Enhanced Synchronization Accuracy in IEEE1588

Various applications require or can benefit from high accuracy of synchronization between networked elements. The White Rabbit (WR) project includes enhancements to the now widespread IEEE1588 Precision Time Protocol (PTP) to support supplying synchronization in the sub-nanosecond level. The WR solutions for achieving enhanced accuracy of synchronization are being studied and analyzed within the work of the High Accuracy sub-committee (SC) of the P1588 Working Group (WG). The work of the High Accuracy SC aims at adding optional protocol features for supporting WR enhancements, and their possible generalizations. The sub-ns accuracy of synchronization achieved in WR can be attributed to mechanisms and methodologies that enhance PTP in two aspects: (1) identification of various contributors of asymmetries in the PTP two-way time transfer, and definition of measurements and calibrations to compensate for their effects, and (2) achieving higher precision in the timestamping of PTP event messages which results in precise roundtrip measurement and precise determination of the offset between master and slave clocks. We first outline the contributions of the above-mentioned aspects to achieving a high accuracy PTP network. We then analyze and formulate in detail the utilization of the Layer-1 (L1) signals for the second aspect. These L1 signals, that are available within the PTP link, are used to enhance synchronization accuracy in general and in particular the timestamping precision. We specify the conditions under which enhanced accuracy is achieved in WR and suggest various possible generalizations.