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WWWombat:
--- Quote from: ejs on October 08, 2017, 08:12:35 PM ---I don't think what it says in the ANFP document means that those are the only values of CAL.
--- End quote ---
So there could be more than that? By being outside the range 0-52, or by taking values that aren't in 2dB steps?
For a normative section, part B of the ANFP is pretty vague about the range. It clearly mentions the 0-52dB in 2dB steps, but it only actually specifies that range as important for the "critical intersection points" on the graphs, not as a definitive statement of the complete range.
--- Quote from: ejs on October 08, 2017, 08:12:35 PM ---The range and precision of kl0 is defined in ITU-T G.997.1, "The value ranges from 0 to 128 dB in steps of 0.1 dB".
--- End quote ---
Thanks. I guess, then:
- That limits the worthwhile upstream PSD graphs (max 24dB) to be approx 240 in number.
- A maximum of 128dB will be roughly equivalent to 6.4km of 0.5mm copper.
Chrysalis:
--- Quote from: WWWombat on October 08, 2017, 07:15:28 PM ---I guess that then covers my earlier doubts about any differing lengths perhaps occurring in the same bundle. What's your take on the tie pair at the cab?
The first restriction seems strange. Surely VDSL2 only works where upstream and downstream bands are separated anyway, never mind the UPBO tweaks? However, if you did allow overlap, then the ensuing NEXT would be made even worse if you tried to reduce upstream power via UPBO.
The second part is a condition that we obviously meet through the tie pair, if no other part.
I tend to think that most crosstalk happens where power is the highest, and so the electrical field is at its greatest. That would mean FEXT is induced most at the DSLAM (and thus in the tie pairs), and least in the drop wires.
It also means that you'd expect less crosstalk where the tie pairs are shortest.
--- End quote ---
yep and remember what happened to my line when they reordered my tie pairs. Massive change in crosstalk levels.
GigabitEthernet:
I sync at 54997, will I get this? I won't get much more than that.
WWWombat:
--- Quote from: WWWombat on October 06, 2017, 05:36:10 PM ---I'm happy to think I've got a good handle on how UPBO gets configured now.
--- End quote ---
Famous last words, eh?
It seems that UPBO can take two forms, and the one we've been discussing here (and, it appears, that BT uses) is a static model.
There is also a dynamic mode, where the DSLAM can make adjustments to subscribers on the fly. I haven't assimilated the details as yet - there doesn't seem to be much point if BT aren't using it!
Source? There is an interesting document, "Guidelines on the Use of DSL Transmission Systems in the BT Access Network", ND1405 rev 4.1.1.
As a whole, the document covers how different DSL systems meet (or don't meet) the ANFP. Section 6.11 is for VDSL2, and includes information about DPBO, static UPBO and dynamic UPBO.
--- Quote from: Chrysalis on October 09, 2017, 02:57:42 AM ---yep and remember what happened to my line when they reordered my tie pairs. Massive change in crosstalk levels.
--- End quote ---
I don't recall that, but it doesn't surprise me.
Chrysalis:
Check my saga here.
http://forum.kitz.co.uk/index.php/topic,20191.0.html
Sorry for the delay got distracted after starting the reply.
The short story if you dont want to read the thread is that a car flattened my cab, openreach had to redo all the tie pairs and feed new power, after work was done my stats were much more favourable. 10-30mbit increase on attainable for DS.
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