It has been a long time since I designed any telephony equipment. I know the E&M circuits are simple conceptually, but there are any number of real world issues that impact the design, which I can't remember much of.
The battery voltage is approximately 48 volts and the circuits are current limited. Control is done with relay contacts in the old days and sensing was done with a relay coil. Now I'm sure that has all been replaced with a few transistors. I tried looking for ICs that would handle this, but came up empty handed. Is there anything out there that is designed for this? I know there are chips for the SLIC and such, but I don't see anything for E&M.
This is not for a circuit to a CO, so there won't be exposure to lightning or AC wire crosses. This will be between a PBX and networking equipment (circuit to packet). I'm not sure it even needs 48 volts since the interface is really current driven. Anyone know if E&M typically uses a lower voltage these days like 12 volts?