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Author Topic: BT DLM advice needed..  (Read 5358 times)

8062282

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Re: BT DLM advice needed..
« Reply #15 on: September 22, 2019, 08:00:51 PM »

Thanks burakkucat :)
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kitz

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Re: BT DLM advice needed..
« Reply #16 on: September 23, 2019, 12:13:30 PM »


Quote
>> I'm still getting the fluctuating SNR, although it doesn't go as high as it did when I was on TalkTalk. 7.8db is the highest on BT, on TT it was going into double figures..
Vdsl uses higher frequencies which can be more susceptible to noise.  Although looking at your QLN and bit loading, most of the noise appears to be affecting the range also used by adsl.   I haven't seen your hlog and can't confirm until I do...  but I suspect your issues are more down to noise rather than the condition of the physical line itself.


Quote
>>
No idea if my speed will go back to the 39Mb I had previously or will this constant up & down SNR end up with me being banded at my current speed of 35Mb.

As mentioned in my previous post, you are not banded.  The line is being limited based on the available SNRM. 
As I also mentioned the line rate would be less if DLM applied Interleaving - which it now has and why you have lost some further sync speed. :(   
I hinted in my post that seeing the SNRM graphs would be useful to see if we could determine any patterns.   It is noise that is causing the underlying changes in sync rate and also causing Err Secs, which obviously DLM doesnt like. 

A zoomed in capture of your bitloading over tones 50 to 500 may also be useful as this appears to be where you are losing a good chunk of your speed.
B*cat is usually very good at spotting  noise due to RFI and radio stations...  although I suspect from the wider view this is not broadcast RFI as the gap appears too wide.



Quote
>> Why also, is somebody expected to pay the same if they're banded at 40/10 & somebody on the same cabinet roughly the same distance can get 55/10.

Because it costs the same to provision the port in the cab and the backhaul fibre where most of the goes, but if anything it is the longer lines (those further from the cab and the exchange) that are the most expensive for Openreach because they have longer copper lines and require more maintenance of cabling and joints etc.   

The longer lines also tend to be more troublesome requiring more Openreach man hours and support for the ISPs.
A line right next to the exchange and cab seldom has any problems and requires short lengths of both fibre and copper, so as far as Openreach are concerned a line capable of 80Mbps is actually cheaper than one which struggles to get 20Mbps.   

Since 21CN and FTTC the use of WDM on fibre makes bandwidth a heck of a lot cheaper than it used to be.  In the old days of 'just adsl', backhaul was an expensive element because it was in limited supply and why traditionally 2Mb was dearer than 512kbps. WDM changed all that but it cost Openreach/BTw multi-millions to install the 21CN equipment as the WDM kit is not cheap     This is the base backhaul on which FTTC/FTTP runs....  so these days there is negligible difference between a 10Mbps line and a 80Mbps connection when it comes to running costs and provisioning.

Unfortunately it's a fact of life that DSL technology does what it can and goes as fast as it can over copper wires.   The longer the copper length, then less the speed :(
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8062282

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Re: BT DLM advice needed..
« Reply #17 on: September 23, 2019, 05:50:49 PM »

Hi Kitz - Thanks for the helpful responses. I've attached some stats which may or may not help. I'll post the zoomed graph of the bit loading after this. Since the re-sync the other morning, errors are right down. Interleave is at 743.



Average error rates (so far) for 23 Sep 2019


CRC erors per hour:  1.52 Down,  0.90 Up
FEC erors per hour:  8089 Down,  2.41 Up
HEC erors per hour:  51.0 Down,  0 Up
ES per hour:         0.45 Down,  0.84 Up
SES per hour:        0 Down,  0 Up
Total ES in the day: 8 Down, 15 Up





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8062282

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Re: BT DLM advice needed..
« Reply #18 on: September 23, 2019, 05:51:42 PM »

Zoomed bit loading..


