Travel code is the code of communication big data travel card, which is also equivalent to health code. China Institute of Information and Communication, together with China Telecom, China Mobile and China Unicom, used mobile phones to receive data, which was obtained through the location of the base station where the users' mobile phones were located, providing free inquiry service for the 654.38+06 billion mobile phone users nationwide. Mobile phone users can query all the city information they have been to before 654.38+04 days through this service. The itinerary code is traceable and can be used to decide whether you can be allowed to take the exam.