This article describes time distribution in a White Rabbit Network. We start by presenting a short overview of the White Rabbit project explaining its requirements to highlight the importance of the timing aspects of the system. We then introduce the technologies used to achieve high clock accuracy, stability and resilience in all the components of the network. In particular, the choice of the IEEE 1588-2008 (PTP) and Synchronous Ethernet standards are explained. In order to accommodate hardwaresupported mechanisms to increase PTP synchronization accuracy, we introduce the White Rabbit extension to PTP (WRPTP). The hardware used to support WRPTP is presented. Measured results of WRPTP performance demonstrate sub-nanosecond accuracy over a 5km fiber optic link with a precision below 10ps and a reduced PTP-message exchange rate. Tests of the implementation show full compatibility with existing PTP gear.

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During May 2012, the CERN-CNGS neutrino beam has been operated for two weeks for a total of ∼ 1.8 × 10 17 p.o.t., with the proton beam made of bunches, few ns wide and separated by 100 ns. This beam structure allows a very accurate time of flight measurement of neutrinos from CERN to LNGS on an event-by-event basis.Both the ICARUS-T600 PMT-DAQ and the CERN-LNGS timing synchronization have been substantially improved for this campaign, taking advantage of additional independent GPS receivers, both at CERN and LNGS as well as of the deployment of the "White Rabbit" protocol both at CERN and LNGS.The ICARUS-T600 detector has collected 25 beam-associated events; the corresponding time of flight has been accurately evaluated, using all different time synchronization paths.The measured neutrino time of flight is compatible with the arrival of all events with speed equivalent to the one of light: the difference between the expected value based on the speed of light and the measured value is δt = tof c −tof ν = 0.10±0.67 stat. ±2.39 syst. ns. This result is in agreement with the value previously reported by the ICARUS Collaboration, δt = 0.3 ± 4.9 stat. ± 9.0 syst. ns, but with improved statistical and systematic accuracy.

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