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Author Topic: Leaving Be*  (Read 24694 times)

Bald_Eagle1

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Re: Leaving Be*
« Reply #60 on: July 20, 2013, 04:14:27 PM »


>>> It may be interesting to see your --pbParams data

Code: [Select]
# xdslcmd info --pbParams
xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 0
Max:    Upstream rate = 35667 Kbps, Downstream rate = 101660 Kbps
Path:   0, Upstream rate = 20000 Kbps, Downstream rate = 79999 Kbps

Discovery Phase (Initial) Band Plan
US: (0,95) (880,1195) (1984,2771)
DS: (32,859) (1216,1959) (2792,4083)
Medley Phase (Final) Band Plan
US: (0,95) (880,1195) (1984,2771)
DS: (32,859) (1216,1959) (2792,4083)
       VDSL Port Details       Upstream        Downstream
Attainable Net Data Rate:      35667 kbps        101660 kbps
Actual Aggregate Tx Power:        5.3 dBm          14.3 dBm
============================================================================
  VDSL Band Status        U0      U1      U2      U3      D1      D2      D3
  Line Attenuation(dB):  0.8     17.9    29.2     N/A    11.1    24.5    38.8

Signal Attenuation(dB):  0.9     17.8    29.0     N/A    11.1    24.5    38.8

        SNR Margin(dB):  15.8    16.3    15.7     N/A    11.5    12.1    11.8

         TX Power(dBm): -4.8    -25.3    4.8      N/A    12.0    7.4     7.2

#


That looks like a really, really good 450m connection.
Nothing to do with being associated with Plusnet & the owner of a site that deals with broadband matters, I presume  :lol:


Here's the pbParams data from another 450m connection to an ECI DSLAM:-

Code: [Select]
Retrain Reason: 0
Max: Upstream rate = 9502 Kbps, Downstream rate = 46048 Kbps
Path: 0, Upstream rate = 10641 Kbps, Downstream rate = 47007 Kbps

Discovery Phase (Initial) Band Plan
US: (0,95) (880,1195) (1984,2771)
DS: (32,859) (1216,1959) (2792,4083)
Medley Phase (Final) Band Plan
US: (0,95) (880,1195) (1984,2771)
DS: (32,859) (1216,1959) (2792,4083)
       VDSL Port Details       Upstream        Downstream
Attainable Net Data Rate:       9502 kbps         46048 kbps
Actual Aggregate Tx Power:        6.9 dBm          11.0 dBm
============================================================================
  VDSL Band Status        U0      U1      U2      U3      D1      D2      D3
  Line Attenuation(dB): 2.2 32.8 50.6   N/A 16.1 42.4 66.5
Signal Attenuation(dB): 2.2 32.7 50.2   N/A 16.1 42.4 66.5
        SNR Margin(dB): 5.5 5.4 5.0   N/A 5.6 5.6 5.6
         TX Power(dBm): -3.6 -9.0 6.4   N/A 8.6 7.4 -4.2
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kitz

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Re: Leaving Be*
« Reply #61 on: July 20, 2013, 07:06:00 PM »

Is that yours BE?  :(  :'(

One thing I notice is the Tx power seems low compared to mine.  Im a novice when it comes vdsl, so dont know what the normal parameters are for  FTTC, but certainly on adsl you'd expect a specific range.
Has anyone done a study on average Tx power on vdsl.... this probably would have been something I would have done in the past days when I had more time (ok I did because back in 2003 I never understood why mine was low compared to everyone else's - which lead me to the discovery of power cut back & PSD masks)

Secondly quality of copper is going to make a difference, a lot of this will depend on the age of your estate.  Over the years BT have used various gauge copper 0.5mm and 0.3mm as well as copper coated aluminium.  With vdsl obviously the chunk of E side has been eliminated, and D side is going to be a lot dependant on when BT first put the lines to an estate in. 

Although this estate is newish, its fed from a much older DP which definitely uses 05.mm gauge from the cab.  The cab Im actually connected to is probably one of the first installed in this town and the DPs put in during an era when the price of copper wasnt such of a concern as it has been over about the past 20 yrs.  No idea what gauge is used on the UG feed for the estate, but since Im near the beginning its a relatively short length to the JBF Im on, compared to the overall distance anyhow.

