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Openreach idiotic DLM

Posts: 33
Thanks: 6
Fixes: 1
Registered: ‎11-10-2018

Openreach idiotic DLM

I am about 80m from the cabinet and normally sync at 80/20 with typical CRC error counts of 1 per 2 days downstream (interleaved but that is another long sad story) and 1 per day upstream. 

The day before yesterday my other half noticed the internet was slow for half an hour or so around lunch time. I checked and saw the modem had racked up some 400k CRC errors downstream but had not lost the connection. This has happened that I noticed twice before, last time about 3 months ago. Someone local has some horrible interference source that they seem to use very occasionally. The time before I checked modem stats while the problem was there and saw the upstream had erratically lost 6db of SNR and the downstream was barely above zero. 

The noise source and slow net for half an hour is annoying but I don't expect there is much chance of finding and doing anything about it unless it becomes more regular. 

What is far more annoying is the idiotic openreach DLM system in it's minute wisdom decided some 12+ hours after the last CRC error that my line would be improved by re-syncing at 10% lower speed and keeping it that way for at least 9 and probably more than 14 days. The same thing it did 3 months ago. 

Openreach don't care they have a monopoly and ISPs don't care because no one can escape the openreach monopoly by switching ISP (only by switching to cable or full fibre). 



Seasoned Hero
Posts: 7,649
Thanks: 3,414
Fixes: 237
Registered: ‎30-06-2016

Re: Openreach idiotic DLM

Let's just accept that DLM is but one part of the enormous bodge that is FTTC, introduced to save the cost and time better spent replacing the last few metres of copper with fibre.

In the medium term it will be seen as an enormous waste of time and resources as it is ripped out and replaced by FTTP.  If only the time and effort put into the development and installation of FTTC had, from the start, been put into FTTP then the chances are that by now we would all have access to a faster, more reliable and possibly cheaper service.

The only thing in FTTC's favour is that it did bring faster internet to many homes relatively quickly, but at what cost when a few years later its inadeqacies would become obvious to anyone who thought about it?

Before anyone jumps in and says that FTTC is not a bodge but a clever way of transferring a relatively high level of data over telephone cable then I agree, it is a very clever technique of which DLM is a part. However from a high level system design aspect it is a bodge. Digital data is taken to a local cabinet where it is converted into multi frequency 'broadband' data susceptible to all the limitations of transmitting high frequencies over analogue lines not designed for this purpose for it to be converted back to digital data by the terminating modem. In the meantime the telephone line is still connected to the exchange where no doubt lives another analogue to digital converter which transmits the voice data down an alternative digital data path. 

I guess the positive side is that it keeps a lot of people in employment and makes a lot of money for BT suits and their shareholders.