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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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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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

Most likely most people lost both wires in their pair and this person was the lucky one

I have a family member who currently gets less than 1mbps over ADSL. We understand the lines in their village are aluminium, which I believe is a fair bit of the problem.

The BT checker rates their line as "ADSL Max Up to 1 -- 0.75 to 2.5 Available".

Reports from other villages in similar circumstances suggest that VDSL is not operating very reliably, and speeds are small fraction of 40mbps.

Is it likely that this new ADSL service would be better for them than VDSL?

Appreciate any advice.

cheers, Martin

IF it becomes available then largely depends how long the line is from the cabinet

Do you mean a short line is better for VDSL, and longer for ADSL? I guess you can't mean the other way around?

So, where is the cutover likely to be, in terms of line speed or attenuation or SNR? Again - specifically in relation to aluminium lines from cabinet to home.

cheers, Martin

In reply to a post by MartinP99:

Do you mean a short line is better for VDSL, and longer for ADSL? I guess you can't mean the other way around?

So, where is the cutover likely to be, in terms of line speed or attenuation or SNR? Again - specifically in relation to aluminium lines from cabinet to home.

cheers, Martin

Both service operate best on shorter line but ADSL can operate better at a longer distance than VDSL....

This is because VDSL uses higher frequencies than ADSL and "evaporate" quicker (if you like) than the lower frequencies of ADSL.

To answer your question "will ADSL work better than VDSL" yes it will but always depends on line length from the cabinet.

Thanks. Given my question was specifically in relation to aluminium lines, can I confirm the answer is also in relation to aluminium lines?

Thanks, Martin

In reply to a post by MartinP99:

Thanks. Given my question was specifically in relation to aluminium lines, can I confirm the answer is also in relation to aluminium lines?

Thanks, Martin

Yes, ADSL will work better over aluminium lines, and considering your current sync rate I would be shocked if that didn't at least triple.

Regards.
Matt

Given that we know nothing about the distance from cabinet to house, it is hard to say what the impact of putting an FTTC cabinet into the village would be.

And because we don't know the distance between exchange and cabinet, we can't know whether cabinet-based ADSL (or 2+) is likely to offer any improvement over cabinet-based VDSL2.

Getting an accurate answer right now will be impossible anyway, because we know very little about what BT intends to do; all we have seen so far is the testing process that they will use for the customer-end modems. The best we can do is speculate wildly.

Finally, in terms of the aluminium, that is pretty hard to gauge. Like copper, speeds also depend on the diameter of the aluminium, not just the length. It also depends what proportion of the length is done in aluminium; it may be partly copper.

vdsl does also use adsl frequencies , so yes it does use higher frequencies but it still uses low frequencies as well.

From what I see the main reason why vdsl is bad at very long distances is the adsl power cutback.

In reply to a post by Chrysalis:

vdsl does also use adsl frequencies , so yes it does use higher frequencies but it still uses low frequencies as well.

From what I see the main reason why vdsl is bad at very long distances is the adsl power cutback.

So if I'm correct you mean the output power of VDSL is low compared to ADSL as it would kills signals on VDSL hence it not having a greater reach.

Which would also mean they would maybe reduce power output of ADSL2+ from an NGA as it may interfere with VDSL signals.

As mentioned previously there's not really much to speak of at the moment as not much detail has been released.

Though a question on my lips is would the ADSL DSLAM be completely separate to VDSL DSLAM or would it be the same equipment with a dual mode activated.

And am I correct in saying that only non LLU providers would be able to use the service if enabled and also would it be active in selected areas or would it be available everywhere VDSL was.

The idea would to use the same FTTC DSLAM.
The service would be availability to any CP that takes the openreach GEA service

I thought as much...

Well its a great idea anyway,

in my area where the cabinet is about 3.7km from the exchange by line length, the entire adsl1 region has almost no vdsl bitloading due to heavy power cutback to protect adsl services.

I agree I cannot be sure if it would be as good on vdsl due to lack of live data.

Since any vdsl modem I have seen is BC with adsl, I assume is the same for vdsl dslams.

