Synchronization of Digital Telecommunications Networks

PREFACE

Network synchronization has gained increasing importance in telecommunications throughout the last 30 years, especially since transmission and switching turned digital. Infact, the quality of most services offered by network operators to their customers is affected by network synchronization performance.

Digital switching equipment requires synchronization in order to avoid slips at input elastic stores. Plain telephone conversations are not affected very much by synchronization slips, but circuit switched data services are affected significantly. Therefore, the deployment of circuit-switched data networks and of ISDN brought about the need for more stringent synchronization requirements.

Network synchronization became a thorny matter for telecommunications operators with the deployment of SDH (Synchronous Digital Hierarchy)/SONET networks, which pose new and more complex requirements on the stability of synchronization systems.

More recently, it has been also recognized that the importance of network synchronization goes way farther than SDH/SONET needs. ATM (Asynchronous Transfer Mode) and cellular mobile telephone networks such as GSM (Global System for Mobility), GPRS (Global Packet Radio Services), UMTS (Universal Mobile Telecommunications Services) are striking examples where the availability of network synchronization references has been proven to affect the quality of service.

Network synchronization addresses any distribution of time and frequency over a network ...