I’m working on a pro bono project for a non-profit public-service organization. The PBX is installed and running using SIP phones at two locations and several people’s homes, and all seems to be working well.
The next step is to implement a Radio-over-IP system where an incident commander can pick up a phone, dial a 3-digit extension, and talk to an aircraft or a ground search team via radio.
I would like to implement the radio interface as a standard analog telephone lookalike that plugs into a standard PBX FXS port. To do that I need to learn all about how the PSTN connections work, i.e. what voltages and signals are generated at the FXS port to drive a telephone ringer, what happens at the FXS port (voltage levels, etc.) when the phone goes off-hook, and how the audio gets superimposed over the voltage levels so that audio, ring signaling, and off-hook/on-hook signaling can all happen on one pair of wires.
Can any of you recommend a good book or (preferably) website I can use to learn about all of this? Yes, I can (and did) google it but have little way of separating the good resources from the bad other than the experiences of people such as yourselves.
Eric / www.rkt-tech.com