Incoming Call Sequence of Events shows the sequence of events that occurs during an incoming call.
Incoming Call Sequence of Events
The following describes the sequence of events shown in Incoming Call Sequence of Events:
Phone B registers with VoIP server - The Security Appliance builds a database of the accessible IP phones behind it by monitoring the outgoing VoIP registration requests. SonicOS/X translates between phone B’s private IP address and the Security Appliance’s public IP address used in registration messages. The VoIP server is unaware that phone B is behind a Security Appliance and has a private IP address—it associates phone B with the Security Appliance’s public IP address.
Phone A initiates a call to phone B - Phone A initiates a call to phone B using a phone number or alias. When sending this information to the VoIP server, it also provides details about the media types and formats it can support as well as the corresponding IP addresses and ports.
VoIP Server validates the call request and sends the request to phone B - The VoIP server sends the call request to the Security Appliance’s public IP address. When it reaches the Security Appliance, SonicOS/X validates the source and content of the request. The Security Appliance then determines phone B’s private IP address.
Phone B rings and is answered - When phone B is answered, it returns information to the VoIP server for the media types and formats it supports as well as the corresponding IP addresses and ports. SonicOS/X translates this private IP information to use the Security Appliance’s public IP address for messages to the VoIP server.
VoIP server returns phone B media IP information to phone A - Phone A now has enough information to begin exchanging media with Phone B. Phone A does not know that Phone B is behind a Security Appliance, as it was given the public address of the Security Appliance by the VoIP Server.
Phone A and phone B exchange audio/video/data through the VoIP server - Using the internal database, SonicOS/X ensures that media comes from only Phone A and is only using the specific media streams permitted by Phone B.