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3dB SNR sync Is my modem failing?

Stumpy21
Rising Star
Posts: 156
Thanks: 6
Fixes: 1
Registered: 13-06-2011

3dB SNR sync Is my modem failing?

Hello
Received my TG585v8 modem when joining Plusnet, May last year.
All has been fine until recently.
Today the router has decided to Sync with a SNR of 3db, giving a sync speed about 1 meg higher than usual and a flakey/slow to load internet connection, even doing a reboot at 9pm has given me the following connection.
Uptime: 0 days, 0:36:20
DSL Type: G.992.3 annex A
Maximum Bandwidth (Up/Down) [kbps/kbps]: 888 / 6,172
Bandwidth (Up/Down) [kbps/kbps]: 440 / 5,976
Data Transferred (Sent/Received) [kB/MB]: 673.00 / 2.88
Output Power (Up/Down) [dBm]: 12.5 / 18.0
Line Attenuation (Up/Down) [dB]: 24.0 / 45.5
SN Margin (Up/Down) [dB]: 24.5 / 3.5
Does this sound like the router is playing up?  Undecided
For the reboots I have even tried switching off the power for 15 minutes, no joy.
I'll try turning the modem off overnight to see if that helps!?
Is ther something else I could be trying?
Derek
18 REPLIES
Stumpy21
Rising Star
Posts: 156
Thanks: 6
Fixes: 1
Registered: 13-06-2011

Re: Is my modem failing?

Hello
Switched modem on just before 8am this morning.
Sync at 3db SNR again, increased to 4db now 10am.
Maybe it could be the exchange equipment rather than the modem ?
Current Stats:
Uptime: 0 days, 2:15:39
DSL Type: G.992.3 annex A
Maximum Bandwidth (Up/Down) [kbps/kbps]: 888 / 6,324
Bandwidth (Up/Down) [kbps/kbps]: 440 / 6,039
Data Transferred (Sent/Received) [MB/MB]: 2.73 / 42.61
Output Power (Up/Down) [dBm]: 12.5 / 18.5
Line Attenuation (Up/Down) [dB]: 23.5 / 46.0
SN Margin (Up/Down) [dB]: 24.0 / 4.0
Derek
Plusnet Alumni (retired) orbrey
Plusnet Alumni (retired)
Posts: 10,540
Registered: 18-07-2007

Re: Is my modem failing?

Hi there,
You've still a couple of months left under warranty so we can replace it if it definitely is the router. Is it still the same after a factory reset, and can you confirm that it works fine with another router if at all possible (or test your own at another premises to confirm it fails in the same way)?
Please let us know either way and we'll do what we can, thanks.
Stumpy21
Rising Star
Posts: 156
Thanks: 6
Fixes: 1
Registered: 13-06-2011

Re: Is my modem failing?

Hello Matt
Thanks for the message.
The only other router I have is my old Orange Livebox.  Shocked
I will try connecting that.
Obviously it won't let me connect to the internet but maybe it will sync and give me some stats. Undecided
Let you know my finding later.
Derek
Stumpy21
Rising Star
Posts: 156
Thanks: 6
Fixes: 1
Registered: 13-06-2011

Re: Is my modem failing?

Hello
OK I have connected my old Orange Livebox to the phone line and I would appear to have the same sync problem with that!
ADSL  Values
Description  Thomson Livebox 2 Mini uk v7.1-h323
Manufacturer  Thomson
SoftwareVersion  6.3.9.6
DestinationAddress  PVC: 0/38
ModulationType  ADSL_G.dmt.bis
ATMEncapsulation  VCMUX
ModemFirmwareVersion  bcm96358_ADSL_PHY_A2pBT009c1.d17d
Status  Up
LinkStatus  Up
LinkType  PPPoA
DataPath  Fast
UpstreamAttenuation  242
DownstreamAttenuation  465
UpstreamNoiseMargin  213
DownstreamNoiseMargin  27
UpstreamMaxRate  888000
DownstreamMaxRate  6747
UpstreamCurrRate  440
DownstreamCurrRate  6491

An even higher sync rate but at 2.7dB SNR if I am reading this correctly. Adding the decimal points in the right places.
Re connect Plusnet router
Uptime: 0 days, 0:09:30
DSL Type: G.992.3 annex A
Maximum Bandwidth (Up/Down) [kbps/kbps]: 888 / 6,272
Bandwidth (Up/Down) [kbps/kbps]: 440 / 6,071
Data Transferred (Sent/Received) [kB/MB]: 251.00 / 1.21
Output Power (Up/Down) [dBm]: 12.0 / 18.5
Line Attenuation (Up/Down) [dB]: 23.5 / 46.0
SN Margin (Up/Down) [dB]: 24.0 / 3.5
So if it is not my router what else could be causing this?  Undecided
Exchange equipment?  
Though if I can get a higher day time sync rate and reliable connection by doing a resync at say 11.30pm maybe I should leave it alone Tongue
Some people pay lots of money for a router to tweak their sync down to 3dB  Wink
Derek
jojopillo
Grafter
Posts: 9,786
Registered: 16-06-2010

Re: 3dB SNR sync Is my modem failing?

Hi Derek,
Your target SNR is currently 3dB, would you like me to set it to 6dB?
Jojo Smiley
Stumpy21
Rising Star
Posts: 156
Thanks: 6
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Registered: 13-06-2011

Re: 3dB SNR sync Is my modem failing?

