s based on the assumption that the network is symmetric; that is, the uplink constant delay and downlink constant delay must be the same. The operator needs to ensure that if asymmetric transport equipment like a microwave radio or Gigabit Passive Optical Network (GPON) is used, they must be equipped with the boundary clock solution to solve the asymmetry issue. Even if we are using symmetric transmission technology like fiber in IP routing, asym- metry could be caused by different fiber lengths in the uplink and downlink directions. This could happen because normally two fibers are required for the uplink and down- link directions. The operator needs to ensure that such "constant" asymmetry will be properly measured and compensated in the boundary clock or slave. The operator should avoid fully utilizing the transmission interface as a congested interface will cause additional queueing time in the transmission equipment, and that could impact the synchronization accuracy. It is recommended to dimension the interface such that less than 80% of the interface capacity will be used for all traffic. The operator should properly plan the backup transmission route to be ready to sup- port ToP with phase synchronization as well SO that the synchronization will not be impacted when transmission re-routing takes place. It is highly recommended to check the synchronization accuracy at the slave. This can be easily done by connecting the BTS with both the GNSS receiver and ToP with phase synchronization. It is important to note that 5G is still in the early phase, and the phase sync require- ments may change, for example, when more advanced features are introduced. In that case, the existing ToP with phase synchronization transmission network planned for the +1.5 us phase error budget may need to be re-planned. 8.7.10 Timing Alignment Between Vendors Even though each vendor can use the same source of timing, the processing delays between equipment may differ, and it is necessary to align the timing for each carrier on the s