduced energy consumption by just over 80% (10mW instead of 64mW), if SKY apply this to its entire LLu customer base (as it does) they stand to save a hell of a lot of money, figures quoted by ASSIA for their default setup are roughly 3kWh per line which is at worst case about 40p per year, times that by 3 million customers and you have a saving of 1.2 million pounds per year - but judging from whats going on with SKY's implementation of the software it would appear SKY have "turned up the savings knob" a bit in an attempt to save even more money, and quite a bit judging from the math.

Like I already mention, 99% of customers would not notice this 10-20% speed decrease, therefore SKY will be more than happy to amend the speeds for those that call because it stands to be a tiny percentage of its customer base and therefore have little impact on their overall yearly savings, but whether the legalities of SKY doing this are proper Iam unsure.

I would like to thank David and especially Mr Slant for his help in shedding light on this matter.

[NewsreadeR]

Interesting, Sky are a Carbon Neutral company, so they should be commended for saving so much energy.

For those that are unhappy, like you say Sky can adjust their line etc

I wonder how many other ISPs do similar and save so much energy?

So in my case, when my sync is at 8meg but produces loads of errors, does this mean that Sky using less power is causing those errors?

Or is it the fact my line is very poor?

And if Sky increased the power on my line, would it get a better sync?

I have a rock steady connection as it is at approx 7meg but I know if it is set higher, then it goes off on one.

In the meantime, have a watch of this great advert!

[NewsreadeR]

I just read on the official forum...

Edit2 - I think for ADSL connections all Sky are really bothered about is whether you can get VoD like Anytime+. The BT Openreach fibre products have multicast coming so the holy grail for Sky here is no dish installs - saves a fortune in installer fees and service calls.

and this

someone on SkyUser said DLM was optimized for VOD

I don't think there has every been any denial to this by Sky, since we published the following back in 2008

Why is this DLM happening?

DLM is being used to stabilise the line quality between the router and the DSLAM in the BT exchange. The reasons for this can be many, but it is often to condition lines to be able to support data that is not tolerant of line errors and router re-syncs. Examples would include VOIP and Streaming Video, there are others too. Generally, web browsing, email, file transfer and general downloads are not noticeably affected by line errors (that are corrected by the line protocols) and so may have existed unnoticed previously.

What Is DLM? Everything you need to know.

I understand what you are saying, and your arguement, but in all reality, if your line is completely stable, and you can watch TV on demand, stream videos etc is that really such a bad thing?

I know someone who works at Sky and will forward this thread to him, to see if it is in anyway possible that what you say is Sky's overall objective, ie to save money.

I have a feeling it is for the objective of potentially selling movies / rentals of content on demand, which is what we have always understood.

ie It is pointless having the highest possible speed, if you can't watch stuff on demand, thus meaning Sky cannot potentionally get extra money off you for doing so.

[thomasjc1]

very interesting read snadge makes total sense

[indefatigable]

Whilst increasing the power on the line might be a result of the manual configuration, I can tell you that there are no settings available to any 1st Tier or CST agents that allow them to manually configure the power output. The settings that can be changed, as you have mentioned, refer to the max delays and line symbols. Configured correctly, these can sometimes allow higher speeds. It is not recommended for many lines, but we will do it at a request.

Also, I notice you are on the Sky Help forum as well, and can see the information put up by Mr Slant. This is one persons suggestion, and whilst it is logical, does not necessarily make it true.

As I said, increased power output is a side effect, not the reason for the increases.

Until someone higher up from Sky decides to release full details about how DLM works, everything is speculation. However as I make these adjustments on a daily basis, I'll say I know a bit more about it than any Non-Sky employee.

Namaste!!!!

[gymno]

just to say, i'm one of those that had a big jump in sync speed during dlm (16381kbps - 19995kbps) without the noise margin changing (7.2db).

and that's with an attenuation of 22.5db, so dlm doesn't always fall short.

[NewsreadeR]

Sky told me that DLM can set lower sync rates without raising the Noise Margin and this is how it does it, by dynamically adjusting Power Output on the line.

Was it definitely Sky?

According to this page,

DSL Expresse Software - ASSIA

The Power Management module helps significantly reduce DSLAM energy costs without compromising speed and reliability.

Is an optional extra, but according to some people I have spoken with, Sky have not actually got this module anyway, which would completely blow your first post and theory out of the water.

Obviously I have no proof, and what I say could be hearsay, but by the same token, so could your first post also be hearsay.

Someone has already posted evidence to the contrary.

If I manage to find out anything else, I will update this thread.

[Scubbie]

Taking into account the Noise Margin differences, Sky matches other ISPs quite well for speed.

By this I mean that if another ISP were to use 7dB on the same line, then the speeds would be the same. Some ISPs do use a higher Noise Margin than Sky.

With a full 'up to' 24mb ADSL2+ broadband, I doubt if the average connection speed would be significantly faster. Since the average for Sky is around 7.8mb, there will always be a significant number who will never appreciate an 'up to' 24mb broadband supplier anyway.

The other thing, it isn't just how much power is consumed, but also what the tolerances are for BTO's ageing copper or copper coated aluminium cables. Pushing too much current could cause more components to burn out more quickly between the telephone exchange and your home.

If speed is so important, consider another provider whom can supply a bonded ADSL2+ connection. This would provide you with double the download and upload connection, but would cost as much as £65 per month (Be's current price).

LINE BONDING

You can double your speed by bonding two lines at your exchange
Up to 44 meg download
Up to 5 meg upload
Unlimited usage
1 static IP address (can upgrade to up to 14 static IPs)

First 3 months free plus free connection with code: LINEBONDING3

£65.00 /month 12 months contract

Don't forget that you will also need to pay two sets of line rental on top of the £65. Of course you are also subject to Be's T&C and FUP.

[Shonk]

Doesnt seem to be a problem on my line
sky are pumping out 20.3db

DriverVersion = 1.75
APIVersion = GS_API_648
DspFirmwareVersion = E.25.41.55 A
RemoteChipVender = GSPN
Linkuptime = 14 day 22 hr 46 min 38 sec
TxBitRate = 1216000
RxBitRate = 19305628
AnnexType = AnnexA
CodeTypeStatus = AnnexA
InterleaveDpDn = 1
InterleaveDpUp = 1
RSCorrectedErrorsDn = 0
RSUnCorrectedErrorsDn = 376
RSCorrectedErrorsUp = 0
RSUnCorrectedErrorsUp = 77
BisDelayDn = 0.25
BisDelayUp = 0.25
LocalSNRMargin = 12.15 dB
LocalLineAttn = 18.5 dB
INPup = 0.00
INPdown = 0.00
LocalTxPower = 8.4 dB
RemoteTxPower = 20.3 dB
RemoteLineAttn = 5.5 dB
RemoteSNRMargin = 9.5 dB

[IWasNotTheEnemy]

Something missed from the OP...

If you get Sky to uncap your line and you reboot first thing in the morning you'll get a faster connection speed at 7dB then if you were to reboot in the evening - SNR doesn't change, speed does