| On-demand delivery of audio and video clips in a vehicular network is a growing area of interest. A given repository of such data items, each with an associated popularity, may be available to the passengers of the vehicles. The vehicles themselves are equipped with a 'TiVO' like device that has several gigabytes of storage and a wireless interface allowing short range communication at 10s to 100s of Megabits per second. The goal is to minimize the latency between request issuance and the time till a copy of the requested item is encountered. This latency is termed the availability latency. This thesis explores two generic tools to alleviate availability latency: (a) data replication (b) data delivery scheduling.; With the replication study, we propose a general optimization formulation that seeks to minimize average availability latency subject to a storage constraint per vehicle. We explore the effects of a family of popularity-based replication schemes on availability latency. When the vehicles follow a 2D random walk based mobility model, via analysis and extensive simulations, we determine the optimal replication scheme that minimizes latency across a wide parameter space with major dimensions being data item size and client trip duration.; Once an appropriate static replication scheme has allocated replicas, the vehicles themselves may be employed as data carriers to further improve availability latency. These data carriers are termed zebroids. However, a zebroid's local storage may be completely exhausted. Hence, to accommodate this new data item, it may need to evict an existing one. Various replacement policies such as LFU, LRU, random etc. are examined and their relative performance is studied. Via analysis and extensive simulations we study the behavior of zebroids as a function of large parameter space comprising data item repository size, storage per vehicle, number of vehicles, popularity distribution of the data items, different replacement schemes for zebroids etc.; We validate the Markov model based observations with two independent validation phases employing (a) freeway traffic information on a city map (b) real world traces from a small bus network. |
