The article presents the engineering and construction process for the deployment of a railway communications network in high-speed lines in Spain. The identification of needs and an optimal network engineering design are the basis for the first phase of the project. The development of an architecture of networking, which is service-oriented, and a strong knowledge in management, planning and coordination, are the basis of the phase of work and commissioning. The article is complemented by the description of the typical telecommunications infrastructure in this kind of lines, divided into a physical level, a level of network and a service level.