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Author Topic: Bits from time using TP-Link router  (Read 3701 times)

renluop

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Bits from time using TP-Link router
« on: June 19, 2014, 11:24:53 AM »

Even though it did not come up to expectations, I did glean some info on SNRM that is making the head itch.

At the time averaged SNRM was ~3dB, but from the detail below I can not see how the 3dB could be obtained. My thoughts are that the router was producing gibberish stats. Your thoughts, explanations?
Code: [Select]
adsl info --SNR
adsl: ADSL driver and PHY status
Status: Showtime
Last Retrain Reason:    8000
Last initialization procedure status:   0
Max:    Upstream rate = 888 Kbps, Downstream rate = 9292 Kbps
Bearer: 0, Upstream rate = 888 Kbps, Downstream rate = 7959 Kbps

Tone number      SNR
   0            0.0000
   1            0.0000
   2            0.0000
   3            0.0000
   4            0.0000
   5            0.0000
   6            23.0000
   7            32.0000
   8            38.0000
   9            41.0000
   10           44.0000
   11           47.0000
   12           50.0000
   13           47.0000
   14           46.0000
   15           47.0000
   16           47.0000
   17           46.0000
   18           46.0000
   19           45.0000
   20           45.0000
   21           46.0000
   22           46.0000
   23           43.0000
   24           42.0000
   25           42.0000
   26           40.0000
   27           40.0000
   28           39.0000
   29           37.0000
   30           35.0000
   31           35.0000
   32           0.0000
   33           41.1250
   34           43.8125
   35           44.7500
   36           44.4375
   37           41.8750
   38           41.0625
   39           45.1875
   40           45.0625
   41           44.8125
   42           44.3750
   43           44.5625
   44           44.8125
   45           44.3750
   46           33.9375
   47           44.8125
   48           44.5625
   49           44.2500
   50           33.6875
   51           43.7500
   52           43.7500
   53           43.6250
   54           43.5625
   55           43.5625
   56           43.5000
   57           43.3125
   58           43.0000
   59           42.7500
   60           42.5625
   61           42.0625
   62           41.8750
   63           42.0000
   64           42.0625
   65           42.0000
   66           41.9375
   67           41.5625
   68           40.9375
   69           40.8125
   70           41.0625
   71           40.7500
   72           40.5625
   73           40.6250
   74           40.5000
   75           40.7500
   76           40.7500
   77           40.2500
   78           40.1250
   79           38.8750
   80           39.0000
   81           39.4375
   82           39.6875
   83           39.0625
   84           39.3125
   85           39.4375
   86           39.1875
   87           38.8750
   88           38.5625
   89           37.9375
   90           37.5000
   91           37.5625
   92           37.4375
   93           37.3750
   94           37.5625
   95           37.8750
   96           37.5625
   97           37.1875
   98           37.1875
   99           36.8750
   100          36.4375
   101          36.4375
   102          36.5625
   103          37.0625
   104          37.5000
   105          37.4375
   106          37.2500
   107          37.0000
   108          36.9375
   109          37.1250
   110          37.9375
   111          36.5000
   112          35.9375
   113          36.3125
   114          36.3750
   115          36.2500
   116          36.1250
   117          35.6250
   118          35.6875
   119          35.6875
   120          35.5000
   121          34.6875
   122          34.8125
   123          35.1875
   124          35.4375
   125          35.5000
   126          35.2500
   127          36.7500
   128          35.6250
   129          34.8125
   130          34.5625
   131          34.4375
   132          34.5625
   133          34.6875
   134          34.7500
   135          34.6875
   136          34.4375
   137          34.4375
   138          34.1250
   139          34.1250
   140          34.4375
   141          34.1875
   142          33.6250
   143          33.4375
   144          33.5000
   145          33.4375
   146          33.6250
   147          33.7500
   148          33.6250
   149          33.0000
   150          32.8750
   151          33.2500
   152          33.2500
   153          33.1250
   154          32.8750
   155          32.9375
   156          32.9375
   157          32.8125
   158          24.9375
   159          32.5000
   160          31.4375
   161          28.8750
   162          31.7500
   163          32.0625
   164          32.0000
   165          31.3125
   166          31.4375
   167          31.4375
   168          31.3125
   169          31.1875
   170          30.9375
   171          30.9375
   172          31.0000
   173          31.3125
   174          31.1250
   175          30.7500
   176          30.5625
   177          30.5625
   178          30.5000
   179          30.3125
   180          30.2500
   181          30.1875
   182          30.0625
   183          29.8750
   184          29.6250
   185          29.4375
   186          29.5625
   187          29.8125
   188          30.5000
   189          29.0000
   190          29.3125
   191          29.8750
   192          23.0625
   193          28.3750
   194          27.6250
   195          27.9375
   196          27.9375
   197          27.8125
   198          27.3125
   199          24.1250
   200          28.1875
   201          28.0000
   202          27.5000
   203          26.6250
   204          26.8750
   205          26.8125
   206          27.1250
   207          27.0625
   208          27.1250
   209          27.0625
   210          27.0000
   211          24.4375
   212          26.5000
   213          26.1250
   214          26.1250
   215          25.9375
   216          26.2500
   217          26.0000
   218          25.8125
   219          25.9375
   220          25.5000
   221          25.1250
   222          25.1875
   223          25.3125
   224          25.1250
   225          25.0625
   226          24.9375
   227          24.6250
   228          24.6875
   229          24.6875
   230          24.0000
   231          24.1250
   232          24.5000
   233          24.5000
   234          24.5000
   235          24.1250
   236          23.8125
   237          19.9375
   238          23.1875
   239          23.4375
   240          23.3125
   241          23.1875
   242          23.1875
   243          22.0625
   244          12.0625
   245          20.6250
   246          22.0000
   247          22.2500
   248          22.0000
   249          21.7500
   250          22.0625
   251          22.0000
   252          21.0625
   253          20.9375
   254          21.3750
   255          21.1875
   256          20.7500
   257          19.8750
   258          20.5000
   259          19.8125
   260          20.2500
   261          20.2500
   262          19.7500
   263          19.8125
   264          19.6250
   265          19.5625
   266          19.1875
   267          19.3125
   268          18.9375
   269          18.9375
   270          18.7500
   271          18.6250
   272          18.3750
   273          18.1250
   274          17.9375
   275          17.2500
   276          16.2500
   277          11.6875
   278          10.0000
   279          15.6875
   280          16.4375
   281          16.3125
   282          15.5625
   283          16.1875
   284          16.0000
   285          15.8125
   286          15.5625
   287          15.1250
   288          15.0625
   289          14.7500
   290          14.5000
   291          14.2500
   292          14.0000
   293          13.8750
   294          13.2500
   295          13.2500
   296          13.0625
   297          12.8125
   298          12.5000
   299          12.3125
   300          12.1875
   301          11.8125
   302          11.3125
   303          11.1875
   304          10.5000
   305          10.3125
   306          10.0000
   307          9.1875
   308          9.4375
   309          9.2500
   310          8.8750
   311          8.5000
   312          8.3750
   313          8.0000
   314          7.2500
   315          0.0000
   316          6.7500
   317          6.5625
   318          6.8125
   319          8.3750
   320          6.8125
   321          7.0000
   322          8.5625
   323          8.5000
   324          8.2500
   325          7.5625
   326          5.2500
   327          6.8750
   328          6.3750
   329          0.0000
   330          0.0000
   331          0.0000

