On the Scalability of Routing Integrated Time Synchronization

Reactive time synchronization is becoming increasingly popular in the realm of wireless sensor networks. Unlike proactive protocols, traditionally implemented as a standalone middleware service that provides a virtual global time to the application layer, reactive techniques establish a common reference time base post facto, i.e. after an event of interest has occurred. In this paper, we present the formal error analysis of a representative reactive technique, the Routing Integrated Time Synchronization protocol (RITS). We show that in the general case, the presence of clock skews cause RITS to scale poorly with the size of the network. Then we identify a special class of sensor network applications that are resilient to this scalability limit. For applications outside this class, we propose an in-network skew compensation strategy that makes RITS scale well with both network size and node density. We provide experimental results using a 45-node network of Berkeley MICA2 motes.