Low bit loading rates

Looking at my line performance through DSL stats, I am slightly puzzled by how the modem and line are performing in the lower tones.

DSL stats screen-shot

From tone 250 upwards everything is fine and as expected, however from 40 to 250 seems to be under-performing based on SNR being low and thus low bit loading rates at 8 rather than up at 14.

I would expect the SNR to ramp up, as it does, from 40 and the notches including those at 167, 211 and 226 are explained by MW transmitters. There are no major noise sources in the property.

What I would like is to see a few more graphs of other lines that are giving speeds of 70-80Mbps to see if what I am seeing is common or is just affecting my line.

I can't post my own at the moment because I'm at work, but I think my line is pretty similar to yours.

I think what you're seeing is a power (PSD) mask, which is applied at the cabinet to cut back power on frequencies that are shared with ADSL. This is to stop the high power VDSL signals from the cabinet at those frequencies from interfering with the weaker ADSL signals from the exchange. The further the cabinet is away from the exchange, the weaker the ADSL signals are and hence the more the power in those frequencies is cut back. I believe there are a handful of PSD masks, and they are applied to a cabinet based on its distance from the exchange.

I defer to the experts on this stuff though - please correct me if I'm wrong.

I was already wondering about that as the cabinet is around 2.7km from the exchange (2.1 direct line) however I seem to remember it previously being significant higher - I might be mistaken though.

One reason I initially discounted it was that ADSL2+ runs up to 2.2MHz and the transition is around 1.1 MHz. However, given the distance from exchange to cabinet, it is likely that the top end frequencies will have "disappeared" by that point so a mask with a change at 1.1Mhz could be correct.

That said, it would still be interesting to see what other are obtaining - and their exchange to cabinet distance.

Edited by MHC (Thu 14-May-15 14:39:39)

Cabinet-to-exchange: 1263m as crow flies

http://s17.postimg.org/e0mnottqn/dsl_tones_0_600.png

Not as harsh in your case ... although it does push out further to around tone 475 which is about 2.1MHz

Yeah, I think that makes sense - nearer the exchange there will be higher ADSL2+ frequencies still in use.

Edited by ip75 (Thu 14-May-15 15:37:33)

Yes - the PSD masks for cabinets closer to the exchange cause less power restriction, but over a wider frequency band. Those further away need to restrict power much more, but only over a shorter band.

Page 30 of the ANFP

Here's my line... I'm about 100m away from the cab (so you see the effect of upstream PBO too), while the cabinet is 1.1km from the exchange (crow flies), and between 1.3 and 1.5km line distance.

DSL stats bitloading

Thanks ...

I really must have been having a bad day this morning not to really think about it!

A pity I could not get the mask choice tweaked _ I might then hit a full 80Mbps!

Mine is here: https://db.tt/Uv7jnmFh

I'm about 250m from the cabinet, and the cabinet is about 3.5km from the exchange.

Much the same as mine ...

What does yours do from tones 32 to 39?