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Inconsistent speed- low SNR high attenuation

Simonleeuk
Grafter
Posts: 26
Registered: 13-08-2014

Inconsistent speed- low SNR high attenuation

Internet speed has been very inconsistent past few months. somedays can be 4.5mb download other days so slow speed test struggles to register a result and even browsing is a crawl and completely unusable. I'm not a network expert but from what I gather from my router stats SNR is very low and attenuation seems ok. Was hoping someone could interpret these stats and any help would be really appreciated.
Mode: ADSL_2plus
Traffic Type: ATM
Status: Up
Link Power State: L0

Downstream Upstream
Line Coding(Trellis): On On
SNR Margin (0.1 dB): 26 245
Attenuation (0.1 dB): 575 342
Output Power (0.1 dBm): 0 128
Attainable Rate (Kbps): 6672 1004

Path 0 Path 1
Downstream Upstream Downstream Upstream
Rate (Kbps): 5746 444 0 0

MSGc (# of bytes in overhead channel message): 60 46 0 0
B (# of bytes in Mux Data Frame): 176 19 0 0
M (# of Mux Data Frames in FEC Data Frame): 1 1 0 0
T (Mux Data Frames over sync bytes): 1 1 0 0
R (# of check bytes in FEC Data Frame): 14 0 0 0
S (ratio of FEC over PMD Data Frame length): 0.9801 1.3675 0.0 0.0
L (# of bits in PMD Data Frame): 1559 117 0 0
D (interleaver depth): 32 1 0 0
Delay (msec): 7.84 0.34 0.0 0.0
INP (DMT symbol): 1.14 0.0 0.0 0.0

Super Frames: 50718407 837508 0 0
Super Frame Errors: 0 0 0 0
RS Words: 3347414898 0 0 0
RS Correctable Errors: 60000939 0 0 0
RS Uncorrectable Errors: 704678 0 0 0

HEC Errors: 0 53318 0 0
OCD Errors: 457 0 0 0
LCD Errors: 0 0 0 0
Total Cells: 2525505724 610396 0 0
Data Cells: 531179073 2082 0 0
Bit Errors: 0 0 0 0

Total ES: 7997 0
Total SES: 969 0
Total UAS: 14 4294967274
I've also posted my current speed and another speed test few days ago and current line speed.
56 REPLIES
Community Veteran
Posts: 5,155
Thanks: 474
Fixes: 19
Registered: 10-06-2010

Re: Inconsistent speed- low SNR high attenuation

It's to be expected that the SNR margin is low because your downstream speed of 5746kbps is remarkably high for the attenuation of 57.5db! The target SNR margin, which is what the SNR margin starts at when the connection is established, is presumably 3db, so 2.6db isn't much lower than that.
Do those stats cover about 10 days? (From the superframe count, 17ms for each superframe.) Were there any thunderstorms over that period, which would have caused a lot of extra errors?
Highlighted
Simonleeuk
Grafter
Posts: 26
Registered: 13-08-2014

Re: Inconsistent speed- low SNR high attenuation

I've been following these line stats for a few months and is pretty consistent. Lots of rain up here but no thunderstorms. As I said networking is not my area but I was under the impression that SNR below 6 is bad and can result in frequent disconnections and problems with line synchronisation?
Simonleeuk
Grafter
Posts: 26
Registered: 13-08-2014

Re: Inconsistent speed- low SNR high attenuation

As I am posting now my connection is struggling to cope loading web pages is awe fully slow. Speed test 0.01mbps download speed. Ping of 2609.
mwarby
Grafter
Posts: 85
Registered: 11-08-2014

Re: Inconsistent speed- low SNR high attenuation

if those SNRs are genuinely 0.1s of dB, they are simply too low to be stable, are you tweaking these on your router ? if not what happens when you reboot the modem ?
Whats happening is your getting packet loss as the connection struggles, but not quite enough to case a disconnect
Martin
Superuser
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Re: Inconsistent speed- low SNR high attenuation

Quote from: Simonleeuk
As I said networking is not my area but I was under the impression that SNR below 6 is bad and can result in frequent disconnections and problems with line synchronisation?

