Issue with SNR + sync speed.

Hi guys,

After about a month or so with of being active, our line has a weird issue that I can't work out.

The line has been stable up until now, SNR has been locked to 6db and sync speeds have been great..until last weekend.

I have contacted the ISP about this issue but I'd like to get some feedback from you guys who may have seen this issue before and know where to look/what to do.

What happens is the SNR will start off at 6db then suddenly either raise or drop. When it raises or drops, the sync speed will also drop to around 2500kbps rather than the 8500kbps+. Yesterday, the connection was fine from around 9am until 4.30am. Here are some graphs showing what's happening.

http://i.imgur.com/pvDjveO.jpg

http://i.imgur.com/HnQ1JAv.jpg


Things I've tried:

Changing filters
Changing RJ11 cable
Changing Routers
Plugging directly into test socket
Changing plug sockets for the router
ISP increased target SNR to 9db (didn't help)

The master socket is the only socket we have wired up. Like I said, it's been stable until now and we haven't changed anything.

Any help with this would be great as it's driving me crazy!


Edit: Current stats:

ADSL Link Downstream Upstream
Connection Speed 2784 kbps 824 kbps
Line Attenuation 52.0 db 20.7 db
Noise Margin 7.7 db 7.0 db

Have a gander at my thread here:

http://forums.thinkbroadband.com/general/t/4212010-s...

Getting to the point, I finally managed to get BT to run diagnostics on my line, and they found 'nothing wrong' - but since they did that, all is back to noraml again. I even had a engineer booked to come around, but cancelled at the 11th hour due to my line mysteriously working properly again.

Nick

I'll take a read in a second but my ISP already did diagnostics and found nothing wrong also

Your ISP can only run certain line tests - BT do some sort of load test on the line (I dunno the specifics), so it is a different test. I got disconnected twice when this was going on (although I didn't know they was testing at the time) and each time sync'ed back at a higher rate. They it is stable again.

Nick

Run Router Stats for a whole 48 hour period with 30 secs samples and post those images.

That looks like an external noise source kicking in and running. My first guess has to be your (or your neighbour's) central heating. Check to see what time it is set to come on at - and compare the two clocks.

Everyone runs their central heating 24/7 around here due to it being included in the rent (apartments).

I don't understand how it can be stable for over 3 weeks then start to become unstable (which also leads me to believe it won't be CH).

Edited by deleted (Sat 23-Feb-13 09:42:29)

can you select G.dmt or G992.1 as the ADSL mode on the router, rather than auto / multimode etc ? See what that syncs at.

I shall do that in a second.


I've just done a quiet line test without the router turned on, line was deadly silent. I turned the router on and lots of noise, crackles and whistling occurred. I moved the router into another room and tried again, same thing. I disconnected the router and the noise went away. My question is, why does this happen, why has it only just started to happen and why does it happen at certain times?

Is there a central stair case which is heated during the day?

With apartments all lines are often bundled together and run in service ducts? Is this the case?

Just as a line can develop a fault, any electrical system can and you cannot rule out CH, fridges, freezers, jacuzzi baths &c just because it was stable for a long time and suddenly it is not.

You certainly need to get several days of stats together and see if there is any commonality.

No, it's an odd apartment setup. It's basically purpose built houses but split into apartments. Houses are attached, 3 storeys then split into apartments. We have a two floor apartment with an apartment below us. On the left of us we're attached but on the right of us there is an outside stairwell which separates us from the next house. I can only assume that there's a line per house bundled into two/three?

I'm going to do the following:

Put router into modem only mode to rule out RF interference
Check the MCB to see how the sockets are split, try a different socket completely
Cry if everything fails

In reply to a post by pspr33:

I've just done a quiet line test without the router turned on, line was deadly silent. I turned the router on and lots of noise, crackles and whistling occurred. I moved the router into another room and tried again, same thing. I disconnected the router and the noise went away. My question is, why does this happen, why has it only just started to happen and why does it happen at certain times?

As a first shot, I think I'd be having uncharitable thoughts about the router power supply... have you one from another piece of kit (same voltage and polarity, at least the same current rating) that you could try?

your noises are audible noise being generated in response to the ADSL frequencies. This could be a filtering problem - unplug everything else from the system and see if it's still there. If it is then try again in the NTE5 test socket with a known good filter and phone to listen in.

Microfilters do fail.

If it's present in the test socket it may be a line fault, see if keeping the phone off-hook affects the speed it connects at.

In reply to a post by yarwell:

Microfilters do fail.

Wouldn't a failed filter tend to show up as some sort of hiss (or other fairly steady noise) on the line, rather than snap, crackle and pop?

