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Author Topic: Bitloading gaps curiosity  (Read 9441 times)

sheddyian

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Bitloading gaps curiosity
« on: March 03, 2014, 02:48:35 PM »

Here's a thing.

On my ADSL2+ connection using a BT HG612 (currently running the Wolfy firmware) I was studying the curious gaps in my bitloading, and note that all but one of them corresponds with an SNR per tone drop to 0 as well (see attached graph).

Roseway's marvellous DSLStats tells me that those tones are

110 474.375kHz
127 547.6875 kHz
188 810.75 kHz
191 823.6875 kHz
243 1047.9375 kHz
291 1254.9375 kHz
348 1500.75 kHz

All of these tones have a drastic drop in SNM and have a zero bitloading.  Adjacent tones have a goodly number of bits allocated and no such SNM problems.

There's one other curious tone, 233 1004.8125 Khz but this does have a low bitloading of 2 and no drop in SNM. 

I then discovered this thread in another place :

http://community.plus.net/forum/index.php?topic=105398.0

Where GrahamC notes in 2012 that he has gaps in his bitloading.  And they are ... :

Quote
Gap1 474kHz-479kHz (Tone110)
Gap2 548kHz-552kHz (Tone127)
Gap3 811kHz-815kHz (Tone188)
Gap4 824kHz-828kHz (Tone191)
Gap5 1048kHz-1052kHz (Tone243)
Gap6 1255kHz-1259kHz (Tone291)
Gap7 1501kHz-1505kHz (Tone348)

Identical to mine! (excepting my tone 233 anomaly)

In that thread, he says he is in East Yorks, which is a good few hundred miles away from me, so it seems a little unlikely we share the same RF interference. 

I notice BaldEagle and a few others of this place commenting in that thread, has anything ever come of why there are those curious gaps?  It does seem like some sort of software/hardware quirk to me.  ???

Ian

Edit : Attributed DSLStats to wrong person  :-[
« Last Edit: March 03, 2014, 08:32:54 PM by sheddyian »
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konrado5

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Re: Btloading gaps curiosity
« Reply #1 on: March 03, 2014, 07:10:15 PM »

Quote from: sheddyian
There's one other curious tone, 233 1004.8125 Khz but this does have a low bitloading of 2 and no drop in SNM.
It's pilot tone. It is selected by router at the time of synchronization establishment. It can be other at every new synchronization.

Best regards
konrado5
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NewtronStar

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Re: Btloading gaps curiosity
« Reply #2 on: March 03, 2014, 07:52:05 PM »

Quote from: sheddyian
There's one other curious tone, 233 1004.8125 Khz but this does have a low bitloading of 2 and no drop in SNM.
It's pilot tone. It is selected by router at the time of synchronization establishment. It can be other at every new synchronization.

Best regards
konrado5

If you want to see some serious missing tones then look at my tones at 1380 and 1710 for me its seems to be Radio Station Interference.
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4candles

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Re: Btloading gaps curiosity
« Reply #3 on: March 03, 2014, 07:59:23 PM »

Curious.  :hmm:

Ian,

I get exactly the same on my ADSL2+, with a DGN2000 (DMT), with the exception that I don't have the anomalous tone 233, or an equivalent. I can't see a way to obtain the MSAN manufacturer.

Whatever it is, it's not AM broadcasts. It's the same 24/7, and I get little interference from BBC Wychbold, which is only about 13 miles as the crow barks.

It does seem like some sort of software/hardware quirk to me.  ???

Me too, and I'd like to know what.
« Last Edit: March 03, 2014, 08:02:44 PM by 4candles »
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sheddyian

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Re: Btloading gaps curiosity
« Reply #4 on: March 03, 2014, 08:32:37 PM »

If you want to see some serious missing tones then look at my tones at 1380 and 1710 for me its seems to be Radio Station Interference.

Yes, pretty miserable that  :(

However, that's exactly how I imagined radio station interference might look on a bitloading graph, taking out chunks of bandwitdh rather than just one tone.

That's the curious thing with my missing tones - they're completely missing (0db) and yet adjacent tones are unaffected, which is why I'm convinced it's not radio interference.


