PlusNet are a a division of BT Retail, were the broadband services we obtain are supplied by BT Wholsale, who in turn obtain their services from BT Openreach. This complex relationship is a requirement due to regulations to ensure that BT Retail effectivly complete like an ISP and Wholesale operate like an LLU provider.
It has been possible diagnose most faults remotely for years, which is facilitated through a serious of tools called Woosh or Whoosh (BT use both names).
These tools facilitate access to a number of functions such as line statistics obtained from the DSLAM (which includes syncronisation rate, attenuation, SNR margin, errored second & HEC errors on both up & downstream), RADIUS information (which highlights the usernames used on the service, online time and various counts on different connections states (rejected, worked, working)) and OSC.
An OSC, or One Shot Check, is a series of tests including a subset of the above tests and plenty of others. These include a copper line test (not as complete as one performed for a voice fault, hense a reason we often advise customers to investigate a potential voice fault), connection analasys (looks for alarms in various aspects of the connection and DSLAM logs, that suggest some imbalance in the line, which can indicate a fault, or odds tones from the customers equipment) and a TAM test.
TAM, or Test Access Matrix, is capable of taking your line out of service for port testing. This means your line is hijacked by equipment and the port your line is connected to, put through its paces to confirm the connection process.
These tests include a modem (basically checks the TAM is capable of working), DSL (checks it can syncronise), ATM (checks for DSL data transfer), PPP (checks if it can authenticate) and ICMP (can it ping an IP, to test if there is real world data transfer available).
The PPP and ICMP tests can be configured to try various usernames and IP addresses. The idea beind, we can test the various logins such as bt_test@startup_domain, bt_test_user@plusdsl.net and even the customers own username and password. We will normally configure the IP to soemthing we know will work, such as the BBC.
In all, these tests are quite extensive, but are limiting in some respects, compared to those used by the BT Wholesale and Openreach diagnostics team (as these tests can be intruvsive and in some cases, damaging to the line).
Were this testing reports inconclusive or pass results, but the customer is adiment that a problems exists, there is little we can do other than to call in the engineers.
To do this, we try to ensure that all appropriate local testing has been performed due to the potential charges.
I am sorry you consider the quoted charges as a threat, though given the cost (£144 ex vat to those that are not aware), there is some understanding behind that.
These are however genuine costs at cost value from BT Wholesale themselves. It is charged in cases were it is shown that end users equipment (filters, phones, modems, cables, sky boxes) is the source of the problem, the fault the customer is reporting is incorrect, the installation the customer has does not meet the needs of the criteria defined for broadband (were this is in the control of the customer), were entry is declined or the customer no longer wants the visit but has failed to notify the service provide 24 hours in advance.
Much of this will have been ruled out though before we get to here, provided the customer has been honest in their testing.
You can see further details on the Special Faults Investigation charges in the following BT Whoesale document, direct from the BT Wholesale price list site.
Broadband Special Faults Investigation ADSL and SDSLIn regards to the "BT don't offer SLAs", this is not true, but it depends what you are trying to define.
An SLA talks about how BT Wholesale will work to respond and action fault reports submitted to them. When things fall outside of this, there must be a reason and we can attempt to progress this further if needed if they fall outside of this.
