Weird Upstream SNR Problem

[Jan8p]

Hi all,

Got a weird problem with my Sky connection (unlimited, not fibre).

It was activated on 10 Dec and was stable at 4000/800 with zero dropouts until 23 Dec, at which point the upstream SNR started going crazy at random times, causing the connection to drop and to reconnect at a lower speed, normally around 4000/450. This has been ongoing since then and is still ongoing now.

Stats until 23 Dec were around 6.5dB SNR downstream with 55dB Att and 9.9dB SNR upstream with 33dB att.

Currently stats are:

Broadband Link	Downstream	Upstream
Connection Speed	4011 kbps	798 kbps
Line Attenuation	55.0 dB	33.7 dB
Noise Margin	6.1 dB	8.8 dB

What happens is the downstream stats remain stable, but completely randomly the upstream SNR drops from 9.9dB down to 8.8/7.7/6.6/5.5/4.4/3.3/2.2/1.1 then either drops out or goes back up in the same intervals.

This can happen at any times of the day, sometimes doing the above for hours before being stable for a while (few hours, up to a day).

It's weird how the upstream SNR is ALWAYS 9.9/8.8/7.7/6.6 etc, it never changes outside that pattern, and when stable it's always 9.9dB. Maybe that's just a feature of the Sky Hub firmware and how it reports upstream SNR though.

I've an openreach engineer coming on Saturday to hopefully resolve the fault but just thought I'd ask you guys and see if you've ever seen anything like it before?

Thanks in advance!

[Scubbie]

Such fluctuations are often related to line issues. Since you already have the BTO Engineer coming, that is a good step.

Other things to check would be to listen for any noise on the line, possible water getting to the line, if it goes underground and possible electrical interference.

[Jan8p]

I've come to the conclusion it's completely out of my control. Router is plugged into test socket and I've unplugged literally everything in the house and it's still the same so if it is interference it's nothing of mine!

Water is a possibility, as I live in an apartment and there are no overhead lines so they must be underground.

Is it possible for BT engineers to pinpoint intermittent faults such as these when the fault isn't actually occurring?

Sods law says everytime I call Sky the line is fine so their line tests all show OK, no doubt it'll be the same when the engineer visits...

[Scubbie]

It really depends on the nature of the fault.

Since you are living in an apartment I should add to the mix that the telephone wiring in blocks of flats is normally rubbish. Basically the builders normally put in the cheap telephone cable which you would use for an extension. This may be passing through a duct with many other cables, which will cause interference due to the various signals going through all the cables.

For a little on some of the possibilities regarding interference from outside sources, take a look at this article:

::. Kitz - REIN .::

[Jan8p]

Openreach engineer has been this morning, done some tests on the line and apparently it's coming back as perfect. Obviously, at the time, the line was connected at it's full speed and full SNR and perfectly stable. 10 mins after he left however, upstream SNR went 9.9/8.8/7.7/6.6/5.5/4.4/3.3/2.2/1.1....back up again, then down, then started dropping the connection!

The BT guy did was quite friendly and helpful however not alot he could do due to there being no fault when he was here and the line testing perfectly. He suggested getting back on to Sky and asking them to raise it as a broadband fault to get a broadband engineer out...

[Scubbie]

That is possible a good idea. A normal BTO Line Engineer will only check the basics.

[Jan8p]

DLM is also now running again on my line, so I'm hoping it doesn't lower the downstream speed as well due to the disconnects..

[Scubbie]

Actually that could work in your favour.

You can nicely argue that as a direct result of the line keep dropping, the dl speed has dropped. Obviously don't do this on purpose though by power cycling your router (it will show on the logs).

You could download and install 'RouterStats Lite'. This doesn't contain settings for the Sky Hub, but it can be customised to do so quite easily.

Internet Software

[Jan8p]

So......after numerous BT engineer visits..I still have this issue.

The latest visit by a broadband engineer yesterday found multiple HR faults on the line. I must say he was pretty good, building up a new line underground from the cab to my property. The result being a much quieter line, going from 4Mb to 5Mb and also a quieter telephone.

However....a few hours after he left the line presented the same fault, upstream SNR going crazy causing dropouts and eventually a 200k upstream speed. I'm getting a bit fed up now.

If I have a new line to the cab, what is left to cause the fault? Is it more likely to be a problem within the premises or the exchange side of the cab?

Any help appreciated!

[Scubbie]

I would suggest a friendly call to Sky. It is possible that the Engineer missed something further down the line. As you are speculating, this could be on the exchange side of the cabinet but I couldn't say.