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I'd like to know details about SNR margin calculation at ADSL2+. I know it is depended on SNR on particular tones, synchronization rate, used tones. What else?
How target SNR margin does his work? Are my router and DSLAM aim to 6 dB SNR margin on every tone or rather merely overall SNR margin 6 dB?
I'm very curious about these issues.
Edited by konrado5 (Sun 03-Nov-13 01:51:37)
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Removed as realised this was inappropriate.
Edited by deleted (Sun 03-Nov-13 11:43:41)
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Another wannabe mod 
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Register (or login) on our website and you will not see this ad.
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It's worth also pointing out I have ADSL2+ rate adaptive servie from polish provider Netia. I'm not complaining.... with several replies.
My broadband basic info/help site - www.robertos.me.uk | Domains,website and mail hosting - Tsohost.
Connection - Plusnet UnLim Fibre (FTTC). Sync ~ 59.2/14.4Mbps @ 600m. - BQM
"Where talent is a dwarf, self-esteem is a giant." - Jean-Antoine Petit-Senn.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Allergy information: This post was manufactured in an environment where nuts are present. It may include traces of understatement, litotes and humour.
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Another wannabe mod
Removed as I realised the post was inappropriate.
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Another wannabe mod
Nope, I have no interest in being a moderator. I just thought I'd ask as it's been sitting there a while with no movement.
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I'd like to know details about SNR margin calculation at ADSL2+. I know it is depended on SNR on particular tones, synchronization rate, used tones. What else?
Calculated per tone. Function of how many bits per symbol can theoretically be packed into each tone, and how many actually are in use. Each 3dB of margin indicates an additional 2 bits per symbol that could theoretically be used on the tone. The individual carriers on each tone are modulated with QAM apart from those that have dropped to 2 bits per symbol, they use QPSK, and those carrying a single bit, which use BPSK.
SNR is calculated with some mathematical wizardry.
How target SNR margin does his work? Are my router and DSLAM aim to 6 dB SNR margin on every tone or rather merely overall SNR margin 6 dB?
Per tone. If your router allows you to dig deeply enough you can see the SNR per tone. The single figure given is an average across all tones in use.
It has to be per tone else you risk allowing individual tones to go too low, and when the SNR drops too low on a particular tone the BER increases, causing impact to quality of service.
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Thank you for reply. I'm not sure whether I understand rightly. Assume on DSLAM target SNR margin is changed from 6 dB to 3 dB. Are tones with only 3 dB SNR margin then enabled or rather only the same tones are used as at 6 dB target SNR margin and also more bits on the same tones?
I've heard SNR margin is depended not only on SNR on particular tones and synchronization rate. I've heard it is also depended on BER. I've notices strange phenomenon on my line. At the lower sychronization rate, higher power output, the same used tones I have sometimes continously lower SNR margin than at the higher synchronization rate, lower power output and the same used tones. For example, I have now 1207 kbps upstream and power output 12.3 dBm but my SNR margis is never higher than 6.8 dB however when I had 1225 kbps and power output 12.1 dBm I had SNR margin for upload about 7.1 dB.
Recently I have strange interferences during first 20 minutes of new synchronization. On upstream SNR margin is only 4.6 dB but after 20 miutes SNR margin is already about 6.6 dB-7.0 dB. Is it not strange much interferences are only at first moments of new synchronization? Only at first moments of synchronization there are bitswaps for upload.
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Thank you for reply. I'm not sure whether I understand rightly. Assume on DSLAM target SNR margin is changed from 6 dB to 3 dB. Are tones with only 3 dB SNR margin then enabled or rather only the same tones are used as at 6 dB target SNR margin and also more bits on the same tones?
Both.
Tones that were previously empty due to inadequate SNR will have 1 or 2 bits in them, depending on their SNR, existing in use tones will have an additional 2 bits per symbol.
I've heard SNR margin is depended not only on SNR on particular tones and synchronization rate. I've heard it is also depended on BER. I've notices strange phenomenon on my line. At the lower sychronization rate, higher power output, the same used tones I have sometimes continously lower SNR margin than at the higher synchronization rate, lower power output and the same used tones. For example, I have now 1207 kbps upstream and power output 12.3 dBm but my SNR margis is never higher than 6.8 dB however when I had 1225 kbps and power output 12.1 dBm I had SNR margin for upload about 7.1 dB.
