Anyone understand BT's G.Fast/Halo 1 FTTC Broadband?
Discussion
Simple answer to this is DLM is seeing a problem on the line and is increasing the snr margin ( reducing speed in the process) in an attempt to stabilise the line. Saying this I would expect you to be experiencing loss of connection at times (over than when it's just DLM dropping the line to adjust the snr). If the engineer is testing the line and not finding an issue and just resetting DLM, DLM will do what it does and drop the speeds back down again as obviously the issue has not been resolved. If no fault has been found after multiple visits I would be pushing for a pair change from dp back to pcp.
minibm said:
Simple answer to this is DLM is seeing a problem on the line and is increasing the snr margin ( reducing speed in the process) in an attempt to stabilise the line. Saying this I would expect you to be experiencing loss of connection at times (over than when it's just DLM dropping the line to adjust the snr). If the engineer is testing the line and not finding an issue and just resetting DLM, DLM will do what it does and drop the speeds back down again as obviously the issue has not been resolved. If no fault has been found after multiple visits I would be pushing for a pair change from dp back to pcp.
Thanks.I'm not seeing any loss of connection (other than when renegotiation is taking place) which makes me think it's a configuration problem somehow.
My next engineer visit won't be too far away judging by the current status so I've got some things to ask of them.
Hopefully you will get it sorted with the next visit, I must admit I don't touch gfast but do ADSL / VDSL (fttc), I know with fttc the snr margin is set at 6db from the beginning of service / DLM reset and can then go as low as 3db to improve speed if the line is stable enough, although wouldn't be surprised if gfast starts at 3db due to the short line length gfast is used on. As well as this DLM is still increasing the snr past 6db on your line, what I'm saying is that it is very unlikely to be a configuration issue. My bet is a small fault on the copper pair that isn't being picked up on test, although it could also be the router itself, the port in the fibre cabinet, or external interference, needle in haystack sometimes unfortunately.
Edited by minibm on Wednesday 17th February 00:21
jeremyc said:
urely the signal and noise levels are what they are for a given connection speed (and line).
On a new piece of copper cable with no external influences yes , unfortunately we have no idea what your line is fed on ( aluminium , various copper sizes , unblocked concentric cable , grease filled unit cable , lead( yes this still exists) or a cable with a lot of vdsl circuits causing overhearing ) its not a straightforward as it may seem ! Throw in the possibility of rein for good measure .Any chance you can walk the route back to the exchange ? or cabinet ?
Anything that might be causing issues at odd times of the day .... street lights that switch on or similar ?
I'd be looking at ...
Repetitive Electrical Impulse Noise ( REIN) or Single Isolated Impulse Noise ( SHINE)
which is a bit beyond the skills of the guys who normally get sent to your house.
If you can establish a pattern .. then it might point to the issue
Anything that might be causing issues at odd times of the day .... street lights that switch on or similar ?
I'd be looking at ...
Repetitive Electrical Impulse Noise ( REIN) or Single Isolated Impulse Noise ( SHINE)
which is a bit beyond the skills of the guys who normally get sent to your house.
If you can establish a pattern .. then it might point to the issue
Chozza said:
Any chance you can walk the route back to the exchange ? or cabinet ?
Anything that might be causing issues at odd times of the day .... street lights that switch on or similar ?
I'd be looking at ...
Repetitive Electrical Impulse Noise ( REIN) or Single Isolated Impulse Noise ( SHINE)
which is a bit beyond the skills of the guys who normally get sent to your house.
If you can establish a pattern .. then it might point to the issue
The route is pretty straightforward I think: house to pole; pole to underground cable back to roadside cabinet.Anything that might be causing issues at odd times of the day .... street lights that switch on or similar ?
I'd be looking at ...
Repetitive Electrical Impulse Noise ( REIN) or Single Isolated Impulse Noise ( SHINE)
which is a bit beyond the skills of the guys who normally get sent to your house.
If you can establish a pattern .. then it might point to the issue
There's no obvious temporal pattern of problems, other than a renegotiation happening around 01:00-02:00 each morning.
I'm making some progress and have managed to speak with a proactive and knowlegeable customer services guy today: he can see I clearly have a problem.
Another visit from Openreach booked for Friday, this time with a Senior Engineer.
I had this once, it was a duff port in the cabinet. Have any "engineers" tried switching the port (if there is spare capacity!)?
Depending on what has been done the choices are, swap the router out (AND PSU!), talking of which, where is the router located?, swap the faceplate (do you have extensions? The faceplate SHOULD isolate them from the DSL signal but if there were a fault it could cause problem, unlikely though), lift & shift copper pair and port in cabinet. However, willy nilly swapping can cause more problems than it solves. REIN is a possibility, anything from a "noisy" LED street light to Christmas lights (if any have been left on as "lock down lights!!). Finally it could simply be cross talk, nothing will fix that apart from a new copper pair.
Simply sticking the JDSU on the copper pair & saying everything's fine mate is not going to fix this, make sure you tell the engineer that!
