Failover Guide

Failover service allows using one PBX as a backup for another one when the latter goes down. This guide describes the supported features and the procedure to set up the service.

WMS version: 3.86

Date: September 2017




  • Main PBX (Primary PBX) – PBX handling the load of a set of users / devices
  • Failover PBX (Backup PBX, Secondary PBX) – PBX which takes over the load of a set of users / devices when their Main PBX becomes unavailable
  • Configuration Source PBX – PBX which has the original configuration
  • Configuration Destination PBX – PBX which received a copy of the Source PBX configuration


  • Minimal WMS version 3.86
  • WMS Network must be set up between the PBXs
  • Failover PBX must be capable of handling the max load (Main + Failover)
    • WPBX HW – Max 1000 users
    • VM – 1 Core – 2 threads of a Xeon Level CPU for each 500 users
  • Primary DNS Server set on devices must be different from Main PBX or a Secondary DNS Server must be available

Currently supported features & scenarios

  • Hot Standby Mode: one Main PBX and one Failover PBX which usually has no load

  • Load Sharing Mode (two Main PBXs which work at the same as Failover for another PBX, usually in couples – requires devices configuration on one single Main PBX and re-provisioning to final Main PBX after initial sync) – coming in the next version

  • Configuration sync: all changes must be applied only to Configuration Source PBX
  • Supported devices:
    • WP (WP600AXX starting from v. 2.8.22; also make sure Android version is up to date)
    • W24FXSR2/W04FXS/W02FXSR2 (except for W01FXS – pre 2015)
    • W04FXO
    • PRI
    • W01/02BRI
    • Incoming SIP trunks (remote operators / devices try to connect to both PBXs)
  • Failover PBX supports the following call scenarios:
    • Internal calls
    • Call groups (except for ‘Call All 32’ strategy)
    • Calls to/from Wildix gateways
    • Calls to/from incoming SIP trunks
    • Call transfer
    • Return from transfer
  • All devices have SIP registration on both main and failover servers simultaneously

Device configuration and switching timeout

Device Main SIP server Failover SIP server Timeouts (s)(switch to backup / main)
WP TCP / 443 (*) TCP / 443(*) 60-105 / 60-105
WP2015 TCP / 443 (*) TCP / 443 (*) 30-60 / 10-60
W24FXSR2 TCP / 443 (*) TCP / 443 (*) 40-45 / 30-90
W04FXS TLS / 443 (*) TLS / 443 (*) 30 / 45-300
W02FXSR2 UDP / 5060 UDP / 5060 30-60 / 10-30
W0XPRI TCP / 443 (*) TCP / 443 (*) 10 / 30-180
W01/02BRI TCP / 443 (*) TCP / 443 (*) 10-60 / 60-180
W04FX0 TLS / 443 (*) TLS / 443 (*) 30 / 45-300
WP600AXX TLS / 443 (*) TLS / 443 (*) -/-

(*) – Alternative or default secure port 443 can be used


Note: in case you’ve been using the old Failover, all the configuration previously set up, must be removed!

Proceed as follows:

  • Activate WMS network between the PBXs
  • Set failover PBX in WMS -> Users -> PBXs:
    • Click Failover column near the PBX you wish to set up failover for
    • Failover setup dialog opens
    • Select the failover PBX from the list
    • Click Ok
  • Make all the configuration on the main PBX (devices, Dialplan, call groups etc.)
  • Make replication of the Main PBX configuration:
    • Access the failover PBX via SSH
    • Run shell script /usr/sbin/sync_pbx
    • Select 1 (Configure)
    • Enter IP of the Main PBX
  • Set failover PBX as secondary DNS server on unsupported devices

Load sharing scenario is coming in the next version.

Current (temporary) limitations/special configuration

  • No support for failover mode via /rw2/etc/phone_failover.conf
  • No support for failover mode via secondary DNS Configuration
  • No Full TLS Support (check the table provided in the Chapter “Device configuration and switching timeout”)
  • It’s necessary to configure separate DHCP server in the local network where phones and gateways are connected
  • It’s necessary to configure separate DNS server to resolve PBX names with local ip addresses
  • Changes to configurations of the PBX which synchronizes its configuration from another one will be lost after each sync, Admin should apply all changes only on the source PBX
  • No notification present on phone’s display when switching to backup PBX in failover scheme
  • Unsupported devices (see the chapter “Failover by DNS”):
    • W-AIR
    • W04BRI
    • W01GSM
    • W01FXS (pre 2015)
    • Outgoing SIP trunks
    • iOS clients
  • No XML Browser-based services like history / phonebooks when connected to failover PBX
  • Call group with ‘Call All 32’ strategy – calls do not work for failover user
  • Call through remote PBXs of WMS network does not work if Main PBX is unavailable
  • Continuity feature does not work after switch to failover PBX
  • Pre-answer services do not work after switch to failover PBX
  • Call to the failover WP480 2015-2016 device can not be completed normally
  • Return from semi-attended transfer is not performed
    • after transfer from remote user to failover user
    • after transfer from failover user to remote user
  • BLF presence status of the local user is unavailable for failover user; call can’t be picked up via BLF key
  • BLF presence status of the failover user is unavailable for local user; call can’t be picked up via BLF key
  • Impossible to perform calls from Kite to failover user via WMS network master PBX in case main PBX is unavailable
  • Email notifications are unavailable for failover user; user features are not available on failover PBX
  • Login/logout via 99 service is restricted for failover user
  • Language and region settings are not synced during sync_pbx script execution

Permanent (not temporary) limitations:

  • No support for W01GSM calls and sms
  • No Chat/VM/user features/recordings/presence
  • History works only if a single remote MySQL or MSSQL backend is set up on all PBXs

Devices Failover by DNS

Unsupported device must use as primary DNS Server Main PBX and as secondary – Failover PBX.

When the Main PBX will be unavailable – device will resolve the domain using the Failover PBX and connect to it.

This configuration will work only if domain is used or another domain shared by both PBXs and inserted in Networking Settings – Hosts.

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