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Odd ADSL2+ behaviour

zombies
Grafter
Posts: 29
Registered: 07-08-2008

Odd ADSL2+ behaviour

We've had the line here installed for about a month now - it's an ADSL2+ connection (my first - since my previous exchanges were all 20CN) and I'm experiencing what can only be described as 'odd' behaviour from it.
Aside from the usual line training disconnects - it seemed quite stable at 12.7Mb downstream and 0.4Mb upstream (I don't have any other measurements for this unfortunately).
Then it disconnected and speed dropped like a stone - had lots and lots of CRC downstream errors and the whole thing was a nightmare, which seemed to sort itself out after a disconnect or 2.
I know you aren't meant to disconnect the router, but I was getting LOTS of CRC downstream errors (had around 2000 in 15 minutes) - and the only thing I could think to do was disconnect it, wait a while and reconnect, hoping it would resolve itself.
Since then, it's been mostly stable - has the odd disconnect at around the 3-day mark - not sure why but again - it seems to work.
What I've encountered lately is my throughput was a nice 12.4Mb and overnight has dropped to 10.7Mb.
Further investigation shows that the PN IP Profile for my line is at 11.3Mb but the BT IP Profile is 12.9Mb.
I still have CRC downstream errors (23 in 1h 6m) - but this is a low number and seem to be par for the course.
Things were stable at 12.2Mb (speedtest) when my Path Mode (downstream) was Interleaved. I had a good sync rate, only a few CRC downstream errors (probably around 17 in 3 days) and it was good.
I notice now it's set it Path Mode (downstream) to FastPath, which seems to have dropped my speed, sync speeds and introduced more CRC downstream errors.
I've opened a ticket and I'm not trying to expedite it by posting here but my confusion is considerable - I don't understand how the line can be perfectly stable at 12.3Mb and yet something disconnects it, changes my Path Mode to FastPath and now I lose a chunk of speed and I have more CRC downstream errors than before. This seems almost counter productive.
I don't have any option on my router for forcibly setting Path Mode (router is an Asus DSL-AC68U - latest firmware).
If anyone has any ideas or explanations for why this might be happening - all I want is a line that's fast and stable (I realise that those 2 requests are only somewhat possible).
Here are the stats for my connection at present (I don't have any stats for previous - things seem about the same except Path Mode downstream):
5 REPLIES
Community Veteran
Posts: 5,109
Thanks: 465
Fixes: 17
Registered: 10-06-2010

Re: Odd ADSL2+ behaviour

Doesn't seem to be any particular problem is the speed in the latest stats. 14272 × 0.882 = 12.5 IP Profile, Plusnet current line speed should update within a few days.
The DLM (Dynamic Line Management) system, which automatically makes adjustments to your line for stability vs. speed, seems very keen on turning off interleaving these days. I asked for interleaving to be switched on recently, it got switched back off after about two days despite loads of errors and one of the days had over 10 disconnects, mostly due to an Openreach man working in the cabinet accidentally disconnecting half of my line. Interleaving and forward error correction allow errors to be corrected, and won't make much difference to the ADSL line rates. Download speeds will be poor to non-existent if your connecting is racking up vast numbers of CRC errors.
Most ADSL lines should probably work OK without interleaving. If you experience times with vast numbers of CRC errors, you probably have bad telephone cabling somewhere in your house, or possibly some electrical device in or near your house that emits more interference than it should onto the frequencies used by the broadband signal (REIN).
Also, you should probably consider having your upstream speed uncapped, the increased upstream speed shouldn't cause any problems, although it's possible a capped upstream speed could be masking a problem.
zombies
Grafter
Posts: 29
Registered: 07-08-2008

Re: Odd ADSL2+ behaviour

Thanks for the extra information ejs  Smiley
My PN Connection Settings (in Member Centre) show I have Interleaving turned on - I'm assuming this is different than what you're talking about?
My concern is that the IP Profile has been good, solid and the line is absolutely fine with interleaving turned on - soon as it puts it back to FastPath, I get CRC downstream errors.
As of writing - I have 466 CRC downstream errors in 4h 22m. This is what concerns me, my understanding is that I should get very few CRC errors at all if my line is good.
I'm not aware of any REIN near or on the line as the CRC errors that I've monitored previously did not seem to have a pattern to them, a disconnect or 2 seemed to sort it out as well, which would be a lot of coincidences if it were REIN. I've done the 'run around the house with an AM radio' trick to find anything with REIN but I didn't find anything anywhere near the router or phone line. (Router is hooked into master socket and uses a microfilter. No other phones on property - just 1 handset which feeds to the others around the house)
However, the internal house wiring is new - as for the quality of the line itself, I have no idea how old that is and I can't see BT changing it any time soon.
Why would my upload speed be capped? Is this a new thing or a legacy thing?
I've had 3 house moves with PN in total, I can't remember the 1st - but the last 2 have been horrific with problems/issues - but all previous broadband had been ADSL, not ADSL2+ capable.
Would uncapping my upload speed help my current issue - or is it more of a diagnostic measure - to see if uncapping it reveals a problem?
Edit: Just to add - my upstream has never been above 0.4Mb - so I think it has always been capped)
Community Veteran
Posts: 5,109
Thanks: 465
Fixes: 17
Registered: 10-06-2010