That's why my first suspicion went for the power supply, they fail too. Rather more often, ime

I've got 3 filters, one of them brand new fitted yesterday. I can't see 3 of them being faulty.

I've turned all of the MCB switches off leaving only the sockets turned on, still noise on the line.

When I disconnect the RJ11 connected to the router from the filter, the noise stops. When I reconnect, there's noise.

This also happens with both routers I have, I can't see it being a failing power supply.

Edited by deleted (Sat 23-Feb-13 10:53:21)

Looking at that graph, and I have seen hundreds, suggests that the problem is an external noise source causing interference on the line. It could be your apartment, a neighbour or even someone down the street.

Looking closely there are five spikes occurring. The line is stable with a little fluctuation, spike, after which the noise fluctuates quite a lot, another spike, and so on ... The spikes are likely to be caused by a motor or pump starting up, or a CH ignition system and then the fluctuating noise from a motor of some sort running.

You say CH is on 24/7 - but what are the temperature settings? Is it set for 20^ofrom 04:30 to 09:00 and 16:00 to 23:00 and then just 14^o for the rest of the day?

I've just tested the phone directly into the test socket and there is definite noise.


Our thermostat is just set to keep the room at 20C, it comes on as and when it needs to. I've taken the batteries out of the thermostat and turned it off at the MCB, still noise. It's definitely nothing in our apartment causing the noise as far as I can see.

I've got 3 filters, one of them brand new fitted yesterday. I can't see 3 of them being faulty.

Is that "I have three filters and I've tried them all, one at a time" or "I have three filters plugged into various phone points" ?

Tried the test socket to eliminate internal wiring ?

Sounds like a line fault or filtering issue from the information so far.

Wouldn't a failed filter tend to show up as some sort of hiss (or other fairly steady noise) on the line, rather than snap, crackle and pop?

probably, but he's getting audible noise in response to the router coming on-line which sounds like a filtering issue or a high resistance fault acting up.

If it was a dry joint the effect can be to pick up lots of RF noise

Not sure if the original poster has tried a different router, as it may be an issue with that

I've just tested the phone directly into the test socket and there is definite noise on the line in the test socket.

In reply to a post by pspr33:

I've just tested the phone directly into the test socket and there is definite noise on the line in the test socket.

with or without the router ?

I've tried two routers, same issue.

Does sound like a high resistance issue, but at the time where it just affects ADSL, over time they usually get worse.

Ruling out all your own hardware including router and then getting a CIDR (or is it CIDT) test done can sometimes help identify it

Andrew

Without.

In reply to a post by MrSaffron:

If it was a dry joint the effect can be to pick up lots of RF noise

That's true, it could tend to act as a rectifier. I hadn't thought of that.

I've tried 3 different filters, 2 RJ11 cables and 2 routers. The issue remains on all hardware.

so a voice fault - you can run a diagnostic test from BT.com if it's a BT line (not LLU)

My line is provided by my ISP, Vivaciti. They ran diagnostics on Thursday and Friday which apparently came back all clear.

If its showing up when NO ADSL hardware/filters are connected to the line, then a voice fault to voice line rental people would be the way to go and don't mention ADSL

In reply to a post by MrSaffron:

If its showing up when NO ADSL hardware/filters are connected to the line, then a voice fault to voice line rental people would be the way to go and don't mention ADSL

So I should start a new ticket?

8.5 Meg, when it is running OK, seems exceptional for 52dB Attenuation.

In reply to a post by XRaySpeX:

8.5 Meg, when it is running OK, seems exceptional for 52dB Attenuation.

It's not usually that high, usually between 35 and 45db.

In reply to a post by pspr33:

http://i.imgur.com/pvDjveO.jpg

I just looked at the graph again - this is EXACTLY the times my line used to drop connection and sync lower and lower and _{lower and :....}.

You are not in Pompey are you? I wondered that when BT fixed my line, they just swapped cabinet connections around so I got yours, and you ended up with mine!

Nick

Edited by deleted (Sat 23-Feb-13 13:22:45)

Ah, that's more like it!

Perhaps that large jump in Attn. is a clue to the issue?

I'm not in Pompey no, I'm in Stoke Would have been funny to find out that did happen though.

I would do a voice only ticket, if there's a well defined voice fault independent of broadband.

Here's the graph from overnight:

NM: http://i.imgur.com/SOhu0dm.jpg
Connection speed: http://i.imgur.com/VihNkXk.jpg

There doesn't seem to be any consistency in when it happens and it didn't sync higher than 3000kbps yesterday, had to use my phone to tether most of the evening.

The SNR plot is awful - but what, I wonder, is causing the spikes?

Keep plotting until you have two full days of data

It's definitely external noise but I have no idea.

