s of how each hop contributes to the total phase error are clearly described in ITU-T G.8271.1. A partial timing support is a cheaper solution because of not all network elements need to support the boundary clock. However, it is indeed not straightforward to design a network with partial timing support: for example, what is the maximum number of hops we can have in the chain without the boundary clock? ITU-T G.8271.2 defines a metric called "pktSelected2wayTE" to measure the phase error of the partial timing support network and help the operator design their network. However, to measure this metric, the operator will require quite detailed analysis of the end-to-end delay in both the uplink and downlink directions of the transmission network and hence a good level of competency is required. This task can be accomplished with dedicated equipment 8 Deployment Aspects which provides the pktSelected2wayTH measurement; however, the equipment is con- sidered quite expensive, and its correct handling will require some technical knowledge. It is also important to note that the design may need to be done more than once, for example, due to transmission network changes or traffic profile changes. For these reasons, it is recommended to deploy full on-path support if possible. It will greatly help the operator to ease the deployment and operational effort. It is important to note that there would, of course, be the case where partial timing support may be unavoidable, for example, a leased line transmission network. Third, to ensure full interoperability of all network elements and to meet the designed limit provided by ITU-T G.8271.1/ITU-T G.8271.2, the operator should respectively use equipment and configurations that are compliant with ITU-T G.8275.1/ITU-T G.8275.2. Finally, the operator needs to ensure that the required accuracy can be achieved and maintained. There could still be a number of problems that could happen in the ToP with phase synchronization solution that operators need to be aware of: IEEE1588-2008 work