POTS fallback in case of Asterisk failure or power outage

I have to setup some configuration at home which should provide smart telephony then all is ok and should fallback to POTS in some sorts of failures.

Hardware I have:

  1. Addpac AP200E SIP/H323 gateway (1FXS+1FXO).
  2. DECT POTS phone (no IP)
  3. Line powered classic POTS phone
  4. Asterisk PBX (Elastix 1.6 in VM on home server)


When Asterisk is OK and power is OK:

  1. Intellectual outgoing call routing.
  2. PBX services on incoming calls - voicemail, time-based call routing, fax reception, etc.
  3. Remote extensions (softphones).
  4. Classic POTS line-powered phone is silent but could dial out.

When Asterisk failed:

  1. FXO relayed to FXS on gateway, so calls are terminated and originated from DECT phone are going to POTS.
  2. Classic POTS line-powered phone is silent, but could dial out.

When power is failed:

  1. Classic POTS line-powered phone is connected to land line, it rings and could dial out via POTS.

What was done already:

  1. (succeed) Gateway FXO port connected to POTS land line and FXS port - to DECT phone.
  2. (succeed) Gateway configured to plar incoming POTS calls to Asterisk.
  3. (succeed) Gateway configured to serve outgoing POTS calls from Asterisk.
  4. (succeed) Gateway configured to register its FXS port as extension on Asterisk.
  5. (failed) Gateway configured to do the POTS backup (if Asterisk is unavailable, then route calls between FXO and FXS in both directions). Gateway do not return to normal operation after backup activation when Asterisk gone online again.
  6. (succeed) Asterisk configured to do incoming POTS call processing and services, then, calls are routed back to FXS port on gateway.
  7. (succeed) Asterisk configured SIP provider trunk and long distance calls routing.
  8. (succeed) POTS phone connected to POTS line parallelly to gateway and rings on incoming calls.

So, I have no POTS backup if Asterisk failed and POTS phone is always ringing, doesn’t matter, if there is day, or 3am.


  1. Have anyone already do the similar setup? Or, another setup but with the similar requirements? Could you somehow describe it?

  2. What hardware and software have you used? Especially, which FXS+FXO gateway have the correct POTS backup function, or another way to find the solution, f.e. some PC FXO/FXS cards?

  3. How could you recommend to modify (simplify, or improve) my setup?

I could do a similar setup. It looks like the problem is the gateway, so you really should only buy a new gateway and you should be OK.

If I would do this sort of thing, I would use a Patton SmartNode gateway.