Master failures in the Precision Time Protocol

Abstract

If all clocks within a distributed system share the same notion of time, the application domain can gain several advantages. Among those is the possibility to implement real-time behavior, accurate time stamping, and event detection. However, with the wide spread application of clock synchronization another topic has to be taken into consideration: the fault tolerance. The well known clock synchronization protocol IEEE1588 (precision time protocol, PTP), is based on a master/slave principle, which has one severe disadvantage. This disadvantage is the fact that the failure of a master automatically requires the re-election of a new master. The start of a master election based on timeout and thus takes a certain time span during which the clocks are not synchronized and thus running freely. Moreover the usage of a new master also requires new delay measurements, which prolong the time of uncertainty as well. This paper analyzes the results of such a master failure and proposes democratic master groups instead of hot-stand-by masters to overcome this problem by. It is shown by means of simulation that the proposed solution will not deteriorate the accuracy of the slave clocks in case of a master failure.