ter ordinary clock with a single mas- ter-only port with characteristics from G.8272. Telecom Grandmaster (T-GM): Another grandmaster with the same characteristics, but it has multiple (master only) ports. Because of 1588-2008 rules, any clock with more than one port is a boundary clock, SO according to that rule, this device is a 1588-2008 boundary clock acting as an (ordinary clock) T-GM. Telecom Boundary Clock (T-BC): A boundary clock that can be a master or a slave to another GM with performance characteristics from G.8273.2. Telecom Transparent Clock (T-TC): An E2E TC as defined in 1588-2008 and with perform- ance characteristics in G.8273.3. Telecom Time Slave Clock (T-TSC): An ordinary slave clock with performance characteristics as defined in G.8273.2. The main features of this profile are as follows: Domain number should be within a range of 24-43 with a default value of 24. Multicast Ethernet (Annex F of 1588-2008) is used to transport the PTP messages. Both the non-forwardable multicast address 01-80-C2-00-00-0E and the forwardable multicast address 01-1B-19-00-00-00 are supported. As outlined in Annex H of this profile, PTP can also be car- ried by the optical transport network (OTN). VLAN tagging is expressly forbidden and SO there is no class of service (CoS) as there is no VLAN header to carry it, although there are some exceptions for T-TCs. Further information on QoS mechanisms are contained in the Chapter 9. Message rates for Sync, Delay_Req, and Delay_Resp are fixed at 16 messages per second, while the message rate for Announce is also fixed at 8 per second. There is no negotiation for timing service; the messages are constantly sent to whichever of the two multicast addresses is configured. Defines an alternate BCMA (aBMCA), allowing PTP ports to be dynamically switched between master and slave states, which enables the profile to support automatic configuration. This mechanism allows the aBMCA to establish an efficient PTP hierarchy based on the Announce messages, discovering the shortest pat