On Mon, 2007-04-16 at 10:01 +0100, Mark Rogers wrote:
That's interesting; is that from personal experience or do you have any references to that "feature" of pulse dial 'phones?
Personal Experience and assumption made based on how I think pulse dialling works.(IANABTE)
The few times I have seen pulse dial phones on a broadband network, dialling using those phones has resulted in a temporary loss of sync (one phone was an old school rotary phone, the other was one of the first generation BT push button phones)
My assumed explanation was as follows
The audible clicks are actually a side effect to how Pulse Dialling works, the technical term for Pulse Dialling is "Loop disconnect".
At it's simplest form a telephone network is a loop of wire with two inductors (one at each end) the inductors being the voice coil in the receiver. You apply a nice bit of bias voltage and if you disconnect and reconnect the line then you get a voltage spike. It's this spike which was used to signal the dialling. 1 spike being 1 2 being 2 and so on. This is why you can still dial a number by whacking the on hook switch on an older telephone (modern phones probably don't provide enough on line inductance to reliably achieve it).
Anyway the transient spike caused by this switch is most likely more than any standard micro-filter could hope to deal with, a few clicks can probably be dealt with by the ADSL modem, but a whole dialling sequence is probably enough to make it think there is a problem and it needs to re-sync.