Vectoring - when and how good?

I've not got an unlocked modem but SamKnows testing and the Plusnet line speed info show my speed steadily declining, I'm assuming this is down to crosstalk as many people seem to be seeing this.

All the stuff I read about vectoring is talking about BT trials which has been the case for a long time now.

So anybody got some better info and can give an educated guess on when BT will be rolling this out nationwide and how good it is likely to be - for instance is it likely that my 350m line which was origininally devilering 70Mbps+ and is now down to a tad over 60Mbps would recover the lost ground.

Is it a hardware change in the cabs or just firmware?
Will the BT provided modem firmware need updating?

Trial expanding to 100 out of 61,000 cabinets which answer wider questions of stability and benefits but if it is crosstalk issues on your slowdown then would expect you to return to original speed

Vectoring will help those with 1km or less loop lengths on FTTC gain more speed, it assumes their are no alien interferers in the bundle as that cannot be removed.

However as with all things in physics there is an equal and opposite downside for those on longer lines or those say using ADSL over the same bundle. They may fail completely in much the same way as long ADSL lines suffered when ADSL2 near exchange subscribers came online.

Vectoring cannot resolve intermodulation issues, this is where non linearities in the line for example cause signals from differing pairs to mix together and produce products (A+B , A-B and all other mathematical combinations).

When you have 100's of lines in a bundle then the situation becomes notably worse.

Vectoring by the very nature of increasing speed/range (up to ~1km) will exacerbate this as more carriers will be usable.

So basically like ADSL2+ to ADSL, the winners here will be those close to the cabinet, the losers... Everybody else

The frequency range used by the VDSL2 17b profile is basically the entire shortwave radio band and encompasses many amateur radio allocations where very high powers are allowed as well as the usual plethora of commercial radio stations , military stuff and those lovely home plugs

ADSL only had to deal with "medium wave" interferers and it did that particularly badly with overhead lines as anybody who saw their profile crash early evening as the sun went down will testify.

So there are many other factors that will affect VDSL / FTTC other than mere crosstalk due to its analogue nature and the inherent issues with twisted copper wires intended for voice.

One thing i respect in my years of work in Radio/Electronics engineering is that the TANSTAAFL rule always applies

In reply to a post by kijoma:

One thing i respect in my years of work in Radio/Electronics engineering is that the TANSTAAFL rule always applies

.. that's the difference between engineering and innovation

In reply to a post by kijoma:

The frequency range used by the VDSL2 17b profile is basically the entire shortwave radio band and encompasses many amateur radio allocations where very high powers are allowed as well as the usual plethora of commercial radio stations , military stuff and those lovely home plugs

ADSL only had to deal with "medium wave" interferers and it did that particularly badly with overhead lines as anybody who saw their profile crash early evening as the sun went down will testify.

The density of radio amateur operators is very low and their periods of operation usually fairly short. Amateur transmissions are narrow band and far lower power than commercial transmitters - voice will be 3kHz tops and a maximum of 400w PEP in the UK. Digital modes and CW (morse) are typically much narrower bandwidth - often just 30Hz or even less and much lower power too. WSPR uses just a few Hz and there have been regular UK - Australia / New Zealand contacts on powers as low as 1mW.

Homeplugs certainly radiate using the house wiring as an antenna and can annoy short wave listeners (they have notch filters to avoid amateur radio bands) but I doubt you'll find anybody who will see higher speeds if they turn theirs off - unless they are faulty.

The big issue with ADSL is always pickup of MW am transmissions after dark and then mainly on ringwires which are not decoupled from the signal pair. Common mode pickup on overhead cabling is less of a problem as can easily be checked by ensuring the ringwire is decoupled when a far smaller noise margin swing will be seen. That will always be the case with engineer installed FTTC.

I won't say there are no other sources of electrical noise impacting VDSL but I strongly suspect that crosstalk will be the biggest which is why BT are looking at vectoring.

I have been involved with plenty of innovation , the rule still applies . one metric can be improved but at the expense of another. The engineering bit is being aware of what will suffer.

Unfortunately there is a product to sell so marketing sell the benefit and keep Engineers well away from talking to the customer . First rule of Dilbert !

In reply to a post by Eeeps:

In reply to a post by kijoma:

One thing i respect in my years of work in Radio/Electronics engineering is that the TANSTAAFL rule always applies

.. that's the difference between engineering and innovation

Yes i agree, it isn't the density of amateur operators so much as the power levels induced into telephone lines. They may be narrow band but the receivers in VDSL chipsets can only cope with so much common mode before the LNA saturates. They are after all a wide open receiver for the entire shortwave band as mooted.

