sip trunk redundancy

Hello,

I have two IPPBX (primary and seconadary) and one sip trunk to each of them. I need to config simple redundancy, when IPPBX 1 is working every calls goes to IPPBX 1, when IPPBX 1 is out of service every calls goes to IPPBX 2. I made it using local-policy:

local-policy
        from-address
                                       *
        to-address
                                       *
        source-realm
                                       access
        description
        activate-time                  N/A
        deactivate-time                N/A
        state                          enabled
        policy-priority                none
        last-modified-by               admin@192.168.254.182
        last-modified-date             2014-02-25 15:13:15
        policy-attribute
                next-hop                       192.168.254.1
                realm                          ippbx1
                action                         none
                terminate-recursion            disabled
                carrier
                start-time                     0000
                end-time                       2400
                days-of-week                   U-S
                cost                           0
                app-protocol
                state                          enabled
                methods
                media-profiles
                lookup                         single
                next-key
                eloc-str-lkup                  disabled
                eloc-str-match
policy-attribute
                next-hop                       192.168.254.2
                realm                          ippbx2
                action                         none
                terminate-recursion            disabled