Depends how it's calculated. Normally BER is not used to calculate SNR as, ideally, BER is zero. The SNR that is provided is after any error correction. When BER is zero error vector magnitude is the usual suspect to provide an SNR value. Where BER isn't zero a calculation can be done to estimate SNR based on BER and modulation in use.
The SNR margin depends on the sync rate, the higher the rate the less margin, the actual SNR itself does not and is the same whether connected at 24Mb or 64kb.
Recently I have strange interferences during first 20 minutes of new synchronization. On upstream SNR margin is only 4.6 dB but after 20 miutes SNR margin is already about 6.6 dB-7.0 dB. Is it not strange much interferences are only at first moments of new synchronization? Only at first moments of synchronization there are bitswaps for upload.
Not really. The same noise that caused the resync in the first place is probably still there for a while afterwards.
I have a similar effect but worse on my own connection, where it repeatedly disconnects over and over again until it reaches an upstream rate it can sustain even with the noise present.
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Tones that were previously empty due to inadequate SNR will have 1 or 2 bits in them, depending on their SNR, existing in use tones will have an additional 2 bits per symbol.
Is it case that tones will be loaded with bits in the way that every tone will have 6 dB unused SNR? I've heard about SNR, SNR on particular tones and SNR margin. I've not heard about SNR margin on particular tones.
Not really. The same noise that caused the resync in the first place is probably still there for a while afterwards.
It was resync did by myself. My ISP recently changed DSLAM. On previous DSLAM I did many recyncs at 5 minutes and I had either 1277 kbps with SNR margin 7.0 dB and power output 11.3-11.9 dBm or 1260-1277 kbps with SNR margin about 6 dB and power output 12.4 dBm. At new DSLAM I have immediately after recyn SNR margin about 4.6 dB, however after 20 minutes SNR margin is 6.8 dB.
Perhaps my Hlog, QLN and SNR on particular tones will be helpful.
http://img849.imageshack.us/img849/276/or97.png
http://img823.imageshack.us/img823/9369/z1mi.png
http://img43.imageshack.us/img43/7920/5xiw.png
My present line stats:
| Text | 1
23
45
67
89
1011
1213
1415
1617
1819
2021
2223
2425
2627
2829
3031
3233
3435
3637
3839
4041
4243
4445
4647
4849
5051
5253
5455
5657
5859
6061
62 | adsl: ADSL driver and PHY status
Status: ShowtimeRetrain Reason: 8000Channel: FAST, Upstream rate = 1209 Kbps, Downstream rate = 15403 Kbps
Link Power State: L0Mode: ADSL2+
Channel: FastTrellis: U:ON /D:ON
Line Status: No DefectTraining Status: Showtime
Down UpSNR (dB): 5.3 6.7
Attn(dB): 25.0 14.8Pwr(dBm): 18.6 12.3
Max(Kbps): 17664 1276Rate (Kbps): 15403 1209
G.dmt framingK: 255(0) 38
R: 0 0S: 1 1
D: 1 1 ADSL2 framing
MSGc: 116 16B: 254 37
M: 1 1T: 1 3
R: 0 0S: 0.5276 0.9967
L: 3866 305D: 1 1
CountersSF: 1969586 32122067
SFErr: 439 1RS: 0 0
RSCorr: 0 0RSUnCorr: 0 0
HEC: 410 0
OCD: 22 0LCD: 0 0
Total Cells: 1491472946 3477151887Data Cells: 414789396 98245202
Drop Cells: 2516Bit Errors: 0 2322
ES: 4765 20
SES: 0 0UAS: 35 988
AS: 513953
INP: 0.00 0.00PER: 16.09 16.44
delay: 0.13 0.24OR: 60.64 10.70
Bitswap: 2920 0
Total time = 1 days 22 hours 46 min 44 sec
SF = 31934406CRC = 4874
LOS = 0LOF = 0
ES = 4765 |
There is now 22:08. Statistics was reseted about 13:20. CRC and ES are in fact from 5 days 22 hours 48 minutes.
