Why might my SNR margin stats suddenly change like this ?

Note the SNR Margin change down/up. There was heavy rain this morning, so I might just know the answer. The average throughput is the same and the line is stable. Does this bode ill for the future however ?

I do notice that my parents, who live next door, with the same pole, same cabinet, and almost the same sync speeds/thoroughput as I have, although their SNR margins are 13/10 dB down/up. They are with Vodafone.

From:

DSLAM/MSAN type: BDCM
Modem/router firmware: Not reported
DSL mode: G.993.2 (VDSL2)
Status: Showtime
Uptime: 40 days, 0:57:55
Resyncs: 0 (since 21 Apr 2017 10:13:35)

Downstream Upstream
Line attenuation (dB): 14.9 6.0
Signal attenuation (dB): Not monitored
Connection speed (kbps): 39999 7448
SNR margin (dB): 4.8 6.7
Power (dBm): 14.0 7.4
Interleave depth: 4 0
INP: 52.00 0
G.INP: Enabled

RSCorr/RS (%):
RSUnCorr/RS (%):
ES/hour:

To:

DSLAM/MSAN type: BDCM
Modem/router firmware: Not reported
DSL mode: G.993.2 (VDSL2)
Status: Showtime
Uptime: 41 days, 5:14:25
Resyncs: 0 (since 21 Apr 2017 10:13:35)

Downstream Upstream
Line attenuation (dB): 14.9 6.0
Signal attenuation (dB): Not monitored
Connection speed (kbps): 39999 7448
SNR margin (dB): 13.7 10.2
Power (dBm): 14.0 7.4
Interleave depth: 4 0
INP: 52.00 0
G.INP: Enabled
RSCorr/RS (%):
RSUnCorr/RS (%):
ES/hour:

Either some noise has switched off which was interfering with your signal or the rain has wet a joint and it is now connecting better.

Your target is much better now, but I would wait and see if it drops again when the rain stops.

or the rain has wet a joint and it is now connecting better.

Wet connections do not improve things on the whole.

Yes,

I noticed that my parents, who switched to vodafone about 3 weeks ago from ADSL Max from Sky, had the same 13/10 dB SNR down/up during the first 10 days and after that still the same SNR with a sync of 39995/9999. Which made me a little jealous. Their speed tests are overall faster than mine.

So either something rather good has happened, and I might get better throughput (even a decent 80/20 profile sync !), or I have a waterlogged line which will start to flake out sometime in the near future, BTO round, moan moan. BTDT.

Your downstream sync suggests a hard 40Mbps cap, which means you are either on a 40/10 service or DLM has capped it at that due to earlier problems. Your attenuation suggests you should be able to get well over 60Mbps.

In either case your upstream sync stinks. It should be up at 9999kbps on 40/10 or higher if on an 80/20 connection.

In reply to a post by RobertoS:

Your downstream sync suggests a hard 40Mbps cap, which means you are either on a 40/10 service or DLM has capped it at that due to earlier problems. Your attenuation suggests you should be able to get well over 60Mbps.

In either case your upstream sync stinks. It should be up at 9999kbps on 40/10 or higher if on an 80/20 connection.

I'm on Zen Unlimited fibre 1 up to 38. I've been on UL fiber 2 before. I saw a maximum of 51Mb downstream for 3 days. It was stable and fast, but the ES/hour were eyebrow raising. It tried 48, 46, 42 .. then settled for 40. I've seen it Sync at 9999 up, but the D/S Sync often drops proportionately I went from 35.5 D/S to 39999 when the lower SNR target was rolled out.

However my line stats have improved since I first got fibre according to the BTW ADSL checker:

VDSL RANGE A DS CLEAN HIGH 64.3 LOW 49 US: HIGH 17 LOW 11.2

VDSL RAGE B DS IMPACTED HIGH 52 LOW 32.4 US: HIGH 14.1 LOW 6.9

A stable 50 down would make me a fairly happy bunny.

heh it just went back to this:

Stats recorded 15 May 2017 18:09:03

DSLAM/MSAN type: BDCM
Modem/router firmware: Not reported
DSL mode: G.993.2 (VDSL2)
Status: Showtime
Uptime: 41 days, 7:13:25
Resyncs: 0 (since 21 Apr 2017 10:13:35)

Downstream Upstream
Line attenuation (dB): 14.9 6.0
Signal attenuation (dB): Not monitored
Connection speed (kbps): 39999 7448
SNR margin (dB): 4.8 6.4
Power (dBm): 14.0 7.3
Interleave depth: 4 0
INP: 52.00 0
G.INP: Enabled

RSCorr/RS (%):
RSUnCorr/RS (%):
ES/hour:

Central heating kicked in? Cooking? TV switched on? (Any in the house if you have multiple ones). Anything at electrical that goes on and off.

I wonder if the maths in the router just went a little screwy and calculated it incorrectly?

The answer is certainly noise, but the question remains - what noise?

