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Standard User konrado5
(newbie) Sun 03-Nov-13 01:47:22
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SNR margin calculation


[link to this post] 		 
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)
Standard User deleted
(deleted) Sun 03-Nov-13 11:17:53
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Re: SNR margin calculation


[re: konrado5] [link to this post] 		 
Removed as realised this was inappropriate.

Edited by deleted (Sun 03-Nov-13 11:43:41)
Standard User deleted
(deleted) Sun 03-Nov-13 11:26:35
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Re: SNR margin calculation


[re: deleted] [link to this post] 		 
Another wannabe mod frown


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Standard User RobertoS
(sensei) Sun 03-Nov-13 11:35:24
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Re: SNR margin calculation


[re: deleted] [link to this post] 		 
It's worth also pointing out
In reply to a post by konrado5:
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.
Standard User deleted
(deleted) Sun 03-Nov-13 11:44:07
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Re: SNR margin calculation


[re: deleted] [link to this post] 		 
In reply to a post by BatBoy:
Another wannabe mod frown


Removed as I realised the post was inappropriate.
Standard User deleted
(deleted) Sun 03-Nov-13 11:47:26
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Re: SNR margin calculation


[re: deleted] [link to this post] 		 
In reply to a post by BatBoy:
Another wannabe mod frown


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.
Standard User deleted
(deleted) Sun 03-Nov-13 12:30:36
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Re: SNR margin calculation


[re: konrado5] [link to this post] 		 
In reply to a post by konrado5:
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.

In reply to a post by konrado5:
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.
Standard User konrado5
(newbie) Sun 03-Nov-13 16:35:54
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Re: SNR margin calculation


[re: deleted] [link to this post] 		 
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.
Standard User deleted
(deleted) Sun 03-Nov-13 20:17:02
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Re: SNR margin calculation


[re: konrado5] [link to this post] 		 
In reply to a post by konrado5:
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.

In reply to a post by konrado5:
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.

In reply to a post by konrado5:
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.
Standard User konrado5
(newbie) Sun 03-Nov-13 21:10:03
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Re: SNR margin calculation


[re: deleted] [link to this post] 		 
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
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4243
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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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