Huge upstream noise margin swings

[DesertRaven]

Hello,

Until a week ago my Sky Broadband was completely stable, almost never dropping the connection, and then 10 days ago it dropped, connected for a few seconds then dropped again must be 50 times over about half an hour. It’s been following this pattern randomly each day since.

Using RouterStats it looks like the problem is the upstream noise margin dropping to zero. (Similar to the screenshot 20:00 to 20:06).

Interestingly DLM stated running again on my line on the same day this all started - odd because it only ran a few weeks back when I upgraded to Unlimited.

Anyone seen something like this before; could it be DLM, my DG834GT having a hardware problem or the DSLAM maybe?

The router is in a filtered faceplate which from previous experience has the same attenuation / noise margin as the Test socket.

It's running ADSL2+, noise margin 6.9db and I can't hear any crackling on the line.

Thanks

[PaulSky]

Put it in the test socket and take another set, if they are the same then it's not your internal setup and it will give you something to look at. You haven't moved to Sky SVBN for telephone have you?

[DesertRaven]

SVBN .... come to think of it I did get a letter from Sky a few weeks back saying they were going to be doing something with my line and it would go-off for a short time over night. I wish I'd paid attention to what it said now.

Reading other posts on SVBN it looks like I've been moved from a DSLAM to a ISAM - I guess in prep for FTTC (supposedly due "late summer 2011" at my exchange according to BT)????

If that's what's happened it makes sense to see DLM running again.

However, previously I used to get 4,096 Kbps down, 800 Kbps up with G.DMT, (even managed to get downstream of 4.5 Mbps after a CST profile tweak) now I only seem to be able to get 3,776 Kbps down and 608 Kbps up.

[Isitme]

There are quite a few reporting a speed reduction after they were moved to Sky's "new highspeed network".

[IWasNotTheEnemy]

For ref, the move to SVBN is nothing to do with FTTC. It's purely to take full ownership of the line from BT onto Sky's ISAMs...as it's one more hurdle for the line to go through it does seem to affect speeds

[DesertRaven]

Thanks everyone for the info!

Damn, I got all excited about FTTC for a moment there!

Unfortunately DLM had been running for 9 days (I'm guessing since the SVBN switchover) before I happened across the fact on MySky - by then it was too late as I'd switched the router off/on a few times trying to fix the connect-drop-connect problems.

Hopefully it’s just a DLM cap causing the reduced speed; will the speed edge back up on its own once the line stabilises or is the only way a friendly Sky CST?

[IWasNotTheEnemy]

I'd call CST and see what they can do for you now - can't hurt!

[DesertRaven]

A quick follow-up on this one; I've noticed that in my case anyway with the move to SVBN / IASM my attenuation has increased for ADSL2+ but not for G.DMT.

Now (IASM / SVBN)

ADSL2+
Connection Speed 4088 kbps 605 kbps
Line Attenuation 55.5 db 33.2 db
Noise Margin 6.6 db 16.0 db

G.DMT
Connection Speed 3776 kbps 608 kbps
Line Attenuation 53.0 db 31.5 db
Noise Margin 10.2 db 16.0 db


Before move (DSLAM, non SVBN)

ADSL2+
Connection Speed 4095 kbps 606 kbps
Line Attenuation 54.0 db 34.8 db
Noise Margin 7.2 db 11.5 db

G.DMT
Connection Speed 4096 kbps 800 kbps
Line Attenuation 53.0 db 31.5 db
Noise Margin 8.8 db 13.0 db

As I switched between ADSL2+ and G.DMT while DLM was running it has assessed each mode independently and capped them accordingly (I probably rebooted a few times when the router was in G.DMT mode).

The speed changes people are seeing when moving to SVBN are probably more down to DLM re-running than the actual move - if you know DLM is running you leave the router alone, however if you don't and your line drops / speed changes you tend to reboot and inadvertently get capped.

(It might be worth moving this thread to DLM, if anyone knows how).