Yes I did mean SNR margin.. Sorry.

I'd assumed that the DLM had decided my line was better syncing with a higher margin - fewer errors. I hadn't thought to leave it on... Perhaps I should see where it takes me. I'm frightened of the DLM though

There were some errors on the line - about 8 CRC errors in 12 hours. And very oddly for a non interleaved line... FEC and HEC errors - but still no more than about 20.

In reply to a post by timl:

I'd assumed that the DLM had decided my line was better syncing with a higher margin - fewer errors.

No - your line is good enough that it reaches 80Mbps without requiring too much signal - so you have extra SNR margin to spare. It is all related to the sync, and nothing to do with DLM.

If "DLM decided" your line needed to sync with higher margin in order to cause fewer errors, it would have chosen to band you, limiting you to a lower speed.

That wouldn't be DLM's first choice though.

DLM would make a different choice first, where it would turn on FEC and interleaving. In your case, those would use more of that "max attainable" speed to carry the extra overhead for FEC, so your SNRM would lower first. If the extra capacity in the "attainable" wasn't quite enough for FEC, then you'd lose a bit of your sync speed too, and still have a 6dB SNRM.

Edited by deleted (Mon 10-Jun-13 13:00:08)

In reply to a post by timl:

There were some errors on the line - about 8 CRC errors in 12 hours. And very oddly for a non interleaved line... FEC and HEC errors - but still no more than about 20.

I take it you are looking at the GUI, rather than the output from the "xdslcmd" on the comand line.

The GUI uses figures from the wrong place for some of those error counts, so isn't to be trusted. It is the FEC figure that it gets wrong, IIRC.

And I'm not sure what the HEC figure really represents. HEC applies to ATM (and PPPoA), which isn't used in FTTC.

I'm not sure if I was looking at the gui or the output from the stats program by BaldEagle1.

So do you also think I should put the HG612 back and see if it recovers to 6db in a week or so? I suppose it would be an interesting experiment.

There are two ways that your SNRM will reduce to 6dB...

1. If the current noise levels stay the same, and your speed increases.

2. If your speed stays the same, and the noise increases.


As you are at 80Mbps (that 110kbps is insignificant here, even if inexplicable), #1 can't happen. There's no "recovery" to happen here.

#2 will mean more noise, more crosstalk, and more interference is happening. I'm not sure I'd class that as "recovery".

Personally, I'd be perfectly happy to keep the 80Mbps sync and the 8.9 dB SNRM.

Even if there is no recovery to expect, I'd still leave the HG612 in place, and collect regular stats from it.

In reply to a post by timl:

I was achieving a full 79999 sync and a achievable of about 97Mb... Now achievable is down to 87Mb and 79889 sync or something weird like that.

Mine was 79999 at first as well, but after 14 months it was down to 65Mb/s with interleaving although this morning it seems interleaving has been removed.

Swapped them back. You're right about stats being more important.

Attainable rate (kbit/s) 88128 34202
SNR margin (dB) 8.2 15.4

Line rate (kbit/s) 79987 20000

An update to my original question

Today I was visited by an SFI engineer who spent six hours on trying to resolve the issue with my upload speed! Ports were swapped over on the cabinet, the wires from the cabinet to outside my house were swapped and after all that my Download speed has now increased (which I was not complaining about) from 55.57 to 65.93, but my Upload speed is still low - was 6.97 now 5.71!.

Various phone calls were made around the Open Reach circuit and it was concluded that

a) They have never had one complaint (locally I presume) of a low upload speed, most people complain about download speed

b) As the original estimate was 13 Upload speed and they have it as 7, as it it more than 50% of that speed they will close the job

c) Work is still going on at the cabinet, 'line tethered', which in this thread has been noted that this could cause my issue. The OR engineers said this also possible, but was unsure as my Download speed has not changed (although got it higher). They said once the work has finished at the end of this week to monitor the line speed for the next 10 days & see what happens.

So, for me, a long day with a 10 meg download increase but a upload speed gone a further 1 meg

I'd be interested to hear your comments.

Are the line stats available from an unlocked modem?

No, but we ran stats over & over with the electronic box they brought with them, everything checks out fine - except the upload speed!