A postal system based digital network and a distance learning application.

다국어 초록 (Multilingual Abstract)

In this thesis, we propose the novel approach of turning storage media transported by the postal system into a general-purpose and transparent digital network, extending pervasive, high-bandwidth, and low-cost connectivity to places such as rural areas in developing countries. We call such a system the Postmanet. To fully realize its potential, however, an end user needs better support than being told to burn discs and toss them into the mail bin. We describe the systems support that we provide in order to achieve the generality, transparency, efficiency, and scalability goals of the system. The issues that we address include: managing "DVD robots" that automate mass-processing of DVDs, application-specific marshaling and unmarshaling of messages, providing best-effort reliable and secure delivery, simultaneous exploitation of conventional connectivity, and a mechanism for distributing and updating application code. Two additional support features are of particular importance.
The first is a distributed object repository that makes available a single name space, on which any sites, including those that lack conventional networking access, can perform read, write, navigation, search, and other operations. This high-level abstraction makes it easier to construct distributed Postmanet applications. It also helps us realize a powerful "network effect," as spontaneous connections are established among sites that enjoy shared access to a common repository. The second is scalable routing. Simply leaving end users to directly swap discs with each other does not scale well, because as many as N2 discs may need to be exchanged at once in an N-node network. We solve this problem by multiplexing/de-multiplexing data to/from a smaller number of discs in transit. This can occur multiple times at dedicated nodes inside the network, or at peer end user nodes. We present routing topologies that can result in a good balance between simultaneously minimizing the number of discs involved and the end-to-end postal latency.
We have built and deployed a real-world application, a rural distance learning system called the Digital StudyHall, on top of the Postmanet . It consists of a network of hubs and spokes, where the hubs are urban centers of excellence, which "radiate" content and methodology into poor villages and slum schools. Our experiences in rural India not only have provided us insights on the type of the systems support that we need, but also have allowed us to study mediation-based pedagogy that has proved promising in extending high-quality education to a needy population. For more information, please visit: http://dsh.cs.washington.edu.