Abstract <p>The paper is devoted to monitoring large-scale telecommunications infrastructures that form the foundation for the delivery of digital services and applications of various kinds, with an emphasis on backbone communication channels. A thorough and insightful analysis of state-of-the-art techniques based on a rich mathematical apparatus, network protocols, and specialized tools for monitoring and measuring industry-accepted quantitative metrics and assessing quality metrics is provided with examples of specific practices and software apparatus. The architectural features and sophisticated measurement techniques for deep inspection of the quality of global computer networks provided by the multi-component perfSONAR service are discussed in detail. General information about the service developed by the international community of information and telecommunications networks of research and education is given, covering its advanced network monitoring capabilities, the extent of its current global implementation, and a few instances of application in significant scientific projects and sustainable collaborations. Special attention is paid to the implementation and continuous operation of the perfSONAR toolkit in the National Research Computer Network of Russia (NIKS), which has increased the potential of the advanced network monitoring and management platform. The highlights of the collection, processing, and interactive visualization of data from regular tests conducted for key backbone communication channels of NIKS using specialized software packages are described and discussed.</p>