Are the plotting scripts available anywhere? If so, I'll try doing my own plotting.
In the meantime, I wanted to point this out...
I noticed the difference between the 2 graphs as being the location of the "gash" (although I'm not sure everyone has the same idea of which bit is being called the gash!): Orly's gash (or dip) appears to end around tone 250, in the SNR graph (ie top graph), while griff_90's gash appears to finish around tone 500 in the same graph (but second down in their image).
I suspect this is indeed caused by the spectral power mask applied at the cabinet - and that the 2 cabinets have different masks.
The document linked above: BT's VDSL Primer from 2009, shows the masks BT intended using at the time. See pages 31 and 32 (of 66).
The masks may put the top of the gash at 600kHz (for cabinets far from the exchange), up to around 2MHz for those closest the exchange.
So... I bet that Orly's cabinet is further from the exchange than griff_90's.
However... I'm not convinced that this document represents the actual deployment at Openreach today. Some of the screen-grabs here show that BT are using US0 (25kHz - 138kHz) which isn't shown in the band-plan 997 in that document, and the spectral mask makes no allowance for it either. I suspect there are some differences in reality...
On a separate note: this mask is a way in which the E-side distance can still affect the bandwidth you see as a customer; the overall behaviour of VDSL2 isn't *just* dependent on the D-side distance.
Would you be able to expand a little on your comment regarding the E-side affecting the bandwidth?
I have been experiencing some low FTTC speed issues & would like to understand where the issues could be, especially as visiting engineers claim my connection is operating as intended.
My download speeds have been a minimum of 10Mb or so down since the first month's excellent speeds.
Edited by Little_bird (Tue 11-Oct-11 12:27:23)