The aim of this thesis is to analyze the current synchronization configuration of the Croatian Railways SDH network and to point out any deficiencies if noticed. A solution is presented for eliminating possible deficiencies. The thesis proposes guidelines for the synchronization configuration during the expansion of the SDH network with new devices in order to achieve higher network robustness, and to reduce the possibility that parts of the network stay unsynchronized. The STM frame structure and the mapping of the most frequent signals into the STM frame are explained at the beginning of this thesis. The elements of network synchronization and the distribution of the synchronization signal and SSM messages are also explained. After demonstrating the current configuration of the Croatian Railways SDH network, Chapter Six explains the methods for managing the network and current synchronization settings operation of the application for calculating the synchronization step. The analysis of the current synchronization settings was conducted by simulating cable breaks and failures in real conditions, without interrupting traffic. After the conducted analysis, Chapter Seven shows the solutions for eliminating the discovered problems, whilst the suggestions for the synchronization configuration after the predicted expansion of the Croatian Railways SDH network are shown in Chapter Eight. Every step of the analysis and every improvement suggestion are simulated in real conditions, and are also checked through simulation within an application. The suggestions for future expansions are simulated only through the application.