When the SNR sometimes goes up at night some of the missing chunks are filled in between 139 & 305. They don't go that high but there's something there. I've added a pic..
« Last Edit: September 23, 2019, 06:23:39 PM by 8062282 »
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burakkucat

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Re: BT DLM advice needed..
« Reply #19 on: September 23, 2019, 06:40:49 PM »

Having now seen the Hlog plot, I am confident that there is no defect in the metallic pathway. The "tail end droop" (at the high frequency end of the plot) is normally only ever seen on those VDSL2 circuits that terminate on an ECI Hi-FOCuS MiniShelf M41 MSAN (configured just as a DSLAM). Have we actually determined which type of electronics resides in the cabinet?

The expanded Bit Loading plot clearly shows where the downstream power back-off (DSPBO) would be applied . . . what I suspect we are seeing is a combination of a deep DSPBO notch and a band of RFI. Referring back to the QLN plot, it is extremely "messy" in that frequency region . . . nothing stands out as being the result of licensed broadcast transmissions. The only comment I can make is that the frequency range is afflicted by a fairly wide band of RFI / EMI. (Could there be someone using an elderly arc-welding set in the vicinity?)
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8062282

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Re: BT DLM advice needed..
« Reply #20 on: September 23, 2019, 07:27:11 PM »

Hi B*cat - Most of that whizzed over the top of my head. Regards the arc-welder. There's a guy who has a hydraulic lift in his garage & he tinkers on cars. Never seen a lot of action outside the house regards customers. I only noticed the lift when I went to pick a parcel up. He's a good half dozen houses away on the other side of my road. The guy next door is always tinkering on cars but I've never seen him use welding equipment. If you know your cabinets, I'm on Bamber Bridge, cabinet 2 (Preston, Lancashire).   If it was an arc welder or similar, would the tones not fill in when it wasn't being used. Apart from when the SNR goes up, they never do..


I just wish the OR engineer had done the lift & shift when I went over to VDSL instead of doing it when I was on ADSL. I don't think I have any leverage now I'm getting above the guaranteed speed. I do have the telephone number of an OR manager but I don't think he would take too kindly to a random out of the blue phone call pleading with him to give me a better line. All there is on the main road from my house to the cabinet is a bargain booze, a sandwich shop, Chinese takeaway, carpet shop & a hardware shop. Nothing that stands out as being a transmitter of interference. Any errors I get are generally late afternoon onwards yet the noise quite often goes down at night & the SNR increases.
« Last Edit: September 23, 2019, 07:29:49 PM by 8062282 »
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burakkucat

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Re: BT DLM advice needed..
« Reply #21 on: September 23, 2019, 08:25:18 PM »

If you know your cabinets, I'm on Bamber Bridge, cabinet 2 (Preston, Lancashire).

After a wave of the magic wand, coupled with an uttering of the required incantation, I can say that your circuit does terminate on ECI electronics.  :-X

Fibre Cabinet    Fibre Status                     Phase      Properties    Vendor      Approx Post
                                                             Passed                    Code
P2               Available from 10th June 2016    15b        478           ECI         PR5 5AS

Quote
If it was an arc welder or similar, would the tones not fill in when it wasn't being used. Apart from when the SNR goes up, they never do..

Yes, your logic is impeccable. I should have really typed "something like an arc welder that is operational 24 hour a day".
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8062282

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Re: BT DLM advice needed..
« Reply #22 on: September 23, 2019, 08:37:01 PM »

After a wave of the magic wand, coupled with an uttering of the required incantation, I can say that your circuit does terminate on ECI electronics.  :-X

Fibre Cabinet    Fibre Status                     Phase      Properties    Vendor      Approx Post
                                                             Passed                    Code
P2               Available from 10th June 2016    15b        478           ECI         PR5 5AS

Yes, your logic is impeccable. I should have really typed "something like an arc welder that is operational 24 hour a day".

No worries I've been through all the bit loading graphs that I have and they're all the same until the SNR goes up at night.
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burakkucat

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Re: BT DLM advice needed..
« Reply #23 on: September 23, 2019, 09:07:15 PM »

I am curious as to the environment in which the two cabinets (P2 and its "fibre twin") are located.

