General Discussion
  >> General Broadband Chatter


Register (or login) on our website and you will not see this ad.


Pages in this thread: 1 | 2 | 3 | (show all)   Print Thread
Standard User tbailey2
(learned) Sun 01-Jul-12 17:09:52
Print Post

ADSL2+ Line - Help with BIG dB drops! [long]


[link to this post]
 
I would be grateful for some help in establishing what is happening on my ADSL line! This post will be long but please bear with me as it gets more interesting towards the end.

Firstly, background which should hopefully answer most of the inevitable questions..

I've been at the current address for 20 years+ and have been a programmer for 40 years+. When I first moved here in 1991, I was working on contract programming for a very well known telecomms company and, as I worked from home, I needed comms. This started out as a dial up modem, then moved to dual-channel ISDN, then to a Kilostream link and then two Kilostream links. I also have two telephone lines.

This has meant a lot of cables into the house, and as I work from the front on the first floor, cables up the wall. At some point about 15 years ago, there were some problems and a BT engineer put in a new cable from the road and remade all the cabling where it emerges from the ground, adding a new black BT junction box just above ground - photo on this link:

External BT Box

The box appears to be sealed so haven't tried to open it. The other white box is the next door neighbour's phone.

With time passing, the ISDN and Kilostream links are naturally no longer in use although the cabling is still there. At least one of the white cables you can see is redundant (I don't know which) - one is our current house Telephone and the black one is my business telephone, Line 1. This was originally a fax line but is now just a telephone line with ADSL on it. It comes straight from the black box up and through the brick wall and into one side of a BT LJU4 Dual Line Master socket that originally had ISDN on both connectors. Consequently I have no NTE5 master socket as such and there is no extension wiring on this socket - just the filter and phone/ADSL. The other half of the wiring on the LJU4 has been disconnected by BT at some point past. There is no bell wire connected, just 2 & 5.

Line 1 has had ADSL + Telephone on it since 2003 (after I successfully ran the campaign to get ADSL to our village of Hurstpierpoint with much help from ADSLGuide.org [this site in its previous incarnation]!). I am about 1.2Km from the exchange as the crow flies, and 2.4Km via the route the cables take and about 0.3 Km from the cabinet in a fairly straight line. The d/l speed on this line has been fine for many years (after I removed myself from Pipex and went to Zen where I have been ever since and been very happy - it's not the cheapest but then you get what you pay for it seems and Zen have excellent support (I see WW III nearly broke out on another thread over customer service).

Downstream line attenuation was around 35dB on plain ADSL and downstream speed generally an actual 5-6 Mb/s. It's filtered (have changed filter recently several times) with a short 18 inch shielded cable to the router which until the end of June was a Vigor 2820n although I don't use the wireless.

Telnet ADSL Max Stats

On July 1st, the line was transferred to ADSL2+ - it looked like I could get a few more Mbps out of the line which proved to be true (now 40db/39dB D/S Attenuation depending on which router, prob 39.5dB, stats to come below). I changed the router to a Billion 7800 just before it went live as I fancied being able to set the Target SNR and it has a good reputation.

Here are the stats from the 2820n on ADLS2+ as a comparison to the ADSL Max one above as I had it running for a short while on the 23rd June:

> adsl status [23rd June]
  --------------------------- ATU-R Info (hw: annex A, f/w: annex A) -----------
   Running Mode            : ADSL2+(G.992.5)       State                : SHOWTIME
   DS Actual Rate          : 10040888 bps   US Actual Rate       :  1132574 bps
   DS Attainable Rate      : 10232000 bps   US Attainable Rate   :  1132000 bps
   DS Path Mode            :  Interleave    US Path Mode         :  Interleave 
   DS Interleave Depth     :       64       US Interleave Depth  :        4 
   NE Current Attenuation  :       39 dB    Cur SNR Margin       :        6  dB
   DS actual PSD           :    20. 4 dB    US actual PSD        :    12. 5   dB
   ADSL Firmware Version   : 232201_A 
  -------------------------------- ATU-C Info ---------------------------------
   Far Current Attenuation :       20 dB    Far SNR Margin       :        6  dB
   CO ITU Version[0]       : 00004946       CO ITU Version[1]    : 0000544e
   DSLAM CHIPSET VENDOR    : < IFTN >
>


All went well until strange drop outs/ loss of sync or, sometimes, Internet access started occurring after a few days. I had RouterStats running (plenty of graphs available!) and had a word with John Owen who having had a look the graphs, suggested getting rid of what was probably local noise might be a good starting point. This proved fairly easy since in umpteen years of cable changes, the long lead from the filter to the router had got wrapped round umpteen power and other cables!

The Target SNR then became much more stable staying generally with +/- 0.5dB. But the dropouts continued - here are some typical examples from various days, you can maybe see a pattern. These are of course within the Training period (although I have seen doubt cast on whether this actually exists for ADSL2+?) and so maybe that was the 'problem'. The 'ramping down' of the SNR on some of the graphs almost looks machine made? Or is it some noise? If it is, it is not apparently in the house after some investigation including turning off the power completely (my room runs on an APC 1.5Kw UPS so that was easy to check and it is pretty random) - an 8dB drop at times is a lot though :

Example drops 1
Example drops 2

Anyway, I eventually discovered a number of things:

1) Once the S/NR drops below about 1.2dB, I lose Internet access (LED goes out on Billion) BUT the line stays synched right down to the point it drops out at 0dB or so (assuming it does). Towards the end of the month I set the Billion up to maintain a 9dB S/N Target to try and avoid the drop outs.

