system information to the mobile station so that its availability at the UMA network cell can be registered with the core cellular network.
After registration is complete, signaling and bearer traffic flow between the mobile station and the serving UNC through an IPsec (IP Security) tunnel. When the mobile station wishes to place a call, for example, it sends UMA packets to the serving UNC requesting a connection. The serving UNC notifies a mobile switching center (MSC) in the core cellular network. The MSC then directs the serving UNC to create a voice path from the mobile station to a voice port on its A-interface. The serving UNC responds by creating a Voice over IP (VoIP) bearer path to the mobile station. Audio is transported back and forth acrossthe IP network as a VoIP data flow on the bearer path. When the serving UNC receives audio data from the mobile station, it is transcoded and directed to a voice port at the A-interface. Similarly, when the serving UNC receives audio data from the MSC, it is transcoded and sent to the mobile station over the bearer path. All communications are passed through the IPsec tunnel for security.
GPRS data services are also available on the UMA network. When a mobile station wishes to access these services, it creates a transport channel to the serving UNC. The transport channel carries GPRS payload packets between the mobile station and the serving UNC. The serving UNC forwards payload packets received from the mobile station to a serving GPRS support node