FTTC based ADSL2+ from BT Openreach

Does anyone know anything about BT Openreach's plans to deploy ADSL2+ from the cabinet?

According to SIN 498 on BT Openreach's web site (see http://www.sinet.bt.com/sinet/SINs/pdf/498v6p0.pdf), BT are looking at offering ADSL2+ from fibre cabinets. This SIN was only updated in September 2014 with the ADSL2+ specifications to be used when deploying from the cabinet instead of the exchange.

On page 34 of the SIN, BT state: "Cabinet based ADSL2plus is used to provide extended reach beyond what is possible with VDSL2.". This would appear to hold out some hope for those of us on long lines from the cabinet, especially in rural communities outside of villages.

It would seem to make sense to do this, as VDSL2 uses high frequencies that drop off rapidly with cable length. I am 1.6Km from my cabinet and I am wondering whether I would get better performance with VDSL2 or ADSL2+ at this distance?

Any thoughts?

Interesting, I'm 4Kl from the exchange but will only be 385m from the new Cab but a lot in and around our village will benefit from this.
But problem with your link !.

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Welcome to the BT Group site. The page you are looking for is either no longer available or has been moved.

Edit .... it's a copyright problem ..I do not think you can link it .
But I found it ok.

Edited by APTMAN (Sun 05-Oct-14 00:24:54)

Try:
http://www.sinet.bt.com/sinet/SINs/pdf/498v6p0.pdf

In reply to a post by APTMAN:

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In reply to a post by RobertoS:

In reply to a post by APTMAN:

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It's got the
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Well found!

I've wondered why they hadn't planned on using this as an obvious way of helping them meet their USC targets.

However, there is a major fly in the ointment...

VDSL2 has to implement deliberate power backoff over the ADSL and 2+ frequencies, to ensure that FTTC subscribers don't swamp the signal of ADSL subscribers coming from the exchange. This deliberate power reduction of VDSL2 is one reason why FTTC coverage peters out at 2km, while ADSL2+ extends way beyond that.

Using the same thinking, ADSL (incl ADSL2+) transmitted from the cabinet would have to be restricted in an identical way, to ensure that it didn't swamp the ADSL (incl 2+) signals being transmitted from the exchange.

And if it has to be restricted in the same way, doesn't it suffer identical range problems to VDSL2?

The only way around this, and to allow transmission at proper power levels to keep the range, would be to force every subscriber whose lines pass through the same cable bundle to swap to cabinet-based DSL service. This method is used in new Zealand, where they started the ball rolling with ADSL2+ cabinets. The downside to competition is that it effectively forces LLU to be banned (per cabinet) once the VDSL2 cabinet is in place.

At 1.6km, you would probably be borderline, depending very much on the gauge of your copper cable. FTTRN would offer you a solution, as would vectoring.

Edited by deleted (Sun 05-Oct-14 02:01:54)

Having read through the test specifications for GEA over ADSL2plus (in annex B), I get a feel for how they intend the product to work.

1. BT specifies that GEA over ADSL2+ is intended for long lines only, so only specify tests with range options of 2km, 2.5km and 3km.

2. For comparison, the corresponding tests in Annex A (for GEA over FTTC) have range options from 100m to 2.2km.

3. The default line profile in the DSLAM would appear to set maximum speeds of 12Mbps down and 1.5Mbps up.

4. Looks like they want to support multicast too - so presumably aims to deploy TV this way too.

5. Use of PSD masks would be needed, as I described in the earlier post.

They could be trialling this in St Ives Cornwall?

We had a storm and a lightning strike near the exchange in St Ives took out all the phones from an area of Carbis Bay (2 miles away). I was fortunate being on FTTC so maintained my broadband, but talking to neighbours over the 5 days before the phone cable was replaced I found that everyone I knew on their old ADSL router also still had the internet connection!

I challenged a Open Reach engineer on how this was possible and he suggested that ADSL only needed one wire of the pair to function! Sounded most peculiar if this was the case and how lightning could be so selective....

I always wondered why FTTC based ADSL2 had not been considered as an option once the fibre was in and now believe it is.

ADSL and FTTC can survive with just one wire working, hence why people often ask if the phone is working when people moan of slow speeds

Thanks, that's interesting, surprised that the lightning affecting over 100 homes was able to be so selective with a random strike to the road and only take out a single wire, but point taken, the OpenReach guy did know what he was talking about