Hello Jojo
Does that mean there isn't a fault at all?  Embarrassed
If my SNR has been lowered automatically due to say an ongoing good connection, until I started playing about over the last couple of days, we will leave it and see what happens.
No point in chasing a problem that may not be there.  Smiley
Derek
jojopillo
Grafter
Posts: 9,786
Registered: 16-06-2010

Re: 3dB SNR sync Is my modem failing?

If it's causing an issue at 3dB I'd raise it to 6dB. At this point I wouldn't say there was a fault as such. If it caused you problems at 6dB then maybe so.
Stumpy21
Rising Star
Posts: 156
Thanks: 6
Fixes: 1
Registered: 13-06-2011

Re: 3dB SNR sync Is my modem failing?

Hello Jojo
It has been working fine all today, no connection problems at all.
I'll keep an eye on RouterStats and maybe do a resync later this evening, if needed, for a more reliable connection.
Leave it with me for a day or two, I'll get back if it is causing me any problems. Now that I know what to expect.  Smiley  My line is usually quite good for noise.
Derek
x47c
Grafter
Posts: 878
Registered: 14-08-2009

Re: 3dB SNR sync Is my modem failing?

I'm assuming you must be on 21CN
...as this system does have the ability to work to a 3dB target noise level - if the line is question is "suitable" - otherwise it defaults to 6dB as a more usual standard though obviously may use higher values for dodgy lines.
21CN manages the line in a more active manner than 20CN which tended to set the parameters in the 10 day initial switch on/training period and then not change them.
(which is why the determined/skilful could then tweak the line without 20CN getting [too] upset)
21CN will change the parameters if the line or other conditions change either up or down
That said,
There do seem some cases where 21CN seems to get a bit confused or takes its active management a bit too far and starts applying inappropiate changes which it then tries to compensate for in other ways - rather than remove its inappropiate change in the first place.
Switching interleaving off during the day and then on during the night day after day every day is one example I've heard off.
I guess some lines just fall into that awkward gap where it oscillates back and fro.
I'm surprised for a 46dB attenuation line that your interleaving is not switched on.
Luzern
Seasoned Pro
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Registered: 31-07-2007

Re: 3dB SNR sync Is my modem failing?

Butt in time again! Grin
Why are crude 3dB steps used when margins are adjusted? Surely not every tweak needs to be a multiple of x2/
No one has to agree with my opinion, but in the time I have left a miracle would be nice.
x47c
Grafter
Posts: 878
Registered: 14-08-2009

Re: 3dB SNR sync Is my modem failing?

No exact idea myself, but...
I'm sure there is something that "3" is a unit of something in the way of margin it needs..... (codeword sizes or something - its outside my tech' competance)
So if it doesn't get 3 the next unit step up is another 3 which gives us the 6 standard default target setting
then the next 3 up which gives us 9 and then 12 and 15 all of which I've known as standard target noise settings being used by the DSLAMS/MSANS for less than perfect lines.
If the above is NOT a correct explanation then possibly that BT/DSLAM programmers/or the G/DMT international standard set some steps in the target noise setup concept which are sufficiently different from each other to ensure its either one or the other.  So 3 and 6 as you say are quite far apart means the control system is unlikely to go barmy and start to oscillate between them - we really do not want a system continually trying to decide if its raining/damp today we'll set the target to 4 rather than 3  - nor do we want customer calls arguing about whether the target margin should be set to 3 or 4.
A bit like interleaving depths appear as only certain numbers 4, 8, 16, 32, and 64 being some of them.  I'm even less sure how the depth of the interleaving is decided, it is clearly more complicated than simply being on or off.
I do recall at the time the G.DMT standard omitting some calculation/stats which might be done continually by the router/DSLAM  to avoid putting too much burden on the computation powers of the modem - which at least suggests that this was an issue and maybe continually adjusting the target by small amounts which is some way is heading towards "seamless rate adaption" both up and down 'on the fly' might have been too much for both ends to handle at that time.
The above are my best educated guesses rather than definitive statements of why!

Stumpy21
Rising Star
Posts: 156
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Registered: 13-06-2011

Re: 3dB SNR sync Is my modem failing?

x47c thanks for all that useful info  Smiley
Quote from: x47c

I'm surprised for a 46dB attenuation line that your interleaving is not switched on.

I thought I did have interleaving switched on.
My ping spec is   0% packet loss - ping 43ms - Jitter 1ms  if that tells the answer?
Derek
Community Veteran
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Registered: 23-09-2010

Re: 3dB SNR sync Is my modem failing?

I've had that "3" problem for quite a while though hopefully Joanne has done something to stabilise it on 6. It seemed that if I held a stable connection for around twenty days or so I would be disconnected then reconnected with the snr dropping by 3.
Probably OK for some but to get a lasting connection, allowing for snr swings I would have to connect at around midnight. But on 6 connecting during the day I could actually get a faster and more stable connection with less of an error rate.
x47c
Grafter
Posts: 878
Registered: 14-08-2009

Re: 3dB SNR sync Is my modem failing?

Re interleaving
The ping answer of 43ms does indeed suggest that interleaving is on - thanks for the additional info.
The jitter result is a measure of how consistent are the pings (ie does each one vary a lot for the next one) - an important value for VOIP
1ms is a good result for a reasonably lengthed line.
I was basing my earlier answer on the router stats line in the one of the posts which says:    "Data path:    FAST"
Ah well, can only assume the router is reporting the path status inaccurately.....................
(I recall some do when the downstream is Interleaved and the upstream is Fast path)