Having had a virtual wander around the area (thanks to Google Maps Street View) I located "Bargain Booze" on the north-west corner of the junction of Brownedge Road and Cedar Avenue.

After a few more minutes, I located P2 on the south-west corner of the junction if Brownedge Road and Todd Lane South. Its "fibre twin" is located by the hedge on the opposite side of Todd Lane South.

Considering the environment, I can see no obvious potential source for the RFI "splat".  :-\
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kitz

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Re: BT DLM advice needed..
« Reply #24 on: September 23, 2019, 11:53:18 PM »

Having now seen the Hlog plot, I am confident that there is no defect in the metallic pathway.
Have we actually determined which type of electronics resides in the cabinet?

I agree, that hlog looks good, nice clean slope.   I suspected it may be,  gut instinct was already telling some sort of REIN/EMI type interference.  I didn't like the look of the bitload and QLN graphs :(

Yes it's definitely an ECI (IFTN:0xd086 on the stats) and its why I'd said in an earlier post he wouldn't get G.INP. :/

Quote
The expanded Bit Loading plot clearly shows where the downstream power back-off (DSPBO) would be applied . . . what I suspect we are seeing is a combination of a deep DSPBO notch and a band of RFI.
   

Thanks 8062282 for providing that I wanted to see a clearer picture of which tones are affected. Tones in that region usually have PSD masks applied.  There are several different PSD masks in use but what we see here is not a result of PSD masking either.

I'm not too certain about the slide on the tail end of the mask area. The RH side usually steps up faster than the beginning and they most certainly do not have a crest smack bang in the middle of them.   Nor do they usually go from 12 bits to zero bits and back up to 12 bits.  Finally PSD masks do not cause the mess displayed at the corresponding tones on your QLN.

Hard to tell from the QLN but the floor at tone 250 is circa -138 dB and lower than the upstream power back off.   Upstream PBO is usually much harsher than PSD masking. 

All the indications are that you have some sort of REIN like issue affecting a fairly wide band of tones. :(
Unfortunately REIN is a pig to solve unless you know where the interference is coming from. 

Quote
I just wish the OR engineer had done the lift & shift when I went over to VDSL instead of doing it when I was on ADSL.

REIN type faults cannot be cured by a lift and shift, nor them putting you on a new d-side. 
The physical line itself looks perfectly good, so no matter what Openreach do to the copper side of things the RFI/EMI doesnt go away and just follows over to the new line :'(

Best I can suggest for now is have a read of this page :- REIN faults

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8062282

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Re: BT DLM advice needed..
« Reply #25 on: September 24, 2019, 07:00:14 AM »

Hi - Thanks for the responses. Just got to work so will repond when I'm home. Here's a link to a post I made in July when I was with TalkTalk. On there is a bitloading graph of when I was with them. https://forum.kitz.co.uk/index.php/topic,23634.0.html  Don't know if the ADSL one can be compared to the VDSL one. The night time ES I had on ADSL have gone away on VDSL so I suppose that one good thing.


P.S - I'm a 'she' in her late 50's. Geeky but not geeky enough. Networking isn't something I've really needed to get involved in, so it's all new to me. Apologies if I sound a bit dumb most of the time :)
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8062282

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Re: BT DLM advice needed..
« Reply #26 on: September 24, 2019, 07:35:41 PM »

Thanks again Kitz & B*cat for your help. There's only 2 of us in the house so 35mb is plenty for the 2 of us.  I have no idea, if it's REIN & where it's coming from. Correct me if I'm wrong but isn't it normal for noise go up at night. I'm guessing with the majority of people being home, there's all sorts being switched on & off & various appliances in the house being used. As my SNR sometimes goes up at night, whatever noise is being created during the day is going away. What kind of distance can REIN travel or is that a difficult question to answer?  I think at some point, I'll do a mass shutdown of everything in the house & un-plug everything to completely rule out everything in the house.   