So although the narrow band interferer seems nothing to worry about , it could in fact block VDSL modems for some radius around it.

It is something to consider as it was less of an issue with ADSL but is a reality for VDSL .

The converse issue is the potential for a lot of angry amateurs when the noise floor on the HF bands rises to an unusable level due to all the open wire radiators (phone lines) spewing out loads of narrow band OFDM carriers across the whole band.

Homeplugs cover both issues above as they are basically VDSL modems transmitting into an open line/aerial, the mains. Their effect on FTTC/VDSL though will probably only be an issue for houses/businesses that have their phone lines running parallel to mains cables, like in trunking or along a wall etc..

Or if overhead phone lines, the incomer runs alongside mains cables to its destination in the property.

I concur on crosstalk being the major issue, vectoring will improve the speed of those on short lines (< 1km) , after this cancelling out interference that is stronger than the desired signal isn't going to work. Especially as the longer lines in a bundle will of experienced crosstalk from all the closer pairs it encounters on its travels.

VDSL is akin to ADSL , it is a way of extracting more use out of existent copper infrastructure investment and for short distances it works. But it is always going to be an analogue medium that with all the best intentions will suffer real world issues relating to interferers/noise/poor cables/corroded joints etc..

The fact it is marketed as fibre broadband and without complaint i find quite remarkable as it is no more Fibre than ADSL was. Just the termination point is a green box, not a DSLAM in the exchange.

On that basis Fixed Wireless is Fibre too

In reply to a post by kwikbreaks:

The density of radio amateur operators is very low and their periods of operation usually fairly short. Amateur transmissions are narrow band and far lower power than commercial transmitters - voice will be 3kHz tops and a maximum of 400w PEP in the UK. Digital modes and CW (morse) are typically much narrower bandwidth - often just 30Hz or even less and much lower power too. WSPR uses just a few Hz and there have been regular UK - Australia / New Zealand contacts on powers as low as 1mW.

Homeplugs certainly radiate using the house wiring as an antenna and can annoy short wave listeners (they have notch filters to avoid amateur radio bands) but I doubt you'll find anybody who will see higher speeds if they turn theirs off - unless they are faulty.

The big issue with ADSL is always pickup of MW am transmissions after dark and then mainly on ringwires which are not decoupled from the signal pair. Common mode pickup on overhead cabling is less of a problem as can easily be checked by ensuring the ringwire is decoupled when a far smaller noise margin swing will be seen. That will always be the case with engineer installed FTTC.

I won't say there are no other sources of electrical noise impacting VDSL but I strongly suspect that crosstalk will be the biggest which is why BT are looking at vectoring.

In reply to a post by kijoma:

I concur on crosstalk being the major issue, vectoring will improve the speed of those on short lines (< 1km) , after this cancelling out interference that is stronger than the desired signal isn't going to work. Especially as the longer lines in a bundle will of experienced crosstalk from all the closer pairs it encounters on its travels.

Its lucky, then, that 90% of lines are shorter than 1km - or at least the segment that carries VDSL2 is shorter than that.

Strictly, I guess it is 90% that are shorter *electrically* (ie less attenuation) than 1km of 0.5mm copper.

BT are incredibly cautious with technologoy rollouts it seems as if they been trialling vectoring for an eternity.

From bits of info in public BT have been rolling out vectoring cards in hauwei cabinets. No known ECI testing or card updates but a plusnet staff member and ignition and andyh say ECI will also get some kind of rollout/testing.

My gut guess is they are right but people on ECI cabinets will probably only see partial recovery as card level vectoring isnt proper vectoring plus I think ECI are behind hauwei on the technology.

I have a feeling vectoring mass rollout will start before end of this year, but I be surprised if its before summer.

Edited by Chrysalis (Tue 24-Feb-15 09:15:56)

Thanks for the info. I'm not desperately worried as the speeds still easily surpass my needs but if it continued downhill at the same sort of rate I'd be on ADSL speeds in a few years, then dialup, then evenually semaphore. Mind you I'm used to slow transmisssion speeds - my WSPR beacon takes just under 2 minutes to send 50 bits of data.

Edited by kwikbreaks (Tue 24-Feb-15 11:32:03)