I need a simulation in NS2.27. Is about wireless network and Mobile IP using SIP as protocol for signaling and AAA (authentication, acounting and authorization). The Home is GPRS network and the Visited is a WiFi (SIP gateway). The Mobile Node is a dual mode interfeace (WIFI-GPRS). And the MN roams of GPRS to WLAN. For registering in the VN use SIP.