Fibre connection keeps dropping since last week

My Unlimited Fibre Extra broadband keeps losing connection with the router reporting "Modem hangup" at regular intervals and losing the connection for several seconds before reconnecting. This makes working from home very difficult as every time the connection is lost I lose IP phone connectivity and I have to re-login to my remote desktop, a lengthy process.

I contacted PN support on 30th April who told my they'd change a setting which would fix the problem, but it hasn't worked as I keep getting the disconnections and a speed test shows that my download speed is around 50% of what it was (69Mbps) before the issue first occurred and upload speed is 30% of what it was previously (19Mbps). I've replaced the fibre modem and tried another router but to no avail.

I have a support ticket open on this issue, I've a feeling there's a fault in the line somewhere that's causing automatic adjustment of the maximum line speeds, or PlusNet support have enabled a setting that's throttling performance in the interest of stability.

After some research and advice, I understand that Modem Hang Up generally means the other end stopped the PPPoE connection,

Has anyone else had similar issues?

If your upstream speed has dropped significantly, that normally points to a phyiscal line problem. Do you have a landline phone? If so, check to see if you have any line noise.

In reply to a post by Grimers:

If your upstream speed has dropped significantly, that normally points to a phyiscal line problem. Do you have a landline phone? If so, check to see if you have any line noise.

There doesn't seem to be any noise when listening to the dial tone on my BT cordless phone, the sound is a bit buzzy but I think that's due to the quality of the internal speaker. From another (different make) cordless phone paired with the DECT base station the line obviously has no noise.

Ok, fair enough. It could be that the broadband section of the pair has become faulty but the landline hasn't, that is rare though. Hmm, are you able to post stats from your router?

I've done another quiet line test dialling 17070 with a bog-standard BT Duet corded phone and I can hear a very small amount of background noise, not very audible but constant with no other noise/spikes. I get the same whether plugging the phone into the master socket outlet or the phone extension (which is what's used for the home phone). I'm pretty sure what I'm hearing is normal rather than noise, it's hard to tell without hearing a sample of what constitutes noise on the line.

What stats do you mean? From the modem's web gui:

Status from the DSL modem:
Profile State UP Speed Down Speed SNR Upstream SNR Downstream
17A SHOWTIME 8491 (Kbps) 44000 (Kbps) 11 (dB) 11 (dB)

Earlier during the week the SNR was 1, then 2, now it's 11 as above.

Speedtest.net reports around 40Mb/s down, 6Mb/s up with a 26ms ping
Prior to this issue I was getting 68Mb/s and 18Mb/s with 12ms ping

Edited by joconnell (Wed 05-May-21 11:29:26)

Physically walk round and look at your cabinet ? I had a similar sudden drop in up and down speed a few years ago, and it turned out to be Openreach were adding in a second cabinet, and were having to double loop everyone's line as a temporary measure, in preparation for adding in the expansion cabinet.

I had reported the speed drop to Plusnet, they reported it to BT OR as a service fault , and their area engineering supervisor phoned me the next day to explain. Said it would last for a couple of weeks. I walked round to the cabinet (which was 1km away, so I didn't normally pass it)
There was no end of stuff going on. Sure enough two weeks later, work completed, all back to normal

Hmm, if the SNR is moving around that much, then there is something wrong. It appears your downstream rate has been banded at 44 Mb and both your upstream and downstream SNRMs are very high at 11 dB.

That sounds odd. That is unlikely to be the case with the OPs issue, as the SNRMs have risen, most likely due to line instability, so more speed would be available if DLM hadn't taken action.

Sadly I don't know the SNR figures before the issue occurred as my modem was a locked-down BTOR ECI model. I now have the Draytek Vigor 130 which provides all the stats I'd want.

Plusnet's tech support have raised a line fault with BTOR after getting me to remove the faceplate on my master socket and testing the line, so hopefully they'll sort it.

