ty. 8.7 Network Synchronization and Coordination Requirements Figure 8.25 ToP with phase Boundary clock synchronization solution. on path support grandmaster ITU-T defines the following two sets of telecom standards to be used for full on-path support and partial on-path support, respectively: ITU-T G.8271.1: Network limits for time synchronization in a packet network with full timing support from the network [11] ITU-T G.8275.1: Telecom profile for phase synchronization with full on-path support ITU-T G.8271.2: Network limits for time synchronization in a packet network with partial timing support from the network [13] ITU-T G.8275.2: Telecom profile for phase synchronization with partial on-path sup- port [14] The first thing that the operator must know is the phase synchronization accuracy requirement of the end application. Only then can the operator start detailed planning of the solution and decide which solution can be used. In TD-LTE, the phase sync require- ment is -1.5 us. The ITU-T has correspondingly designed ITU-T G.8271.1 and ITU-T G.8271.2 to meet +1.5 us requirement at the end application. ITU-T G.8271.1 designs, for example, the maximum number of boundary clocks that can be supported between the grandmaster and slave to meet the +1.5 us requirement. The operator can therefore easily follow this network limit definition to roll out the TD-LTE network. Fortunately, the 5G phase synchronization requirement is the same as for TD-LTE, that is, + 1.5 us, and hence both ITU-T G.8271.1 and ITU-T G.8271.2 can be fully reused for 5G. Second, the operator needs to decide if it will provide full on-path support or partial on-path support. Full on-path support provides a more reliable, more accurate phase synchronization solution but comes at probably higher cost of deployment, as every transmission hops must support the boundary clock/transparent clock. It may also be easier to deploy this solution as the accuracy achievable at the slave (BTS) can be con- cretely estimated from the number of hops. The detail