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Author Topic: Hint of G.fast's future from the NICC Open Forum 2016 event  (Read 3258 times)

ejs

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Hint of G.fast's future from the NICC Open Forum 2016 event
« on: November 15, 2016, 04:05:54 PM »

http://www.niccstandards.org.uk/meetings/forum-2016.cfm

From Kevin Foster's .pptx file, which is the one about DSL:
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Ground breaking work ongoing enabling co-existence of G.fast and VDSL2 in the region up to 17.6MHz which will lead to update to BT ANFP and guidelines

The current ANFP (Access Network Frequency Plan) document only allows G.fast to start from 19MHz, above the frequencies used by VDSL2. Higher frequencies have shorter range. Presumably BT want to use G.fast on the lower frequencies currently used by VDSL2 to improve its reach. VDSL2 is FDD (uses different frequencies for upstream and downstream at the same time) whereas G.fast is TDD (uses the entire spectrum for either upstream or downstream, only one direction at a time), and I believe the current school of thought is that they can't co-exist on the same frequencies. So it'll be interesting to see what they come up with.
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burakkucat

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Re: Hint of G.fast's future from the NICC Open Forum 2016 event
« Reply #1 on: November 15, 2016, 06:15:00 PM »

VDSL2 is FDD (uses different frequencies for upstream and downstream at the same time) whereas G.fast is TDD (uses the entire spectrum for either upstream or downstream, only one direction at a time), and I believe the current school of thought is that they can't co-exist on the same frequencies.

Indeed.

Quote
So it'll be interesting to see what they come up with.

I, too, will be following the developments with interest.
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ejs

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Re: Hint of G.fast's future from the NICC Open Forum 2016 event
« Reply #2 on: April 29, 2017, 09:33:29 AM »

Apparently Openreach will be doing some sort of proof-of-concept FTTC and G.fast "Spectrum Refarming" trial from 11 May 2017 in All Hallows.
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burakkucat

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Re: Hint of G.fast's future from the NICC Open Forum 2016 event
« Reply #3 on: April 29, 2017, 04:03:09 PM »

. . . from 11 May 2017 in All Hallows.

Would that be the All Hallows on the north Kent cost, Thames estuary?
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ejs

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Re: Hint of G.fast's future from the NICC Open Forum 2016 event
« Reply #4 on: April 29, 2017, 04:29:20 PM »

I don't actually know, nor do I have any further details.
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les-70

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Re: Hint of G.fast's future from the NICC Open Forum 2016 event
« Reply #5 on: April 29, 2017, 04:56:32 PM »

  I just hope that BT's G.fast intention of having the fast connections go faster does not lead to the slow going slower.  One might reasonably have hoped that reducing cross talk for the slow connections would be a priority.
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ejs

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Re: Hint of G.fast's future from the NICC Open Forum 2016 event
« Reply #6 on: April 29, 2017, 05:30:43 PM »

It occurred to me that G.fast could possibly use the VDSL2 frequencies in a similar manner to how VDSL2 uses the ADSL2+ frequencies. As in, G.fast downstream on the VDSL2 downstream bands, and G.fast upstream on the VDSL2 upstream bands. Although the on/off nature of the G.fast TDD transmissions might still pose a problem for VDSL2.

@les-70
But crosstalk is less of a problem for the slower connections which can only use lower frequencies. Much like how crosstalk isn't a big problem for ADSL connections.
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Chrysalis

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Re: Hint of G.fast's future from the NICC Open Forum 2016 event
« Reply #7 on: April 29, 2017, 05:35:43 PM »

yeah this is bad news for vdsl, as one could have expected crosstalk to decrease on vdsl with g.fast takeup, but if they going to use the vdsl frequencies instead it will remain, may still get worse or better depending on power masking but I would expect by only a marginal amount.

ejs based on most QLN graphs I seen. crosstalk is worst on the lower vdsl tones.

A neighbour of mine reckons he syncs about 2mbit higher on adsl now compared to 3 years ago, which could be well be down to less adsl crosstalk.  Thats 7mbit vs his previous of 5mbit so a decent %.

Also if you look at some adsl2+ snr graphs, there was sometimes a noticeable jump in the adsl2+ range vs the adsl1 range, probably due to crosstalk from adsl1 lines.  I think kitz has mentioned this as well on here.
« Last Edit: April 29, 2017, 05:39:49 PM by Chrysalis »
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ejs

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Re: Hint of G.fast's future from the NICC Open Forum 2016 event
« Reply #8 on: April 29, 2017, 05:49:02 PM »

ejs based on most QLN graphs I seen. crosstalk is worst on the lower vdsl tones.

Have you taken into account that the signal will be stronger on the lower tones? Due to higher frequencies being attenuated more. The noise levels may well be higher on the lower frequencies, but the relative impact, on the signal, will be lower.
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WWWombat

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Re: Hint of G.fast's future from the NICC Open Forum 2016 event
« Reply #9 on: April 29, 2017, 06:52:40 PM »

It occurred to me that G.fast could possibly use the VDSL2 frequencies in a similar manner to how VDSL2 uses the ADSL2+ frequencies. As in, G.fast downstream on the VDSL2 downstream bands, and G.fast upstream on the VDSL2 upstream bands. Although the on/off nature of the G.fast TDD transmissions might still pose a problem for VDSL2.

At first, I thought the reuse would be like the way VDSL2 has power masks for ADSL2+ ... when further from the exchange, the higher ADSL2+ frequencies can be re-allocated to VDSL2.

But a few extra seconds of thought made me realise that the same dropoff in usage wouldn't happen for G.Fast, when being targeted close to the cabinet.

Your suggestion makes sense, though. NEXT would likely be catastrophic, so restricting G.Fast to existing directions would make sense.

On top of this, G.Fast adds discontinuous transmission functionality, so that it only transmits when needed. If they could make use of that feature such that the VDSL2 frequencies only got used when all the other tones were full, that would minimise interference.
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WWWombat

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Re: Hint of G.fast's future from the NICC Open Forum 2016 event
« Reply #10 on: April 29, 2017, 06:56:43 PM »

Would that be the All Hallows on the north Kent cost, Thames estuary?

That could be true - Gillingham is one of the early trial locations.

An interesting fact ... Allhallows exchange has 7 existing FTTC cabinets. But every single one was BDUK subsidised. A hint that BDUK cabinets are not necessarily excluded...
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niemand

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Re: Hint of G.fast's future from the NICC Open Forum 2016 event
« Reply #11 on: May 02, 2017, 01:29:06 PM »

Naturally. The main costs, power and fibre, have been dealt with. Some BDUK cabinets will inevitably be in the group that present the cheapest way to reach the coverage target.
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