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[phi2008]

I stand corrected. 

[ejs]

One of the G.fast offerings will have maximum speeds of 160/30, so a minimum of 150 seems unlikely.

[Bowdon]

I've not got a G.fast pod on my cabinet

Also a question, if more people are now sync'ing at higher speeds, does this increase crosstalk?

[gt94sss2]

Both my parents line and my brother have BT Infinity 1 atm - checking with him today, he got the 'boost' email on Friday and is close enough to the cabinet that I think he should get the full 80/20 but won't notice it

I guess I should get around to fixing my parents line as that should normally sync at 55/10 (no email received by them yet) and is about 52/10 atm.

They both also have g.fast pods attached to their cabinets.

Ironically, I'm due to move to Sheffield for the next few months - just around the corner from Plusnet's HQ actually - and can you get FTTC or cable there.. no  (despite it being a heavy student/professional area)

[WWWombat]

Also a question, if more people are now sync'ing at higher speeds, does this increase crosstalk?

Where the extra speed comes from carrying bits on tones that were silent, then yes. Where it comes from carrying more bits on tones that were used before, then no.

I believe that the latter case is much more likely than the former, so the overall answer is: no, not much.

[skyeci]

Line now at 79088 on the ds..

Wish I had mum's line...so jeaulos right now lol


55/10  76/20  79/20  whilst paying bt infinity 1. Dlm has dropped snr to 4.5 (huawei)

[ejs]

Also a question, if more people are now sync'ing at higher speeds, does this increase crosstalk?

That would depend on if the transmitted power is reduced when the speed is capped, I don't think this is being done.

[WWWombat]

That would depend on if the transmitted power is reduced when the speed is capped, I don't think this is being done.

If some lines were being held to a reduced power (on an individual tone), wouldn't that make them into a crosstalk victim?

If the whole point of the DPBO process is to minimise crosstalk into/from ADSL lines, and to balance the power between the two systems, then it follows that every VDSL2 line has to transmit at the same power level too. At least logically.

[Chrysalis]

That would depend on if the transmitted power is reduced when the speed is capped, I don't think this is being done.

I agree, seems unlikely based on what I have seen.

[kitz]

Where the extra speed comes from carrying bits on tones that were silent, then yes. Where it comes from carrying more bits on tones that were used before, then no.

I believe that the latter case is much more likely than the former, so the overall answer is: no, not much.

DSL uses the water fill method to load bits into tones.   Therefore the latter case should be true.

If more people are now sync'ing at higher speeds, does this increase crosstalk?

Missed this earlier - In theory, No it won't cause additional crosstalk because no new tones are available on the line. The only time more tones are made available is upon a change of technology ie adsl, adsl2, vdsl1, vdsl2.

One of the reasons we see more crosstalk when neighbouring lines upgrade to FTTC is previously they will have only been using the frequencies up to 2.2 MHz.   When they get vdsl2 they now get up to ~4000 bins to play with.  The waterfill method ensures that a line should always make use of the highest tone it can even if the SNR on that tone is only sufficient to load 1 bit.   

If you give a line more speed to play with by removing the 40/55 limit then it will just fill up existing tones.  For those lines which are capable of achieving higher speeds, the 40/55 is in effect an artificial cap which halts the water fill process once sufficient bits are loaded to reach 40/55Mbps. Remove the cap and it just keeps filling until it either reaches 80Mbps or its natural limit for the line.


---
ETA

The limits set at the DSLAM aren't the same as any capping done by the ISP.  If a line is set as 80/20 at the DSLAM, the line will still sync as high as it can.  The ISP caps by restricting the maximum throughput speed.

Any banding by DLM is done at the DSLAM and affects bitload.

[WWWombat]

I agree about the water-filling having the effect of spreading bits over every feasible tone. The one technicality that I wonder about is when power backoff is in play - whether it works in opposition to water-filling sometimes.

In the downstream case, I don't think we see this kind of opposition. The power is reduced by a fixed amount for all lines, which then has a fixed impact to the SNR values, and so a fixed impact as to whether a tone is "feasible" or not. Water-filling will still use as many tones as it can; it just doesn't get many bits in the affected tones.

In the upstream case, I'm less sure. The power reduction isn't fixed, so it is plausible that, sometimes, a power setting for a nearby subscriber causes it to use the U2 band in preference to U1 ... whereas higher power could allow U1 to be used. I'm unsure as to whether the dynamic system works in a way that accounts for the desired capacity. For example, would a 10Mbps subscriber would end up using lower power than a 20Mbps subscriber, simply because the extra power would end up merely giving superfluous excess SNRM?

(If it isn't obvious what I mean, consider a "water-filling" algorithm that starts with the lowest power on every tone, and then starts to water-fill by gradually turning up the power across all tones until enough bits have been allocated.)

[ejs]

What else is there to complain about?

How about:
Will all these Infinity 1 customers with more bandwidth lead to peak-time congestion?

[Black Sheep]

He he he ..... ^^^ 

[Ronski]

What else is there to complain about?

Three little letters.................E....................C..................I 

[skyeci]

   - classic

Three little letters.................E....................C..................I