When pondering this new question, don't forget that crosstalk is a primary consideration in FTTC: it could be caused by someone turning their own modem on and off overnight, or when on holiday.

Wrong type of snow? Leaves on the line? It's still at:

Connection speed (kbps): 39999 7448
SNR margin (dB): 4.8 6.4

Well, I hope it stays that way.

I would prefer it if the SNR margin was higher, tbh. Then, it means if a crosstalker came online, they may not impact your SNR margin's as much if at all. It may be a good idea to note down the times at which this happens (both ways) and see if you can find a pattern.

Edited by deleted (Wed 17-May-17 20:05:14)

It is higher in the daytime.

Connection speed (kbps): 39999 7448
SNR margin (dB): 13.7 10.2

It falls in the evening and overnight, which is normal.

Not only that but the higher values are as per next door.

What is abnormal is the amount of impact whatever the cause of the he drop is has. We have no evidence that I recall that it is cross-talk.

As the noise source will be of the same size every time, judging by the stats we have been given, having a higher nose margin would simply give the OP a lower speed still. The SNRM drop would still happen. But it doesn't affect the throughput at all.

Not only that, but as already established, he is on a 40/10 service. So his downstream speed is at the maximum he can get. The upstream however looks quite low.

Edit, struck out the typed "he".

Edited by RobertoS (Wed 17-May-17 23:55:21)

Firstly, I didn't say it was crosstalk. I said that if a crosstalker came online, then it would have an effect on the SNR margin's, but more so if the noise was present at the time. Secondly, the likelihood of the downstream SNR margin dropping by that amount just by normal RF noise increasing, is very low. The cause is due to a source of electrical interference. Thirdly, yes, a higher downstream SNR margin would give a lower speed, but I didn't say that the downstream SNR margin should be set higher... What I meant was that if the downstream SNR margin remained at its set level of around 13 dB, it would mean that if a crosstalker came online, then it would be more likely for the downstream rate to remain at 39999 Kbps, as there would be less noise.

I also noticed that the upstream rate is quite low, but so is mine and apparently my copper pair is "perfect"...

Interference = lower speed not vice versa.

Edited by deleted (Wed 17-May-17 20:38:33)

In reply to a post by RobertoS:

It is higher in the daytime.

Connection speed (kbps): 39999 7448
SNR margin (dB): 13.7 10.2

It falls in the evening and overnight, which is normal.

Not only that but the higher values are as per next door.

Not only that, but as already established, he is on a 40/10 service. So his downstream speed is at the maximum he can get. The upstream however looks quite low.

The SNR Margin anomaly hasn't repeated itself so far. I think I was prompted to post about it because of next door's figures. They are now 3.5 weeks into their new Vodafone FTTC and the line is stable, with a median throughput a few Mb better than mine. Their attenuation is also higher, c. 21dB d/s 13dB u/s IIRC. Unfortunately I didn't write it down. I must look again. Also the BTW ADSL checker gives identical figures for their line.

There is more copper between me and the pole. They are closer and more direct. Their line goes through a brick wall, up the wall, and thence to the pole. Mine goes from living room through the wall/ceiling/across the loft to the back gable end and exits under the eaves. My line is actually retained in place at one point on its path to the pole by a metal bracket on their roof. I should really take some photo's.

My upstream sync has almost always been 7000-8500 Mb since I had FTTC installed in May 2015. It is strange. It decided to drop to 32500Mb d/s around February, which caused the u/s to sync at 9999Mb.

Edited by TygerTyger2010 (Wed 17-May-17 22:25:24)

In reply to a post by WilliamGrimsley:

Firstly, I didn't say it was crosstalk. I said that if a crosstalker came online, then it would have an effect on the SNR margin's, but more so if the noise was present at the time.

No, you didn't. "I would prefer it if the SNR margin was higher, tbh. Then, it means if a crosstalker came online, they may not impact your SNR margin's as much if at all".

Quite apart from the fact that even if you had, it would have been rubbish. If a source of cross-talk starts up it affects the SNRM, whatever that is at the time.

Secondly, the likelihood of the downstream SNR margin dropping by that amount just by normal RF noise increasing, is very low. The cause is due to a source of electrical interference.

That's what I said, only I didn't claim to know the precise cause. All "noise" in this context is by definition electromagnetic. (Incidentally, "The cause is due to ..." is duplication within itself. I hesitate to use the grammatical "is an example of redundancy" as it isn't quite).

Thirdly, yes, a higher downstream SNR margin would give a lower speed, but I didn't say that the downstream SNR margin should be set higher...

What does "I would prefer it if the SNR margin was higher, tbh" mean?

What I meant was that if the downstream SNR margin remained at its set level of around 13 dB, it would mean that if a crosstalker came online, then it would be more likely for the downstream rate to remain at 39999 Kbps, as there would be less noise.

Gibberish. You are getting mixed up between the noise margin dropping dramatically for an undiagnosed reason, and the possible consequences of that large drop if a second source of noise caused by a cross-talker came online whilst the drop was prevailing.

