Call flows

This section describes inbound and outbound call flows and explains roles taken by the FortiVoice phone system at the main office and the FortiVoice LSG unit at the branch office.

This section includes the following topics:

• Inbound call flow
• Inbound call flow with a network impairment or failure
• Outbound call flow
• Outbound call flow when the branch office is down
• Outbound call flow when the main office trunk is down
• Outbound call flow for a 911 or emergency medical services call
• Outbound call flow with a PSTN failover

Inbound call flow

Inbound calls come into the system through the primary rate interface (PRI) or voice-over-IP (VoIP) service. The main office handles all inbound calls. The main office routes an inbound call to the right extension at the branch office.

The main office sends Session Initiation Protocol (SIP) and Real Transport Protocol (RTP) traffic directly to the phone, not to the branch office.

Inbound call flow with a network impairment or failure

If there is a network impairment or failure, a call may not reach the extension at the branch office. The main office routes the call according to the unavailable call handling settings which is typically to send the call to the voicemail.

Outbound call flow

In an outbound call flow, the phone sends calls to the branch office. The branch office relays SIP traffic directly to the main office. The main office processes outbound calls.

Outbound call flow when the branch office is down

If the branch office is down, the outbound call flow changes depending on the phone model as explained in the following two scenarios:

• If the branch office does not respond, the call fails. The phone automatically attempts to send any future outbound calls to the main office directly. This scenario applies to all Fortinet phone models (except the Fortinet FortiFone FON-870i).

• If the branch office does not respond, the call fails. The phone does not automatically attempt to send any future outbound calls to the main office directly. This scenario applies to the Fortinet FortiFone FON-870i.

Outbound call flow when the main office trunk is down

If the main office trunk stops working, the branch office system can handle calls.

If you enable the Central trunk fallback to branch feature on the main office unit, the main office sends an error code to the branch office when the main office trunk is down. The branch office can then locally handle calls. You may also need to set up an outbound call route on the branch office unit to handle this failover scenario.

Details about enabling the Central trunk fallback to branch feature are included in Adding a survivability branch.

Details about creating an outbound call route are included in Creating an outbound call route for failover scenarios.

Outbound call flow for a 911 or emergency medical services call

For routing 911 or emergency medical services (EMS) calls, administrators have the following two options:

• The branch office routes emergency calls to branch lines and then to PSTN lines: This is the preferred routing method because PSTN lines always have the correct civic address setup with the public safety answering point (PSAP) service. For this scenario, administrators must make sure that the survivability branch setup on the FortiVoice phone system at the main office has the Emergency call option set to handled by branch, not to the default (handled by central).
• The main office routes emergency calls: The administrator at the main office manages emergency calls initiated from different extensions to route them to a line that has an address mapped to that location. The carrier providing the phone service, PRI, or VoIP handles the civic address mapping. However, the administrator works with the carrier to make sure that phone numbers map to the correct civic addresses. To configure a profile to manage emergency calls and extensions, access the web-based manager of the FortiVoice phone system at the main office and go to Phone System > Profiles > Location.

Outbound call flow with a PSTN failover

If the connection between the branch office system and the main office stops working, the branch office routes the call out through its local lines. The phone is unaware of any problems in the network because the call still goes through. You may also need to set up an outbound call route on the branch office unit to handle this PSTN failover scenario. Details about creating an outbound call route are included in Creating an outbound call route for failover scenarios.

During a connection outage, the following call behaviors apply:

• Calls from the main office cannot reach the branch office.
• Calls from the branch office cannot reach the main office.
• Calls from one branch office cannot reach another branch office. However, calls from one extension can reach another extension at the same branch.
• The branch office voicemail responds to a login. However, recorded messages are unavailable because the branch office voicemail cannot synchronize with the main office voicemail which stores all call recordings.