Every Spring Festival, hundreds of millions of people travel across China to reunite with family. Behind this massive movement lies not just the world's largest high-speed rail network, but also a powerful tool almost everyone carries in their pocket: 12306, the world's largest real-time ticketing system. (Produced by Huang Jingjing, Xie Runjia, Zhang Jian, Di Jingyuan and Chu Chu; Intern Shan Hanzhang also contributed to the video.)