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Author Topic: A few questions about VDSL2.  (Read 820 times)

Weaver

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A few questions about VDSL2.
« on: January 27, 2022, 10:33:44 AM »

I have a few questions about VDSL2.

1. Is there a VDSL2 pilot tone? And does it have data modulated on it sometimes? This is 2 bits for my ADSL2 lines; whatís the VDSL2 equivalent if any?
2. Whatís the name - I simply forget - of the per-tone pattern of permitted tx power used in xDSL: PSD ? spectral mask ? power something ? "profile" too, in VDSL2 and G.Fast ?
3. I believe that the above is all about controlling crosstalk, no? Is the tx-power per tone pattern a general thing which is the same for all the lines of an operator such as for example BT? Or is it tuned for each line to best fit the real crosstalk vulnerability in that location? (And thus get the max tx power you can get away with where there are no active neighbouring vulnerable conductors - a vain hope prob.)
4. Whatís the story with VDSL2 "profiles"?
5. Does G.FAST have similar profiles?
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Reformed

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Re: A few questions about VDSL2.
« Reply #1 on: February 02, 2022, 01:16:51 AM »

'1. Is there a VDSL2 pilot tone?' Yes. It can carry data, modulated at 4-QAM, 2 bits per symbol.
2: Spectral mask - a list of tones to either be power limited or notched out entirely.
3. Nope the mask is to mitigate crosstalk with ADSL alongside avoiding certain frequencies already in use for other things.
4. The first part of the profile is how high the DSL goes bandwidth wise: 8, 17, 30, 35; the second a letter corresponding to a pre-built specification for the quantity, width, and frequency of each upstream and downstream band.
5. Not really. VDSL uses frequency division multiplexing, G.fast uses time division multiplexing so it's less profiles and more allocating time between the two directions.

gt94sss2

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Re: A few questions about VDSL2.
« Reply #2 on: February 02, 2022, 06:39:43 PM »

To add on 3 - the masks are set on a per DSLAM cabinet basis.
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Black Sheep

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Re: A few questions about VDSL2.
« Reply #3 on: February 02, 2022, 07:15:08 PM »

To add on 3 - the masks are set on a per DSLAM cabinet basis.

Indeed so - CAL - Cabinet Assigned Loss.
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Weaver

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Re: A few questions about VDSL2.
« Reply #4 on: February 02, 2022, 08:16:33 PM »

Thank you for the very generous replies. Iíve been reading some of what Kitz wrote on the subject too. I just knew nothing at all about VDSL2, have literally never even seen it, didnít exist round here until a few years back and of course I donít get out.

Looks like I will miss a generation of DSL altogether and, who knows, might see FTTP first.
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Reformed

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Re: A few questions about VDSL2.
« Reply #5 on: February 04, 2022, 02:09:58 PM »

Pleasure. You will indeed miss a couple of generations. A very good thing.

Weaver

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Re: A few questions about VDSL2.
« Reply #6 on: February 04, 2022, 04:35:48 PM »

I would like to have owned a G.Fast modem; have great admiration for the triumph of kitchen-sink design that has gone into the spec and has been realised in full by Openreachís systems. Vectoring and SRA both finally available from OR, because they had no choice. Mind you, making the copper that short is definitely cheating.
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Reformed

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Re: A few questions about VDSL2.
« Reply #7 on: February 04, 2022, 07:03:35 PM »

https://en.wikipedia.org/wiki/100_Gigabit_Ethernet#40GBASE-T might hit the spot to scratch the data over analogue itch.

Weaver

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Re: A few questions about VDSL2.
« Reply #8 on: February 04, 2022, 07:08:53 PM »

Reformd is quite correct. A last hurrah for electrons.
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Reformed

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Re: A few questions about VDSL2.
« Reply #9 on: February 04, 2022, 08:19:33 PM »

Nearly!

https://www.maximummidrange.com/CAB-D-4Q-400-2-5.html

400G over copper which in that case is split 4x100 but can certainly manage a single link. Gotta love that.

Alex Atkin UK

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Re: A few questions about VDSL2.
« Reply #10 on: February 04, 2022, 08:42:16 PM »

https://en.wikipedia.org/wiki/100_Gigabit_Ethernet#40GBASE-T might hit the spot to scratch the data over analogue itch.

Absolute madness, considering how much power 10G-BASE-T uses, I don't want to think how much cooling that would need.

Nearly!

https://www.maximummidrange.com/CAB-D-4Q-400-2-5.html

400G over copper which in that case is split 4x100 but can certainly manage a single link. Gotta love that.

To me DAC doesn't count as its pretty much an extension of the PCB traces into other switches.

Does make you wonder when we'll a point where DAC isn't possible though.
« Last Edit: February 04, 2022, 08:51:06 PM by Alex Atkin UK »
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