Edited by konrado5 (Sun 03-Nov-13 21:11:14)
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I wonder what the big hole starting around 1.6 MHz is about on the SNR graph.
Each tone should be loaded to an SNR margin equal to the target, give or take a bit for the fact that bits/tone is an integer value. Some low frequencies may be higher in SNR margin if they hit the bits/tone ceiling.
--
Phil
MaxDSL - goes as fast as it can and doesn't read the line checker first.
MaxDSL diagnostics |
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Best guess there's a slight compatibility issue between the chipsets in the DSLAM and in your router, causing a sub-optimal negotiation.
These happen, hence why some CPE sync somewhat higher than others on the exact same line.
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Perhaps he was a WWII 'das boot' submariner operating the sonar, and is obsessed with *ping* *ping*
Nick
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Best guess there's a slight compatibility issue between the chipsets in the DSLAM and in your router, causing a sub-optimal negotiation.
I don't think the above is cause. What in it would consist? Is my router only at some connections incompatible with DSLAM and also badly measures SNR margin? Furtermore, DSLAM was changed, the problem is still actual.
Edited by konrado5 (Mon 04-Nov-13 19:30:14)
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Best guess there's a slight compatibility issue between the chipsets in the DSLAM and in your router, causing a sub-optimal negotiation.
I don't think the above is cause. What in it would consist? Is my router only at some connections incompatible with DSLAM and also badly measures SNR margin? Furtermore, DSLAM was changed, the problem is still actual.
You said the problem started when you moved to the new DSLAM.
My ISP recently changed DSLAM. On previous DSLAM I did many recyncs at 5 minutes and I had either 1277 kbps with SNR margin 7.0 dB and power output 11.3-11.9 dBm or 1260-1277 kbps with SNR margin about 6 dB and power output 12.4 dBm. At new DSLAM I have immediately after recyn SNR margin about 4.6 dB, however after 20 minutes SNR margin is 6.8 dB.
It would seem fair to say that the DSLAM has a different chipset, or that the new DSLAM has a defective port / line card.
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Thanks. *Leaves thread*
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You said the problem started when you moved to the new DSLAM.
I apologize but my English is poor. I had something else in mind. At new DSLAM I have immediately after recync SNR margin about 4.6 dB, however after 20 minutes SNR margin is 6.8 dB. I have only one errored second for upload at three days and 0 bitswaps except first 20 minutes of new synchronization. However both on new and old DSLAM I have often lower SNR margin at lower synchronization rate, higher power output and the same used tones than at higher synchronization rate, higher power output and the same used tones.
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Actually why's this in the fibre broadband section too?
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At new DSLAM I have immediately after recync SNR margin about 4.6 dB, however after 20 minutes SNR margin is 6.8 dB. I have only one errored second for upload at three days and 0 bitswaps except first 20 minutes of new synchronization.
so there were bitswaps or not, in this first 20 minutes ?
--
Phil
MaxDSL - goes as fast as it can and doesn't read the line checker first.
MaxDSL diagnostics
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Nice of you to read Kitz's advice about SNRM konrado5!
HE LINKED TO IT SEVERAL TIMES!!!!
And once again, you're REPEATING yourself and being rude!
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At new DSLAM I have immediately after recync SNR margin about 4.6 dB, however after 20 minutes SNR margin is 6.8 dB. I have only one errored second for upload at three days and 0 bitswaps except first 20 minutes of new synchronization.
so there were bitswaps or not, in this first 20 minutes ?
There were bitswaps only in the first 20 minutes.
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Nice of you to read Kitz's advice about SNRM konrado5!
HE LINKED TO IT SEVERAL TIMES!!!!
And once again, you're REPEATING yourself and being rude!
I've read it what Kitz adviced but there I didn't found such details. I have general knowledge about SNRM.
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You're just silly then. It clearly answers most of your questions.
Oh and you've opened another thread. STOP IT!!!!!!!
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There were bitswaps only in the first 20 minutes.
so the increase in SNRM you observed could have resulted from the bitswaps ?
--
Phil
MaxDSL - goes as fast as it can and doesn't read the line checker first.
MaxDSL diagnostics
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