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IEEE 1588 Technology
TTC's Network-based Data Acquisition Units (MnDAUs) use Ethernet as the communication medium for transport data, device configuration and performance query. This traffic can cause jitter and delay, due to switch latency, network load, etc., that affect synchronization of system-wide clocks and sequence of data to the recorder
The combination of jitter and delay with high-speed data transfer creates the potential for the introduction of significant error into data capture and post-hoc analysis. TTC prevents the consequences of network congestion in its high-speed avionics MnDAU networks by using the IEEE 1588 Precision Time Protocol (PTP). The advantages of IEEE 1588 PTP that are being proven in TTC's Fast Ethernet products will become even more significant at 1 Gbps data transfer rates. (see Gigabit Airborne Network Switch with IEEE-1588 Time)
The IEEE 1588 PTP synchronizes local clocks in network devices using the same Ethernet network that transports data. Synchronization has been proven within the sub-microsecond range. Furthermore, compared with other synchronization protocols, the 1588 PTP provides a more accurate synchronization with more efficient use of network resources.
Each MnDAU has an IEEE 1588 interface module equipped with a slave clock for time stamping data. Slave clocks are synchronized to the most accurate network clock, the grand master clock. Incoming data is time stamped as closely as possible to the physical layer, eliminating any impact of the protocol stack and operating system on the accuracy of the timestamp. Using an FPGA, a timestamp is applied at the MII bus before the MAC. This results in 15µsec timestamp accuracy for the PTP.
TTC also employs the IEEE 1588 boundary clock model for its network switch. The boundary clock serves as a master clock to synchronize all networked DAUs. However, it is programmed as a slave clock in communication with the grand master clock. The switch is also designed to be a grand master clock for the network, using a GPS receiver for the time source. This implementation results in network clock synchronization accurate to 300 nanoseconds.
In summary, using the IEEE 1588 Precision Time Protocol, TTC has maximized the precision of network time synchronization and minimized the effect of network jitter error on subsequent data analysis.