Kitz Forum
Broadband Related => ADSL Issues => Topic started by: sheddyian on March 03, 2014, 02:48:35 PM
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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 (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 ... :
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 :-[
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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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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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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.
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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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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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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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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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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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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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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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A TalkTalk service. MSAN using an Infineon chipset. Huawei HG622 modem/router. Link configured to operate in ADSL2 mode.
The raw bit-loading data --
# 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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Bang goes my theory then. :)
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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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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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DSLstats gives you this information on the Stats page. Or you can login via telnet and use the command xdslcmd info --vendor
Ah, thank you! I thought I'd seen something like that, but had a look earlier and couldn't find it - ended up thinking I'd imagined it, or seen it on someone else's system ;D
Anyway, mine says :
DSLAM/MSAN type: IFTN:0x71c6 / v0x71c6
Which means nothing to me :'( A google of either/both those numbers doesn't seem to explain much either - was hoping for a handy table of manufacturers and versions :)
Can anyone enlighten me?
Ian
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IFTN is Infineon. Mine is almost the same, but it's v0x71c8. That's described as the chipset version number.
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As well as the traditional pilot tone, some isp networks also use test tones. I believe the TT network does so. Test tones may carry 2 bits, and although there may be a preference for the test tone, it isn't always the same.
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Anyway, mine says :
DSLAM/MSAN type: IFTN:0x71c6 / v0x71c6
I see --
# xdslcmd info --vendor
xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 8000
Max: Upstream rate = 1084 Kbps, Downstream rate = 7032 Kbps
Channel: INTR, Upstream rate = 1020 Kbps, Downstream rate = 6050 Kbps
ChipSet Vendor Id: IFTN:0x71c6
ChipSet VersionNumber: 0x71c6
ChipSet SerialNumber:
#
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It gets more curious.
I've just connected up the old TP-Link TD8961ND (version1) modem, which synched just under 1 meg lower than the BT HG612, and got the bitloading plot from it's command line interface.
There's only 1 gap, at tone 83!
All those other gaps that I see on the HG612 are in use, with a bitloading that seems consistent with the neighbouring tones (ie gradually tapering off into the higher tones).
What do you make of that? ???
Ian
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Too much attention to minute details, maybe? ::)
Having made that observational query, the pesky cat goes and hides . . . :paperbag:
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Too much attention to minute details, maybe? ::)
Well, yeah ;D
but..
seems a bit odd, and got my curiosity!
Ian
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Having seen the response, b*cat now backs out of the brown paper bag and promises to be serious. (Until next time!) :angel:
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Too much attention to minute details, maybe? ::)
Well, yeah ;D
but..
seems a bit odd, and got my curiosity!
Ian
:D What did curiosity do to the CAT ?
"but, satisfaction brought it back" ;)
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:D What did curiosity do to the CAT ?
Increased their ADSL2+ bandwidth by up to 5 tones? :D
Ian
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Too much attention to minute details, maybe?
Minute details are very curious.
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Add me to the curious too - I have gaps in exactly the same places. This is on Zen with a Billion 7800N router. Strangely the early tones such as 110 to 243 had plenty of data loaded on them when I was on 20CN ADSL1 a couple months ago.
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Here is my current Bitloading graph (ADSL2 mode, due to line length and quality) --
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Hi
Just to add I was with TalkTalk up to a few weeks ago and never had those gaps.
ADSL and VDSL is a best effort service, with all sorts of hacks and tricks to try and work around the problems of sending high bit-rate data over wires never designed for it, and all these sorts of oddities are just part and parcel of that unfortunately.
The missing tones may be added to allow gaps for other lines pilot tones, or something TalkTalk has added on some equipment to disable those tones for a reason only known to them. BeThere did something similar which was always a cause of bafflement to many why they did it, as it prevented some from joining the 24Mbit club :)
Even if you identify the cause of the missing tones, I doubt very much you could ever fix or change it to get them back.
Regards
Phil
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Even if you identify the cause of the missing tones, I doubt very much you could ever fix or change it to get them back.
Probably true, but curious kittehs just like to know these things. ;)