I moved into this estate shortly before adsl became available, back in the days when no-one ever thought of things like attenuation and loop length.  Although I am very close to the exchange because this estate is fed via an old cab and DP the loop length is relatively long and literally does go all round the houses ..  but even so Ive always been able to exceed estimations and at once upon a time I had a rock steady full 24Mbps down 2.6 Mbps up with Be*.... well until more recently that is.

I think with vdsl its going to be a bit more difficult to estimate speeds as accurately as we could with adsl2+ because so much more is dependant on the type of copper used by BT locally.
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burakkucat

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Re: Leaving Be*
« Reply #62 on: July 20, 2013, 07:23:02 PM »

Is that yours BE?  :(  :'(

No I believe that is a service based in Ewhurst, which has received the attention of an Eagle-eye.  ;)
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kitz

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Re: Leaving Be*
« Reply #63 on: July 20, 2013, 07:39:01 PM »

That's terrible!  :o
That's the PN equivalent of 'please reinstall Windows' then?  :'(
Quote
Each time it suggests switching the BT modem off for 30 seconds
Please don't do that from now on. :no:


I know, but Im not the type that wanted to phone up PN just for the hell of it...  and perhaps then be referred back by asking if Id done all the troubleshooting in their booklet.   I wanted to be able to fix it myself without spending time hanging on the phone.

I didnt realise that they had my profile down as adsl2+ in their systems rather than fttc, which is why I couldnt authenticate properly.

Quote
DLM monitors that number of resyncs by examining the recorded up time in each 15 mins time slot.  If there was 15 mins up-time in one time slot, and less than 15 mins in the next then it would record that a 'forced (i.e. unsolicited) resync' had occurred.  If at least two time slots back-to-back have no up time, it will (should  :-X) determine that this was a solicited resync e.g. following the EU powering down the line, and ignore it for the purposes of determining instability.

and that is exactly the reason why earlier in this thread, that once Id done all the suggested 'trouble shooting' that I wanted to let my line settle for a while before putting the Huawei on and I didnt want to push my luck.

What I wasnt aware of is the 'first day' period of grace.     Ive been away from the BT DLM now for about 5+ years and although once upon a time I did know a fair bit about it.. its one of those things that when youre not effected by it yourself then you perhaps dont always follow closely whats going on because you dont see it first hand. 

I loved Be*s DLM.   It worked and gave the EU so much control over their line.   None of this hidden mystery stuff and IP profiles.
However I suppose I can grudgingly admit I know why BT do it..  and I can imagine ' Old Aunt Edith' could muck up her line to become unstable because she didnt know what she was doing with being presented the opportunity of setting your own line profiles  :-X   

Quote
I know that Asbo has proved on another thread that (becuase of 'last gasp' communications between the modem and the DSLAM - at least the Huawei ones!) that powering it down prevents line-errors being recorded, which you would otherwise get if you just unplugged it from the line (either at the modem or NTE), which DLM would frown on.

Ahhhhhhhh   the joys of dying gasp and its effects on the DLM.   Something else LLU freed me from...  and something else Ive had more than one rants about going back to the early days of maxdsl...   lol coming back to a BTw based ISP brings memories flooding back.   If you search history back far enough theres possibly several posts by me on this topic across various forums, and how either some routers werent sending the dying gasp signal.. or the BTw DLM was ignoring it.  iirc all dsl modems are supposed to hold on to a small amount of energy in reserve sufficient to send the dying gasp message to the DSLAM in the event of power failures etc.
Its a long time ago now, but the Voyager routers didnt seem to do this very well - or back then BTs DLMs didnt care.