I didn't realise that there was 2 cabinets. How does that work?  My house is down the road towards the bargain booze. Is there two sets of lines from the exchange, one fibre going to the fibre cabinet & 1 copper to cabinet 2. How do they get the copper lines connected to the fibre cabinet?

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burakkucat

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Re: BT DLM advice needed..
« Reply #27 on: September 24, 2019, 09:32:09 PM »

I didn't realise that there was 2 cabinets. How does that work?  My house is down the road towards the bargain booze. Is there two sets of lines from the exchange, one fibre going to the fibre cabinet & 1 copper to cabinet 2. How do they get the copper lines connected to the fibre cabinet?

The existing telephony PCP (primary cross-connection point), P2, is a junction point between the cable(s) from the serving (telephony) exchange, the E-side cable(s), and those cables, the D-side, that then radiate out to distribution points (DPs) which will be close to the end-users' (EUs') premises. From the DP, there will either be an underground feed or an aerial drop to the actual premises, at which point there may be a "lead in" cable.

When P2's "fibre twin" was installed, it needed to be near a source of mains electricity (for the DSLAM, the active electronics) and near to the existing telephony PCP. The optical fibre cable that connects to the DSLAM will come from a fibre "head-end" exchange and not your serving telephony exchange. In your case, I'm guessing that Preston is the fibre head-end exchange. (I suspect that kitz will be able to say, for sure . . .)

Between the PCP and its "fibre twin" cabinet, there exist a pair of "tie cables". Each cable contains a pair for every VDSL2 service. When your service was deployed, an engineer attended the PCP and removed the link between the E- and D-side cables for your line. Your E-side pair was then extended across to the "fibre twin" cabinet via the E-side tie-cable. It then passes through a low-pass filter and onto a line card port of the DSLAM. That same point is also connected to a pair in the D-side tie-cable, which takes it back to the PCP. That pair was then connected to your D-side pair, which then feeds both the telephony and broadband signal to your home.

Hopefully that makes some sense.  :)
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burakkucat

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Re: BT DLM advice needed..
« Reply #28 on: September 24, 2019, 09:38:53 PM »

Yes it's definitely an ECI (IFTN:0xd086 on the stats) and its why I'd said in an earlier post he wouldn't get G.INP. :/

As you will have no doubt guessed, the grumpy old black cat failed to note what was right under his nose!  ;)
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8062282

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Re: BT DLM advice needed..
« Reply #29 on: September 24, 2019, 09:49:56 PM »

The existing telephony PCP (primary cross-connection point), P2, is a junction point between the cable(s) from the serving (telephony) exchange, the E-side cable(s), and those cables, the D-side, that then radiate out to distribution points (DPs) which will be close to the end-users' (EUs') premises. From the DP, there will either be an underground feed or an aerial drop to the actual premises, at which point there may be a "lead in" cable.

When P2's "fibre twin" was installed, it needed to be near a source of mains electricity (for the DSLAM, the active electronics) and near to the existing telephony PCP. The optical fibre cable that connects to the DSLAM will come from a fibre "head-end" exchange and not your serving telephony exchange. In your case, I'm guessing that Preston is the fibre head-end exchange. (I suspect that kitz will be able to say, for sure . . .)

Between the PCP and its "fibre twin" cabinet, there exist a pair of "tie cables". Each cable contains a pair for every VDSL2 service. When your service was deployed, an engineer attended the PCP and removed the link between the E- and D-side cables for your line. Your E-side pair was then extended across to the "fibre twin" cabinet via the E-side tie-cable. It then passes through a low-pass filter and onto a line card port of the DSLAM. That same point is also connected to a pair in the D-side tie-cable, which takes it back to the PCP. That pair was then connected to your D-side pair, which then feeds both the telephony and broadband signal to your home.

Hopefully that makes some sense.  :)
Hi - I wasn't expecting that. I somehow thought there was a bunch of cables underneath the road from the fibre cabinet to the copper cabinet & they just disconnected the copper & connected the fibre. After thinking about it, I realised if they did that, it'd be so much easier to put the fibre cabinet next to the other one..


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