A packet-based precise timing and synchronous DAQ network for the LHAASO project

Aiming to high sensitivity and wide spectrum of cosmic ray detection, the Large High Altitude Air Shower Observatory (LHAASO) project consists of over 10,000 detectors of different types, spreading over 1.2 km2. To precisely reconstruct the air shower events with high angular resolution, all detector electronics and digitizers should work in synchronous acquisition mode with a global timing error less than < 5 ns (rms). This large scale and high precision timing requirement exceeds the capability or feasibility of traditional methods such as GPS and echo-delay calibration. Recently an emerging method named White Rabbit (WR) was proposed and demonstrated as a cost-effective solution that combines Gigabit Ethernet data transfer and subnanosecond precision timing transfer over the same fiber media. Furthermore, the White Rabbit network also enables direct digitization and trigger-less data acquisition mode for each detector, which will greatly reduce the complexity and improve the performance of the data acquisition (DAQ) system. In this paper we will demonstrate the design and development status of a WR timing and DAQ network in the LHAASO project.