Synchronization techniques in backhauling networks

Synchronization in transport networks was a hot topic for telecom in early 90´s with the advent of SDH, replacing PDH. When packet networks and the Internet began to spread, it subsided for some years, until mobile technologies evolved from TDM (2G) to packets (3G, 4G). Nowadays the transport of frequency and time over transport networks is one of the most debated topics both in the industry and within international standard bodies, presenting several challenging aspects that even tend to multiply as new technologies not originally thought to carry synchronization are used for mobile backhauling, ranging from packets (L2 and L3), to TDM and WDM (OTN, CPRI). In this paper we analyse from a technical and economical point of view common problems and solutions related to the transport of frequency and time across several types of TDM and packet networks, summarizing latest research results, open issues and possible directions for evolution.