There are of course three different power masks, anyone know at what distance from the exchange these take effect? Asking as can then do something like look at the Huawei cabinets and split them into the three power masks to see if any difference.
Actually, there are more masks than that. There is one separate mask for every valid value of "CAL" (Cabinet assigned loss).
NICC's ND1602 (found here
) specifies the mask in appendix B. Unfortunately, it uses a table and a few formulae to actually specify the mask, so it is hard to see.
It then goes on to say:
The reason for the very long list of frequencies in column one is that the entered values ensure the functions are calculated at all the critical intersection points of the columns for a wide range of values of CAL (0 to 52 dB in steps of 2 dB).
I take that to mean there are 27 different masks.
The graph in the document
shows what the mask looks like for 6 of the 27 masks.
CAL (Cabinet Assigned Loss) is the same as the insertion loss measured at 300kHz ... which is the same thing that is seen as attenuation back in plain ADSL.
For BT's standard 0.5mm copper, that IL is 10dB per km. So a CAL of 10 means the cabinet is roughly 1km from the exchange, line length. Stepping CAL by 2dB means there is a new mask for every 200m or so.
Of course, we know that cables tend to leave the exchange in a narrower gauge, to fit into the ducts. As they start to separate out in different directions, they are jointed to wider gauge cables. Physical distances, therefore, will tend to be a little less.
What impact does the mask have on speed?
I've always maintained that the mask has the biggest impact on the middle values of CAL, say values 20-30.
Looking at the graph above, if CAL=0 (ie cabinet within 100m of the exchange), there is no extra masking, so no slowdown. If CAL=50, the mask only applies to the 200-500kHz spectrum; the other 1.7MHz isn't masked ... so slowdown is minimised.
I recently found an old, but interesting, article on "The art of Spectral Management
Downstream power back-off for VDSL2". This describes what and why we have the PSD masks, and it also graphs the impact ... In this case, it has examples of cabs sited at 0km, 1.5km, 2.5km and 3.5km.
We don't know that TNO used the same mask as BT, and they're unlikely to use the same cable, so the results aren't fully comparable, but give a flavour.