The WiMAX Forum has defined a two-tiered mobility management to minimize handover delay and packet loss. However, it leads to another problem: When to perform ASN GW relocation? The standards only define the ASN GW relocation procedures without specifying when the ASN GW relocation should be performed. It is left for vendors and operators to develop their own proprietary solutions. In this paper, we propose an algorithm, which incorporates traditional Admission Control (AC) and Wiener Process (WP)-based prediction algorithms to determine when to carry out ASN GW relocation. We further develop an analytical model to analyze the proposed algorithm. Simulations are also conducted to evaluate the performance of the proposed algorithm. The results show that the proposed algorithm can improve the performance significantly in terms of blocking probability, dropping probability, average serving rate, and average signaling overhead.

The IETF NEtwork MObility (NEMO) working group has considered how to enable an entire network to move from one location to another. Mobile Virtual Private Network (VPN) has been developed to secure mobile user's communication between untrusted external networks and the protected private internal network. However, the IETF's mobile VPN does not address how to support NEMO. In addition, it is not suitable for real-time applications. In this paper, we propose architecture and protocols to support VPN in NEMO, which is called Secure NEMO (SeNEMO). The proposed SeNEMO, based on Session Initiation Protocol (SIP), is specifically designed for real-time applications over VPN. It allows an entire network to move and still maintains session continuity. In addition to analyzing the security vulnerabilities, we also propose analytical models to evaluate the performance of the proposed SeNEMO. The analysis is validated by extensive simulations. The results show that the proposed SeNEMO can reduce signaling cost significantly.

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-based MVPN with the IETF MVPN. The results show that the proposed SIP-based MVPN can reduce packet delivery cost significantly. It is especially suitable for real-time applications.

WiMAX forum is developing and standardizing the end-to-end network architecture. The access service network (ASN) gateway (GW) plays a critical role in the system. How to reduce the load in the ASN GW has become an important issue. However, the standards only define the ASN GW relocation procedure without specifying when the relocation should be performed. In a real development, the key challenge to reduce the load of an ASN GW heavily relies on the decision of an appropriate time to relocate the MSs in an ASN GW. In this paper, we propose two effective ASN GW relocation algorithms. They can accurately estimate the traffic load and decide when to perform ASN GW relocation. The proposed algorithms can be accomplished by ASN GW alone. There is no need to exchange information among ASN GWs or get any help from other servers. They are fully compatible with existing systems and should be easy to implement. Extensive simulations have been performed to investigate the performance of the proposed algorithms. The results show that the proposed algorithms can increase overall throughput and reduce the loads of ASN GWs.

A mobile virtual private network (VPN) has been developed to secure a mobile user's communication between entrusted external networks and the protected private internal network. IETF's solution, however, leads to some problems: where the external HA (home agent) should be put; how to trust the external HA; the overhead of three tunnels. We propose an alternative SIP-based mobile VPN. Because the proposed architecture is based on SIP (session initiation protocol), 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 in IETF's mobile VPN. Besides, by using SRTP, cRTP, MIKEY, Diameter SIP Application, and MIDCOM ALG, the proposed architecture can also provide VPN services for mobile users effectively. The proposed technique has been implemented in a mobile VPN testbed. Empirical experiments with a VoIP application were conducted to analyze the performance in terms of bandwidth consumption, end-to-end delay, and handoff latency.