Enhancing interactive web applications in hybrid networks

Mobile Internet users have several options today including high bandwidth cellular data services such as 3G, that may be the choice for many. However, the ubiquity and low cost of WiFi suggests an attractive alternative, namely, opportunistic use of open WiFi access points (APs) or planned municipal mesh networks. Unfortunately, for vehicular users, the intermittent nature of WiFi connectivity makes it challenging to support popular interactive applications such as Web search and browsing. Our work is driven by two questions. 1) How can we enable system support for interactive web applications to tolerate disruptions in WiFi connectivity from mobile nodes? 2) Can opportunistic mobile-to-mobile (m2m) transfers enhance application performance over only using APs, and if so, under what conditions and by how much? We present Thedu, a system that enables access to Web search from moving vehicles. The key idea is to use aggressive prefetching to transform the interactive Web search application into a one-shot request/response process. We deployed a prototype of Thedu on the DieselNet testbed in Amherst, MA, consisting of transit buses averaging 21 on the road at a time. Our deployment results show that Thedu can deliver 4 times as many relevant web pages than not using Thedu. A bus receives relevant web pages with a mean delay of 2.3 minutes and within 0.55 minutes in areas with high AP density. Thedu augments AP connectivity with m2m transfers using a utility-driven DTN routing algorithm and uses caching to exploit query locality. Our analytic model and trace-driven simulations suggest that m2m routing yields little benefit over using APs alone even under moderately dense AP deployment such as in Amherst. With sparsely deployed APs as may be the case in rural areas, our conclusions are more mixed: m2m routing with caching improves the number of relevant responses delivered per bus by up to 58%, but the mean delay is significantly high at 6.7 minutes, calling into question its practicality for interactive applications.