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Author Topic: ADSL, VDSL2 pedantry  (Read 481 times)

Weaver

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ADSL, VDSL2 pedantry
« on: January 22, 2022, 06:46:34 PM »

Being truly pedantic, as is my wont, I would say that VDSL2 is a type of ADSL. However I suspect that some people would regard them nowadays as being disjoint, no? What do you say? If this thinking is right what should we call ADSL that is not VDSL ? (Considering the ‘mere ADSL’ type of usage, which I frown on, even though I understand it.)
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gt94sss2

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Re: ADSL, VDSL2 pedantry
« Reply #1 on: January 22, 2022, 06:52:14 PM »

I thought that they were called xDSL or DSL with ADSL/VDSL etc being different types of xDSL
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Weaver

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Re: ADSL, VDSL2 pedantry
« Reply #2 on: January 22, 2022, 07:24:10 PM »

I hear you. My thinking is that A stands for asymmetric and VDSL2 is also asymmetric - ie it is not SDSL - and it is definitely DSL so that means that VDSL is a type of ADSL2. But as I said, I believe that some people’s usage doesn’t agree with my pedantic definition. I would say that "ADSL" is not the same thing as "xDSL" because "xDSL" includes SDSL whereas "ADSL" does not.
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meritez

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Re: ADSL, VDSL2 pedantry
« Reply #3 on: January 22, 2022, 07:41:11 PM »

VDSL is Variable, ADSL is Assymetric.

We used to sell a single Symmetric SDSL up until 2016, anyway.

Assymetric :having parts that fail to correspond to one another in shape, size, or arrangement; lacking symmetry.
Variable: able to be changed or adapted.

You can have VDSL with symmetrical upstream and downstream sync, which completely falls out of the definition of assymetric.
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Weaver

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Re: ADSL, VDSL2 pedantry
« Reply #4 on: January 22, 2022, 07:52:57 PM »

Agreed. As things stand, as services are commonly delivered, FTTC/VDSL2 and G.FAST are asymmetric in that their upstream and downstream speeds are different, no?
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burakkucat

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Re: ADSL, VDSL2 pedantry
« Reply #5 on: January 22, 2022, 07:57:24 PM »

My view . . .

ADSL     (ITU-T G.992.1)
ADSL2   (ITU-T G.992.3)
ADSL2+ (ITU-T G.992.5)
VDSL2   (ITU-T G.993.2)

. . . along with HDSL, SDSL, VDSL, etc, etc, (whose ITU-T recommendation numbers that I do not have committed to memory), are all sub-sets of xDSL.

In other words I will use xDSL when the "flavour" of the particular DSL sub-sets is irrelevant.
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burakkucat

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Re: ADSL, VDSL2 pedantry
« Reply #6 on: January 22, 2022, 08:09:07 PM »

VDSL is Variable, . . .

The ITU-T G.993.2 recommendation has the title "Very high speed digital subscriber line transceivers 2 (VDSL2)".

Section four of that recommendation has the definition "VDSL    Very High Speed Digital Subscriber Line".
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j0hn

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Re: ADSL, VDSL2 pedantry
« Reply #7 on: January 22, 2022, 08:42:40 PM »

I would say that VDSL2 is a type of ADSL.

I would disagree with that.
It's a type of DSL, or xDSL, but not a type of ADSL.

VDSL is Variable, ADSL is Assymetric.

They are both variable. The V in VDSL doesn't stand for variable but rather "Very High Speed".
VDSL2 can be both asymmetric or symmetric depending on the profile used.

G.Fast is also a type of xDSL, with the name apparently coming from the ITU-T G series of recommendations/standards.
As in G.9700.
The Fast meaning Fast access to subscriber terminals.
« Last Edit: January 22, 2022, 08:46:45 PM by j0hn »
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Reformed

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Re: ADSL, VDSL2 pedantry
« Reply #8 on: January 23, 2022, 12:28:30 AM »

Agreed. As things stand, as services are commonly delivered, FTTC/VDSL2 and G.FAST are asymmetric in that their upstream and downstream speeds are different, no?

As commonly delivered however all have symmetrical capability.

ADSL is a type of DSL. As is VDSL. As is G.fast. All from the same lineage.

ADSL cannot be symmetrical. VDSL can be through frequency profiles and G.fast can be just by configuring equal time between upstream and down.

Closer to my experience DoCSIS 1 offers a user a share of one 27(rarely), 38 or 50 Mbit (EuroDOCSIS) channel downstream and one 2.25, 4.5 or 9 Mbit channel upstream, from a choice of up to 6 but more commonly 4 channels.

Total RF consumption 6-8 MHz downstream, 3.2 MHz fro. a single modem.

DoCSIS 2 same downstream, upstreams up to 27 Mbit but still only one at once. Downstream unchanged, upstream to 6.4 MHz width with higher order modulations.

DoCSIS 3 - up to 32 downstream channels of 38 or 50 Mbit combined, up to 8 upstreams bonded of up to 27 Mbit each. 32 channels in the UK = 256 MHz of RF. The upstreams in UK 4-6 bonded 6.4 MHz wide channels, 25.6-38.4 MHz. Some bond 8, so 51.2 MHz.

DoCSIS 3.1 - As 3 + 2 * 192 MHz OFDMA delivering 5 Gbit. Also 2 upstream OFDMA channels of up to 96 MHz each, very dependent on how clean the cable network is but 2 Gbit/s of capacity upstream isn't unfeasible.

Fully loading it you're talking a single modem accessing 256 MHz of 3.0 SC-QAM, 1.6Gbit, and bonding that with 384 MHz of OFDM, delivering pre-overheads, while the others mentioned these, 4608 Mbps. Lop 10% for overheads say 5.7 Gbit/s to a single device is feasible. Upstream 2 96 MHz channels would have to partially overlap with the SC-QAM but best case that would run in a mixed mode and 1.5 Gbit is feasible.

4 versions of DoCSIS. Don't think we could call 3.1 a type of 1.0 even though both use SC-QAM carriers still.