Simon,
Martin is near the mark.  A SNRM below 6dB is not necessarily bad, it all depends upon the line, in much the same way that a SNRM above 6dB may or may not be "bad".
6dB is the normal target SNRM used for synching up a line, thereafter SNRM will vary depending on the ambient electrical noise.  If noise increases, SNRM goes down.  The target SNRM needs to be high enough to mitigate ambient noise pushing the current SNRM so low that there is no useful margin left.  Therefore on bad lines, the target SNRM might be set higher than 6dB.  Conversely on very good lines, the target SNRM can be set at 3dB to gain more synch speed, at the risk of encountering more errors and thereby significantly reducing the effective data transfer speed.
What one needs to know in respect of your line is why is the SNRM presently so low?  Is a tweak in the router forcing it low to get the best possible synch speed but then unwittingly causing transmission errors which hammers the throughput speed?  As ejs noted above, your synch speed is exceedingly high for the line's attenuation.  This makes me thing that this router is doing naughty things to the DLM by forcing the SNRM below 3dB.
Or is the SNRM being depressed by electrical interference (REIN)?
The latter is a night mare and needs to be discerned by running something like routerstats to monitor the SNRM over time.  What is the router?  It might do this for you.

Can you please check through all of the router settings and see if there is anything there which is tweaking the SNRM.  Thereafter, I think there needs to be a discussion with PlusNet about checking / setting / resetting the target SNRM value.  This will shave a bit off the synch speed, but it ought to deliver better data throughput speeds.
Kevin
Simonleeuk
Grafter
Posts: 26
Registered: 13-08-2014

Re: Inconsistent speed- low SNR high attenuation

Thanks for the input guys.  No haven't tweaked anything in router settings everything is default I'm currently using a tp link w8960n with original firmware. Yes the figures displayed are in 0.1db. You right about one thing connection is not stable and has been driving me nuts. I don't mind a slight slow down in download speed from time to time but this is affecting just simple internet browsing where pages just hang for minutes before loading. When you say electrical interference can this be caused by my computer located next to the master socket because my computer and most of my electrical connections are located in the same corner near the telephone master socket? In terms of bad line I can't imagine this would be the case because I live on a new build estate so imagine all the copper is brand new. I've reset router and stats seem pretty similar

Statistics -- xDSL

Mode: ADSL_2plus
Traffic Type: ATM
Status: Up
Link Power State: L0

Downstream Upstream
Line Coding(Trellis): On On
SNR Margin (0.1 dB): 29 230
Attenuation (0.1 dB): 575 341
Output Power (0.1 dBm): 0 128
Attainable Rate (Kbps): 6476 1024

Path 0 Path 1
Downstream Upstream Downstream Upstream
Rate (Kbps): 5778 444 0 0

MSGc (# of bytes in overhead channel message): 59 46 0 0
B (# of bytes in Mux Data Frame): 180 19 0 0
M (# of Mux Data Frames in FEC Data Frame): 1 1 0 0
T (Mux Data Frames over sync bytes): 1 1 0 0
R (# of check bytes in FEC Data Frame): 14 0 0 0
S (ratio of FEC over PMD Data Frame length): 0.9968 1.3675 0.0 0.0
L (# of bits in PMD Data Frame): 1565 117 0 0
D (interleaver depth): 32 1 0 0
Delay (msec): 7.97 0.34 0.0 0.0
INP (DMT symbol): 1.14 0.0 0.0 0.0

Super Frames: 3281 2990 0 0
Super Frame Errors: 0 0 0 0
RS Words: 213284 0 0 0
RS Correctable Errors: 112 0 0 0
RS Uncorrectable Errors: 0 0 0 0

HEC Errors: 0 0 0 0
OCD Errors: 0 0 0 0
LCD Errors: 0 0 0 0
Total Cells: 725618 498608 0 0
Data Cells: 203 3950 0 0
Bit Errors: 0 0 0 0

