What is the third-party recruitment of high-speed rail?

Human resources company. High-speed rail recruitment is not re-recruited by the General Administration of Railways, but entrusted to a third-party railway company. The person recruited belongs to a third party, that is to say, the flight attendants recruited do not belong to the railway head office, but belong to the human resources company. Third-party railways have contracts with railway companies to recruit them. His full name is Railway Travel Service Company. But he is not a regular railway worker. He is an independent private company. Mainly for some work of railway group company.