How fast can the cabinets go?

Curious what the theoretical maximum speed the BT cabinets can support?

For example if BT decided to supply say 120/30 in addition to 80/20 can the cabinets do it? And is there a reason why it has to be fixed rate, and not just maximising the line like the old ADSLmax did.

ADSL Max did not maximise the line . It was capped at 8128/448kbps though there was an option not all ISPs offered of 8128/832kbps.

8Mbps is 8192kbps.

80/20 isn't a fixed rate anyway, as I'm sure you realise. It's just a product cap, enabling different speed products to be offered at different prices.

The theoretical maxima are shown in the VDSL2 table on this page. Openreach use Profile 17a. The rest of the reduction from the theoretical maximum will be down to a number of factors, mainly technical in order to provide a fairly stable and economically viable service.

I doubt if, apart from G.FAST, they will offer anything faster as the priority now seems to be FTTP. Which in the end will replace FTTC almost everywhere anyway.

Thanks for that link, Bob. I wonder why Openreach aren't using VDSL2-Vplus...

Because!

They have no proper reason not to?

Edited by deleted (Tue 02-Oct-18 15:59:04)

BT chose to go G-Fast which if nothing else reduces the line length as the G-Fast pods are attached to the PCP therefore eliminating travel from the DSLAM to the PCP which can add up to 50m or so to the path length.

Right, but surely Vplus would benefit more users, especially for those who are too far from the nodes?

Edited by deleted (Tue 02-Oct-18 17:08:38)

The table Robert referred to suggests that Vplus is good to around 250m. Which isn't so different from G-Fast which by its nature has a shorter path length since it removes the copper link between DSLAM and PCP from the equation.

Of course, the DSLAM already has fibre and power whereas both need to be supplied to the PCP. OTOH since only a subset of the lines served by the DSLAM would benefit fewer ports/line cards need to be provided for G-Fast whereas possibly all would need to be upgraded for VPlus.

Edit:
I should mentioned that I have no knowledge or experience regarding either VPlus or G-Fast other than that I've read here and elsewhere.

Edited by deleted (Tue 02-Oct-18 17:32:34)

I usually find that cabinets are going as fast as they can prior to being fixed, probably as fast as about 60 mph on the back of a flatbed. I imagine they could go a bit faster and still be intact. They tend not to move once they�re in place.

They can burst to quite a lick when hit by a wayward car

VDSL Plus and other variants gained most of their long distance improvements from ADSL/ADSL2+ not being present.

So in a market where two large MPF providers want to continue turning of ADSL2+ services is some years away still.

Also a lot hinges on how mature the chipsets are, what prices are offered etc

G.fast in the dense cities gives a nice quick competitor to cable and even competitors full fibre services, the popularity will hinge on peak time performance i.e. full fibre is great buy if sell lots price low has lots of congestion it may feel no faster and gaming could even be worse than VDSL2.

That's not the fastest they can go while still being intact though.

I'm sure a few have traveled on planes so could get a good lick of speed on a 747.

Elon Musk could improve on that, for a fee. He already has a car up there to help as well.

That is true, didn't think of that. Could slingshot one around the moon (or a planet or other heavenly body) - that could get a good speed going. But, I think the costs may be astronomical and it is more likely that a cabinet has already been on a plane than into space...

AIUI a cabinet can also go quite quickly after a general election. It can disappear from sight in a moment.

Not really.

The biggest issue with BT's network is OFCOM's insistence that they never discontinue old kit.

This is why FTTP isn't being pursued that aggressively - OFCOM insist they still maintain the copper so that Sky/Talktalk et al can sell [censored] ADSL2 over it.

It's also why VDSL2+ 17a could never even achieve the theoretical max - OFCOM won't let them reuse the ADSL frequencies from the cabinet because it might cause crosstalk for ADSL customers so VDSL has to be "notched".

