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Author Topic: My strange Hlog finally EXPLAINED  (Read 12297 times)

konrado5

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My strange Hlog finally EXPLAINED
« on: February 24, 2016, 12:18:10 AM »

It seems I've finally discovered why my Hlog has a lot of undulations and lazy roll. It is related to the PSD masks or something of this kind.

The first attached Hlog is my Hlog. The second attached hlog is hlog of other user from Poland. This Hlog does not contain strange undulations. The third Hlog is Hlog of one other Polish user. This is somewhat undulated Hlog. I've highlighted similar patterns of Hlog by green.

On the second Hlog there is noticable risement of attenuation at the place of my lazy roll. On the third Hlog there are noticable similar undulations at the same place. It implicates that my Hlog measurement is the most sensitive to the PSD masks or something else of this kind. Perhaps my DSLAM reports very inaccurately output power at the attenuation measurement moment. It is important because attenuation is difference between output power and input power.

Best regards
konrado5
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konrado5

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Re: My strange Hlog finally EXPLAINED
« Reply #1 on: February 26, 2016, 03:33:17 PM »

What do you think about my explanation?
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William Grimsley

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Re: My strange Hlog finally EXPLAINED
« Reply #2 on: February 26, 2016, 04:59:07 PM »

What do you think about my explanation?

Not sure.
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konrado5

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Re: My strange Hlog finally EXPLAINED
« Reply #3 on: February 27, 2016, 04:41:28 PM »

Why not sure?
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konrado5

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Re: My strange Hlog finally EXPLAINED
« Reply #4 on: February 28, 2016, 11:19:02 PM »

burakkucat: what do you think about it? Especially with you I've talking about this Hlog.

Best regards
konrado5
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burakkucat

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Re: My strange Hlog finally EXPLAINED
« Reply #5 on: February 28, 2016, 11:56:19 PM »

Three different circuits, in Poland.
  • Do you know if they are all with the same ISP/CP?
  • Do you know if they are all terminated on the same make and model of DSLAM?
  • Do you know if they all have the same PSD mask applied?
I am trying to think why there should be evidence of the PSD mask shown in the corresponding Hlog plot. At the moment I am having trouble convincing myself that it could be possible.

I am happy to agree that the attenuation may be expressed in terms of the received and transmitted power.

I am prepared to accept that certain equipment may be incorrectly reporting certain values.

At the moment, all I can say is that you have prepared a plausible theory but not, unfortunately, a proof.
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konrado5

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Re: My strange Hlog finally EXPLAINED
« Reply #6 on: February 29, 2016, 12:17:32 AM »

Quote from: burakkucat
Do you know if they are all with the same ISP/CP?
These users have other ISP.
Quote from: burakkucat
Do you know if they are all terminated on the same make and model of DSLAM
They also have BDCM DSLAM but not the same model.

Quote from: burakkucat
I am trying to think why there should be evidence of the PSD mask shown in the corresponding Hlog plot. At the moment I am having trouble convincing myself that it could be possible.
Is there other way to explain coincidence of patterns on Hlogs?
Furthermore, G992-3 mentions some accurracy issues with Hlog for ADSL2.
Quote from: ITU-T G.922.3 (04/2009)
The accuracy requirements for the downstream HLOGps (HLOGps_ds) shall apply only to the
following subcarriers (with the corresponding frequency ranges being a part of the passband), and
only if not within the downstream BLACKOUTset (see clause 8.13.2.4):

Annexes A and I:
Subcarriers 46 to 208.

Annex L:
Subcarriers 46 to 104.

Annexes B, J and M: Subcarriers 92 to 208.
Moerover, my lazy roll correspond to the end of AnnexM EU-56 upstream band.

Quote from: burakkucat
Do you know if they all have the same PSD mask applied?
It is possible. Notice: all of them have HAM band mask (1.8-2.0 Mhz).

Best regards
konrado5
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kitz

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Re: My strange Hlog finally EXPLAINED
« Reply #7 on: February 29, 2016, 12:31:28 AM »

I'm not at the pc,  so haven't looked at the graphs... but iirc and going from memory which ones they are, those HAM tones which are blocked are specific to the msan make and model.
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kitz

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Re: My strange Hlog finally EXPLAINED
« Reply #8 on: February 29, 2016, 12:36:38 AM »

Meant to also add

Again I'm going entirely off memory,  but when I was looking deeply into konrados stats last year, there was something which transmitted on those frequencies in Poland, but can't remember now what it was. I suspect the differing amount of undulations in the various  graphs could depend on how close to a transmitter they are?
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konrado5

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Re: My strange Hlog finally EXPLAINED
« Reply #9 on: April 11, 2016, 11:28:48 PM »

By chance I've got evidence that my Hlog is affected by measurement errors. I had reconnection and my DSLAM by mistake connected with target SNR margin 15 dB for donwstream and 17 db for upstream and other power output profile. By mistake because as I reconnected again I got again usual 6 dB SNR margin.