 
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roseway

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Re: Bits from time using TP-Link router
« Reply #1 on: June 19, 2014, 11:37:19 AM »

You're mixing up SNR and SNRM (SNR Margin). The 3 dB would undoubtedly have been the SNRM at that time, and it's not inconsistent with the SNR per tone values you quote above. The SNRM is the margin between the actual SNR and a level of SNR which is defined by the manufacturer based on expected error rates. Broadly speaking, this base level of SNR is the SNR at which the device is likely to lose the ability to hold the connection.  SNR in this case is an average of the SNR values over the tone range.
« Last Edit: June 19, 2014, 11:40:37 AM by roseway »
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krypton

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Re: Bits from time using TP-Link router
« Reply #2 on: June 19, 2014, 04:31:36 PM »

You can calculate the SNRM for every single tone if you multiply the bitloading value with 3 and subtract this from the SNR.
Broadcom DslDiag tool shows a graph with SNRM for every tone. Maybe DSLstats can also do this someday  :)
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roseway

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Re: Bits from time using TP-Link router
« Reply #3 on: June 19, 2014, 06:41:43 PM »

That's an interesting suggestion. It's implied in the bitloading graph if the SNR per tone is included, giving a visual indication of the headroom, but a specific graph could be a useful addition to the diagnostic armoury.

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kitz

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Re: Bits from time using TP-Link router
« Reply #4 on: June 19, 2014, 09:32:29 PM »

Unfortunately the calculation isnt quite so simple as that :(  Theres an additional step during bit allocation process which allows for overheads & lea-way for BER and bitswap.

