| Load balancing has proven to be an effective way for achieving good performance and high scalability in distributed systems, and a great deal of research has been conducted in this domain in the past. In addition to distributed systems in general, load balancing is also used in heterogeneous distributed environments that use the Common Object Request Broker Architecture (CORBA) based middleware for achieving interoperability. So far, most of the research on load balancing has been concerned with wired systems, and little work has focused on wireless systems, in which certain inherent characteristics, such as low communication bandwidth, high delay and high packet drop rate, call for careful examination.; This thesis investigates the performances of load balancing strategies for CORBA-based systems focusing particularly on wireless environments. Each strategy reflects a distinct combination of a request mapping policy and an interaction pattern among the three components in the load balancing system: client, server and balancer. Using the commercially available CORBA-compliant software "Orbix E2A Application Server Platform 5.1", a performance prototype of a load balancing system is designed and implemented. A wireless network is emulated with a well-known network emulation package, NIST Net. Based on extensive performance measurements, the effects of different workload factors on the performances of the different load balancing strategies are described, and derived insights are also discussed. In particular, a comparison of the effects of wired and wireless environments on the performances of various load balancing strategies is presented. |
