Do you agree that some of these 8800 stats are decidely questionable?
Should I just leave the 8800 to get on with its background co-operation with the DLM and hope that everything just settles down later on?
The copper leg is approx 700 metres long. That's the walked route (underground ducts), so initially I was expecting the line to sync at 30 - 35M bps, with a commensurate data rate somewhat below that. The Openreach speedtester had predicted 37 - 40M bps.
My first FTTC line was 650m of 0.5mm copper.
On the original 8MHz profile used by BT, it couldn't quite manage 40/10 speeds (the top packages at the time), and tended to sync at around 38/10.
When BT swapped to 17MHz profiles in 2011 (but before they started selling the 80Mbps packages), it managed 40/10 easily, and reported an attainable of around 60Mbps.
Increased takeup would have almost certainly caused crosstalk, and reduced those numbers, but I moved out soon after.
I'd been aware that Openreach normally sets the target SNR on downstream to 6dB and, sure enough, that was the SNR that the line was working at just after I first got it all working. But a couple of days later I had to restart the 8800 a number of times in the course of doing its firmware update, and therefore I'm not now surprised to find that the DLM has bumped up the SNR to 9dB. Could that at least be a partial explanation for the 26 figure? I assume that, in time, the 9dB will drop back down toward 6dB again.
You should only expect the modem to be running with an "actual SNRM" value that matches the "target SNRM" value of 6dB when it is synchronised at something below the package maximum.
You are sync'ed at the maximum, on a line capable of a higher speed. The modem is thus under-utilising the line, leaving it with spare SNRM capacity over and above the target: 3.1dB spare at the moment.
Note that DLM does not bump up your "actual SNRM"; changes in the "actual" reflect the combination of "spare SNRM" from the time of the sync and subsequent changes in noise (which can be more than 3dB). DLM doesn't even bump up the "target SNRM" in FTTC at all. Trials are starting to try out reductions to 5, 4 or 3dB though.
What DLM would do instead, if it saw the need, is to "band" you: setting an artificial maximum sync speed. When the modem syncs, you'd see it reach a few killobits below a round figure (eg 36997 kbps), and a higher SNRM.
Having spare SNRM capacity does not cause a slowdown of throughput.
The throughput figure will still be based on the sync speed. You have a 40Mbps sync, so will have an "IP profile" of around 37.7Mbps. That's the maximum throughput of IP-level packet data (including IP headers); a download of a large batch will result in a user throughput in the region of 36-37Mbps ... provided the server can keep up.
Interleave depth was originally 1 and 1, but is now 16 and 1.
With an initial interleaving depth of 1, you were on fastpath with no error correction. With a change to 16, DLM has turned on error protection in the form of G.INP retransmission.
This change can improve speeds for a line, because there is a perceived coding gain from the protection. That is probably why your actual SNRM has increased from 6dB to 9dB, and your attainable speed has increased.
Note: DLM actually sets the "INP" and "delay" parameters, and the modem/DSLAM choose an appropriate depth during synchronisation. It can be better to monitor INP and "delay", rather than depth.
Frankly, I can't believe the 8800's figures for the Rate. Both the Down and Up Rate figures are recorded as all but maximum! And notice that the attenuation figure for Up is zero, and clearly that's impossible.
It certainly looks like the sync figures are right. For more details, you probably want to connect via telnet, and get figures out from the command line.
If you want to monitor 24x7, there are monitoring programs available here:
Both "DSLstats" and "HG612 modem stats" are capable of monitoring an 8800NL. In fact, the 8800NL behaves very similarly to the HG612.
The attenuation figure is always shown as zero, upstream.
Incidentally, within the 8800's user settings there's something called 'Fullcone NAT'. Anyone know anything about that? Given that my 8800 connection is straighforward PPPoE (no bridging or additional firewalls), do I need to select and use Fullcone NAT?
I just have "NAT" ticked, with "fullcone NAT" left off, as the default setting. I've needed nothing else.
Whether that is what you want depends on your own uses. Take a look here: