Directed diffusion: a scalable and robust communication paradigm for sensor networks
MobiCom '00 Proceedings of the 6th annual international conference on Mobile computing and networking
Time, clocks, and the ordering of events in a distributed system
Communications of the ACM
Time synchronization in ad hoc networks
MobiHoc '01 Proceedings of the 2nd ACM international symposium on Mobile ad hoc networking & computing
Wireless sensor networks: a new regime for time synchronization
ACM SIGCOMM Computer Communication Review
Habitat monitoring: application driver for wireless communications technology
ACM SIGCOMM Computer Communication Review - Workshop on data communication in Latin America and the Caribbean
Timing-sync protocol for sensor networks
Proceedings of the 1st international conference on Embedded networked sensor systems
Fine-grained network time synchronization using reference broadcasts
OSDI '02 Proceedings of the 5th symposium on Operating systems design and implementationCopyright restrictions prevent ACM from being able to make the PDFs for this conference available for downloading
Proceedings of the 3rd international conference on Embedded networked sensor systems
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To infer correctly application semantics, sensor network applications often need accurate times on observations that are reported from distributed sensor nodes. Since the nodes' local clocks can go out-of-sync due to clock drifts, a networked time synchronization protocol is needed to synchronize their clocks to a reference clock. This paper provides performance modeling and comparison between two time synchronization protocols: TPSN clock synchronization (clock-sync) and TSS event synchronization (event-sync). Their main difference is that the TPSN clock-sync synchronizes all nodes' local clocks to a global reference clock, whereas TSS event-sync synchronizes events' generation times from different local nodes to their sink nodes' clocks. Although these two time synchronization protocols have their respective limitations in application scenarios, they are comparable in that they also share a large domain with none of these limitations. This paper evaluates these two protocols by considering different ad-hoc network sizes, node mobility levels, and traffic volumes. In order to fully understand the tradeoffs between these two time synchronization protocols, we have derived analytical models on their performances and conducted simulations to measure the impact of these variables. Both the simulation results and analytical models show that (1) event-sync provides much better accuracy than clock-sync, (2) under very high node mobility level, clock-sync may achieve better accuracy than event-sync, and (3) under increasing traffic volume clock-sync scales better.