Data or index: a trade-off in mobile delay tolerant networks

Acquiring content through mobile networks is a basic and general topic. Mobile nodes have two different ways of obtaining data. The first method is to download data quickly through 3G/4G networks, which is expensive. The second way is to get data from other nodes by means of delay tolerant networks (DTN), which are much cheaper, but are time-consuming. Throwboxes deployed in DTN act as fixed ferry nodes. The index records the historical encounter information, in order to give the mobile nodes predictive abilities regarding future encounter events. We try to compare the effectiveness when we replace some space for the data to index. We bring forward an index-based buffer space management mechanism for throwboxes, by which mobile nodes can have the chance to fetch data at a lower total cost. Preliminary simulations demonstrate that the buffer space allocation strategy is affected by some system parameters, and that replacing some space for data with an index can lower the system total cost significantly in most cases. Simulation results also show that the index-based buffer space management mechanism outperforms other mechanisms which only store data items or hold an index of static size.