Depending on what has been done the choices are, swap the router out (AND PSU!), talking of which, where is the router located?, swap the faceplate (do you have extensions? The faceplate SHOULD isolate them from the DSL signal but if there were a fault it could cause problem, unlikely though), lift & shift copper pair and port in cabinet. However, willy nilly swapping can cause more problems than it solves. REIN is a possibility, anything from a "noisy" LED street light to Christmas lights (if any have been left on as "lock down lights!!). Finally it could simply be cross talk, nothing will fix that apart from a new copper pair.
Simply sticking the JDSU on the copper pair & saying everything's fine mate is not going to fix this, make sure you tell the engineer that!
Dave_ST220 said:
I had this once, it was a duff port in the cabinet. Have any "engineers" tried switching the port (if there is spare capacity!)?
Depending on what has been done the choices are, swap the router out (AND PSU!), talking of which, where is the router located?, swap the faceplate (do you have extensions? The faceplate SHOULD isolate them from the DSL signal but if there were a fault it could cause problem, unlikely though), lift & shift copper pair and port in cabinet. However, willy nilly swapping can cause more problems than it solves. REIN is a possibility, anything from a "noisy" LED street light to Christmas lights (if any have been left on as "lock down lights!!). Finally it could simply be cross talk, nothing will fix that apart from a new copper pair.
Simply sticking the JDSU on the copper pair & saying everything's fine mate is not going to fix this, make sure you tell the engineer that!
All good advice - thanks.Depending on what has been done the choices are, swap the router out (AND PSU!), talking of which, where is the router located?, swap the faceplate (do you have extensions? The faceplate SHOULD isolate them from the DSL signal but if there were a fault it could cause problem, unlikely though), lift & shift copper pair and port in cabinet. However, willy nilly swapping can cause more problems than it solves. REIN is a possibility, anything from a "noisy" LED street light to Christmas lights (if any have been left on as "lock down lights!!). Finally it could simply be cross talk, nothing will fix that apart from a new copper pair.
Simply sticking the JDSU on the copper pair & saying everything's fine mate is not going to fix this, make sure you tell the engineer that!
They're sending me a new router/hub (but in the words of the customer service guy "I doubt that will fix it").
Router is located on my desk, about three feet from the socket.
No extensions.
I'll see if they can swap port and/or copper pair in cabinet, and if there's a spare copper pair that can run from cabinet to pole.
As you can see, my performance degradation trend is now very clear from my monitoring (blue line is downstream sync speed, orange line SNR margin):
jeremyc said:
Dave_ST220 said:
Good stuff
Do you happen to know if the target SNR Margin is configurable in the DLM?I still reckon the DLM is trying to get to an unrealistic SNR margin by continuously reducing line speed.
DLM should only increase snr / reduce sync speed because it is seeing drops in connection and or errors. If DLM see's a stable error free line it will reduce the snr down to give maximum sync (or if it is already at that point it should leave the line alone)
The target snr on fttc is 6db to start with, I'm guessing 3db on gfast, the target snr is exactly that, a target and what the line should run at error free. If the line had a intermittent fault, the snr could go below the target snr, causing errors/ drop of connection. This is when DLM will intervene and increase the target snr to compensate for the fault. There is only one reason for a high snr, DLM is seeing a problem and trying to compensate.
The target snr on fttc is 6db to start with, I'm guessing 3db on gfast, the target snr is exactly that, a target and what the line should run at error free. If the line had a intermittent fault, the snr could go below the target snr, causing errors/ drop of connection. This is when DLM will intervene and increase the target snr to compensate for the fault. There is only one reason for a high snr, DLM is seeing a problem and trying to compensate.
Edited by minibm on Thursday 18th February 20:04
jeremyc said:
o you happen to know if the target SNR Margin is configurable in the DLM?
I believe it is technically possible to manually set a target SNR margin, but it's not something that is done and in any case a DLM reset would remove any such setting anyway.For GEA services OpenReach run DLM fully automated - even down to resets only being actionable by an Engineer. They have trailed are are rolling out a system for ISP's to request DLM resets but the ISP has to "subscribe" to it as an additional chargeable service.
I think you've got an intermittent copper fault or some external interference causing this. The graph looks entirely normal between 26th Jan - 2nd Feb - it must be recording some errors and DLM is lowering the sync speed which is increasing the SNR margin. You need to get Openreach to have a look at those errors and establish if they are occurring steadily all the time - which is indicative that the current sync speed is too fast for the line quality, or if they happen in bursts which may indicate when the fault in occurring. In either case, DLM is doing exactly what it's supposed to.
The massive drop on the 3rd Feb is when the fault occurred, which must have been due to a massive number of errors on the line and DLM has tried to compensate by dropping the sync speed - again, it's doing what it's supposed to do. You then get the bounce but a continued increase in SNR and drop in sync speed over the following few days which indicates DLM is still seeing errors at the lower sync speed - which indicates that the errors are not as a result of the sync speed being too high, but due to an underlying fault.
Unfortunately all you can do is keep reporting it and be as nice as you can the OpenReach guys and ask them what they can do to escalate it or if there are any changes they can make to rule out potential problems. You could ask if there is anything they could leave on the line for 24-48hours to monitor things but OR guys only seem to have 1 test unit and need it for the next job.
