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Author Topic: 24MB to 75% of the country by 2011.  (Read 6327 times)

kitz

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Re: 24MB to 75% of the country by 2011.
« Reply #15 on: September 30, 2009, 12:00:44 PM »

I was actually told (unofficially) by a member of Plusnet support staff, that to be able to achieve speeds of 20Mbps you would actually have to live in the exchange, and while some of the buildings are quite large I don't think that's gonna fly. 

Deterioration of the line can also have an impact, and theres nothing in place to ensure that a line is maintained to a certain standard so the line is optimised for adsl.

I myself am one of those that could be classed as 'living in the exchange'.   In theory I should easily be able to get 24Mb..  and for a while I did, but my line has slowly deteriorated over the past year to 21.5Mb... and thats with just a 3dB margin.

OK I do appreciate Im lucky to be able to get the higher speeds..  But Im less than 200m from the exchange and to see a deterioration of 2.5Mb is still a hefty chunk.. and my line is vastly under-performing.
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waltergmw

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Re: 24MB to 75% of the country by 2011.
« Reply #16 on: September 30, 2009, 12:07:41 PM »

Really the Nation doesn't deserve a bald Kitz !!!!!!!!!!!!!!

Walter
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Chrysalis

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Re: 24MB to 75% of the country by 2011.
« Reply #17 on: October 11, 2009, 10:49:24 PM »

Here is my thoughts on BT's adsl2+ rollout.  I have a long line on ukonline's LLU service.

BT utilise dynamic line management (DLM) the aim is to keep their support costs down by automating line settings to deal with noise/interference on the line.  My own experience of this was it either didnt react when required or was too sensitive.  DLM potentially could have been good but the major flaws with it I see were the fact it could not be turned off and BT would not easily reset profiles back to 6db.  On 21CN (adsl2+) I expected DLM to stay but a better version of it that was improved based on BT learning from the problems on their adsl max service, the reality was they seemed to copy from sky's poor DLM and the new version is over agressive in reducing synch speed.  Again like the old version isp's cannot overide it they can only adjust the algorithm used.

BT also utilise BRAS IP profiling, this in effect caps line speed to a specific level, ideally just below the synch speed.  The problem with this is the steps between the profiles are too large and that it takes far too long to recover to higher profiles following a low synch.  BT again did not learn from their adsl1 experience and have a horrid BRAS profiling system for adsl2+.  In addition we have no real explanation as to why the system even exists, the excuse was on adsl max it was required because of the ATM backhaul, however BT now utilise a IP backhaul the same as the LLU isp's but have persisted with the BRAS profile system.  My hatred for it stems from the fact I have a line that would resynch in the morning (due to working hour noise bursts) and again at night resulting in what was in affect a 2 tier line, the BRAS profile requiring a 3/5 day wait couldnt keep up and as such when I synched high like in the weekend day times I couldnt fully utilise my line due to a low BRAS profile, basically when I synched high it was rarely in excess of 3/5 days.

So why am I better off on ukonline LLU?

1 - No DLM, manual line management is how I want it, by luck the default line settings were decent for me, 7db and fast path on adsl1.  Now I am on 6db and fast path on adsl2. (not adsl2+).
2 - No BRAS profiling, my line is stable but it does mean if I do have a sudden change of speed such as when doing stuff on my router or during noise bursts (see later) then I immediatly get my speed back when synch speed recovers.
3 - SRA, (seamless rate adaptation).  A brilliant improvement in adsl2/+ that is a godsend for long/noisy lines.  Basically does what DLM was aiming to do but do it properly.  The synch speed will adapt to line conditions without dropping connectivity, it can move the synch speed downwards or upwards.  This allows a line to synch agressively knowing that if noise occurs the line will adapt and synch will remain stable.  The downside of SRA is it seems to be sensitive to router/firmware compatability with the dslam chipset to work properly, I have no idea why BTw are not even attempting to utilise SRA.

To give you an idea of how my line has performed on BTw and ukonline is as follows.

On BTw the few weeks before I moved to LLU I was typically synching at around 5700kbit with a 9db profile on fast path, I would need to manually resynch every 1-5 days tho due to excessive line errors creeping in when bitswapping broke.  I experimented with interleaving which boosted the synch to around 7000kbit but was less stable than fast path, not fully sure why but I think the higher synch was probably part of it.  Bitswapping appeared to work far better on fast path.

After my move to ukonline all noise bursts that were occuring immediatly stopped, this obviously helped a lot.  On adsl1 for a while I was sustaining around 5600-6000kbit for a week or 2 at a time.  Eventually I volunteered for a adsl2 fast path trial and got myself the router to go with it so I could utilise SRA.  This completely transformed my line allowing me to have a aggressive synch and keep stability.

Now in optimal conditions I can synch over 7300kbit and in poor conditions (like in middle of night) at around 6000kbit, SRA will hover the synch between these points, the synch will stay up for weeks/months through thunder storms etc. no problem.  Recently I have started getting noise bursts again but SRA also deals with it fine.

In summary I agree with kitz DLM/PROFILING is whats murdering BT, they persist with auto,ated systems and tech support who refuse to acknowledge faults is dragging people to LLU in droves.
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