Alu FTTC line

I have two FTTC lines, both are delivered from a street pole, over a couple of neighbours gardens.

I get ~45-48 down, and 5.5-6.8 up, on both lines. Neither has any extension wiring etc, just a master socket with faceplate.

BT wholesale checker estimates the following:

FTTC Range A (Clean) 60 40 16.2 9.9 -- Available
FTTC Range B (Impacted) 50.2 30 15.8 7.2 -- Available

As you can see, I'm within the (rather wide) range for the Clean estimate on the downstream, but below even the low end of the impacted estimate on the up, on both lines.

I talked PlusNet/BT into sending an engineer to look at one of the lines, and I've been told that the run from pole back to cab is Aluminium, and there is nothing they can do.

Bit annoying that it's still below estimates - to me the line is faulty - but is this the sort of impact you'd expect from Aluminium?

Bitloading Graph from DSLstats:
http://i.imgur.com/cdRKx6I.png

Stats:

xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 3
Last initialization procedure status: 0
Max: Upstream rate = 7037 Kbps, Downstream rate = 47992 Kbps
Bearer: 0, Upstream rate = 6866 Kbps, Downstream rate = 47993 Kbps

Link Power State: L0
Mode: VDSL2 Annex B
VDSL2 Profile: Profile 17a
TPS-TC: PTM Mode(0x0)
Trellis: U:ON /D:ON
Line Status: No Defect
Training Status: Showtime
Down Up
SNR (dB): 6.2 6.0
Attn(dB): 21.9 0.0
Pwr(dBm): 12.9 3.1

The fact that is aluminium is NOT a fault although It may not be optimum.

Looking at the graph there is something wrong - some notches at tones 1050, 2050, 2130, 2160 (approx) and then a drop to zero at 2330 whereas U2 normally goes up to 2775. I would not expect to see a sudden drastic cut off - and that is not due to aluminium. Do you know what is causing those notches? They could explain some of the lack of upstream speed.

Can you capture the Bitloading Graph with the SNR superimposed.

In reply to a post by MHC:

The fact that is aluminium is NOT a fault although It may not be optimum.

Looking at the graph there is something wrong - some notches at tones 1050, 2050, 2130, 2160 (approx) and then a drop to zero at 2330 whereas U2 normally goes up to 2775. I would not expect to see a sudden drastic cut off - and that is not due to aluminium. Do you know what is causing those notches? They could explain some of the lack of upstream speed.

Can you capture the Bitloading Graph with the SNR superimposed.

Don't know how to superimpose them, but here is a snapshot of all the graphs...

http://imgur.com/a/BhmPG

I assumed the drop off at 2330 or so was just because alu didn't carry higher frequencies well?

No idea what is causing the notches, although the engineer apparently did a pair swap so I don't suppose I'm going to talk BT into much else!

In DSL Stats select <Configuration>, then <Items to monitor> Under Others, ensure SNR per Tone, Show as sepatate graph, & Include with bitloading are checked..


From what I can see, with ZERO loading from 2100, to just under 2300 and nothing from 2300 up that could be where you are losing quite a bit of upstream.

Yes, aluminium does not work as well at higher frequencies, however it is not a sharp cut off. I would expect to see the SNR drop from 10 down to 0 over a large block of tones - possibly up to 400.

Edited by MHC (Tue 01-Sep-15 19:06:04)

http://i.imgur.com/W1eAdf1.png

That's actually a much more helpful graph!

Still not sure what else I can do though

Now you see ... That block with zero bitloading - even if it was at 1 bit per tone you could be looking at maybe up to 10% improvement.

there are also a couple of nasties in the downstream too - 1700 to 1750 ...

I would suggest a "managed" reboot tomorrow morning. Power off the hub, without disconnecting the line. Wait 5 minutes and then disconnect the line. Wait say 15 minutes, make sure you have minimal devices on in the house - no lights, no TV &c. Power up tyeh modem and wait 5 minutes for it to fully boot. Then reconnect the line - give it a minute or so and then recheck the stats/graph.

Long shot, but don't happen to have a radio ham living near by?

Interesting thought ...

The Amateur HF bands are here: http://rsgb.org/main/operating/band-plans/hf/

Tone 2342 is at 10.1 MHz Might explain the missing top end but not the missing block.

At least you have a single run of Al and not a 120m section between two copper sections with deteriorating joints. The recent very heavy rain doesn't appear to have helped as I've lost another 8 Mbps off my sync speed unless it's just a coincidence.

In reply to a post by nemeth782:

xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 3
Last initialization procedure status: 0
Max: Upstream rate = 7037 Kbps, Downstream rate = 47992 Kbps
Bearer: 0, Upstream rate = 6866 Kbps, Downstream rate = 47993 Kbps

Link Power State: L0
Mode: VDSL2 Annex B
VDSL2 Profile: Profile 17a
TPS-TC: PTM Mode(0x0)
Trellis: U:ON /D:ON
Line Status: No Defect
Training Status: Showtime
Down Up
SNR (dB): 6.2 6.0
Attn(dB): 21.9 0.0
Pwr(dBm): 12.9 3.1

Looking at other lines on MyDSLWebStats, with an attenuation of 22dB or so, you can see speeds of 43/7 - 50/8. It seems to be fairly common to see upstream speeds of 7-8Mbps alongside downstream speeds anywhere from 35Mbps to 50mbps.

In reply to a post by nemeth782:

Don't know how to superimpose them, but here is a snapshot of all the graphs...

http://imgur.com/a/BhmPG

What I notice most especially is that there is no obvious "power mask" in the downstream D1 band.

Ordinarily, I'd expect to see a *big* trough in SNR and bit-loading values somewhere between tones 200 and 500.

For example, mine looks like this, with a trough at tone 325:
http://postimg.org/image/vlcbhlakn/

What distance is the cabinet from the exchange?

Of course, if power is reduced, speeds will end up even lower...