Voice Call Redundancy
The information in this topic applies only to voice calls, not to SMS messages or email.
For voice calls, VTScada keeps track, not only of each contact's phone number, but also the method used to place that call. If more than one method of placing a call is available (Twilio, VOIP, or modem) and one of those methods fails, VTScada will continue making calls using whatever method is still available. If all methods configured on a machine that can be reached by the Alarm Notification Server are working, all methods are used; VTScada does not define a primary call-out method and then switch to the alternate only when the primary fails. For example, with VOIP configured on Server-A and Twilio configured on Client-B, the server will round-robin between both VOIP and Twilio for voice callouts.
On any given workstation, you can have VOIP, Twilio, and voice modems configured. Only one VOIP configuration can be set up on a given workstation, and only one Twilio configuration can be set up on a given workstation. Any workstation that the application is running on can host any number of voice modems for redundancy. The Call Manager Status widget will only display one call interface for voice modems. You can use the Modem Status widget to display more detailed information on individual voice modems.
If a voice call method fails, an internal counter for that method will be incremented. If the counter exceeds the CallManagerBadCallLimit setting, a voice call failure alarm will become active. The alarm will normalize when the first successful call occurs using that method. When a voice call failure alarm is raised, it will have a priority as defined by CallManagerAlarmPriority.
When configuring the order of servers, note that the Call Manager does not have its own service, but instead follows on the Alarm Notification service to define the order of backup servers.
In many cases, Twilio and VOIP configurations should be disabled globally and instead, enabled and configured for specific workstations. If a configuration is enabled globally, it will make calls only from the current Alarm Notification server. This might be desired if any one out of multiple servers will use the same VOIP settings when it is the current server.
A global configuration such as this will not work with all VOIP solutions or Twilio configurations.