2) However, under normal circumstances when the line is steady, I can stay synched at 0.3dB for at least 18 hours with a sync speed of around 10Mb/s+ (12,086@3db).

3) If and when the S/NR eventually recovers of its own accord then the speed returns. If it has resynched due to a drop out then I generally lose connection speed of course. Shortly after the DLM ramps up the S/NR Target as the graphs clearly show in several cases. My Zen profile data show the speed varying wildly some time afterwards:

Zen Line Data

4) BUT, and this may be important, if I manually resynch the router while I have lost Internet access but am still synched, all immediately returns as it was with no DLM subsequently springing into action. Odd? Maybe it's the router??? So I tried the Vigor 2820n and also a cheap Tenda (based on a TP Link), the latter running currently for four days but the results are the same as the Billion as you will see.

5) The line can be stable on ADSL2+ for up to four days so far with no massive drops.

A second ADSL line

Due to a project I'm starting work on, I now found I needed a second ADSL feed for a few months - as I have a spare line already, I decided to add ADSL to it via Zen again on a monthly contract and this went live yesterday (amazingly, four days before it was supposed to!). Checks showed that it should be a bit faster than the current one - the telephone number line checkers consistently showed 5Mb/s for my current line and potentially 6Mb/s for new one. Maybe this would be my new permanent line and solve the dropout problem?

The line is of course on the same BT underground cable and if anything will be a bit noisier as it's currently an extension off a very old BT logo'd master with split faceplate downstairs. However, I have filtered it at both sockets for now and I guess it doesn't affect what is about to happen as it is a separate pair after all...

I decided to put this line on a second (secondhand) Billion 7800n router but set so it didn't affect the target S/NR when rebooted. And am determined to leave it alone for 10 days if necessary to see what happens. At the moment, the router LAN output goes straight into a laptop which has RouterStats running on it. No other connection to my own LAN, NAS boxes etc or any other equipment .

Out of the box, it connected at 6dB and 9,847 Kbps and had been that way pretty well for about 18 hours at a +/-0.5 dB rate

Until 10.58.52 today that is - and this is the point at which I have now become totally confused!!

Below is a composite of RouterStats graphs from both lines, original at the top and new one below, over the same time period as near as I can make it with the aid of Photoshop (the logs show the relevant timings are identical).

Line Comparisons

They are self-explanatory I hope.

Line 1 dropped and then ramped down to 0dB from ~3dB and lost synch - (this is the Tenda router so no S/NR management possible), resynched back at 3dB and then (I assume) the DLM kicked in. The graph now looks very familiar if you look at earlier examples...

Line 2 appears to have some mystic affinity to Line 1 but didn't lose synch - it was 3dB higher in the first place though. This line lost d/l speed to about 2Mb/s during the second low period but kept at about 8.5Mb/s during the first low period. Sync rate is still 9,847 which ties in with an 8.5Mb/s d/l.

My best guess based on these two graphs is now noise -or maybe an exchange fault if both lines actually end up on the same equipment. But why does resynching the router immediately stop the problem?

If it helps, here are graphs of Bits & Attenuation before (top) and during (bottom) an 8dB drop:

Bits & Attenuation Comparison

And my US noise isn't good either (taken today but it's always like this [on both lines]):

Upstream Noise Margin

It would be nice if it was a line fault somehow as I could get all my cabling/sockets sorted! If anyone needs more data I probably have it but didn't want to go from what may be complete to total overload on this post to solve that these drops are. I expect it's simple really.

Okay - over to the experts please. Thanks.

FWIW my live stats off Line 1 are linked in my sig. Any red graph traces are my own alarm limits. Stats are a bit restricted currently as the Tenda doesn't do Telnet - waddya expect for £11!

Tony confused

==
Tony
Hurstpierpoint, West Sussex
My Live Router Stats

ZeN Active + ZeN Lite

Edited by tbailey2 (Sun 01-Jul-12 20:44:47)

Administrator MrSaffron
(staff) Sun 01-Jul-12 17:18:53
Print Post

Re: ADSL2+ Line - Help with BIG dB drops! [long]


[re: tbailey2] [link to this post]
 
A line fault would affect one line and not the other usually.

The fact the noise spike is common to both, suggests something external to the BT network generating noise at the right frequncies to kill ADSL and ADSL2+.

Try and grab a bin plot the next time you see the issue, and you may see a bin or two suffering badly, and the frequency might lead you to identify it.

How often are the drop outs? If less than once a day, then that is just life, and why people opt for full fibre FTTP to get away from RF noise for business use. If its ten or more times an hour, then you might get some help from BT SFI in identifying source, but would need to be very regular.

