Basic VoIP call flow

The following describes a basic VoIP call flow:

1. A user picks up a telephone, and then the modular voice card detects the user’s off-hook action in real time.

2. The modular voice card transmits the off-hook signal to the VoIP signal processing module on the VoIP gateway.

3. The VoIP signal processing module generates dial tones.

4. The user hears dial tones played by the session application and begins dialing before the dial tone timer expires.

5. The session application collects the digits dialed by the user.

6. The session application compares the collected digits with the match template while collecting digits.

7. After finding a match template for the called number, the originating VoIP gateway maps the number to the terminating VoIP gateway.

8. The originating VoIP gateway initiates a VoIP call to the terminating VoIP gateway over the IP network and establishes a logical channel for the call to send and receive voice data.

9. The terminating VoIP gateway receives the call from the IP network and seeks the destination telephone according to the match template. If the call is to be processed by a PBX, the terminating VoIP gateway passes the call through PSTN signaling to the PBX for processing until the destination telephone is connected. When the calling party or the called party hangs up, the conversation ends.