[Asterisk-Users] Asterisk PBX and backup Circuits

[kurt x]

I am interested to know how one would calculate the amount of PSTN
connection needed for backup on an Asterisk PBX that is being setup to
receive its DIDs via a VoIP provide.  To sum up what I am
implementing:  I am porting my DIDs to a VoIP provide so I will need a
back up plan in place if the Data network fails.  In addition, 911
will always be going out the PSTN so I know I need at least one POTs
circuit.  Calls inbound and outbound will always routed through the
data network.

Thanks,

Kurt