On the Study of Constrained-Connections Migration in Mobile Wireless Systems

• Main Authors: Ko-Shung Chen, 陳國雄
• Other Authors: Nen-Fu Huang
• Format: Others
• Language: en_US
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/87246001592563176035

博士 === 國立清華大學 === 資訊工程學系 === 90 === Demand of mobile wireless services for people has been created greatly due to the phenomenal development and rapid deployment in the area of mobile computing and wireless communications. The demand forces numbers of researchers to explore and develop a variety of new and applicable technologies, one of which is successfully to integrate the wireless access techniques into the existing high-speed wireline (fixed) communication networks to form one big mobile and wireless system. In such a big system, the wireless portion is to provide the access of mobile terminals while the wired part is to extend the area of mobile services. One obvious goal is to provide wireless broadband access that offers point-to-point, multipoint and point-to-multipoint communications between fixed and/or mobile terminals. The wireless system has a major difference from the wired system that is users’ mobility. In order to providing transparent handoff services and efficient resource utilization, the active connections over the mobile and wireless networks must be maintained carefully. Moreover, for satisfying a variety of new multimedia applications, the management of the constrained connections has also to be seriously controlled for achieving the QoS guarantee. Connection migration for the roaming terminals becomes an important issue for the service availability. For maximizing the resources utilization and still providing QoS guarantee within mobile and wireless systems, this study investigates the constrained connections migration problem in three aspects. First, we examine the constrained unicast-connections migration problem and then propose a Constrained Paths Migration Scheme (CPMS) for finding low-cost path, which still satisfies the end-to-end delay constraint over mobile and wireless networks. Instead of using straightforward shortest path approach, CPMS adopts feasible-search optimization strategy to content the dynamics of mobile wireless networks. CPMS automatically recognizes inefficient paths and efficiently migrates them to the efficient ones. CPMS operates in a branch-and-bound manner to reduce control overheads. CPMS maintains low-cost paths with QoS constraints during user roaming. The timing synchronization of data flow is also controlled successfully. Simulation will be used to reveal that CPMS can accommodate a larger number of paths in mobile wireless systems. Next, we extend CPMS and consider the multicasting problem in the context of generic wireless systems. Specifically, a novel Constrained Tree Migration Scheme (CTMS) is created to support multicast services in mobile wireless networks. The salient features of the novel CTMS include: 1) automatically recognizing the inefficiency of the multicast trees, then migrating them to better ones, while maintaining the QoS guarantees specified by mobile users; 2) conserving network resources by maintaining a low-cost multicast tree, thus accommodating more users; 3) operating efficiently in a truly distributed manner through event driven and diffusing computations, thus increasing the degree of scalability; 4) synchronizing data transmission flow for transparency during the tree migration, and thus providing seamless handoff control. Furthermore, the novel CTMS also handles the concurrent migration problem effectively within the wireless system, thus eliminating the oscillation paradox. Extensive simulation results show that CTMS can significantly reduce the resources used per multicast tree, thus achieving both low handoff-dropping/join-blocking rate and high resource utilization. As WDM-based optical networks are becoming the right choice for the next-generation Internet networks to transport high-speed IP traffic, the leading role of wireless ATM (WATM) networks will be undoubtedly replaced with wireless WDM (WWDM) networks for providing high quality of services to mobile users. Meanwhile, multicasting has played an increasingly important role in many conventional and emerging applications, such as teleconferencing and distributed games. Although efforts to support multicasting over WATM networks have been considerable, multicasting over WWDM networks has seldom been addressed. Conventional operations for setting up and tearing down optical connections in WDM networks are not intuitively applied to WWDM networks due to the provisioning of handoff. Additionally, the multicast optical tree constructed may become inefficient due to the lack of sufficient and available wavelengths. Following the movement of roaming members, the tree may thus expand and consume excessive resources, and may violate the QoS constraint. Therefore, how to provide efficient support for multicasting over the new WWDM networks merits careful examination. Finally, a Constrained Optical Tree Migration Scheme (COTMS) is proposed to support multicast services in WWDM networks. COTMS is an enhancement of CTMS for adapting to the characteristic of WDM-based backbone networks. CTMS can properly deal with the constrained tree migration problem for generic wireless networks, and COTMS inherits the efficiencies of CTMS entirely. Simulation results show that COTMS can markedly reduce the resources used per multicast tree, thus achieving both low handoff-dropping/join-blocking rate and high resource utilization. More importantly, we demonstrate how COTMS incorporating crossover optical switch discovery can be used to support real-time traffic for heterogeneous (i.e., unicast and multicast) connections in a uniform and unified manner. The proposed scheme is also suitable for routing over fully mobile (ad hoc) networks in which multiple frequencies are used for data communications.