Hi, thanks,

Could someone refer me to following stuffs:
- approved stundard and limitation examples for thelephone equipment
- ring generation circuit and SLIC examples, ANs.

Simon, my traget is to connect/add an unit to an existing phone CONNECTED
to the public line already. And let's say, there is no way to cat in the
line.
So, relay or any other switching device is not suitable.

As to the ring experiments, as far as I see at this moment, the ring
signal must be ~86V(20Hz) driven over the idle line offset (+/-48VDC)
(the numbers maybe are not exact).
I tested the ringing with ~50V(50Hz) while an analogue phone connected
to a PBX. The ring was produced by the phone(but it can be depended on
its ringing circuit), and the PBX's line is still live.

Thanks,
Oleg