Re: Odd ADSL2+ behaviour

The interleaving control in the member centre only allows you to ask Plusnet to have interleaving always off. There are three options for interleaving, always on, always off, and the usual, auto, where the DLM automatically switches interleaving on if there is some instability or high error rate problem it decides it needs to try to fix.
You will always get some CRC errors, especially with interleaving off. 466 in 4h 22m is about 2 per minute, which won't cause any issues. Some modems just seem to aim for higher speeds which consequentially results in more errors, others go for slightly lower speeds, which will have fewer errors. I believe some of the Asus DSL models, using TrendChip chipsets (the TC in the firmware version), are the higher speed and possibly less stable type.
If you disconnect and re-connect while there's some problem present causing large numbers of CRC errors, you'll generally re-connect at a lower speed, the modem essentially avoids the problem. The modem establishes the best speed it can for the target noise margin. If there's a lot of noise present at the time it connects, it'll attain a lower speed. If the noise on the frequencies used by the ADSL signals increases at a later time, the modem will try to maintain the connection, the increased noise may reduce the current SNR margin and/or increase the number of CRC errors.
The important thing about the internal wiring is that twisted pair cable was used, and if you have more than one phone socket, even with nothing plugged in, how the sockets are connected together. You can tell if it's twisted pair cabling from the colours of the individual wires. A typical cable might have a blue pair, one wire blue with small white stripes, the other white with small blue stripes, and an orange pair and perhaps a green pair with similar colouring.
Sorry about the distraction about uncapping the upstream, it has nothing whatsoever to do with the current problem, but ought to be done anyway. It seems to be a new thing, in the past Plusnet capped it by default, then they went round uncapping everyone, now new customers are supposed to be uncapped by default, but somehow new customers keep appearing on the forums with capped upstreams. Apparently it happens if the order for your line was placed manually and whoever did it didn't select the right option for the upstream.
zombies
Grafter
Posts: 29
Registered: 07-08-2008

Re: Odd ADSL2+ behaviour

Ok - so the upshot seems to be - leave things as they are in terms of the router, don't try to change anything and it should (touch wood) fix itself?
We have 1 phone socket in total and no others throughout the house, does the twisted pair wiring thing still apply?
I can check it at some point but if it's only 1 socket (no extension sockets at all), does it make any difference?
As for Upstream uncapping - I'm a very old customer, was with PN when they were Force 9, so I was in the first round of capped upstream.  Smiley
Will give some thought as to whether it's worth removing the cap - it's always downstream I tend to need more of than upstream and that works fine for what I need at present.
My other thought was bypassing my speed issue by simply having fibre put in instead, but I don't want to do this in the hope I'll get 30Mb by an estimate, yet barely get 20Mb instead. (I can't get the 76Mb package for some reason - perhaps distance from exchange?) (My original BT line estimate was 15.5Mb and PN estimated 14Mb, yet I get 12.4Mb on a good day and around 10Mb... so perhaps these estimates are optimistic?)
Community Veteran
Posts: 5,109
Thanks: 465
Fixes: 17
Registered: 10-06-2010

Re: Odd ADSL2+ behaviour

Yes, all the telephone cable needs to be twisted pair, but everything up to and including the master socket is Openreach's responsibility to fix, you're probably not strictly supposed to remove the back part of a master socket to look inside it, only the lower front part is end-user removable.
Uncapped upstream is only available (free of charge) on ADSL2+ capable connections, so it wouldn't have been available to you when you were on 20CN.
It's tends to be more difficult to track down something that was just a one off, or only happens occasionally. The estimate may refer to the ADSL line rate reported by the modem, 14272k, and not the speed you'll get when actually downloading something, which will be less due to various overheads (most of which have been taken into account to get the IP Profile value).
The 76Mb FTTC package isn't available based on your FTTC estimated speeds, which largely depend on the distance to your cabinet. The 76Mb (80/20) Fibre Extra package wouldn't give you any extra download speed, if your 30Mb estimate is accurate, although it would give you more upload speed than the 38Mb (40/2) Fibre package. Plusnet won't let people with lower than 40Mb estimated speeds order the 76Mb package, this limitation is imposed by Plusnet's systems, not BTWholesale / Openreach.