Fibre Capping

[#1]

Can you tell me how you are able to cap a line. Mine has been pretty unstable since BT changed the SNR limits to 3db.I sync around 72 meg currently but am experiencing snr drops to less than 1db during the day which then causes a disconnect.

I have attached a graph showing what is happening to my snr on a daily basic. If possible can you cap my connecton at 70 meg or can you assign a target snr of 5db?

[#2]

You may be overthinking this. Maybe you would be better off reporting constant drops and let others diagnose the problem.

[#3]

I know my line and how it did perform with a 6db noise margin, It hardly ever dropped. I was with BT but they just take too long to sort out any problems so I moved to PN. I am very happy with the connection, just some days its horrendous, like today, less than 0.5db margin and unable to do a thing. Reboot router, back to 3.6db now @ 72265. Its not like it does it at busier times either, the snr nose dives during the early hours of the morning too. If it was a line problem then surely DLM would rate my line down, but its not.

I was just asking basically how fibre gets capped. Is it by a speed, eg 70meg, or by a target SNR. If so limiting my connection speed to 70 meg or 5db target would give me a couple of snr to allow it some fluctuation. I understand how the network works, I just dont know how the ISP can control it. Thought it would be better to ask here before raising another ticket. 

[#4 · Accepted solution]

Hi @Ballz

I have checked the line for you, and there is currently a battery contact fault on the line. This has been raised through to Openreach for you, and they will get an engineer out for you within 48 hours. The work is entirely external at the moment, and you don't need to be in the property for the fix.

[#5]

Thanks deank. I will monitor the situation over the next few days. 

[#6]

Hi @Ballz,  I have used sync-capping on my own modems for some of the same reasons as you.  I think you can do this only with modems like the Huawei HG612 or Zyxel VMG1312-B10A that have a broadcom chipset, that also allow you to telnet or ssh into the modem and issue a command that starts "xdslcmd configure --maxDataRate".  If you google that string, you'll soon enough find some forums bulging with advice about how to go about this, and why you might want to.  Personally, I find it a bit of a dark art, but in my case it did what I wanted.  I capped my 80/20 line somewhere around 65/15 for a month or two, and my SNR margins climbed to comfortable levels, and my DS attainable shot up above 100Mbps. 

I don't *think* an ISP like plusnet can do this "at the other end" of the line. However, like everything else in broadband, it's difficult to be sure. For example there is something mysterious called (I think) a "BRAS profile" that can be imposed on you -- the purpose of that seems to be to ameliorate congestion between you and the ISP .. or something. I don't think its anything to do with sync rates or copper lines, but more to do with how your ISP has provisioned the path between themselves and your exchange.  Or maybe it's BT who imposes it. (Try googling " Why does BT apply an IP / bRAS profile?".)

You may have much more expertise in these things than me. But I wouldn't recommend dashing into sync-capping etc without a fair bit of careful research.  You are dealing with DLM, which is about as friendly and predictable as a 20-foot alligator.

[#7]

So, I got home today to no broadband and an openreach guy at the end of the street.

I had to go post a letter so as I went passed I asked him if he was sorting my line, he asked the house number and yep, it was mine. He said he moved the port as the one I was on has a fault, but the new port he moved it to also has a similar fault so he was in the process of moving it again. 20 mins later I'm back online. I understand I now have to go through the 10 days of DLM again with it being a newly assigned port. Im currently connected but a lot slower than before. On the plus side my upload seems to have come back from the 13 meg i was stuck at. 

Current connection : PPPoE is up -​ Down Rate=54274Kbps, Up Rate=19999Kbps; SNR Margin Down=6.0dB, Up=6.0dB

So I'm roughly 18 meg down on downstream, but with more db to drop on my SNR. And im currently 6.5 meg better off on my upload. Im kind of happy to wait now see if I return to my original 65/20 when DLM shifts me to 3db. 

Thanks again to the Plusnet staff on here for the absolutely super fast support.

[#8]

Hi @Ballz

Glad to hear the engineer that attended appears to have resolved the problem. I'll update the ticket on the account and send it back to you with a copy of the engineer notes.

Monitor the connection and if problems resurface or the downstream doesn't increase then let us know. 

[#9]

Look at the last 24 hours SNR. Amazing. Thanks again Plusnet. Looks like this is going to be much more stable after my DLM period is over. I will mark this as resolved already I think. The Drop out is where the engineer had it off yesterday, then since 6.0+ db on both up and downstream with only minor changes.

[#10]

So, It went off for the first time during last night and shifted me to 5db on the downstream. Now connected @ 64766/19999 @ 5db SNR. Awesome. If I have increased 10 meg with a 1db shift I might even see the full 80 meg soon.

[#11]

So today this started happening again, absolutely fine until around 8-9am today then it started its spiky lines again and a disconnect in the middle.

[#12]

I'm sorry to hear that this issue has started happening again. I've tested your line today, however the test isn't picking up the cause of this issue. For reference, the test result is as follows:

GEA Test Detail
Circuit ID	NA	Service ID	BBEUXXXXXXXX

Test Outcome	Pass
Test Outcome Code	GTC_FTTC_SERVICE_0000
Description	GEA service test completed and no fault found .
Main Fault Location	OK
Sync Status	In Sync
Downstream Speed	67.9 Mbps
Upstream Speed	20.0 Mbps
Appointment Required	N
Fault Report Advised	N
NTE Power Status	PowerOn
Voice Line Test Result	Pass
Bridge Tap	Not Detected
Repetitive Electrical Impulse Noise	Not Detected
Estimated Line Length In Metres	681.7
Upstream Rate Assessment	Very Good
Downstream Rate Assessment	Very Good
Interference Pattern	Regular Interference Observed Daily
Service Impact	No Impact Observed
Interference Duration Longest Occurrence	From 11:00 to 16:00
Interference Location	Customer Premise
Home Wiring Problem	Not Detected
Downstream Policing Discard Rate	0.0
Customer Traffic Level	Upstream and Downstream Traffic Detected
Technology	VDSL
Profile Name	0.128M-80M Downstream, Interleaving Low - 0.128M-20M Upstream, Error Protection Off
Time Stamp	2018-08-08T23:00:00

Parameters	MIN	MAX	AVG
Down Stream Line Rate	54.2 Mbps	71.0 Mbps	60.0 Mbps
Up Stream Line Rate	20.0 Mbps	20.0 Mbps	20.0 Mbps
Up Time	808.0 Sec	900.0 Sec	899.4 Sec
Retrains	0.0	1.0	0.0

Current and Last 15 Minute Bin Performance
Parameters	Last Traffic Count(Upto 15 mins)	Current Traffic Count(Upto 15 mins)
Start Time Stamp	2018-08-14T10:54:56Z	2018-08-14T11:09:56Z
Ingress Code Violation	0	0
Egress Code Violation	0	0
Errored Seconds	0	0
Severely Errored Seconds	0	0
Unavailable Seconds	0	0

Please can you run through our troubleshooting guides here and let us know how you get on. Please report the issue here and let us know when you've completed it - we'll then be able to investigate this further for you.

[#13]

It hasn't become unstable yet, which is a good thing. I think that its just DLM tweaking my line to the max. The SNR spikes are still occuring but only between the 3-5db range. It seems DLM has tweaked me to 4db now, 67933/19999. Which is pretty much what I have always had so I'm still very happy because my upload has returned and the quality of the line is much better, lower pings, less dropouts.