Fingers crossed. If the fault's present in the test socket, then you don't have to worry about being charged etc.

Latest status reported from the modem shows some amazing stats for my line, 17000 (Kbps) upstream, 75370 (Kbps) downstream and SNR up and down is 0 (dB)

Sadly the speedtest is the same result as before. BT aren't due to start work on the line fault until Tuesday so I'm surprised about the above figures.

In reply to a post by joconnell:

Latest status reported from the modem shows some amazing stats for my line, 17000 (Kbps) upstream, 75370 (Kbps) downstream and SNR up and down is 0 (dB)

That looks more like a power cut. Either your substation or the fibre cabinet. Or a reboot of the cabinet DSLAM triggered by Openreach.

You will have been one of the first to reconnect, with little or no crosstalk. Then al the other modems came online and reduced your margin to zero. You are likely but not certain to have a re-sync very soon. (Some modems can hold sync as low as -1dB margin).

Yes, that's the only downside of having a quick syncing modem!

An update on the situation - the fault is fixed.

BT Openreach guy came on Tuesday and after plugging in his equipment to my master socket and running tests, agreed there was a problem but couldn't pinpoint the root cause, so he replaced the master socket faceplate with a new up-to-date version and also replaced the PCB in the small junction box where the phone line comes in from outside.

The Vigor fibre modem showed sync speed of 79995 down and 20000 up with 3dB SNR and although speed tests showed ping times of around 12ms and upload speed of around 18Mbps, the download speed was still limited to around 48Mbps, compared with the 69-70Mbps speed before the fault.

This weekend I replaced a couple of 50cm cat6 patch cables that connect my router to the fibre modem and connect the router to the main network switch that serves the LAN, replacing them with 100cm cat6 cables so that there's less cable strain. I retried the speedtest which reported 73Mbps download speed!

I haven't yet retried with the original shorter cables (they're reused elsewhere) but it does seem a coincidence that after replacing them with longer cables, the DL speed increased by so much. I wonder if the Draytek Vigor 130 modem is responsible for the increase in maximum DL speed from 69Mbps to 73Mbps?

Oddly, running the BT Wholesale speed test on my iPhone (with only WiFi active) reports DL speed of 292Mbps. On FTTC? I wish!

ISPs are supposed to shape traffic to the client based on the sync rate in order to avoid excessive traffic loss (per SIN498 section 2.1.7).

Plusnet certainly do, you can see 'Current Line Speed (Download)' in the user control panel under Broadband, AFAIK they use 92.5% of sync rate, there are encoding and encapsulation overheads to make allowances for.

After faults on a couple of different lines I have seen this value to sometimes get stuck at a figure based on the sync rate when the fault was present, occasionally dropping the PPPoE session will pick up the changes, other times it has required support calls asking them to reset their figure. In your case changing the modem - router network cable would have dropped the PPPoE session.

In reply to a post by tdw42:

ISPs are supposed to shape traffic to the client based on the sync rate in order to avoid excessive traffic loss (per SIN498 section 2.1.7).

Plusnet certainly do, you can see 'Current Line Speed (Download)' in the user control panel under Broadband, AFAIK they use 92.5% of sync rate, there are encoding and encapsulation overheads to make allowances for.

After faults on a couple of different lines I have seen this value to sometimes get stuck at a figure based on the sync rate when the fault was present, occasionally dropping the PPPoE session will pick up the changes, other times it has required support calls asking them to reset their figure. In your case changing the modem - router network cable would have dropped the PPPoE session.

I wasn't aware of that, it does explain the maximum speeds I'm getting then.

I don't think the actual cables would cause the lower speed but as tdw42 stated the disconnection would cause the PPPoE session to be restarted, this could have updated the BT Wholesale IP profile and the Plusnet Current Line speed profile.

The Current Line Speed profile only affects users with a Static WAN IP address, due to different network equipment used for them.

In any case your speeds seem to be fixed now.