Andrew Ferguson, andrew@thinkbroadband.com
www.thinkbroadband.com - formerly known as ADSLguide.org.uk
The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User tbailey2
(learned) Sun 01-Jul-12 17:25:38
Print Post

Re: ADSL2+ Line - Help with BIG dB drops! [long]


[re: MrSaffron] [link to this post]
 
Hi Andrew!

They are both ADSL2+ - there is a bin plot link in there, both before and during and it looks a mess...

Most I've seen is three in one day, usually one, others none. If it is noise, I can live with it, just set the alarms in RS and get the Billion to resync... Duration is also very variable from minutes to hours.

==
Tony
Hurstpierpoint, West Sussex
My Live Router Stats

ZeN Active + ZeN Lite

Edited by tbailey2 (Sun 01-Jul-12 17:26:24)


Register (or login) on our website and you will not see this ad.

Standard User tbailey2
(regular) Sun 01-Jul-12 17:28:45
Print Post

Re: ADSL2+ Line - Help with BIG dB drops! [long]


[re: MrSaffron] [link to this post]
 
And fibre for here is just a dream ...

What I don't understand if it is noise is why resynching the router stops it?

==
Tony
Hurstpierpoint, West Sussex
My Live Router Stats

ZeN Active + ZeN Lite

Edited by tbailey2 (Sun 01-Jul-12 17:32:08)

Administrator MrSaffron
(staff) Sun 01-Jul-12 17:31:18
Print Post

Re: ADSL2+ Line - Help with BIG dB drops! [long]


[re: tbailey2] [link to this post]
 
NOTE: I said full fibre (FTTP), FTTC can still be prone to RF interference like this.

Bin plot has no obvious holes, so suggests broad spectrum noise, e.g. something being switched off/on or on/off just occassionally

Andrew Ferguson, andrew@thinkbroadband.com
www.thinkbroadband.com - formerly known as ADSLguide.org.uk
The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User tbailey2
(regular) Sun 01-Jul-12 17:32:55
Print Post

Re: ADSL2+ Line - Help with BIG dB drops! [long]


[re: MrSaffron] [link to this post]
 
Point taken, have amended...

==
Tony
Hurstpierpoint, West Sussex
My Live Router Stats

ZeN Active + ZeN Lite
Standard User Zarjaz
(knowledge is power) Sun 01-Jul-12 17:50:56
Print Post

Re: ADSL2+ Line - Help with BIG dB drops! [long]


[re: tbailey2] [link to this post]
 
The top of the black box pictured should easily slide upwards. I wonder if the two lines share a common cable from the black box to your office (or where ever the BB kit is) and that there is an issue with this cable. Course could be anywhere between exchange and you. Can you show us a photo of the inside of the external box ?

Standard User tbailey2
(regular) Sun 01-Jul-12 17:58:04
Print Post

Re: ADSL2+ Line - Help with BIG dB drops! [long]


[re: Zarjaz] [link to this post]
 
I will do that, there appeared to be a circular locking device at the bottom. The lines are two separate cables set up at different times (one white going up via the downstairs junction through the PVC of the window, the other black which is Line 1, the other white one that goes straight up is not used or connected at my end) although the parent BT cable is obviously the same one in all cases.

FWIW the disruptions last a minimum of about 25 mins up to several hours (if I can actually wait to find out!). The twice I have restarted the router after a few mins if it drops, it has come back minus the 'noise'. I will have to put the Billion back on as I want to drop the PPOA session only during a drop and reconnect and see what happens. The Tenda won't let me do that but at least it proved it wasn't the router. I'll try to catch more graphs next time.

==
Tony
Hurstpierpoint, West Sussex
My Live Router Stats

ZeN Active + ZeN Lite

Edited by tbailey2 (Sun 01-Jul-12 18:35:44)

Standard User Zarjaz
(knowledge is power) Sun 01-Jul-12 18:01:39
Print Post

Re: ADSL2+ Line - Help with BIG dB drops! [long]


[re: tbailey2] [link to this post]
 
Power supply on something you are rebooting causing the noise ?

Standard User tbailey2
(regular) Sun 01-Jul-12 18:32:38
Print Post

Re: ADSL2+ Line - Help with BIG dB drops! [long]


[re: Zarjaz] [link to this post]
 
In reply to a post by Zarjaz:
Power supply on something you are rebooting causing the noise ?

A possibility I suppose but it's happened now across four different routers each with its own 12v power brick and only one has been in use at any time until yesterday...

I am in a semi-rural country lane BTW with fields in three directions but the cable from the cabinet near the southern end will run along a main road through the village itself to the exchange. I can't immediately think of any major engineering machinery/works along the way. The line was clear of any interference (if that is what it is) all day yesterday (Friday) and last week from Sunday until Wednesday.

The UPS is because we have overhead power and lots of glitches - a complete drop yesterday for 5 secs but the sync held up although there is a big bouncy spike in the S/N graph in both directions when it happened.

==
Tony
Hurstpierpoint, West Sussex
My Live Router Stats

ZeN Active + ZeN Lite
Pages in this thread: 1 | 2 | 3 | (show all)   Print Thread

Jump to