A Cautionary Tale

[Rik]

For the record, my VCXO is -9.6ppm.

[Tacitus]

For the record, my VCXO is -9.6ppm.

It all points to an exchange problem.

[Rik]

It does, Tac, but we know BT won't admit that. One day, the linecard will fail and you'll find the number drops dramatically.

[davej99]

Which, since mine show, -120 (the 'dud' one) and -112.6 (the current V6) suggests that the theory is broadly correct.  -120 seems to be right on the edge since it prompted the 2700 to post a msg saying something looked wrong.  Current 2700 is not far off at -112.6 but is obviously far enough from the danger zone to enable it to work.

The only way we will get to the bottom of it is as Rik suggests - put a scope on the main socket and see what the readings are.  Alternatively BT could look at what's happening in the exchange and try swapping the card, but we've already ruled that out.....

If we can get two modems to show normal, IE a few ppm, on a known good line and >100ppm on your line, Tacitus, then I think we have a case, or at least an arguable case, to go back to BT and say, "Sorry, we have grounds to believe the exchange card was/is out of spec and therefore the call-out was justified."  You could ask, "Are you sure you can rule out an unstable remote oscillator causing high local ppm's and my modem to loose sync?"  

There is no hope of using a scope because I think the transmission covers phase modulated tones across the spectrum from 100kHz to over 1MHz and I am speculating somewhere in the mush there is a reference tone to lock in your local demodulator. But I am just guessing. It will take some complex kit to do the job. You might get some insight from RouterStats, which sometimes uses Telnet to give bits per tone, bit swaps per tone and SNR per tone. It might be you will see high bits swaps if demodulation is unstable.

At the end of the day you need a dialogue with a BT and enough bluff to rattle their cage. Perhaps argue, "I have high local oscillator ppm's on two proven good modems, surely there is still a problem." Or maybe, "I saw high ppm's on two proven good modems when I called you out - surely there was a problem?"

Sorry, I can't be much help. I will go away and brush up my understanding of ADSL - but I may be some time. Then I'll write a book "ADSL for BT Dummies." Mayday, Mayday, Mayday. Request assistance. ADSL expert needed. BT need not attend!!

[Rik]

 

The problem always will be that BT are judge and jury. To prove them wrong would almost certainly cost more than the fee they have charged. It might be worth having a word with Trading Standards though.

[davej99]

I think the lesson for the future, as a user group, is to prepare a case before calling in BT. For example if we had got our heads together on VCXO's at the start, proving high ppm's using two routers on two different lines, then it might have been possible to argue the case for a no charge call. In other words, instead of asking BT to tell us if there was a fault, we ask if such and such is a fault.

The call out charge is now becoming a real issue. Is it designed to force customers to live with problems? Is it a way to boosts profits? Is it challenging the customers sense of trust? Does it raise in our minds the notion that we are being had? May be we should start writing to Watchdog because public opinion is one of the few avenues left open.

[Rik]

I suspect it's a way of boosting profits, Dave. Openreach is the one monopoly BT still have.

[pctech]

definitely a way of boosting profits as landline use is falling.

[Rik]

Exactly.

[pctech]

Was a little annoyed to read that O2 awarded a contract to manage the backhaul for the mobile network to BT.

[Rik]

Ironic, really.

[Ted]

If it helps at all, the VCXO Frequency Offset: on my line is  -7.3 ppm. 2700hgv V5, on a good line with 8128 sync.

[pctech]

Ironic, really.

But then of course it was in fact BT Wireless though as I've said before I've had no complaints and been with them over 4 years now.