Recent advancement in personal communication services (PCS) provides wireless multimedia services for users on the move. For establishing the convenient access environment, the evolution of IP-based integrated scheme becomes very urgent for public wireless access systems. In this paper, we clarify the well-known issues of integrating the general packet radio service (GPRS) network and IEEE 802.11 wireless local area network (WLAN). These issues include the inconsistence in transmission rate and coverage area, the difficulty in seamless handoff, the complexities of mobile IP and address translations, and so on. Based on classified cases, we propose the circular probe strategy (CPS) to solve the IP translations and measure the precise handoff latency of a mobile node roaming from one network to another. This latency information helps a mobile node and its home agent (HA) to decide the appropriate handoff timing, to maximize the data transmission rate, and to perform seamless handoff in the heterogeneous system. We also proposed the smart access point (AP) mechanism to reduce the overhead of CPS and to provide precise handoff latency information for mobile nodes (MNs) to select the most appropriate AP for association. Experiment results demonstrate that the proposed smart handoff scheme performs better than traditional algorithms in terms of handoff time in the integrated network.

An ad hoc wireless network is a collection of mobile hosts that self-forming a temporary network without any required intervention of centralized system. In such environment, mobile hosts, which are not within transmission range from each other, require some other intermediate hosts to forward their packets to form a multi-hop communication. In this paper, an ad hoc network is modeled as a graph. Two nodes within the transmission range of each other are connected by an edge. Given a finite set of mobile nodes, a finite set of edges and a new multicast request, the wireless multicast tree problem (WMTP) is to find a multicast tree for the request so that the multicast loss probability is minimized. We prove the WMTP is NP-complete and a heuristic algorithm, called Degree-Based Multicast Routing Algorithm (DBMRA), is proposed. Based on the DBMRA, one algorithm was proposed to establish backup nodes for the multicast tree to improve the reliability. A node is needed to be backup only when it has a high probability to disconnect the multicast tree seriously. The qualification of a node to be backup is subject to a computed threshold, which is determined by a statistic analysis. The theoretical and experimental analyses are presented to characterize the performance of our algorithms.

IP multicasting has naturally been considered the ideal technique to be used with multimedia communications but is difficult to mobile hosts due to the addition of mobility in the host group. In this paper, we propose a novel multicast algorithm, namely time and distance-based multicast algorithm (TDBMA), for IPv6-based mobile networks. TDBMA intends to trade off between the shortest delivery path and the frequency of the multicast tree reconfiguration. When a mobile host (MH) moves into a new foreign network which is managed by a foreign network router and re-subscribes to an existing multicast tree, the foreign network router uses the TDBMA to determine whether the MH joins the multicast tree directly or receives the tunneled multicast packets from its home agent (HA). The TDBMA is subject to two key factors, called time and distance. The visited foreign network router can join the multicast tree directly only when the value of both time and distance is true. The simulation results have shown that TDBMA has better performance than other algorithms, especially in the case where the number of MHs is large.