Abstract :- :-
Pocket Switched Networks take advantage of social contacts to
opportunistically create data paths over time. This work employs empirical
traces to examine the effect of the human contact process on data delivery in
such networks. The contact occurrence distribution is found to be highly
uneven: contacts between a few node pairs occur too frequently, leading to
inadequate mixing in the network, while the majority of contacts occur rarely,
but are essential for global connectivity. This distribution of contacts leads
to a significant variation in the fraction of node pairs that can be connected
over time windows of similar duration.
Good time windows tend to have a large
clique of nodes that can all reach each other. It is shown that the clustering
coefficient of the contact graph over a time window is a good predictor of
achievable connectivity. We then examine all successful paths found by flooding
and show that though delivery times vary widely, randomly sampling a small
number of paths between each source and destination is sufficient to yield a
delivery time distribution close to that of flooding over all paths. This
result suggests that the rate at which the network can deliver data is
remarkably robust to path failures.
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