Quote
At the other end of the spectrum from that which you are currently experiencing with your PN PPPoE, quite often (becuase the TG firmware has the wrong PPP timeouts set by PN) a modem resync will not be detected by PN's RADIUS servers, as it happens too quickly within the PPP timeout - But DLM has seen it (rather like the garden shed in Bill & Ben)!!!!!  :lol:

Oh gawd...  this really is like a stroll down memory lane today.   Im experiencing deja vu...  and now recalling why I rejoiced when Be came here and I was suddenly free from stuck bRAS profiles and the BTw DLM..  and stale sessions.   I guess I need to bring myself back up to date again.  :'(
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kitz

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Re: Leaving Be*
« Reply #64 on: July 20, 2013, 07:44:07 PM »

Is that yours BE?  :(  :'(

No I believe that is a service based in Ewhurst, which has received the attention of an Eagle-eye.  ;)

So why is the power output so low?  Does anyone know?   This surely will be having an effect on the achievable sync speeds.
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Bald_Eagle1

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Re: Leaving Be*
« Reply #65 on: July 20, 2013, 09:50:46 PM »

Is that yours BE?  :(  :'(


No, it's not mine.

I'm connected to a Huawei DSLAM with a D-side length of around 1000m, so mine's much worse.

Quote

One thing I notice is the Tx power seems low compared to mine.  Im a novice when it comes vdsl, so dont know what the normal parameters are for  FTTC, but certainly on adsl you'd expect a specific range.
Has anyone done a study on average Tx power on vdsl.... this probably would have been something I would have done in the past days when I had more time (ok I did because back in 2003 I never understood why mine was low compared to everyone else's - which lead me to the discovery of power cut back & PSD masks)


It's a little harder to consider averages with VDSL2 connections as the stats are split up per frequency band plan.

This is my connection:-

Code: [Select]

Retrain Reason: 2
Max: Upstream rate = 4282 Kbps, Downstream rate = 19336 Kbps
Path: 0, Upstream rate = 4333 Kbps, Downstream rate = 19023 Kbps

Discovery Phase (Initial) Band Plan
US: (0,95) (868,1207) (1972,2783)
DS: (32,859) (1216,1963) (2792,3959)
Medley Phase (Final) Band Plan
US: (0,95) (868,1207)
DS: (32,859)
       VDSL Port Details       Upstream        Downstream
Attainable Net Data Rate:       4282 kbps         19336 kbps
Actual Aggregate Tx Power:        6.2 dBm          11.3 dBm
============================================================================
  VDSL Band Status        U0      U1      U2      U3      D1      D2      D3
  Line Attenuation(dB): 8.3 56.1   N/A   N/A 22.2 65.7 0.1
Signal Attenuation(dB): 8.3 55.6   N/A   N/A 22.2   N/A   N/A
        SNR Margin(dB): 5.9 6.1   N/A   N/A 6.3   N/A   N/A
         TX Power(dBm): -4.2 5.8   N/A   N/A 11.3   N/A   N/A


DS TX Power is reported as 11.3 dBm but as can be seen, these days I can only use the lowest frequency band.


Quote
Secondly quality of copper is going to make a difference, a lot of this will depend on the age of your estate.  Over the years BT have used various gauge copper 0.5mm and 0.3mm as well as copper coated aluminium.  With vdsl obviously the chunk of E side has been eliminated, and D side is going to be a lot dependant on when BT first put the lines to an estate in. 

Although this estate is newish, its fed from a much older DP which definitely uses 05.mm gauge from the cab.  The cab Im actually connected to is probably one of the first installed in this town and the DPs put in during an era when the price of copper wasnt such of a concern as it has been over about the past 20 yrs.  No idea what gauge is used on the UG feed for the estate, but since Im near the beginning its a relatively short length to the JBF Im on, compared to the overall distance anyhow.

I moved into this estate shortly before adsl became available, back in the days when no-one ever thought of things like attenuation and loop length.  Although I am very close to the exchange because this estate is fed via an old cab and DP the loop length is relatively long and literally does go all round the houses ..  but even so Ive always been able to exceed estimations and at once upon a time I had a rock steady full 24Mbps down 2.6 Mbps up with Be*.... well until more recently that is.

I think with vdsl its going to be a bit more difficult to estimate speeds as accurately as we could with adsl2+ because so much more is dependant on the type of copper used by BT locally.

