National Infrastructure for Clock Network Services: CITAF

National time and frequency dissemination networks are being developed in many countries; also international connections are being established. In the contribution we present Czech Infrastructure for Time and Frequency as a noncommercial, open activity focused on the transfer of accurate time and very stable frequency using optical networks. The national optical infrastructure for time and frequency transfer is operated on top of the CESNET network infrastructure, to have operational cost under control. We also address actually running and planned upgrades and future development plans regarding wavelength bands and considered geographic extensions. We will also focus on creation of bidirectional dark channels on different wavebands within shared fibers together with bidirectional compensation of fiber losses. Single path bidirectional amplification utilizing lumped optical amplifiers is sensitive to feedback from fiber line like back scattering and reflections and in case of increased feedback can produce unwanted oscillations, which potentially interfere with parallel data transmissions. We will also briefly mention the CLONETS-DS project working on design study for coherent Pan-European time and frequency dissemination network, which would connect national networks and provide different services based on time and frequency for a wide range of users.