ance is that, after implementation, you may find that "your mileage may vary." A number of other profiles are designed with the aim to rectify that situation. 7.5.1 Telecom Profiles There are three telecom profiles: G.8265.1: Telecom profile for frequency synchronization G.8275.1: Telecom profile for phase/time synchronization with full timing support from the network G.8275.2: Telecom profile for phase/time synchronization with partial timing support from the network The selection of the appropriate profile is based on the use case and network topology. Figure 7-13 gives an illustration of the different profiles. The first profile is for the distribution of frequency synchronization, SO it shows only the master clock receiving a frequency signal (from a PRC/PRS), while the phase/time profiles are shown receiving phase and time, as well as frequency, from a PRTC. IP unicast, IPv4 mandatory S=Slave, M=Master IPv6 allowed PTP processed only at each end, G.8265.1 telecom profile T-GM = Telecom Grandmaster PTP-aware network Ethernet T-BC Telecom multicast Boundary Clock T-TSC = Telecom Time Slave Clock PTP with full on-path timing support, G.8275.1 telecom profile T-BC-P = Telecom T-BC-P Boundary Clock- IPv4 unicast Partial IPv6 optional TSC-P PTP-unaware T-TSC-P = Telecom PTP-unaware Time Slave Clock- network network Partial PTP with partial timing support, G.8275.2 telecom profile Figure 7-13 The Three Telecom Profiles The first profile specifically disallows PTP assistance from the network (meaning it does not allow boundary or transparent clocks). The second profile mandates that every node must be a PTP clock (boundary or transparent), and the third profile allows PTP assistance where it is possible. Note how the bottom two phase/time profiles have a new set of names for their clocks, generally constructed by adding the word "Telecom" to the front of each IEEE 1588 term. These clock types are defined elsewhere in G.8275 and their features and performance are specified in the G.8273.x family of recommendationssee