I've just been conparing my current stats to the op's and notice that in the bit loading graph and the SNR graph my graphs have the blocks missing above 2750Khz, why is this and I presume this is why my DS rates are a lot lower even though I'm about 450 meters, where as he estimates 600 meters?

I presume from the bit loading graph that my connection is not using the highest band at all?

Also his first and second red blocks both look stronger.


My graphs

Your graph shows that your bit loading stops at tone 2750 (about 12 MHz, I think), though that's the end of the upstream. The last downstream tone is around 1950. So indeed - you aren't using any of the D3 block.

The sync process has chosen not to use the tones above 2750 because it doesn't think it can carry any data on there. That comes about from the SNR measurements at each tone. But you can't see any information about the SNR values in D3, so i think the next-best place to look is the HLog graph.

On the whole, the OP's line seems to start getting iffy around tone 3300, and stops at tone 3500. At HLog graph is showing values of around -62 or -63dB at these tones. The SNR graph looks to be in the 6-7dB region at this point.

On your HLog graph, D3 starts (tone 2750) around -62dB, suggesting that there isn't quite the margin needed to carry data (but only just).

I do notice that your QLN graph is not as smooth in D3 as the OP's. I'm not sure what we can infer with that though.

In reply to a post by R0NSKI:

I've just been conparing my current stats to the op's and notice that in the bit loading graph and the SNR graph my graphs have the blocks missing above 2750Khz, why is this and I presume this is why my DS rates are a lot lower even though I'm about 450 meters, where as he estimates 600 meters?

I wonder if your line has more "junction" points than mine? Or there is some aluminium in your line?

My line had to be repaired the morning of the install - luckily the FTTC installing OR engineer found the fault early and raised a fault call and a separate OR engineer turned up at my door at noon to test the line - as he thought he'd fixed the issue (and he had). The issue was apparently "battery" and caused by poor / very old joints in the BT network but physically within my block of flats. (ie, all our lines travel through various meter cupboards, one of them has a junction box and for some reason two lines were slightly touching).

I also know from my SFI visit in 2010 that the jelly crimps in the street installed in the 70s when the block of flats was built were replaced on my line due to the fault in three manhole covers - but nobody else's. The SFI visit was arranged by BE because I was getting constant disconnections on a line that had been good (did get 18meg in 2008, then dropped to 14meg by 2012).

My FTTC speeds are lower today than on installation (50/10), but they've stabilised around 46/10 - that's on speed testers.

Thanks for the input wwwombat & jchamier.

As far as I know we are on copper lines, this is what the engineer said, but he was not from our area, so could only go on what was coming into the house.

Is it unusual for the D3 block to be unused on a 450 meter line length?

I've just come back, and looked at this one:

In reply to a post by RobertoS:

I'm almost exactly 600m away as well. Just done these.

Very clean D-side here.

On topic comment:
Your D3 QLN bounces around a little. I wonder if this indicates something about your line.

Off topic comment:
The bit-loading graph shows a problem that I come across sometimes... which is mostly visible in D1, but actually is a problem in the tones up to 1023: All the values seem to be lower than you'd expect.

I get this sometimes, more often than I'd like, but it seems to be a problem with the statistics data presented by the modem rather than the actual state of the line. I can get the 2 different sets of data at different times, even with no sync inbetween - and no difference in the headline speed. You'd expect, if there really was a huge reduction in bit-loading in this area, that there'd be a corresponding drop in speed.