A trial has been running looking into whether Openreach can squeeze more speed out of VDSL2 for some lines with no hardware changes in the cabinet or by the customers VDSL2 modem and it seems on Monday 20th March, this limited area trial is set to go national.
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. The monitoring is not new, the Openreach DLM (Dynamic Line Management) is constantly running, the change is that while 6dB is currently the lowest target noise margin modems are told to negotiate the connection at and now for lines that look like they can cope with lower margins without undue numbers of errors lower margins will be allowed. The bonus is thus more download speed without any cost.
It is thought the trial involved some 40,000 lines and we presume Openreach has seen positive results from the trial, we are monitoring what we believe is the trail area but to date have not seen an observable difference, but this may be that the 40,000 lines is swamped by those not in the trial but still in the area we've been monitoring. It may be once we run the Q1/2017 analysis in a couple of weeks we can see some indication of a difference, or it may take many more months once things go national.
The way the target noise margin's work mean that if your line is stable, then it does not matter if you connect at 21,232 Kbps or 44,536 Kbps its all about if the DLM thinks the line is stable and suitable for trying a lower margin, what will differ is the amount of benefit different people see and many people may see no change at all. Its important to emphasis that the drop is in 1dB steps down to a minimum of 3dB, and the margin may return back to the 6dB level if things do not look stable.
Sweating the assets to squeeze what might be just be a 2 Mbps average increase seems like a lot of work for little extra speed, but for individuals it might be worth much more speed, and given that across the UK if most users getting 24 Mbps were to see speeds jump to 30 Mbps this could mean that models on performance versus distance would have to change and a 6 Mbps jump for lines in the 1km long region would be worth 0.6 percentage points to the UK superfast total. CAUTION Don't take the 0.6 change as been what we expect from the roll-out, it is just an illustrative figure and we will only change our model if we see a significant change, in the past monitoring experience against our model was more difficult but since Autumn 2016 we have automated this so we can keep a better eye on how all the various changes are affecting the model we use.
Update 7pm While the trial is moving national, it is not happening overnight, but will be done in phases. The phasing is to allow Openreach and the broadband providers to assess how things are progressing. The phased roll-out should complete by September.