In this thesis, we propose a Dynamically Configurable NAT (DCNAT), a hybrid web cache replacement algorithm, a web session handoff mechanism, and a Topology- and-Direction-aware link layer fast handoff scheme to support continuous web access and real-time information pushing for mobile hosts that may visit private networks. These four approaches together provide convenient Internet access in mobile environments and NAT environments.
For the NAT inbound session problem, we propose Dynamically Configurable NAT (DCNAT) so that a host situates in Internet can spontaneously establish inbound session and push instant information to hosts beneath NAT networks. DCNAT enables NAT inbound session by a Binding Entry Request procedure to create NAT binding entries. The dynamic creation of NAT binding entries makes DCNAT very flexible in supporting inbound accesses to the ports/services opened dynamically by the private nodes behind an NAT router. Besides, with DCNAT, a content service provider can push information contents spontaneously to subscribers that are widely spreading and beneath different private networks with NAT. With the dynamic creation of NAT binding entries, DCNAT provides lower blocking probability and better scalability by using just one or several public IP addresses.
In order to improve web cache performance, we propose a hybrid web cache replacement algorithm that divides a cache space into two zones, a hot zone and a cold zone, and adopt a simple LRU replacement algorithm for the hot zone and a complex GD-Family replacement algorithm for the cold zone. This hybrid replacement algorithm combines the advantage of SLRU, LRU, and GD-Family algorithms but applies a complex GD-Family replacement algorithm only to a portion of the cache where strict object ordering is much significant to the overall cache performance. Therefore it can achieve a high DHR just slightly lower than that of GDSP and a high BHR just slightly lower than that of LRU while incurs much less maintenance cost, comparing with GD-Family algorithms.
To resume a web browsing session after a user changes the device that he uses to browse
Internet, we propose a web session handoff system that can hand over not only stateless but also stateful sessions between homogenous or heterogeneous user devices to enable uninterrupted and seamless web accesses. Compared with client-based approaches, our design has several advantages, such as less modification to user devices, practicability, and fault tolerance. We have implemented a UAP on a PC and client programs for both PC and PDA.
The implementation can successfully hand over between PC and PDA a stateful session for online shopping applications.
To speed up the process of handoff between 802.11 APs, we propose a Topology-and-Direction-aware fast handoff scheme that resolves a reduced set of candidate APs according to AP topology, MN’s its moving trend and/or MN’s position. The proposed approach further benefits handoff by allowing 802.11 station reassociates directly with an AP without performing AP discovery during handoff. Besides, the topology-and- movement-aware candidate-AP generation scheme can work in conjunction with the existing fast-handoff schemes that leverage pre-authentication, proactive key distribution, or context transfer.
In the future, we will evaluate more hybrid algorithms that combine algorithms other than LRU and GD-Family. Furthermore, we will study the applicability of hybrid policy in other applications, such as web cache on user devices with limited cache space and memory paging in computer system.
There is still further improvement to the proposed web session handoff system. First, we will improve our client program to collect more assistant information so that the UAP can be more light-weighted and session information can be handed over completely. Besides, since session tracking generates additional processing and storage load to UAPs, we will perform a quantitative analysis on workload and storage space problem of UAPs. Furthermore, we will also apply and refer previous research in scalable hierarchical proxies to design a system that contains multiple cooperated UAPs.
The practicability of the proposed Topology-and-Direction-aware fast handoff approach depends on the accuracy of measurement of MN’ moving trend and/or position, especially in indoor environments. Therefore, we will study and implement moving trend estimation
mechanism to verify the practicability of the Topology-and-Direction-aware fast handoff approach.
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