Kitz Forum
Broadband Related => Broadband Technology => Topic started by: ejs 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.
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.
-
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.
-
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.
-
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.
-
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?
-
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
-
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.
-
I found some estimated numbers for LR-VDSL:
- 100,000 - 250,000 lines
- 4500 - 8500 cabinets
- requiring migrations for 0.5 - 1.2 million lines (presumably this is migrating all the ADSL lines on a cabinet serving LR-VDSL to FTTC, LR or normal VDSL2 depending on the length of each D-side line)
LR-VDSL also means that those 4500 - 8500 cabinets will have vectoring.
-
So something like 5-10% of all cabinets are impacted, and 3-5% of all lines need migrating off ADSL, to target LR improvements on 1% of lines.
I wonder how many of those cabinets will need upgrading to have sufficient capacity for all the migrations.
-
For those following along at home the ITU amendment approval process is grinding forward slowly:
G.993.2 (2015) Amd.3 - Very high speed digital subscriber line transceivers 2 (VDSL2) - Amendment 3 (http://www.itu.int/ITU-T/aap/AAPRecDetails.aspx?AAPSeqNo=7890)
G.993.5 (2015) Amd.2 - Self-FEXT cancellation (vectoring) for use with VDSL2 transceivers: Amendment 2 (http://www.itu.int/ITU-T/aap/AAPRecDetails.aspx?AAPSeqNo=7891)
-
It probably looks like Openreach won't be using much Long Reach VDSL2 now anyway:
From: http://www.offta.org.uk/updates/otaupdate2017November.htm
CFPCG (Copper & Fibre Products Commercial Group)
Following the industry consultation Openreach announced that they were not pursuing Long Reach VDSL as a solution to USO for broadband. It was recognised that the impact on CP's would be both potentially complex and costly.
I'm assuming that not pursuing it for the USO indicates that they won't be using it much at all.
-
Basically shot down because it meant Sky and TalkTalk couldn't sell cheap ADSL on those cabinets. LLU ADSL is serious business, it's what people are crying out for.
-
It probably looks like Openreach won't be using much Long Reach VDSL2 now anyway:
I hadn't seen it stated in as formal a place as the OTA before, but it does look like the death of LR-VDSL. There doesn't even seem to be any conditional statements, like it is being considered for exchanges where no LLU is in place.
I'm assuming that not pursuing it for the USO indicates that they won't be using it much at all.
That's what I infer.
As LR-VDSL was one of the technologies that BT intended to use in its offer to meet the USO (funded via wholesale top-up charges), I'd also expect that offer is now defunct too. At the very least, it would need a re-plan and a new budget.
It also looked like that offer was dead for the same reason as LR-VDSL: interference from LLU operators, presumably unwilling to pay the wholesale charge or perhaps feeling that non-BT-based suppliers won't chip in. But I vaguely recall BT touting it again recently, so perhaps they are still pursuing it in a different form.
At the very least, however, it must be infuriating to not be able to help those customers on non-LLU exchanges because of demands by LLU operators that aren't willing to take on anything loss-inducing. Yet Ofcom clings to hope.