Yeah probably LLU is probably a no go with cabinet based adsl services. Although LLU providers can still use their backhaul so still would be cheap backhaul costs for them.

Edited by Chrysalis (Mon 06-Oct-14 18:22:01)

Well its something we will find out as it unveils I suppose.

In reply to a post by Chrysalis:

in my area where the cabinet is about 3.7km from the exchange by line length, the entire adsl1 region has almost no vdsl bitloading due to heavy power cutback to protect adsl services.

What about the ADSL2+ region (1.1-2.2MHz)?

I just checked here, and was quite surprised. The cabinet is around 1.2 - 1.5km from the exchange, depending on the route used.

Judging by my SNR/tone graph, tone 320 gets the minimum power, and full power is restored by tone 375.

That's quite a short distance, so I guess it tells us that the copper between exchange & cabinet is quite thin.

For comparison, my old house was 1km from the exchange, and the minimum power was at tone 480 there.

the start of the adsl2+ region is part of the cutback I think to about tone 300-350. But by that point my signal is no longer able to do full 15 bits per tone, the power cutback is on the lowest tones. On my line its taking at least 15mbit attainable sync off.

Edited by Chrysalis (Tue 07-Oct-14 14:30:36)

In reply to a post by Chrysalis:

On my line its taking at least 15mbit attainable sync off.

I've never tried working that out for my line...

Apart from the cutback, my maximum bit-loading is 13 over a very wide plateau (tone 65 through to 535). The cutback dip is from tone 90 through to 375, and drops down to 4 bits, making (almost) a nice triangle.

I make it that it has lost around 1,300 bits because of power cutback, which I reckon to be worth just over 5Mbps.

As a cross-check, I reckon I can fit 16 triangles of that size over the downstream bit-loading graph, and 1/16th of 80Mbps is indeed 5Mbps.

The shape of my cutback matches the diagram in part B of the ANFP, for the line labelled "CAL=30". That happens to be the middle level of the CAL values.

Most theoretical speed-distance graphs suggest that you'd get around 15Mbps at 2km; I'd guess that ADSL2+ would lose an identical amount of speed if it were sourced from my cab, so the top speed here would be likely to be around 10Mbps.

In reply to a post by Ribble:

The idea would to use the same FTTC DSLAM.
The service would be availability to any CP that takes the openreach GEA service

still rubbish anyway cos BT limit ADSL2+ at 12Meg capped! (not 24Meg)

I will be sure to tell them to abandon the product then and offer no help to those too far to get VDSL

In reply to a post by MrSaffron:

I will be sure to tell them to abandon the product then and offer no help to those too far to get VDSL

No, BT Openreach should have two FTTC's cabinet in halfway between in houses will be no problem at all. Reason is BT doesn't want two cabinets in same area. And a silly to put cabinet long distance away from some houses who unable to get VDSL because too long over 3km away. So, putting two cabinets each 1.5km rather than 3km away will solves it.

Edited by adslmax (Tue 07-Oct-14 19:40:25)

Why is BT Wholesale haven't updated on their BT Availability Checker for FTTC ADSL2+ estimate speed?

Does anyone actually know if this is available? I'd rip both their arms off!

I am +6km from the exchange in an EO only area, BT have installed cabinets where they make sense. They have installed 2 of them, each of them are near the two largeish groups of houses, one of them very close the exchange the other at about 4km from the exchange just before the phone lines split up like a spiders web. This still puts me at 1.6km from the cabinet.

Your over simplified solution is in many situations not practical in the real world.

It doesn't exist as a service yet, if it ever does.

Ribble - is my cabinet start to cross talk now?

Don't understand

In reply to a post by adslmax:

Reason is BT doesn't want two cabinets in same area.

Except that is what they are doing with FTTRN.

And a silly to put cabinet long distance away from some houses who unable to get VDSL because too long over 3km away.

They're not choosing to do that deliberately. It just happens to come out that way with the PCP's location ... which dates back decades.

So, putting two cabinets each 1.5km rather than 3km away will solves it.

But makes it financially unviable.

Guess you can't have your cake and eat it.

Yes.

