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Hosted SIP Phones with Full FXO Survivability Sample Configuration

Hosted SIP Phones with Full FXO Survivability Sample Configuration

Hosted SIP Phones with Full FXO Survivability Sample Configuration

The sample configuration below contains the options needed for inbound FXO, outbound FXO, and local survivability of hosted SIP phones registered through the AOS SIP Proxy.  For the sample configuration, the following is assumed about the application:

  • IP interfaces, routing, and firewall features not referenced in this document have already been configured.
  • The unit is equipped with a FXO port.
  • The ERL tool, which determines the correct impedance value to use for the analog PSTN line, has already been run on products that support it .  Please reference the AOS Feature Matrix to confirm Auto-ERL capabilities.  Details regarding usage of the ERL tool can be found in the Analog Configuration and Trunk Troubleshooting Guide.  Products that do not support the ERL tool may need to issue the command blind-dial under the analog voice trunk.
  • There are no other voice trunks or voice grouped-trunks configured.
  • The SIP phones register to their SIP server using ten digit numbers (i.e. 256-555-1234), but the application requires local SIP phone to SIP phone calls be made using the last four digits of the phone number during survivability (i.e. 1234).
  • The customer requires that multiple SIP phones ring on inbound FXO calls while in survivability.  A ring-all ring-group is configured to accommodate this requirement.
  • 10 digit local dialing is in use on the FXO trunks.

The following are key notes regarding the application:

  • The SIP phone facing IP address of the AOS device will need to be configured as the phones’ default gateway and DNS server.
  • The AOS device will be configured to act as a DNS proxy, which is required during survivability when a FQDN is used for the provisioning server, SIP server, outbound proxy, or registrar. The command voip name-service host <FQDN> sip udp ensures that the specified FQDN persists even when connectivity to the unit’s DNS server has been lost.  An entry will need to be made for every FQDN the SIP phones are configured for, whether that be for provisioning or to send SIP traffic to.  If a phone fails to resolve a FQDN, the phone will potentially not boot up , register or make/receive phone calls .
  • The unit can be configured to allow the registration of SIP phones during failover with the sip proxy failover accept-registrations command. This configuration command is desirable if the end users reboot their phones during survivability. When choosing whether or not to use this command, be aware that the command opens the unit up to accept ALL registrations during survivability.  This means that any rogue SIP device on the LAN can register to the unit during survivability and make calls to other SIP proxy users or out the FXO trunk(s).
  • If you would like to route emergency calls out the FXO port(s), you can optionally add the command sip proxy emergency-call-routing accept 911.

Additional Resources:


domain-proxy failover

domain-lookup database local



ip dhcp pool "PHONES"





  timezone-offset -6:00


interface eth 0/2

  ip address

  ip access-policy PHONES

  media-gateway ip primary

  no shutdown



voice forward-mode local


voice trunk T01 type analog supervision loop-start

  connect fxo 0/0

  trunk-number 2565551000


voice grouped-trunk FXO

  trunk T01

  accept 411 cost 0

  accept 611 cost 0

  accept 911 cost 0

  accept NXX-NXX-XXXX cost 0

  accept 1-NXX-NXX-XXXX cost 0

  accept 011-X$ cost 0


voice ring-group 2565551000

  type all

  member 2565551200

  login-member 2565551200

  member 2565551201

  login-member 2565551201

  member 2565551202

  login-member 2565551202



sip proxy

sip proxy transparent


sip proxy failover match-digits 4


sip proxy failover accept-registrations

sip proxy failover direct-inbound


voip name-service host sip udp

voip name-service host sip udp

Version history
Last update:
‎05-23-2014 11:33 AM
Updated by: