Network timing and synchronization used to be fairly straightforward. Basestations were connected using 2Mbps links synchronized to a central master clock. Expensive OCXO crystals costing several hundred dollars or more provided holdover times of many hours, allowing almost instant recovery after outages of hours or more. In many networks, a single technical designer might be responsible for the synchronization across the network on a part-time basis.
The enormous growth in mobile broadband data is leading to growing numbers of small cells, especially Metrocells, connected using IP/Ethernet backhaul. This, combined with the introduction of stricter timing requirements for LTE and LTE-Advanced, has some implications for the choice of wireless backhaul technologies used. Here, we explain the technology and discuss the alternatives.