Mobile Virtual Private Network (MVPN) has been developed to secure mobile user's communication between untrusted external networks and protected private internal network. The IETF's solution, however, leads to some problems: where should we put the external Home Agent (HA), how could we trust the external HA, and overhead of three tunnels. In this paper, we propose an alternative SIP-based MVPN. Because the proposed architecture is based on SIP, the problems inherited from Mobile IP are not problems in our architecture. In addition, there is no need to tunnel a packet three times as that in IETF MVPN. In this paper, we also propose analytical models to evaluate and compare the performance of the proposed SIP-basedMVPN with the IETF MVPN. The results show that the proposed SIP-basedMVPN can reduce packet delivery cost significantly. It is especially suitable for real-time applications.