The plotting continues..

In reply to a post by MHC:

The SNR plot is awful - but what, I wonder, is causing the spikes?

Keep plotting until you have two full days of data

This is around 45 hours worth of plot data:

http://i.imgur.com/0byfSfS.jpg

Looking at that graph and the one from Saturday - what happened at 04:30 on Saturday? You may not know but all looked OK until that time and from then on it has gone haywire.

How often do you get quiet/stable periods such as that shown on Friday night to early Saturday AM.

No idea what happened at 4.30 on Saturday, I was sleeping

Well, this morning I've unplugged from the test socket, plugged everything back in as normal and seem to have gotten a stable connection *touches wood*. I have changed routers though as I was going to plot another 48 hours with our second router to see if there was a difference.

Current stats:

Link Information

Uptime: 0 days, 0:30:51
Modulation: G.992.5 annex A
Bandwidth (Up/Down) [kbps/kbps]: 1.274 / 9.111
Data Transferred (Sent/Received) [MB/MB]: 15,76 / 312,22
Output Power (Up/Down) [dBm]: 11,5 / 19,0
Line Attenuation (Up/Down) [dB]: 23,5 / 42,0
SN Margin (Up/Down) [dB]: 6,5 / 6,0


I really don't know what's going on here but I don't want to change anything now but the current router is only an old Wireless G and I *need* Wireless N for streaming

Leave it running and see what happens.

For Wireless N - can you put your router into a slave mode so it can just act as a WAP off teh router connected to te line?

I'm going to see if it does have slave mode, hopefully it will. It's a Netgear DGN2000 V2.

I've just powered on the Netgear and it made the SNR drop to 5.5db instead of a decently stable 6db. I've got a feeling I'm working with a dodgy power supply on the Netgear.

Just turn off DHCP and give it a fixed IP address. Connect it to the other and see what happens.

Done and working fine

SNR is stable at 5.5db now, will keep monitoring.

Get an image posted in an hour or so.


Also, even though the Netgear is connected, try to avoid using it for that hour. Then, start using the wireless side to the maximum which will start to load the power supply and see what effect that has on the line - run for an hour. Then turn off completely and keep monitoring the line.

In reply to a post by MHC:

Get an image posted in an hour or so.


Also, even though the Netgear is connected, try to avoid using it for that hour. Then, start using the wireless side to the maximum which will start to load the power supply and see what effect that has on the line - run for an hour. Then turn off completely and keep monitoring the line.

Here are the last couple of hours:

http://i.imgur.com/M6XwRFc.jpg

I was doing a lot of streaming on the network and transferring files between PC's during this time.

That suggests it is not a line related fault but electronically noisy equipment pushing out RFI. Which is what a heating pump or fridge wuld do - but you have eliminated those.

If, as you think, the PSU on your second router is noisy or failing then there will be radiated noise, which would explain your earlier comment about a 0.5dB drop and also conducted. It will be on the power rails supplying the modem, and transferred to the line when it will badly affect the SNR and will also affect processing of the incoming signal too.

Just keep monitoring.

Just when I thought things were solid, this happens:


http://i.imgur.com/Po6omzP.jpg


It had been at a stable 5.5/6db for the last few days and I haven't changed anything to make the noise start again. I am beginning to think that I should get a new PSU for the second router which may solve this issue.

Time to get digging through my 'box 'o' [censored]'.

EDIT:

Unplugged second router completely, noise still very apparent.

Edited by deleted (Wed 27-Feb-13 17:09:45)

Just a short burst or is it carrying on? Does it stop when you disconnect the other PSU?

It *was* carrying on even with the other PSU disconnected.

However, I just disconnected everything and plugged the phone directly into the master socket, there was audible noise. I unscrewed the master socket and plugged into the test socket, no noise. I've just stuck the filter into the test socket and the connection is back to normal. I've got a feeling there's an issue with the socket but have no real way to prove this.


Thanks again for replying too


EDIT: Quiet line test (17070) is free to call, right?

Edited by deleted (Wed 27-Feb-13 17:34:37)

Yes, 17070 is free - but don't abuse it.


Have a good look at te socket and check that all pins look OK and are not bent.


Did you do anything at the time it all failed? Something that might have caused it?


Just monitor it and see, next time it happens go round and turn off everything in te house and see if it continues before disconnecting.

I don't think I abuse it, just check to see if noise is apparent when things like this happen.

The socket connections look fine (they were the first thing I checked when it first started to happen). Am I allowed to unscrew the actual socket completely?

I did nothing at all, I was sitting at my PC when I noticed the connection drop.

Technically no. But if you are careful when you take it off, and only check for loose connections and don't fiddle you should be OK.