I also noticed that the upstream rate is quite low, but so is mine and apparently my copper pair is "perfect"...

You flounced out (I think it might have been for the second time) over five weeks ago with this post, after many highly knowledgeable posters had criticised you for obsessing about your connection which was behaving perfectly normally, and for often posting misleading or even wrong information to people such as the OP for which you were frequently criticised.

I refer the OP and yourself to an earlier David_W post in that thread. I did start to add links here to following posts but it would be easier for you both to read that thread in Flat mode from that post at Sun 09-Apr-17 10:44:09 to your final one at Sun 09-Apr-17 12:14:45. Mine at Sun 09-Apr-17 12:01:56 in particular gives two very salient quotes from yours that was later deleted.

Interference = lower speed not vice versa.

Interference that isn't sufficient to cause a disconnection and reconnection at a lower speed has no effect at all on speed except and extremely high levels where the modem can be overwhelmed by error correction. I'm talking things like tens of thousands of FECs per minute.

Edited by RobertoS (Thu 18-May-17 00:21:41)

Sorry Tyger, I got rather tied up with what you can see.

If you mean the margin isn't jumping up in the daytime any more that looks a bit serious, as it suggests something is putting a lot of noise on your line but not on your neighbour's. To me it could mean an intermittent fault that has gone hard.

I don't know if you use the landline phone. I hope you have a phone! If so, please see if you get a dial-tone when you lift the handset. If you do, please dial 17070 which normally offers the quiet line test amongst other options. For most ISPs it is Option 2. It should be effectively silent except for the repeating message.

If you don't get a dial-tone then one wire of your pair has been intermittently disconnecting and has now finally completely done so.

Could be cross talk from his neighbour.

If you mean the margin isn't jumping up in the daytime any more that looks a bit serious, as it suggests something is putting a lot of noise on your line but not on your neighbour's. To me it could mean an intermittent fault that has gone hard.

I don't know if you use the landline phone. I hope you have a phone! If so, please see if you get a dial-tone when you lift the handset. If you do, please dial 17070 which normally offers the quiet line test amongst other options. For most ISPs it is Option 2. It should be effectively silent except for the repeating message.

The margin does vary about 0.3-0.4dB, mostly on the upstream, on a 24 hour cycle.
It's stable within that range, except for this instance. It still remains at the usual level.

I may have posted about SNR the issue too quickly. I was just surprised to see it jump to such an unusual reading.

I use my landline all the time. The line has a light, but noticeable background hiss. I've also noticed on occasion a brief "Skwirk" noise while the other end is ringing after dialling out. I do recall one time after a call,(this was months ago), that I had no net connection and I had to mains reset the router to get it back.

This is nothing to how it used to be. When I moved in to this house in 2009 the line crackled to various degrees, and got so bad it was unusable for weeks at a time on occasion. That was on ADSL Max.

The crackling was still there when I got FTTC in May 2015. For the first 6 months lots of jitter and the throughput was about that of ADSL2+ with a sync of 39999/7999.

After a lightning strike in November 2015 and a repair by BTO the voice noise was fixed. My line was stable with no crackling and little jitter. I had a problem with water on the line after that, early last year, which reduced my connection to 11Mb down, with no usable phone, just crackling. They put me on a new pair. Before that happened the DLM had decided to drop the connection to 35.5Mb down. It went back up to 39999 after the lower SNR rollout in March.

You've totally misunderstood my post... I highly doubt that the OP wants to go to that thread as it is of no help to anyone. You've hijacked this thread. Nice one, "elder". Whoops!

I agree with Banger.

Edited by deleted (Thu 18-May-17 08:33:55)

That's easily checked Tim. They are his parents. Get them to switch off their modem. I'd also expect them to have the same power dBm as him so he should be putting out similar cross-talk to them. Which he apparently isn't. We don't know about other neighbours of course, but that is always a possibility.

Don't forget, the high rate of SNRM is what we would expect from the attenuation and estimates.

AIUI cross-talk is normally somewhere where the copper is running in a bundle, often at the cabinet link. It doesn't depend on proximity of end users.

What might be worth checking though is what we usually do within the home of a user with noise problems, as we have here. Check out whatever electrical/electronic devices his parents have and whennthey are switched in and off.

As you know, diagnosis is a question of elimination, first of things easily checked. My asking the OP about the phone side of things being one of the standard steps. Unfortunately not being the answer.

Pity. The phone not working, or crackling like mad would have been just what we wanted.

A variation of less than 1dB over 24 hours is no problem at all. Even two or three dB is common. That's why the default sync-time margin on both ADSLx and FTTC was 6dB for years. Not long ago BT Wholesale introduced 3dB on ADSL2+ for stable low-error lines, and more recently Openreach have started to roll out 5, 4 and 3dB on FTTC. Though it has been suggested that although they have moved on from pilots to a wider area the main rollout has been paused until September.

Tim knows a lot about that. He's a beneficiary .

I'm a bit stuck for a suggestion for the next step I'm aftraid.