Mobile IP provides mobility support for hosts connected to the Internet without changing their IP addresses. Route optimization strategies complement Mobile IP, to alleviate triangle routing, by informing correspondent hosts of the mobile host's care-of address. In this paper, we propose further strategies that are compatible with route optimization and its security model. First, foreign agents buffer packets for a mobile host and send them to its new location when it leaves. Second, hierarchical foreign agent management reduces the administrative overhead of frequent local handoffs, using an extension of the Mobile IP registration process so security can be maintained. Duplicate packets due to buffer handover are eliminated with the cooperation of mobile hosts. Simulation results show substantial performance improvements in terms of throughput, registration overhead, lost and duplicate packets during a handoff, without restrictions on physical placement of foreign agents. 1.

Recent advances in low-power VLSI technologies have resulted in the proliferation of inexpensive mobile computing devices. Their rising popularity has increased the demand for wireless networking technologies that will enable them to connect to the Internet regardless of their physical location. This has resulted in the formation of a logical hierarchy of wireless networks, where low-bandwidth networks with wider coverage areas are layered on top of clusters of high-bandwidth networks with smaller coverage areas. These are called wireless overlay networks. Previous research has looked at using wireless overlay networks to enhance the connectivity of mobile computing devices as they move in and out of coverage areas by providing them with interfaces for each layer and then dynamically switching to upper layers when lower layers become unavailable. In this paper, we address the problem of performance robbing congestion "hot spots" that occur in the lower layers. We first present several new performance measures for wireless overlay networks, and then propose several load balancing algorithms that are designed to spread the network load across the overlays. This is a work in progress, with simulation results forthcoming.

The continuous development of wireless networks and mobile devices has motivated an intense research in mobile data services. Some of these services provide the user with context-aware information. Specifically, location-based services and location-dependent queries have attracted a lot of interest. In this article, the existing literature in the field of location-dependent query processing is reviewed. The technological context (mobile computing) and support middleware (such as moving object databases and data stream technology) are described, location-based services and locationdependent queries are defined and classified, and different query processing approaches are reviewed and compared.

The continuous development of wireless networks and mobile devices has motivated an intense research in mobile data services. Some of these services provide the user with context-aware information. Specifically, location-based services and location-dependent queries have attracted a lot of interest. In this article, the existing literature in the field of location-dependent query processing is reviewed. The technological context (mobile computing) and support middleware (such as moving object databases and data stream technology) are described, location-based services and locationdependent queries are defined and classified, and different query processing approaches are reviewed and compared.