Kitz Forum
Broadband Related => Broadband Technology => Topic started by: Weaver on January 27, 2022, 10:33:44 AM
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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; what’s the VDSL2 equivalent if any?
2. What’s 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. What’s the story with VDSL2 "profiles"?
5. Does G.FAST have similar profiles?
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'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.
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To add on 3 - the masks are set on a per DSLAM cabinet basis.
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To add on 3 - the masks are set on a per DSLAM cabinet basis.
Indeed so - CAL - Cabinet Assigned Loss.
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Thank you for the very generous replies. I’ve 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, didn’t exist round here until a few years back and of course I don’t get out.
Looks like I will miss a generation of DSL altogether and, who knows, might see FTTP first.
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Pleasure. You will indeed miss a couple of generations. A very good thing.
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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 Openreach’s 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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https://en.wikipedia.org/wiki/100_Gigabit_Ethernet#40GBASE-T might hit the spot to scratch the data over analogue itch.
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Reformd is quite correct. A last hurrah for electrons.
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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.
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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.