For eg from my stats

Tone 42
SNR = 54.3750 dB   
bits loaded = 14 

54.3750 - (14*3 = 42) = 12.3750

yet my SNR Margin at tone 42 is actually 8.3 dB


Tone 671
SNR =  43.6875 dB
bits loaded = 10

43.6875 - (10*3 = 30) = 13.6875

Actual SNR Margin = 8.4 dB


However the fact that dslDiagnostics can get SNRMargin per individual tone implies that these must be available somehow - just not through the CLI.   Im assuming it gets information direct from the Busybox shell?  iirc someone was going to attempt to reverse engineer it, but afaik didnt get very far.
« Last Edit: June 19, 2014, 09:35:54 PM by kitz »
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burakkucat

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Re: Bits from time using TP-Link router
« Reply #5 on: June 19, 2014, 10:01:22 PM »

However the fact that dslDiagnostics can get SNRMargin per individual tone implies that these must be available somehow - just not through the CLI.   Im assuming it gets information direct from the Busybox shell?  iirc someone was going to attempt to reverse engineer it, but afaik didnt get very far.

That has invoked a vague recollection . . . Hunting around in the what-not I came across some files, one of which has the following header --

Code: [Select]
/************************************************************************************
 * asbobcmdiagclient.c  v0.2                                                        *
 *                                                                                  *
 * Interrogate a Broadcom-chipset router for stats via its diagnostic port udp/5100 *
 *   GPL3 (c) 2012 asbokid <removed>                                                *
 *                                                                                  *
 * Compile for Linux/gcc with                                                       *
 *  $  gcc -o asbobcmdiagclient asbobcmdiagclient.c                                 *
 *                                                                                  *
 * Compile for Microsoft Windows (XP onwards) using mingw-gcc with:                 *
 *  C:/> i586-mingw32msvc-gcc asbobcmdiagclient.c -lws2_32 -o asbobcmdiagclient.exe *
 *     (minGW available from http://www.mingw.org/)                                 *
 *                                                                                  *
 ************************************************************************************/

I wonder if there is a fellow kitizen who feels up to "having a go"?  :-\
« Last Edit: June 19, 2014, 11:39:33 PM by burakkucat »
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roseway

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Re: Bits from time using TP-Link router
« Reply #6 on: June 19, 2014, 10:48:23 PM »

I'd be very interested in having a go, but I fear that there aren't enough hours in the day.
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krypton

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Re: Bits from time using TP-Link router
« Reply #7 on: June 19, 2014, 11:06:48 PM »

Unfortunately the calculation isnt quite so simple as that ...
You're right, it is not exactly 3 dB per bit. Maybe the difference is caused by additional error protection data transmitted on this channels? I don't know.

That's an interesting suggestion.
...but it seems not as easy as I thought.
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burakkucat

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Re: Bits from time using TP-Link router
« Reply #8 on: June 19, 2014, 11:43:31 PM »

I'd be very interested in having a go, but I fear that there aren't enough hours in the day.

If you could find 61 seconds to a minute, 61 minutes to the hour and 25 hours to the day, then I will be willing to send you all the code . . . it's all been written under GPLv3.
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roseway

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Re: Bits from time using TP-Link router
« Reply #9 on: June 20, 2014, 07:31:26 AM »

If you could bundle it up for me I'll certainly be pleased to have a look at it to see what's involved.
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Bald_Eagle1

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Re: Bits from time using TP-Link router
« Reply #10 on: June 20, 2014, 05:17:33 PM »

I'll have a look too, if it's of any use.

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konrado5

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Re: Bits from time using TP-Link router
« Reply #11 on: June 23, 2014, 05:29:13 PM »

Unfortunately the calculation isnt quite so simple as that ...
You're right, it is not exactly 3 dB per bit. Maybe the difference is caused by additional error protection data transmitted on this channels? I don't know.
The SNR margin is the excess SNR over that required for a pre-defined Bit Error Rate (BER) 10^7. This is not as simple what SNR is required to this BER. There is SNR gap value 9.8 dB minus coding gain. For example, Trellis encoding gives about 5.5 dB coding gain. This is reason why synchronization rate was lower with trelliss off than with trellis on. But calculation is very complex. Here is the way of bit-loading calculation.
http://books.google.pl/books?id=m77kZl71gysC&pg=PA204&lpg=PA204&dq=ADSL+%22SNR+gap%22+%22coding+gain%22&source=bl&ots=wy0oU5lfS7&sig=ASxGP_9ndU5YrgdG02Cj2bEuKKA&hl=pl&sa=X&ei=pFaoU_6OG4XP4QS8y4DACg&ved=0CDIQ6AEwAg#v=onepage&q=ADSL%20%22SNR%20gap%22%20%22coding%20gain%22&f=false
« Last Edit: June 23, 2014, 05:33:00 PM by konrado5 »
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renluop

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Re: Bits from time using TP-Link router
« Reply #12 on: June 23, 2014, 07:34:16 PM »

Were it not in Polish it might be informative so here is English version.

Kon! Could you give section and paragraph numbers, please?

Now to the brains for comment, should they wish. ;D
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konrado5

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Re: Bits from time using TP-Link router
« Reply #13 on: June 23, 2014, 07:54:32 PM »

7.4.4.3 chapter
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anything