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[shadow4dog]

Hi,

I've had FTTC for about 2 years, ever since the cabinet went live. My house is about 75m from the FTTC box, 110m from the PCP and my D-side is about 250M

At first the DLM gave me the full 79999, 20000 but as take up increased speed and errors went up and as of this morning the line syncs at about 68Mb @ 6db noise margin. The line had been synced up for about 24 days.

This afternoon my line re-synced, to my amazement back at 79998, 20000 but on a 3db noise margin! I didn't think BTs DLM supported 3db margins! Is this something new or part of the profile management Speed, Reliability, Gaming or whatever they are.

I'm fully expecting it to revert to 6db in the coming days... it's currently at 2.6db

I'm definitely not complaining I'm just interested on why DLM has decided to do this now... is this a new behavior for the DLM, maybe it's just had a firmware update. I know my HG612 had a firmware update at the end of last year...

[WWWombat]

I've certainly not seen it use anything other than a 6dB target before.

[shadow4dog]

I looked at Deadmans situation were they found themselves on a 3db profile after a power cut. I haven't ruled out a powercut as the modem was obviously reset, though I have another FTTC line connected to the same cabinet, same power socket. It didn't resync, but for around 30 minutes it believed it had a slightly higher noise margin (6.8db vs 6.1db)

At the time of the re-sync it appears the HG612 briefly believed it was synced with a 10db margin. And since that anomaly it's been hanging on with that 2.6db margin for dear life.

My stats are currently sent up to mydslwebstats.

Tim

[burakkucat]

My house is about 75m from the FTTC box, 110m from the PCP and my D-side is about 250M

My attempt to analyse the above . . .

House to fibre cabinet ~75 metres  (1)
House to PCP ~110 metres  (2)
D-side reported (by an Openreach technician, perhaps?) as ~250 metres  (3)

The approximate length of the tie cables will be the difference between (1) and (2), so subtracting (1) from (2) gives 35 metres.
Assuming the D-side length is from Openreach network records or by a TDR measurement, then the total length of metallic pathway for the VDSL2 signal will be (3) plus the difference between (1) and (2),
i.e. (250 + 35) metres = 285 metres.

[shadow4dog]

I think you're spot on. The Openreach engineer said it went all over the place. 

[burakkucat]

b*cat bows to acknowledge the complement. 

For a copper pathway of approximately 285 metres in length I would expect your downstream synchronisation speed to be somewhere in the range of 55 to 68 Mbps, depending upon wire diameter, joint quality, the presence of other "disturbers", phase of the moon, etc. The fact that you were originally at (essentially) 80 Mbps and then dropped, over time, to 68 Mbps makes me think that your circuit is above the average build quality.

[tommy45]

My D'side pair length will be around the 300-350 mtr mark has an DS attenuation level of 13.6db and a DS SNR value of 7.3db  Reported by the HG612 modem, i get the full 80/20 sync rates and have done for some 22months ,( Apart from a few short term instances where dlm intervened )

[shadow4dog]

Do you guys think I should restart the modem? if I didn't have an unlocked device I wouldn't have known it had happened and wouldn't be worried now!  8)

The stats are available on mywebstats website but to summarize, I'm getting about 10 ES an hour and about 5 SES in 48 hours. I normally get maybe 1 SES a week and 5 ES an hour.

Thanks
Tim

[Chrysalis]

10 ES an hour is fine.

[NewtronStar]

Do you guys think I should restart the modem? if I didn't have an unlocked device I wouldn't have

As it's a false SNRM reading and the SRNRM should be as close to 6.0dB or above if your line as some spare left. I personally would reboot the FTTC modem.

[shadow4dog]

I rebooted it, and it's now gone back to a 6db profile with a sync speed of 66Mb and an attainable of 65Mb As it was a false SNR I figured the DLM would think I was on a 6db profile and it's next step would be to interleave the line... which is way worse than a tiny loss of speed.

Thanks for the advice guys, really helpful.

Tim

[NewtronStar]

I think it was a good idea to reboot the modem as your errored seconds had started to increase since the false SNRM came into effect 

[WWWombat]

Ooh ... just learnt a new way to look at MDWS  8)