Communications via a SIP Gateway.

A SIP gateway is a service provided that allows you to connect to non-SIP devices, such as the public telephone network. These services usually have to be paid for.

Figure. Gateway chart.

The initiation of the call is the same up to the point where the SIP gateway is reached.

The Big Picture

The SIP server allows you to offer a complete voice communication solution to your users.

Figure. Voice communication.