Hit and Bandwidth Optimal Caching for Wireless Data Access Networks

For many data access applications, the availability of the most updated information is a fundamental and rigid requirement. In spite of many technological improvements, in wireless networks, wireless channels (or bandwidth) are the most scarce resources and hence are expensive. Data access from remote sites heavily depends on these expensive resources. Due to affordable smart mobile devices and tremendous popularity of various Internet-based services, demand for data from these mobile devices are growing very fast. In many cases, it is becoming impossible for the wireless data service providers to satisfy the demand for data using the current network infrastructures. An efficient caching scheme at the client side can soothe the problem by reducing the amount of data transferred over the wireless channels. However, an update event makes the associated cached data objects obsolete and useless for the applications. Frequencies of data update, as well as data access play essential roles in cache access and replacement policies. Intuitively, frequently accessed and infrequently updated objects should be given higher preference while preserving in the cache. However, modeling this intuition is challenging, particularly in a network environment where updates are injected by both the server and the clients, distributed all over networks. In this thesis, we strive to make three inter-related contributions. Firstly, we propose two enhanced cache access policies. The access policies ensure strong consistency of the cached data objects through proactive or reactive interactions with the data server. At the same time, these policies collect information about access and update frequencies of hosted objects to facilitate efficient deployment of the cache replacement policy. Secondly, we design a replacement policy which plays the decision maker role when there is a new object to accommodate in a fully occupied cache. The statistical information collected by the access policies enables the decision making process. This process is modeled around the idea of preserving frequently accessed but less frequently updated objects in the cache. Thirdly, we analytically show that a cache management scheme with the proposed replacement policy bundled with any of the cache access policies guarantees optimum amount of data transmission by increasing the number of effective hits in the cache system. Results from both analysis and our extensive simulations demonstrate that the proposed policies outperform the popular Least Frequently Used (LFU) policy in terms of both effective hits and bandwidth consumption. Moreover, our flexible system model makes the proposed policies equally applicable to applications for the existing 3G, as well as upcoming LTE, LTE Advanced and WiMAX wireless data access networks

A model for composible and extensible parallel architectural skeletons

Application of pattern-based approaches to parallel programming is an active area of research today. The main objective of pattern-based approaches to parallel programming is to facilitate the reuse of frequently occurring structures for parallelism whereby a user supplies mostly the application specific code-components and the programming environment generates most of the code for parallelization. Parallel Architectural Skeleton (PAS) is such a pattern-based parallel programming model and environment. The PAS model provides a generic way of describing the architectural/structural aspects of patterns in message-passing parallel computing. Application development using PAS is hierarchical, similar to conventional parallel programming using MPI, however with the added benefit of re-usability and high level patterns. Like most other pattern-based parallel programming models, the benefits of PAS were offset by some of its drawbacks such as difficulty in: (1) extending PAS and (2) skeleton composition. SuperPAS is an extension of PAS that addresses these issues. SuperPAS provides a skeleton description language to describe a skeleton in a generic way. Using SuperPAS, a skeleton developer can extend PAS by adding new skeletons to the skeleton repository (i.e., extensibility). SuperPAS also makes the PAS system more flexible by defining composition of skeletons. In this thesis, we describe the model and description language for SuperPAS and elaborate its use through examples

An inexpensive unstructured platform for wireless mobile peer-to-peer networks

In this paper, we propose an unstructured platform, namely Inexpensive Peer-to-Peer Subsystem (IPPS), for wireless mobile peer-to-peer networks. The platform addresses the constraints of expensive bandwidth of wireless medium, and limited memory and computing power of mobile devices. It uses a computationally-, memory requirement-and communication-wise inexpensive gossip protocol as the main maintenance operation, and exploits location information of the wireless nodes to minimize the number of link-level messages for communication between peers. As a result, the platform is not only lightweight by itself, but also provides a low cost framework for different peer-to-peer applications. In addition, further enhancements are introduced to enrich the platform with robustness and tolerance to failures without incurring any additional computational and memory complexity, and communication between peers. In specific, we propose schemes for a peer (1) to chose a partner for a gossip iteration, (2) to maintain the neighbors, and (3) to leave the peer-to-peer network. Simulation results are given to demonstrate the performance of the platform