G.Fast is notched to 17mhz so as not to interfere with VDSL2, and if they deployed VDSL2+ it would end up reducing the maximum speed of G.Fast.

If they just replaced one product with the next, VDSL syncs would be about 10mbit higher (from the use of the ADSL frequencies) and G.Fast where available would get ~60-70m higher syncs than it does. All they need to do is turn off the old product and move everyone on that node onto the new one.

If it could use all the frequencies, VDSL would never perform worse than ADSL, and G.Fast would always be at least as fast as VDSL, etc.

The early ones came on a cargo plane from China, so they have done 500-600MPH with a following wind.

Within the UK around 60 on a motorway would be more normal!

I don't feel too proud about what I've started.

Ahh, I see! Thanks for the explanation. It makes total sense, cutting corners as usual!

In reply to a post by nemeth782:

It's also why VDSL2+ 17a could never even achieve the theoretical max - OFCOM won't let them reuse the ADSL frequencies from the cabinet because it might cause crosstalk for ADSL customers so VDSL has to be "notched".

VDSL2 VPlus/35b is not 17 MHz, but rather 35 MHz. We currently use 17a, not 35b, and VDSL2 VPlus does not exist in 17a variant, but can co-exist with pre-existing 17a deployments.

In reference to ADSL and VDSL overlay, Power Spectral Density (PSD) masks are in place to "protect" ADSL signals from being impacted from VDSL. Of course, this impacts VDSL performance (and sadly, I don't know by how much).

In reply to a post by nemeth782:

G.Fast is notched to 17mhz so as not to interfere with VDSL2, and if they deployed VDSL2+ it would end up reducing the maximum speed of G.Fast.

The starting frequency of G.fast is actually 19 MHz in Openreach deployments, and uses the range 19-106 MHz currently. As you are aware, this is to reduce the impact of G.fast on VDSL 17a.

VDSL 35b won't be rolled out because the density is less compared to 17a and because it would probably cost a lot more money than worth at this point as I cannot remember if vendors have compatibility with 35b profile with the current hardware rolled out across the UK.

In reply to a post by nemeth782:

If they just replaced one product with the next, VDSL syncs would be about 10mbit higher (from the use of the ADSL frequencies) and G.Fast where available would get ~60-70m higher syncs than it does. All they need to do is turn off the old product and move everyone on that node onto the new one.

If it could use all the frequencies, VDSL would never perform worse than ADSL, and G.Fast would always be at least as fast as VDSL, etc.

Aggressively curtailing older technologies would be the best case for increasing speeds/freeing up bandwidth among newer technologies that use radio frequencies. It is essentially the same premise for mobile networks, TV and radio too as what happened with the digital switchover, adjustments in the TV broadcasting frequencies for 4G, etc.

As you said previously, providers have investments in ADSL2+ technologies. Sky and TalkTalk in particular have a huge LLU presence. This was a lot of money invested into their network. Phasing out technologies is not just a problem of moving people over to the newer technologies, but is also a financial issue.

Edited by deleted (Thu 04-Oct-18 00:06:00)

In reply to a post by RobertoS:

ADSL Max did not maximise the line . It was capped at 8128/448kbps though there was an option not all ISPs offered of 8128/832kbps.

8Mbps is 8192kbps.

8Mbps is 8,000kbps or if you prefer 8,000,000 bits per second. Communications speeds use base 10 not binary / base 2. You can read various gack on this but the fact that Gigabit Ethernet is 1 billion bits per second and Fast Ethernet 100 million bits per second per the IEEE standards should suffice.

Pedantic I know but that's the price you pay for being a serial pedant. Karma

You're right of course. Mea culpa.

However my version does fit the accepted one for ADSL Max. And the correct version only invalidates that final sentence of my post. The main content is true .

Plus, on O2/Be and other LLU systems all of which were on ADSL2+ DSLAMs in those days, the 8Mbs options all sync'ed at "up to" 8192kbps.