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Author Topic: Long Reach VDSL2 details  (Read 1297 times)

ejs

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Long Reach VDSL2 details
« on: May 14, 2017, 08:38:18 PM »

There are a few more details about the proposed Long Reach VDSL2 (LR-VDSL) in the recently published Openreach consultation document.

The most interesting thing I learned was that it is not going to be merely using existing VDSL2 specifications, there are new amendments to the G.993.2 and G.993.5 ITU documents expected to be approved in late 2017 or 2018.
Quote
Changes to the VDSL protocol to enable it to synchronise on long loops and to ensure VDSL always outperforms ADSL2+ from the exchange.

This means the current LR-VDSL trials are not quite using the same technology as what it will ultimately use.

Apparently most vectoring ready modems should be firmware upgradeable to support the new LR-VDSL changes.

I'm assuming that reference to ADSL2+ also includes outperforming ADSL2 from the exchange.
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WWWombat

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Re: Long Reach VDSL2 details
« Reply #1 on: May 14, 2017, 09:18:53 PM »

This means the current LR-VDSL trials are not quite using the same technology as what it will ultimately use.

I recall that Openreach showed graphs of the potential improvements - and they had 2 variants of LR-VDSL. The 2nd, better, variant was theoretical ... so I guess that related to future spec changes.

I'm trying to figure how to ever guarantee better performance than exchange-based ADSL2+. Presumably you have to at least emulate ADSL2+ in the lower bands, or (at the very least) mimic the transmission power and bit allocation rules. That probably affects power masks downstream, and UPBO upstream.
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aesmith

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Re: Long Reach VDSL2 details
« Reply #2 on: May 19, 2017, 08:01:46 PM »

I'm trying to figure how to ever guarantee better performance than exchange-based ADSL2+.

Are they trying to?   I thought the idea might be for BT to be able to decommission all DSL from the exchanges, and serve everything from the cabinets.
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ejs

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Re: Long Reach VDSL2 details
« Reply #3 on: May 19, 2017, 09:07:32 PM »

They need to migrate everyone on the LR-VDSL cabinet to FTTC (either LR-VDSL or ordinary), otherwise the LR-VDSL signals would adversely affect the ADSL signals from the exchange. So if they are going to do mandatory migrations for everyone on the cabinet, they don't want anyone to end up with lower speeds. The consultation document is also about the particulars of organising the migrations with the CPs.
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WWWombat

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Re: Long Reach VDSL2 details
« Reply #4 on: May 20, 2017, 01:11:54 PM »

I thought the idea might be for BT to be able to decommission all DSL from the exchanges, and serve everything from the cabinets.

I don't think that BT has enough ports in the cabinets for this to happen generally across the country. And, in any case, BT don't own all the DSL equipment in the exchanges.

When BT want to provide LR-VDSL, it will have to be targeted at specific cabinets - and those specific cabinets will have to have enough ports to migrate all ADSL.

Passing thought: I get a feeling that we've recently seen a lot more Huawei-288 cabinets, relative to the smaller ones, than was seen in the commercial rollout. I wonder if this kind of migration has already been budgeted for?
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Ronski

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Re: Long Reach VDSL2 details
« Reply #5 on: May 24, 2017, 07:35:35 PM »

Passing thought: I get a feeling that we've recently seen a lot more Huawei-288 cabinets, relative to the smaller ones, than was seen in the commercial rollout. I wonder if this kind of migration has already been budgeted for?

All the second cabs around here have been 288 port Huawei cabs, be great to get ADSL from the cab, pretty much everyone will benefit but a big hurdle is LLU
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ejs

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Re: Long Reach VDSL2 details
« Reply #6 on: May 25, 2017, 03:30:11 PM »

This won't be ADSLx from the cab.

A couple of years ago, they must have considered using ADSL2+ from the cabinet, and it was added to BT SIN 498, but they must have changed their minds since then.
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