Total ES: 0 0
Total SES: 0 0
Total UAS: 15 15
mwarby
Grafter
Posts: 85
Registered: 11-08-2014

Re: Inconsistent speed- low SNR high attenuation

I would warn that tweaking SNR is a road to misery on long lines, I speak from experience
What happens is that you end up constantly trying to counter BT's DLM and you can end up with 15dB margins set on BTs system. As the offsets used in these tweak are often percentages each time you have to up it trying to counter DLM the less stable your line becomes
The only tweak which sometimes be useful is tweaking to increase the margin, which gets you more stability but a slower speed, but these das the ISP can ask BT for a stable or super stable setting which does the same thing, but without the trickery
Martin
mwarby
Grafter
Posts: 85
Registered: 11-08-2014

Re: Inconsistent speed- low SNR high attenuation

Have you always used this modem (or used it for a long time)?
Is this a recent problem or an ongoing one ?
Just wondering if a new modem is the cause, or whether something else has changed
One suspicion would be a faulty modem, I wonder if recent lightning has caused damage.
Martin
Superuser
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Posts: 12,261
Thanks: 3,553
Fixes: 22
Registered: 22-08-2007

Re: Inconsistent speed- low SNR high attenuation

Hi Simon,
The "expectation" for a line having an attenuation (effectively length) of 57dB (4.1km) is 3.5Mbps - you are getting 5.7Mbps.  Note that you cannot do anything about attenuation, short of moving to a house nearer the exchange!  Grin
It looks like your TARGET SNRM is 3dB - I suggest that it would be worth while having a conversation with PluseNet (via this thread) to look at error counts and consider moving the TARGET SNRM to 6dB.  At worse this is going to move the synch rate to 4.5Mbps, which is still well within expectations.  Though the synch rate will be reduced, the effective data rate should be markedly improved due to there being fewer errors on the line.
If you feel up to it, setting up a TBB BQM plot as described here - http://community.plus.net/forum/index.php/topic,106312.0.html - would be useful, though if you do not have affixed IP address, it will need re-doing after each disconnect.
Kevin
Community Veteran
Posts: 2,286
Thanks: 109
Fixes: 4
Registered: 18-02-2013

Re: Inconsistent speed- low SNR high attenuation

Why are you testing with wifi ?
Simonleeuk
Grafter
Posts: 26
Registered: 13-08-2014

Re: Inconsistent speed- low SNR high attenuation

I've gone through router setting can't see any settings that mentions SNRM or whether tweaking this is even possible with my router. I've had this router for a couple of years and has been pretty reliable but have been thinking of investing in an asus ac66u to see whether it would help. I'm not trying to cast blame but this has been the case ever since joining Plusnet and connection has been hit and miss but been unbearable the past few months. This could be just coincidence so I want to eliminate anything on my end first.
mwarby
Grafter
Posts: 85
Registered: 11-08-2014

Re: Inconsistent speed- low SNR high attenuation

I'd try and borrow another modem and post stats from that, at least it would rule that out. For whatever reason your modem is pushing the line very hard, I'd expect to see that with any ISP using BTs 21CN
It may also be worth trying directly into the master socket (the test socket behind the faceplate) just to eliminate wiring
Martin
Superuser
Superuser
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Fixes: 22
Registered: 22-08-2007

Re: Inconsistent speed- low SNR high attenuation

Quote from: 11110_110
Why are you testing with wifi ?

As always, this is a good question, one I failed to ask and yes the results could be indicative of speed testing over wifi - however what did I miss for you to believe they were conducted over wifi?  Cheesy
Simonleeuk
Grafter
Posts: 26
Registered: 13-08-2014

Re: Inconsistent speed- low SNR high attenuation

Yeah I appreciate postings speed tests via wifi not ideal, but it's really just to give an idea of the vast inconsistency of my connection. My connection is pretty rubbish anyway so Ethernet results pretty similar.
Thanks Townman for your suggestions. Yeh looking at other threads Plusnet moderators on this forum seem to be really helpful so hopefully they can have a look into this for me. Anyway way of prompting them to join the thread? Wink