Any mobile telecommunications network requires syntonization among its various elements. The need to exploit the available radio spectrum efficiently and providing new kinds of services render frequency syntonization insufcient. Phase and time-of-day synchronization will be necessary in the future. Thus, network operators are searching for efficient and reliable synchronization architectures. In this article, an example of such an architecture, applicable to fifth generation mobile networks, is presented, based on the requirements published in the latest ITU-T Recommendations. For supervision of the performance of the synchronization network, the technology of optical time transfer (OTT) is proposed, which allows dissemination of an accurate timescale such as a UTC realization to selected nodes of a coherent network primary reference time clock. The OTT realized so far and its current and future role in the network of Deutsche Telekom are discussed, and representative measurement results are shown.

Funding: - European Union (EU), Horizon 2020, EMPIR, 18SIB06, TiFOON, Advanced time/frequency comparison and dissemination through optical telecommunication networks - European Union (EU), Horizon 2020, EMPIR Polish National Science Center grant 2017/26/M/ST7/00128, Joint distribution of optical carrier, time and RF frequency with stabilized fiber optic links