Synchronization of ad hoc Clock Networks (1506.07584v1)

Abstract: We introduce a graph-theoretic approach to synchronizing clocks in an {\em ad hoc} network of $N$~timepieces. Clocks naturally drift away from being synchronized because of many physical factors. The manual way of clock synchronization suffers from an inherrent propagation of the so called "clock drift" due to "word-of-mouth effect." The current standard way of automated clock synchronization is either via radio band transmission of the global clock or via the software-based Network Time Protocol (NTP). Synchronization via radio band transmission suffers from the wave transmission delay, while the client-server-based NTP does not scale to increased number of clients as well as to unforeseen server overload conditions (e.g., flash crowd and time-of-day effects). Further, the trivial running time of NTP for synchronizing an $N$-node network, where each node is a clock and the NTP server follows a single-port communication model, is~$\bigO(N)$. We introduce in this paper a $\bigO(\log N)$ time for synchronizing the clocks in exchange for an increase of $\bigO(N)$ in space complexity, though through creative "tweaking," we later reduced the space requirement to~$\bigO(1)$. Our graph-theoretic protocol assumes that the network is $\K_N$, while the subset of clocks are in an embedded circulant graph $\C_{n<N}^q$ with $q$~jumps and clock information is communicated through circular shifts within the $\C_{n<N}^q$. All $N$~nodes communicate via a single-port duplex channel model. Theoretically, this synchronization protocol allows for $N(\log N)^{-1} - 1$ more synchronizations than the client-server-based one. Empirically through statistically replicated multi-agent-based microsimulation runs, our protocol allows at most 80\% of the clocks synchronized compared to the current protocol which only allows up to 30\% after some steady-state time.