UTC time synchronization of clocks in wide-area networks in the low-nanosecond range is currently possible only through GNSS. End-user applications, however, often do not use the GNSS time signals themselves. Rather, GNSS is used as a time reference for NTP servers or PTPv2 Grandmasters, which distribute time to end users over (often local-area) telecommunication networks. Consequently, for many such network synchronization systems GNSS forms a single point of failure. This crucial dependence on GNSS can be mitigated, but this typically involves (expensive) point solutions which provide holdover only for limited periods of time, and which still may be vulnerable to GNSS system time errors or meaconing attacks.

In this paper we present an alternative time synchronization architecture which is entirely network-based, and can run independently from GNSS. At the core of this architecture is a wide-area time-synchronization network based on CERN’s White Rabbit (WR) protocol, implemented through so-called Timing Switches and long-haul WDM methods for low-cost fiber access. At each core site, Timing Switches feed the WR reference time-of-day (having MTIE with respect to the reference clock below 1 ns) to end users over local branches through either WR, PTPv2, NTP, or a combination of analog signals and GNSS time code. By connecting the WR Grandmaster timing switch to a UTC(k) time scale having dedicated satellite links to other UTC time scales, this time synchronization architecture can be made both independent of GNSS and traceable to UTC. Test results obtained with such a multiprotocol time synchronization architecture will be presented.