The nuclear option is to order another service on a new line and bin the existing one. You'll have to bear the install costs though, but it will give you a new copper path - albeit probably over the same trunk cables. Might work, might not.
Situations like this are as a result of providing a modern data service over a copper infrastructure designed over 100 years ago and charging £30 a month split between an infrastructure owner and an ISP. You can't have experienced specialist engineers sent to every job - it just doesn't stack up financially. The sooner we have FTTP everywhere the better - but nobody wants to pay for it.
You have probably identified the two most likely causes.
It is not your SNR margin at the point where you look at it but some averaged / minimum SNR over a period as observed by the DLM. And it also possible that the target SNR margin has been adjusted due to the resetting of the connection.
Basically you need to find someone who knows what they are doing and cares about the result to look at it which isn't easy.
It is not your SNR margin at the point where you look at it but some averaged / minimum SNR over a period as observed by the DLM. And it also possible that the target SNR margin has been adjusted due to the resetting of the connection.
Basically you need to find someone who knows what they are doing and cares about the result to look at it which isn't easy.
CharlesElliott said:
Basically you need to find someone who knows what they are doing and cares about the result to look at it which isn't easy.
Depending on where you are in your current contract, maybe take AA up on their "we will fix your line" offer. If they can't get it fixed in a month then you can leave and it's a free month. They claim to have only paid out once in 10 years but I'd be inclined to give them a little longer at the moment. They got my line from 30ish to 78 with only one one visit from Openreach and something in the backhaul from TT. Openreach were telling me that their tests couldn't work as there was no dial tone. My line is a Direct Connect so there is no phone service (I have VoIP) and hence no dial tone, one conversation between AA and Openreach sorted that.https://www.aa.net.uk/broadband/we-will-fix-your-l...
They are niche and expensive and some on PH will put them down but they do know what they are talking about. Even if they fix it their minimum term is only 1 month so you could move to them, let them see if they can fix and leave after a month. Next option is 6 months. Still have data limits at either 300Gb or 2TB. Son's Xbox use in school hols and two of us WFH push us beyond 300GB but 2TB is effectively unlimited for most (50% of any unused quota carries over).
Just waiting for them to get onto City Fibre's FTTP network which will actually save me money as I can then ditch the copper line rental.
stemll said:
CharlesElliott said:
Basically you need to find someone who knows what they are doing and cares about the result to look at it which isn't easy.
Depending on where you are in your current contract, maybe take AA up on their "we will fix your line" offer. If they can't get it fixed in a month then you can leave and it's a free month. They claim to have only paid out once in 10 years but I'd be inclined to give them a little longer at the moment. They got my line from 30ish to 78 with only one one visit from Openreach and something in the backhaul from TT. Openreach were telling me that their tests couldn't work as there was no dial tone. My line is a Direct Connect so there is no phone service (I have VoIP) and hence no dial tone, one conversation between AA and Openreach sorted that.https://www.aa.net.uk/broadband/we-will-fix-your-l...
They are niche and expensive and some on PH will put them down but they do know what they are talking about. Even if they fix it their minimum term is only 1 month so you could move to them, let them see if they can fix and leave after a month. Next option is 6 months. Still have data limits at either 300Gb or 2TB. Son's Xbox use in school hols and two of us WFH push us beyond 300GB but 2TB is effectively unlimited for most (50% of any unused quota carries over).
Just waiting for them to get onto City Fibre's FTTP network which will actually save me money as I can then ditch the copper line rental.
Thanks for all your comments and suggestions. An update after my eighth(!) Openreach engineer visit.
They have decided that whilst all of the connection infrastructure is working fine, I'm just too far from the cabinet, right on the limit of what G.Fast at these speeds can deliver reliably. So the next test is for my service to be 'downgraded' to a slower speed and to see if that can be delivered in a stable and reliable way - I'm now on a 150Mbps max download (100Mbps guaranteed) rather than the previous 250Mbps max/150Mbps guaranteed. Watch this space...
The lesson learned here is that the BT tool for checking what is possible to deliver on a given line is probably optimistic and that they maybe need to wind back their speeds for line lengths from the cabinet at the bounds of G.Fast. Unfortunately it has resulted in a lose:lose outcome in this case - I get a slower service, BT gets less revenue from me. Bring on FTTP I say.
They have decided that whilst all of the connection infrastructure is working fine, I'm just too far from the cabinet, right on the limit of what G.Fast at these speeds can deliver reliably. So the next test is for my service to be 'downgraded' to a slower speed and to see if that can be delivered in a stable and reliable way - I'm now on a 150Mbps max download (100Mbps guaranteed) rather than the previous 250Mbps max/150Mbps guaranteed. Watch this space...
The lesson learned here is that the BT tool for checking what is possible to deliver on a given line is probably optimistic and that they maybe need to wind back their speeds for line lengths from the cabinet at the bounds of G.Fast. Unfortunately it has resulted in a lose:lose outcome in this case - I get a slower service, BT gets less revenue from me. Bring on FTTP I say.
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