Not only the type of copper, but at the higher frequencies in play, attenuation, interference & crosstalk play a much larger part, particularly on longer lines.

1 or 2 dB increase in attenuation-wise can seriously affect some connections.

« Last Edit: July 20, 2013, 10:05:07 PM by Bald_Eagle1 »
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Bald_Eagle1

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Re: Leaving Be*
« Reply #66 on: July 20, 2013, 09:59:16 PM »

Is that yours BE?  :(  :'(

No I believe that is a service based in Ewhurst, which has received the attention of an Eagle-eye.  ;)

It is indeed very similar to an Ewhurst connection, but it's actually someone else's.
He too can't get to the bottom of why it's so poor.

There is a school of thought that VDSL2 output power is decreased for cabinets a long way from the exchange - to avoid swamping the already weak ADSL signals that have travelled all the way from the exchange.

e.g. my cabinet is around 4.4km from the exchange, so ADSL signals won't be too strong at all by the time they reach the cabinet.

At the additional 1000m or so to my home from the cabinet, I could only achieve 1 Mbps on ADSL (on a good day).

FWIW, see the attached graph for how power in the 2nd DS band (D2) has deteriorated on my connection since Christmas.
It's been a big fat zero since DLM was reset/re-calculated 13th July.

Now, whether that's the result of lower sync speed or the lower sync speed is a result of reduced power, I just don't know.
Neither did the visiting engineer.

« Last Edit: July 20, 2013, 10:26:40 PM by Bald_Eagle1 »
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Black Sheep

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Re: Leaving Be*
« Reply #67 on: July 21, 2013, 12:06:46 PM »

Is that yours BE?  :(  :'(

No I believe that is a service based in Ewhurst, which has received the attention of an Eagle-eye.  ;)

It is indeed very similar to an Ewhurst connection, but it's actually someone else's.
He too can't get to the bottom of why it's so poor.

There is a school of thought that VDSL2 output power is decreased for cabinets a long way from the exchange - to avoid swamping the already weak ADSL signals that have travelled all the way from the exchange.

e.g. my cabinet is around 4.4km from the exchange, so ADSL signals won't be too strong at all by the time they reach the cabinet.

At the additional 1000m or so to my home from the cabinet, I could only achieve 1 Mbps on ADSL (on a good day).

FWIW, see the attached graph for how power in the 2nd DS band (D2) has deteriorated on my connection since Christmas.
It's been a big fat zero since DLM was reset/re-calculated 13th July.

Now, whether that's the result of lower sync speed or the lower sync speed is a result of reduced power, I just don't know.
Neither did the visiting engineer.

That very same 'school of thought', was told to myself and others, on a recent course I attended.
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kitz

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Re: Leaving Be*
« Reply #68 on: July 21, 2013, 12:29:40 PM »

Quote
There is a school of thought that VDSL2 output power is decreased for cabinets a long way from the exchange - to avoid swamping the already weak ADSL signals that have travelled all the way from the exchange.

That does actually make a lot of sense and it wouldn't surprise me.
A neighbour subscribed to adsl1/2+ using the same DP as someone on VDSL could possibly experience cross-talk from his vdsl neighbour.


I tried to research power cutback & PSD masks several years ago & unfortunately there was very little information in public domain about the PSD profiles.  All I know is that for adsl there were 4 separate profiles in use by BT which are dependant on line length.
The shorter lines are the ones which have more power cutback applied, particularly to the lower end of the frequency range, but all tones in the adsl1 frequency are cut back to some extent for short lines. 
 
Its a long time since I looked, but I never could find anything that documented how much cutback was applied to which tones for each of the 4 profiles. 
All I can say is that from my own observations an adsl1 PSD mask profile for short lines would reduce tx power from about 20dBm to about 12dBm.
On adsl 2+ (aside from the very early frequencies) its a bit harder to see the effects of PSD masks, but on a short line looking at the bit loading graph you can sometimes still see slight bump as you move into adsl2+ tone territory, where they seem to get no obvious restrictions.


