Well I know it won't show up in the log, but if there is a re synch won't it show a line state report (eg down & up)?

What do you mean by a line report?

The root of all your confusion is that the the router at both ends of the line, you and Plusnet, can be unaware that the line has re-sync'ed. (Which is why I am doubtful that you are right when you say you have had a rock-steady connection - so far as I know there is no way you could know this without an unlocked modem or something like a FritzBox).

That being the case, the IP Profile doesn't get reset. So is wrong.

But when you do a reconnection of the router/PPP session, both ends become aware of it and most importantly so does the Openreach DLM. The result is, that although at this point there is no re-sync, the Openreach DLM sends out a message about the sync and the BTW/WBC DLM changes the IP Profile to the value it should already have been.

Okay RobertoS. If your replies were more clear (you & others) it would result in me understanding! Can it bethat complicated for you to clearly explain in plain English? I know you are trying to help.

So, in part I was correct. Wait & see.

The connection can resync "on the fly" very quickly - taking 16 seconds or less.

Usually these on the fly resyncs are too quick to be detected by the router, so the router does NOT initiate a new PPP session.

A new PPP session is needed to get the IP Profile updated.

So, your sync speed could go up or down, yet the IP Profile can remain the same.

I suspect that your connection has been resyncing on the fly, but only when you forced a new PPP session via the router was the IP Profile updated.

You may well have seen lower throughput speeds than your incorrect IP Profile suggested you should have seen. Although you may not have actually noticed the lower throughput speeds.

Those lower speeds would have been due to the connection resyncing at a lower speed.

Now, if the other way round & the connection resyncs on the fly at a higher speed, yet the router hasn't forced a new PPP session, your throughput speeds will be restricted by the incorrectly too low IP Profile.

A new PPP session initated via the router in those circumstances will increase your IP Profile & thus allow the higher speeds.

There is no way that initiating a new PPP session via the router should cause a resync.

These on the fly resyncs where a new PPP session is not also initiated are NOT detected in ISPs' own logs.

So, in my case, when my connection was very unstable, resyncing on the fly a number of times each day, Plusnet were unaware of it & understandably initially claimed my connection was in fact stable.

It was only when I unlocked the HG612 modem & started logging & graphing connection stats 24/7 that I was able to prove my connection's real instability.

Even so, it took 11 months & numerous engineer visits to get a resolution.
My connection doesn't have great speeds due to distance from the cabinet, but it is now as stable as a rock (Thanks to Plusnet's persistence in regularly chasing BT on my behalf).

The main fault actually turned out to be a poor connection between the underground cable & the pole top DP that in wet & cold weather worked reasonably well, but deteriorated rapidly as the weather became warm & dry.

As mentioned by Bob P, Plusnet's own Current Line Speed profile can take a couple of days or so to update, based on BT's delta reports that signify a changed sync speed and or IP Profile (not 100% sure which) - Bob?.

This can also temporarily restrict throughput speeds.

HTH.

EDIT:-

With an unlocked HG612 modem, along with the logging/graphing scripts data, this is what an on the fly resync looks like from the modem's own inbuilt log (when enabled):-

2012-11-10 11:8:28 Notice 104500 DSL activate succeed
2012-11-10 11:8:12 Notice 104500 DSL deactivate

Notice the 16 second duration.

Edited by deleted (Tue 12-Feb-13 23:34:51)

Thanks for the explanations, Bald_Eagle1, RobertoS and others. That has filled several gaps in my understanding, but now lead on to several further questions I'm not clear about:

1. So what is the point of the BT IP Profile? If the DSL link syncs at a given speed and the IP Profile is then set to about 0.97 of that value, so what? What is it used for? Is it used for flow control? If so, what's the point? The actual DSL line rate could have dropped below the IP Profile value unnoticed, in which case it achieves nothing. And in any case, the actual DSL line rate limits the throughput on the line. Am I missing something obvious? I've never properly understood BT's DLM!!
   
2. What is the point of Plusnet setting it's own IP profile on top of BT's IP Profile? If BT is rate controlling the line, what's the point of Plusnet adding its own "speed limit" on top?
   
3. My perception, from observation and reading posts in these forums, is that BTOR field engineers trying to fix DSL line faults seem to work entirely blind apart from what their own test gear can tell them. The BTOR NMC must have access to excellent diagnostic stats and logs from the modems at both ends of each line, yet I get the impression this information is rarely used and rarely fed to the field engineer. Yet it ought to make the fault finding process much easier. Or is my perception wrong?

Can anyone illuminate these issues for me, please?

Probably traffic management as you say. By setting the Plusnet connection to 97% of the BT IP Profile, they can be pretty sure they aren't saturating the connection (which would affect their traffic management).

I think you have that mixed up Oliver.

On FTTC the BT IP Profile is 96.79% of the sync rate. The Plusnet Current line speed seems to be set to 37(?) or 78, depending on the product.

On ADSL2+ I believe the Current line speed is set to the IP Profile rounded down to 1 decimal place.

But either way the Plusnet throughput speed is set lower than the maximum line speed of the line as set by BT? That was my point, in relation to traffic management and saturation.

Or do Plusnet actually synch the line lower themselves?

Edited by Oliver341 (Wed 13-Feb-13 12:55:39)

We don't affect the sync of the line, we set the profile on our site to match the one reported on a BT Speedtest.

With the new Unlimited products PN staff have said/suggested that the speeds will be as fast as the line allows so in reality the sync speed will be as fast as the line allows but the throughput speed from the PN network won't be i.e. it is throttled managed?