DLM line testing example and over-capping

I've been hitting the 18 meg synch cap set on my line profile which previously I could not reach, so my line seems to have improved. Since I was hitting the cap I requested line testing to be re-started. Line was dropped each day at around 2:30 am by DLM, no other drops occurred.

Day 1: 18 mb cap, 6 dB NM (no change from before)
Day 2: 18 mb cap, 3 dB NM
Day 3: 19 mb cap, 3 dB NM
Day 4: 19 mb cap, 6 dB NM (18.6 meg synch, effectively no synch cap)
Day 5: 18 mb cap, 3 dB NM
Day 6: 18 mb cap, 6 dB NM (end of DLM, current speed)

What's interesting is that there was no difference in noise margin between the 19 mb cap @ 6 dB NM and the 18 mb cap @ 6 dB, which supports the theory that output power is reduced when the cap is hit. This doesn't really make sense, since it's the extra noise margin on a line that adds stability, which seems to nullify the point of capping the speed (if stability is indeed Sky's reason for capping).

Since the line was stable throughout the test, I am disappointed that DLM chose to cap at 18 meg when the 19 meg profiles were perfectly stable. Yes, I'm aware that 18 meg speed is good, but I think this test highlights the case of Sky over-capping synch speeds when a line is perfectly capable of attaining a bit more, in this case resulting in 0.6 meg being lost.

In reply to a post by Oliver341:

I've been hitting the 18 meg synch cap set on my line profile which previously I could not reach, so my line seems to have improved. Since I was hitting the cap I requested line testing to be re-started. Line was dropped each day at around 2:30 am by DLM, no other drops occurred.

Day 1: 18 mb cap, 6 dB NM (no change from before)
Day 2: 18 mb cap, 3 dB NM
Day 3: 19 mb cap, 3 dB NM
Day 4: 19 mb cap, 6 dB NM (18.6 meg synch, effectively no synch cap)
Day 5: 18 mb cap, 3 dB NM
Day 6: 18 mb cap, 6 dB NM (end of DLM, current speed)

What's interesting is that there was no difference in noise margin between the 19 mb cap @ 6 dB NM and the 18 mb cap @ 6 dB, which supports the theory that output power is reduced when the cap is hit. This doesn't really make sense, since it's the extra noise margin on a line that adds stability, which seems to nullify the point of capping the speed (if stability is indeed Sky's reason for capping).

Since the line was stable throughout the test, I am disappointed that DLM chose to cap at 18 meg when the 19 meg profiles were perfectly stable. Yes, I'm aware that 18 meg speed is good, but I think this test highlights the case of Sky over-capping synch speeds when a line is perfectly capable of attaining a bit more, in this case resulting in 0.6 meg being lost.

there is crosstalk on adsl also so that policy would help neighbouring lines, but yes it does no good for your line.

Is there a screen you can view that shows the profile?

or is it just logical deductions knowing what profile setting you on?

In reply to a post by Chrysalis:

Is there a screen you can view that shows the profile?

Yeah, in My Sky there is a page that tells you the current line profile speed set by DLM. However, my own page still hasn't updated from the time it ran at around this time last year (18 meg down, 1.3 meg up, same as my current profile following line testing). I have noticed before though that this page isn't always "in synch" with what line profile is in operation, especially when line profiles are set manually by staff.