Modeling and Comparison of Two Time Synchronization Protocols

• Main Authors: Jr-Ben Tian, 田知本
• Other Authors: Hao-Hua Chu
• Format: Others
• Language: en_US
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/39756769418677741853

碩士 === 國立臺灣大學 === 資訊工程學研究所 === 94 === 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 and real experiments to measure the impact of these variables. The experimental results, simulation results, and analytical models all 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. A selection guideline is derived showing how to choose the optimal class of time synchronization protocols under different sensor network dynamics, traffic dynamics, and application requirements.