TS), where PTP is used as a backup timing source to a local GNSS primary source. This backup is only meant to be used in the case of a local outage of GNSS and for a limited period (commonly 72 hours). Partial timing support (PTS) from the network, where PTP (carried over the transport network) is the primary source of synchronization, but elements in the network do not process PTP to re- duce the time error. From the scope of the recommendation: This Recommendation addresses the distribution of time and phase across a network, using the packet-based method with partial timing support to the protocol level from the network. In particular, it applies to the assisted partial timing support (APTS) and partial timing sup- port (PTS) architectures described in [ITU-T G.8275] and the precision time protocol (PTP) profile defined in [ITU-T G.8275.2]. Note that because the network defined here has only partial timing support, PTP must be carried by IP (either IPv4 or IPv6) and therefore is closely associated with the G.8275.2 telecom profile that uses PTP over IP (PTPoIP). It is this recommendation that covers three new PTP clock types: T-BC-P Telecom Boundary Clock with partial support T-TSC-A Telecom Time Slave Clock with assisted partial support T-TSC-P Telecom Time Slave Clock with partial support The -P clocks are boundary and slave clocks embedded in a network with PTP timing support avail- able only from a subset of the network elements. The T-TSC-A is a PTP slave clock assisted by a local time reference (normally a GNSS receiver) in the same partially aware topology. Figure 8-4 shows the topology of a network terminated in a T-TSC-A. Local time reference (such as GNSS) application T-TSC-A PRTC, Partial timing support (GNSS- packet network assisted) Figure 8-4 Network Terminating in a T-TSC-A Assisted Partial Slave Clock (Based on Figure of ITU-T Recommendation G.8271.2) This recommendation includes the following main topic and appendixes: Network limits at the various points in the network at A' and A through E A