  Traditionally, Bluetooth has been deemed unsuitable for sustaining a
large-scale multi-hop network. There are two main reasons: severe frequency
channel collisions under a large-scale network and high complexity of designing
an efficient formation protocol. In this work, we reconsider this viewpoint
from a practical usability perspective and aim to realize the buried potential
of Bluetooth. Firstly, we find that the collision probability under a
low-overhead network is fairly small, which is acceptable for practical
applications. Secondly, we propose BlueSky, a complete system solution to
provide necessary networking functionalities for Bluetooth. In BlueSky, we
develop a connection maintenance mechanism for mitigating the influence of
collisions and a network formation protocol for reliable packet transmissions.
We implement BlueSky on Windows Mobile using 100 commercial smartphones.
Comprehensive usability evaluations demonstrate the negligible overheads of
BlueSky and its good network performance. In particular, 90%-95% of the whole
100 nodes can participate in the communication smoothly.
