Theses Doctoral

Minimally Invasive Solutions to Challenges Posed by Mobility Changes

Reich, Joshua

Today, things have changed radically. As network technologies have proliferated and evolved, the components of, and participants in, computerized systems have become increasingly decoupled. Users travel and commute while connecting to their office computer or home media server. Hardware devices may be carried by users, move on their own, or reside in data centers, never to be seen or touched by end-users. Even operating systems (OSes) and applications may now migrate across the network while executing, thanks to advances in virtualization that are only just beginning to remake the computing landscape. The decoupling of users, devices, and software has invalidated properties that enabled desired functionality: resulting in compromised function. Power interfaces utilize physi- cal user interactions to determine when transitions between high and lower power states should occur; what happens when users are no longer physically present? Operating system execution often relies on components such as CPU and local disk responding with tightly bounded delays; what should be done when the OS itself is in the process of migrating between two separate physical machines? The fundamental question explored by this dissertation is: Can we find highly adoptable solutions to restore desired functionality that has been lost because of changed mobility characteristics? Our emphasis on adoptability stems from pragmatic concerns: if a solution is difficult to adopt, it is highly unlikely to be used. Consequently, while many potential approaches may involve changes to the network itself, our work focuses on modifying end-point behavior. We show that practical solutions implemented solely in software and deployed only on network endpoints can be developed for a wide problem range. We consider concrete challenges arising from user, device, and software mobility changes, affecting sub-disciplines spanning cloud computing, green computing, and wireless networks. Cloud Computing: Users increasingly utilize virtual machine (VM) technology to migrate and replicate OS and software amongst networked hosts. Traditional execution required one VM image copy on each host's local storage. By transitioning to networked execution, dozens, if not hundreds, of VM replicas may now be distributed from a single networked storage location to a commensurately large set of physical machines. As these systems expand, they have come to be plagued by boot storms (and similar problems) caused when networked access to storage becomes a major bottleneck, drastically delaying VM distribution and execution. Can we develop techniques that resolve this network bottleneck without the need for expensive hardware over-provisioning? Green Computing: Remote access technologies have enabled users to travel while still interacting with computational machinery left in the office or home. Yet, energy savings mechanisms have traditionally relied on the activity of attached peripherals to determine power usage. The shift to remote interaction, which bypasses physically attached peripherals, has effectively broken these energy savings mechanisms. Can we build an economic and practical system that accommodates energy efficiency without compromising the fluid remote interactions users have now come to expect? Wireless Computing: Increasingly advanced mobile devices have provoked a shift towards heavy usage of 3G and 4G bandwidth use. Accordingly, the capacity of infrastructure wireless networks becomes increasingly strained. Can we find a way of supplementing this relatively low-latency infrastructure with high-latency, high-bandwidth opportunistic content exchange? In each scenario, we design a solution that aims to strike the proper balance between adoptability and technical efficiency - producing what we believe are rigorous, practical and adoptable solutions.



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More About This Work

Academic Units
Computer Science
Thesis Advisors
Misra, Vishal
Ph.D., Columbia University
Published Here
August 29, 2011