Ian
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sheddyian

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Re: Btloading gaps curiosity
« Reply #5 on: March 03, 2014, 08:42:49 PM »

I get exactly the same on my ADSL2+, with a DGN2000 (DMT), with the exception that I don't have the anomalous tone 233, or an equivalent. I can't see a way to obtain the MSAN manufacturer.

Whatever it is, it's not AM broadcasts. It's the same 24/7, and I get little interference from BBC Wychbold, which is only about 13 miles as the crow barks.

That's very interesting! 

You're evidently nowhere near me, but as we both think, it doesn't seem to be AM interference.

I think Konrado5 is right, tone 233 for me could be some kind of pilot tone, thinking about it I have seen it move about between reboots.  The other 0db tones which we both share don't move around for me.

I don't know what equipment I'm connected to either, the modem is a BT HG612. 

However, what I have just realised is I've got some home-made plots from an old TP-Link ADSL2+ modem that I made in January 2013, and they don't show those missing tones - each plot has just 1 significantly missing tone.

I suppose the thing to do will be to connect that old modem back up and get some data from it and see if the missing tones are constant now or a product of using the HG612.

Though you're not using an HG612, so....   ???

Ian

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NewtronStar

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Re: Btloading gaps curiosity
« Reply #6 on: March 03, 2014, 08:47:43 PM »

which is why I'm convinced it's not radio interference.

Ian

Yes I think your correct as RSI (Radio Station Interference) gives a U shape in the SNR tones not always as some Radio Station are much stronger and cause's a complete blank of tones in that frequency spread. 
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roseway

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Re: Bitloading gaps curiosity
« Reply #7 on: March 03, 2014, 09:10:45 PM »

Tones 110 and 127 are almost certainly TalkTalk pilot/control tones - everyone on TalkTalk (I believe) sees these tones at zero. I also have gaps at the other tones you mention (but not 233) so maybe they're all specific to TT.
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sheddyian

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Re: Bitloading gaps curiosity
« Reply #8 on: March 03, 2014, 09:14:45 PM »

I've just discovered a copy of the text output from a friend's Thompson Technicolor TG585V8, in December 2012, located 50 miles North of me, shows the following missing tones

 48 *
110
127
188
191
243
291
348

All of those tones, bar the first, are the same as my missing tones.  And again, they're individual missing tones, with no impact on adjacent tones.

If this is by design, then I wonder why?  And if by design, why didn't I see this on the old TP-Link modem?

All very curious  ???


Ian
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sheddyian

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Re: Bitloading gaps curiosity
« Reply #9 on: March 03, 2014, 09:17:39 PM »

Tones 110 and 127 are almost certainly TalkTalk pilot/control tones - everyone on TalkTalk (I believe) sees these tones at zero. I also have gaps at the other tones you mention (but not 233) so maybe they're all specific to TT.

I think the tone 233 thing is a red herring here, unlike the other missing tones it's not measured at 0db and does carry 2 bits in my case.

You could be right about the TalkTalk thing, tho why my older Tp-Link modem didn't show these as missing just over a year ago, and why my friend (on Plusnet) sees the same missing tones does muddy that theory a bit.

Ian
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4candles

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Re: Bitloading gaps curiosity
« Reply #10 on: March 03, 2014, 10:30:14 PM »

Googling around, it seems that the ADSL2+ pilot is variable, and can carry 2 bits. In my attachment above it would seem to be 196, which carries only two bits but has similar (normal) SNR to adjacent tones.

I'm also on Plusnet.
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burakkucat

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Re: Bitloading gaps curiosity
« Reply #11 on: March 03, 2014, 10:42:18 PM »

A TalkTalk service. MSAN using an Infineon chipset. Huawei HG622 modem/router. Link configured to operate in ADSL2 mode.