Bearer: 0, Upstream rate = 381 Kbps, Downstream rate = 10647 Kbps

Link Power State:       L0
Mode:                   ADSL2+
TPS-TC:                 ATM Mode
Trellis:                U:ON /D:ON
Line Status:            No Defect
Training Status:        Showtime
                Down            Up
SNR (dB):        15.0            17.2
Attn(dB):        23.0            14.1
Pwr(dBm):        18.9            12.4

Usually I have following stats.

Bearer: 0, Upstream rate = 1221 Kbps, Downstream rate = 15725 Kbps
Link Power State:       L0
Mode:                   ADSL2+
TPS-TC:                 ATM Mode
Trellis:                U:ON /D:ON
Line Status:            No Defect
Training Status:        Showtime
                Down            Up
SNR (dB):        6.2             6.7
Attn(dB):        23.0            15.2
Pwr(dBm):        18.6            12.1

On mistaken connection I've got slightly better Hlog (less undulations) and utterly other QLN. QLN on 15 dB target margin seems to indicate bridge taps.
« Last Edit: April 11, 2016, 11:34:03 PM by konrado5 »
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konrado5

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Re: My strange Hlog finally EXPLAINED
« Reply #10 on: April 11, 2016, 11:29:29 PM »

QLN attached.
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konrado5

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Re: My strange Hlog finally EXPLAINED
« Reply #11 on: April 12, 2016, 02:21:55 PM »

burakkucat: what do you think about it?
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burakkucat

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Re: My strange Hlog finally EXPLAINED
« Reply #12 on: April 12, 2016, 03:21:56 PM »

To me, it still looks like a mystery.

At some time, we have all experienced an anomalous resynchronisation event. You have captured the data from one such event. I am not sure what conclusion can be deduced from that data.

I will agree that the shape of the dips, present in the QLN plot (from the anomalous resynchronisation event), look similar to the dip(s) that would be seen in an Hlog plot from a circuit which has the defect of a bridging tap. However it is wrong to make any conclusion that a bridging tap is present in the circuit from what can be seen in the QLN plot.

A QLN plot would give indications of possible RF ingress, the state of the overall AC balance of the pair, cross-talk from adjacent circuits, etc.

An Hlog plot would give indications of possible physical defects in the circuit, the presence of bridging tap(s), of oxidised high resistance or semi-conducting joints, the overall attenuation loss of the conductors, etc.
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konrado5

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Re: My strange Hlog finally EXPLAINED
« Reply #13 on: April 12, 2016, 04:01:59 PM »

Today  I had second anomalous resynchronization event with SNR margin 15 dB. I had hlog15dB again . Do you see that this Hlog have more regular shape. It implicates that usual hlog is strongly affected by measurement errors related to power output configuration.
« Last Edit: April 12, 2016, 04:14:52 PM by konrado5 »
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burakkucat

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Re: My strange Hlog finally EXPLAINED
« Reply #14 on: April 12, 2016, 05:16:25 PM »

Ah, now I understand what you were trying to explain! Thank you.

Yes, I agree that the Hlog plot (obtained with a 15 dB SNRM) does look the better of the two. There is not a great deal of difference between the two plots but a small difference can be seen.

I wonder if a "thought experiment" can be performed? Let us assume that you have the ability to remotely configure the DSLAM to adjust the target SNRM that is applied to your circuit. How would we expect to see the Hlog plot vary for each 3 dB increase in target SNRM? I am not sure . . .

Having just typed the above paragraph, I now wonder if the target SNRM is even applied to the circuit before the DSLAM and modem have measured & exchanged the data required to calculate the transfer function. (The transfer function is what is being displayed in an Hlog plot, in logarithmic form.) The question is what occurs first. My feeling is that the transfer function is first determined and then, once the loop-loss of the circuit is know, the power output of the transceivers (at each end of the loop) are adjusted. Finally the target SNRM is applied. But I may be wrong . . .

Perhaps you could examine the ITU-T Recommendations Document G.992.3 [1] and also the Broadband Forum Technical Report TR-138 [2] to see if those documents clarify the process?



[1] https://www.itu.int/rec/T-REC-G.992.3/en
[2] https://www.broadband-forum.org/technical/trlist.php
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