So...... with VDSL.... because the e-side is now out of the loop (literally), then yes the fttc line is going to become the new 'short' neighbouring line.  The further away from the exchange the cab is, then its more likely it is that a vdsl line could cause x-talk to any adsl lines in the vicinity, which as you already pointed out on a long line is going to be a bit delicate as it is....  so it wouldnt surprise me if there are vdsl power masks based on cab distance.

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kitz

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Re: Leaving Be*
« Reply #69 on: July 21, 2013, 12:34:41 PM »

That very same 'school of thought', was told to myself and others, on a recent course I attended.

Sorry BS, I didnt see your post when I started typing my reply,  do you have any further info on this ie such as how many profiles and distances?
or was it just as we are doing here and pointing out the obvious as to yes it makes perfect sense that there would likely be vdsl specific power profiles to protect the very long lines.


----

However, Ive still no idea why BE's line would suddenly be reduced for no apparent reason  ???
« Last Edit: July 21, 2013, 12:36:58 PM by kitz »
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kitz

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Re: Leaving Be*
« Reply #70 on: July 21, 2013, 01:06:49 PM »

BTW

I noticed yesterday that the DLM seemed to turn interleaving off, it may or may not be a co-incidence, but looking back on DSLstats, it possibly occurred some time around the drop in PPP session, as Ive not had any recorded FECs since then.


Secondly Ive also just noticed that my intermittent EMI/REIN/upstream line fault appears to be back  :'(   Ive taken that back to the other thread.
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Black Sheep

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Re: Leaving Be*
« Reply #71 on: July 21, 2013, 01:57:59 PM »

That very same 'school of thought', was told to myself and others, on a recent course I attended.

Sorry BS, I didnt see your post when I started typing my reply,  do you have any further info on this ie such as how many profiles and distances?
or was it just as we are doing here and pointing out the obvious as to yes it makes perfect sense that there would likely be vdsl specific power profiles to protect the very long lines.


----

However, Ive still no idea why BE's line would suddenly be reduced for no apparent reason  ???

Yes, it was basically 'chit chat' from our trainer. I personally wasn't aware of this, but he said the power back-off was related to the ANFP, especially on long distance Cabs. He also commented that he knew of instances of this, whereby the synch speed at the Cab would be less than the 40/80Meg one may expect. I haven't ever experienced this situation, and my patch is semi-rural/semi-urban.

Perhaps on some of the extreme rural routes, Wales, Highlands of Scotland, Lake District/Peak District etc, this may occur ??
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Bald_Eagle1

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Re: Leaving Be*
« Reply #72 on: July 21, 2013, 02:29:37 PM »


Yes, it was basically 'chit chat' from our trainer. I personally wasn't aware of this, but he said the power back-off was related to the ANFP, especially on long distance Cabs. He also commented that he knew of instances of this, whereby the synch speed at the Cab would be less than the 40/80Meg one may expect. I haven't ever experienced this situation, and my patch is semi-rural/semi-urban.

Perhaps on some of the extreme rural routes, Wales, Highlands of Scotland, Lake District/Peak District etc, this may occur ??

Or dare I mention it, some of the slightly less extreme semi-rural routes e.g. the outskirts of a town where D-side length may be around 1000m with the cab itself being over 4 km from the exchange?  ;)

Is 4 km classed as long distance?

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burakkucat

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Re: Leaving Be*
« Reply #73 on: July 21, 2013, 02:35:26 PM »

Is 4 km classed as long distance?

For an ADSL2+/ADSL2/G.Dmt service I would say that distance is significant.  ;)
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Black Sheep

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Re: Leaving Be*
« Reply #74 on: July 21, 2013, 05:13:23 PM »

I find myself agreeing with B*Cat (as always)  ;D.

I'm afraid I'm not privy to information, as to what dictates the distance (in dB, not Km I would guess ?) a Cabinet would require 'PBO' to be applied ?? As we know, your Cabinet is very busy with well over 100 EU's as well, so maybe it is being 'held off' to some degree ??
I wouldn't have a clue, but I'm left wondering if this in fact is worth pursuing with your ISP, BE ?? They may have the clout to get an answer ??   
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