Opportunistic networks exploit human mobility and consequent
device-to-device ad hoc contacts to disseminate content in a
"store-carry-forward" fashion. In opportunistic networks,
disconnections and highly variable delays caused by human mobility are
the norm. Another major challenge in opportunistic communications
arises from the small form factor of mobile devices which introduces
resource limitations compared to static computing systems. Lastly,
human mobility and social interactions have a large impact on the
structure and performance of opportunistic networks, hence,
understanding these phenomena is crucial for the design of efficient
algorithms and applications.
In this work, we take an experimental approach to better understand
opportunistic mobile social networks. We design and implement of
MobiClique, a communication middleware for opportunistic mobile social
networking. MobiClique takes advantage of user mobility and social
relationships to forward messages in an opportunistic manner. We
perform a large-scale MobiClique experiment with 76 people, where we
collect social network information (i.e. their Facebook profiles), and
ad hoc contact and communication traces. We use the collected data
with three other data sets to analyse in detail the time-varying
structure and epidemic content dissemination in opportunistic
networks. Most of the related works have focused on the pairwise
contact history among users in conference or campus environments. We
claim that given the density of these networks, this approach leads to
a biased understanding of the content dissemination process. We design
a methodology to break the contact traces down into "temporal
communities", i.e., groups of people who meet periodically during an
experiment. We show that these communities correlate with people's
social communities. As in previous works, we observe that efficient
content dissemination is mostly due to high contact rate users.
However, we show that high contact rate users that are more frequently
involved in temporal communities contribute less to the dissemination
process, leading us to conjecture that social communities tend to
limit the efficiency of content dissemination in opportunistic mobile
social networks.