 distribution with full timing support from the network. It provides the necessary details to utilize IEEE 1588 in a manner consistent with the architecture described in Recommendation ITU-T G.8275. The parameters defined in this version of the profile are chosen based on the case where physical layer frequency support is provided, and the case without physical layer frequency support (i.e., PTP only) is for further study. The profile is the final piece that completes the puzzle, as it is the protocol implementation that de- livers the solution outlined in the architecture and network topology recommendations. G.8275.1 is the recommended profile to deploy phase timing in a transport network for best-in-class perform- ance. It requires full timing support from the network (which may be difficult for some operators who do not own their own transport links), but it will deliver to expectations. This recommendation includes the following main topics, annexes, and appendixes: Details on the use of PTP for phase/time distribution, including selection of some PTP options available in IEEE 1588-2008. This includes the PTP mapping (Ethernet multicast), message types, BMCA, and which types of clocks are supported. Annex A, "ITU-T P profile for phase/time distribution with full timing support from the net- work." This annex contains the main details such as allowed values for datasets, TLVs, flag val- ues, and SO on. Annex B, "Options to establish the PTP topology using the Alternate BMCA" (moved to G.8275 along with Annex C, Annex E, and Appendix V). Annex H, "Transport of PTP over OTN." Appendix III, "Considerations on the choice of the PTP Ethernet multicast destination address." Discusses the issues around the choice of MAC address for the multicast traffic (normally con- figurable in the clock). Appendix V, "Description of PTP clock modes and associated contents of Announce messages" (moved to G.8275). Appendix VII, "Relationship between clockClass and holdover specification." Section 6.2.7 has a special note on the us