Dynamic Reconfiguration of IP Domain Middleware Stacks to Support Multicast Multimedia Distribution in a Heterogeneous Environment

Seamless connectivity to multiple wireless networks independently of a fixed point is becoming increasingly important for mobile devices however wireless networks differ in bandwidth, size and access costs each requiring protocol functions to enable devices to communicate efficiently. In addition, due to the divergence of users and applications, traditional stacks are frequently enriched with additional functionality such as transport protocol functionality, synchronisation and presentation coding which can lead to a performance bottleneck due to the insufficient processing power and memory of portable devices. We argue that an extensible middleware is needed to cover small resource constrained devices to full-fledged desktop computers thus we investigate dynamic micro-protocols which enable devices to adopt specific protocol stacks at runtime in an attempt to optimise the stack to the functionality that is actually required by the application thus eliminating additional overhead functionality provided by generic stacks. A side effect of this is that it allows devices such as PDAs to offer protocol functions, which would not normally be available due to their memory constraints. Memory constrained devices are catered for through the deployment of a client-proxy overlay network where proxies offload processing. The problem of the ‘common denominator bandwidth’ is overcome through multicast media groups where clients subscribe to different quality of services in accordance with resource availability and move between groups according to bandwidth availability over time. Our end result is a Java middleware for multimedia streaming to heterogeneous mobile clients, utilising dynamic configuration of protocols with respect to application requirements and available network resources. Performance is increased through application specific tailored protocols and reducing protocol complexity allows stacks to fit inside the limited memory space of current mobile devices. We evaluate the dynamic reconfigurability of the middleware and present some new results from a series of applications utilising runtime adaptation.