As I said in the article I wrote no dates or prices available yet

The negative reaction from some corners might also make them think twice about deploying it

I will look at mine again tomorrow after some sleep to see if I may have over estimated

In reply to a post by adslmax:

BT Openreach should have two FTTC's cabinet in halfway between in houses will be no problem at all. Reason is BT doesn't want two cabinets in same area. And a silly to put cabinet long distance away from some houses who unable to get VDSL because too long over 3km away. So, putting two cabinets each 1.5km rather than 3km away will solves it.

To put an FTTC cabinet 1.5km nearer the far houses would mean also putting a PCP there for those lines. That's a rather major task.

On top of which the last few houses on the first cab would get very upset when the next house down their street got 80/20 from the new one.

The only way it works fairly with a 3km gap would be to put the new one 2km from the first and feed both ways for 1km. Making it even more expensive and non-viable.

Also opening up a national demand never to be more than 1km from a cabinet.

In reply to a post by RobertoS:

In reply to a post by adslmax:

because too long over 3km away. So, putting two cabinets each 1.5km rather than 3km away will solves it.

To put an FTTC cabinet 1.5km nearer the far houses would mean also putting a PCP there for those lines. That's a rather major task.

It also belies the statistics, and simple mathematics.

The Sagentia report indicates that there are about 2% of lines that have a D-side length of more than 1.5km. This 2% of lines is the starting point of the market for this product.

If there are 300 lines on a cabinet (the national average), then on average, only 6 lines exist out beyond 1.5km. @adslmax is making a lot of fuss (an awful lot of fuss) about a very small group.

In some cases, there's a good chance the long lines are roughly in the same direction - so a cab would work. For the kind of size we're talking, that 2% doesn't merit a full FTTC cabinet as we see them today - something sized like the FTTRN node would do ... which we know BT are already working on; part of the target market gets dealt with that way.

In other cases (especially the very rural), the long lines are more likely to radiate in all directions, so you'd need more than 1 cabinet to cope with them (it would more likely require at least 6 cabinets to fully surround the original). That becomes even more of an economic problem.

If BT find it hard to make a cabinet of 300 lines commercially viable, adding 6 cabinets for 6 long lines is never going to work.

It is almost certainly a very small group that this is going to work with.

If ADSL1 was available in the first instance if that helped to limits the affect on the co-located VDSL2 lines would be appreciated. The proposal makes a lot of sense.

In reply to a post by MrSaffron:

Most likely most people lost both wires in their pair and this person was the lucky one

No, this was the strange thing, even the local paper reported on the hundreds that lost their phone connection but unusually most still had an internet connection!

Sounds more like a blown line card, or subrack, in the exchange.

In reply to a post by WWWombat:

Sounds more like a blown line card, or subrack, in the exchange.

The big delay we faced waiting for the repair was the road where the lightning struck is a main route in/out of St Ives or a better description is 'the main route' for St Ives! The Highways restricted Friday and Saturday working to avoid impacting the holiday makers, so on the Monday night the road was closed and they did an overnight cable replacement, so it was definitely a fried cable!
So in summary a fried cable, hundreds lost their telephone service but most still had internet......

As a follow-up, I found another NICC document that describes the use of DSL systems:
http://www.niccstandards.org.uk/files/current/ND1405...

Section 6.9.1.2 describes the use of ADSL2+ in a cabinet, with the phrase "The [DSLAM transmit power] mask for all Annex (A, B, I, J, and M) is not supported by the ANFP without downstream spectrum shaping" - so we definitely will see power shaping/reduction applied at the cabinet.

The document includes a graph (figure 25) that shows the standard ADSL2+ power mask overlaid over the power shaping masks that apply to VDSL2 at the cabinet.

Even without the dips associated with the power cutback, it can be seen that the maximum power at the cab, for the bulk of the frequency range, is about 10 dBm/Hz lower than the maximum power from the exchange.

That's going to hit the speeds available too: I reckon that is worth 2 bits on every tone up to about 1.2MHz, then 1 bit up to 1.4MHz; equivalent to losing approx 4Mbps.

