By means of so-called Scatternets, Bluetooth provides the ability to 
construct robust wireless multi-hop networks. In this paper we propose a 
practical protocol for time synchronization of such Bluetooth multi-hop 
networks. Our protocol makes use of the internal clock maintained by 
Bluetooth, requires minimal communication overhead, and provides an accuracy 
of few milliseconds across multiple hops. The protocol has been implemented 
and evaluated on BTnodes, an embedded computing platform which uses Bluetooth 
for ad hoc networking.