The raw bit-loading data --

Code: [Select]
# xdslcmd info --Bits
xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 8000
Max: Upstream rate = 1088 Kbps, Downstream rate = 6392 Kbps
Channel: INTR, Upstream rate = 1020 Kbps, Downstream rate = 6050 Kbps

Tone number      Bit Allocation
   0 0
   1 0
   2 0
   3 0
   4 0
   5 0
   6 5
   7 7
   8 8
   9 9
   10 11
   11 12
   12 12
   13 12
   14 13
   15 12
   16 13
   17 12
   18 12
   19 12
   20 12
   21 12
   22 11
   23 11
   24 12
   25 11
   26 10
   27 11
   28 10
   29 9
   30 8
   31 7
   32 0
   33 11
   34 11
   35 12
   36 12
   37 12
   38 12
   39 13
   40 13
   41 13
   42 13
   43 13
   44 13
   45 13
   46 10
   47 13
   48 13
   49 13
   50 14
   51 13
   52 14
   53 14
   54 14
   55 14
   56 13
   57 14
   58 13
   59 14
   60 13
   61 13
   62 13
   63 13
   64 13
   65 13
   66 13
   67 13
   68 13
   69 13
   70 13
   71 13
   72 13
   73 13
   74 13
   75 13
   76 13
   77 13
   78 12
   79 12
   80 12
   81 12
   82 12
   83 12
   84 12
   85 12
   86 12
   87 2
   88 12
   89 12
   90 12
   91 12
   92 12
   93 12
   94 12
   95 12
   96 12
   97 12
   98 11
   99 12
   100 12
   101 11
   102 11
   103 12
   104 11
   105 11
   106 12
   107 11
   108 11
   109 11
   110 12
   111 11
   112 11
   113 11
   114 11
   115 11
   116 11
   117 11
   118 11
   119 11
   120 11
   121 11
   122 11
   123 10
   124 11
   125 10
   126 11
   127 9
   128 10
   129 10
   130 10
   131 10
   132 10
   133 0
   134 10
   135 10
   136 9
   137 10
   138 10
   139 10
   140 9
   141 10
   142 10
   143 10
   144 8
   145 9
   146 8
   147 0
   148 6
   149 8
   150 7
   151 7
   152 0
   153 8
   154 7
   155 6
   156 4
   157 4
   158 5
   159 4
   160 2
   161 0
   162 3
   163 5
   164 6
   165 5
   166 7
   167 6
   168 7
   169 5
   170 5
   171 5
   172 5
   173 3
   174 5
   175 5
   176 6
   177 3
   178 5
   179 5
   180 5
   181 5
   182 6
   183 5
   184 4
   185 5
   186 4
   187 6
   188 2
   189 6
   190 5
   191 5
   192 4
   193 5
   194 3
   195 5
   196 5
   197 5
   198 1
   199 3
   200 0
   201 2
   202 3
   203 3
   204 3
   205 3
   206 3
   207 2
   208 3
   209 1
   210 1
   211 0
   212 1
   213 2
   214 3
   215 3
   216 3
   217 3
   218 3
   219 0
   220 3
   221 2
   222 4
   223 3
   224 4
   225 3
   226 3
   227 2
   228 2
   229 3
   230 3
   231 3
   232 2
   233 3
   234 2
   235 3
   236 3
   237 3
   238 0
   239 3
   240 3
   241 3
   242 3
   243 2
   244 0
   245 1
   246 0
   247 2
   248 1
   249 0
   250 0
   251 0
   252 0
   253 0
   254 0
   255 0
#

The graph plotted from the above data --
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roseway

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Re: Bitloading gaps curiosity
« Reply #12 on: March 03, 2014, 11:14:01 PM »

Bang goes my theory then. :)
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  Eric

sheddyian

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Re: Bitloading gaps curiosity
« Reply #13 on: March 04, 2014, 11:23:37 AM »

Well, so far the common factors are ADSL (obviously) and Plusnet or TalkTalk.

My friend with the gaps last year is on a long line, I'm not sure if they were synching on ADSL2+ at the time - I certainly am and always have.

Does anyone know if there's a telnet command for the HG612 that will tell you what MSAN it's connected to?  A quick google didn't help me here.

I'll get the TP link modem out later and see if I can persuade it to work for long enough to give me some output (it overheats in a big way - it runs best as a bare board with no case!)

Ian
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roseway

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Re: Bitloading gaps curiosity
« Reply #14 on: March 04, 2014, 01:01:02 PM »

Quote
Does anyone know if there's a telnet command for the HG612 that will tell you what MSAN it's connected to?

DSLstats gives you this information on the Stats page. Or you can login via telnet and use the command xdslcmd info --vendor
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