And, If I've read it correctly, the ADSL (not 2+) power mask allows that variant to be transmitted from the exchange at 3 dBm/Hz higher than ADSL2+ (which might explain why, on long lines, restricting the modem to ADSL does better than allowing use of ADSL2+). That too wouldn't be allowed at the cabinet, and would be brought back down to the VDSL2 levels.

Nobody knows the availability or pricing of this yet.

My pcp is serving quite a few on 1.5km plus more on 1km because of its stupid position

nice info, by the way I think adsl2 is best for long lines providing the dsl modem works properly on it.

When i was on ukonline, the sync speed was lower and stability was worth with adsl2+ than adsl2, my adsl2 sync was as good as adsl1 but had the benefit of SRA.

In answer to my own question and having read the detail of the replies below (thank you everyone), it seems that at 1.6km I am much better off on VDSL2. FTTC has just been enabled on my cabinet and I was fortunate to have one of the first installs on Monday this week. My initial sync at 1.6Km from the cabinet was 20Mbit/s (up from 1.3Mbit/s when using ADSL2+ to the exchange!), but as I write, my connection speed has reduced to 17.5Mbit/s. I think this might be due to interference from other lines that have gone live this week.

Since my VDSL2 speed of 17.5Mbit/s is better than the 12Mbit limit that would be applied to an ADSL2+ connection from the cabinet, I am clearly better off on VDSL2. It seems that the BT testing guidenlines show that the sweet spot for ADLS2+ connectivity from the cabinet will be 2 - 3 km from the cabinet.

I would be really interested to see other people's connection speed vs. distance to the cabinet. Most of the statistics I can find on the Internet seem to be old, so I'm wondering whether the performance I am seeing is good or not given the line length to the cabinet.

I'm approx 9km from the exchange and have 0.5mb on ADSL2. My fibre cabinet is approx 2km away but this is too far to be offered FTTC despite my neighbour being given an estimate of 16mb, so I am exactly the person this is aimed at. I would say the 12mb limit is to prevent people sticking on the ADSL product which I would imagine will be cheaper as per the option 3 with fibre product from BT, rather than go for fibre, especially if they are within 5 or so mb of a more expensive Infinity product.

"My fibre cabinet is approx 2km away but this is too far to be offered FTTC "

Err really? FTTC works at that distance though I appreciate it may not be the best technology for speed.

Err really? FTTC works at that distance though I appreciate it may not be the best technology for speed.

Err Really? How does 4.8Mbps on Fibre grab you? Oh, same price as 78Mbps, of course..................

Why is 4.8 Mbps the same price as 78 Mbps?

When I looked the 40/2 product can be had for £13.50 versus £15 for 40/20 or £30 for the 80/20.

FTTC does have some element of speed/performance pricing involved.

Yes, my mistake - same price as 40Mbps - much more acceptable.................

Which might drop another £4 to £5 a month if TalkTalk gets it way anyway.

As things stand the TalkTalk 40 Meg service is cheaper than some other providers ADSL services.

Err Really? How does 4.8Mbps on Fibre grab you? Oh, same price as 78Mbps, of course..................

The cost to the service provider is essentially the same regardless of your speed, all the more so if you were to download and upload the same amount albeit at a considerably slower rate.

Well i'm getting 0.5mb on an up to 24mb product so the cost thing isn't really an issue for me. If I could get 2mb on a fibre product i'd take it, but because it doesn't show on the address checker (with talktalk so no number check) I just get stonewalled by sales.
So frustrating that I know my line can be quicker but I can't get anyone to sell me anything! I'm even considering BET at this stage!

This scheme would be great on our exchange, it is a Market1 exchange and never had 21CN enabled so we are all on ADSL1 MaxDSL connections still, despite paying more per month.

The two new cabinets have been installed and BTO are currently running new Fibre to these cabinets, it should go live in December, it should have gone live this month but a duct was blocked and a road needs closing for it to be cleared and then have the Fibre blown.

The two cabinets are large enough to handle all the lines in the area, so the exchange itself could become defunct and the ANFP problems could be avoided by moving the ADLS2+ connection to the cabinet, would be great to trial this new scheme if BT are looking for locations.