Mobile Backhaul

6.8 Conclusions

Switching from TDM to packet networks has required significant research, development, and standardization activity within the area of synchronization. A second burst of activity has been caused by the definition of new time synchronized cellular technologies that are expected to be widely adopted.

In the case of frequency synchronization there are two choices. In the case of no on-path support there is a choice between Synchronous Ethernet and packet based technologies such as PTP. Synchronous Ethernet can provide high-quality synchronization regardless of network load. One of the drawbacks is the need for full on-path support, which might not be available for a long time from some leased line operators. Another problem is associated with 1-Gbit/s and 10-Gbit/s copper Ethernet links that cannot change the direction of synchronization for protection switching purposes in a reasonable time. PTP can, in principle, be used from day one in all packet networks, because it does not need on-path support. There are some risks though because large load variations combined with a high number of hops may lead to performance limits being exceeded. In terms of deployments over the first two years PTP has been very reliable though.

Time synchronization has been for a long time a requirement in CDMA networks. LTE and the increasing number of small cells will explode the number of time synchronized base stations in several years, increasing the need for network based synchronization. ...