White-Rabbit -> Synchronization
White Rabbit provides synchronization
- of sub-nanosecond accuracy
- of picoseconds precision
- among few thousands nodes
- over large distances (tens of kilometers)
White Rabbit synchronization is a combination of:
- Precision Time Protocol (PTP)
- Synchronous Ethernet (SyncE)
- Digital Dual-Mixer Time Difference (DDMTD) phase detection
White Rabbit synchronization method is
- defined as a Profile of the Precision Time Protocol
- compatible with the Precision Time Protocol and interoperable with standard PTP gear
- referred to as WR PTP
- described in White Rabbit Specification
Short description of WR PTP
The accuracy of the PTP synchronization is implementation-dependent. The standard is foreseen for sub-nanosecond accuracies. However, such performance is not achieved in typical PTP implementations. WR achieves sub-nanosecond accuracy by basing its time distribution on PTP standard and addressing the following issues limiting PTP’s performance:
- Limited precision and resolution of timestamps
- Unknown link asymmetry
- The quality of the PTP-syntonization depending on the exchange rate of PTP messages
- Synchronization fluctuation during switchover between redundant connections or network reconfiguration
In order to address these issues two further technologies are used and combined with PTP: SyncE and DDMTD phase detection. The combination enables for network-wide sub-nanosecond accuracy of synchronization but requires additional (to standard PTP) logic and data exchange. These add-ons are incorporated into PTP with WR extension, called WR PTP.