 simultaneously at an acceptable level of timing accuracy. The lesson to take away is that you should not expect, unless you have confirmed otherwise, that putting PTP over a link enabled with MACsec will deliver accurate phase/time. There is not much point in buying a top-quality T-BC that performs at the level of Class C but then lose 200 ns of time accuracy in the MACsec implementation. 11.6 Summary This chapter outlined the factors to consider when deploying a timing solution to support 4G/LTE, LTE-A, and 5G mobile networks. The basic aspects to consider are the type of mobile technology being used, the topology and size of the network (including who provides the circuits), and the type and reach of the cell site. These elements will determine whether the radio system requires fre- quency synchronization only or phase/time/frequency synchronization and will indicate the best ap- proach to constructing the timing solution. The design of the timing solution will likely incorporate a combination of GNSS and atomic clocks as a source of time, together with a transport network carrying the timing signal using packet and/or physical timing signals. The details of the design in any one segment of the network requires know- ledge of the local factors such as the type and characteristics of the transport system and the ability of the network and nodes to support timing-aware features-such as whether the network elements support being a PTP T-BC. The evolution of the RAN is a special case, especially where the operator has adopted the central- ized CRAN architecture and has introduced technology splits in the radio processing stack-con- nected by an FH (and possibly MH) network. This introduces a need for much higher accuracy phase alignment, although within clusters of cell sites coordinating with each other-known as rel- ative phase alignment. One vital consideration is the ability of the timing solution to survive any possible events that could lead to disruption of the timing signal, either from space or within the