Section: 5.27.1.7 Support for PTP grandmaster function in 5GS
Content: The 5GS that is configured to operate as a time-aware system or Boundary Clock may support acting as a PTP grandmaster for a (g)PTP domain. The configuration of PTP instances in DS-TT and NW-TT for PTP grandmaster function is described in clause K.2. The following options may be supported (per DS-TT) for the 5GS to generate the Sync, Follow_Up and Announce messages for the Leader ports on the DS-TT: a) NW-TT generates the Sync, Follow_Up and Announce messages on behalf of DS-TT (e.g. if DS-TT does not support this). The NW-TT/UPF forwards the generated Sync, Follow_Up and Announce messages to the PDU session(s) related to the Leader ports on the DS-TT(s). The NW-TT timestamps the (g)PTP event message when the event message is sent to the PDU Session, and adds TSi corresponding to the timestamp to the Sync message and the OriginTimestamp corresponding to the timestamp to Sync message (if one-step operation is used) or PreciseOriginTimestamp corresponding to the timestamp to Follow_Up message (if two-step operation is used), and sets the cumulative rateRatio value with 1. The OriginTimestamp or PreciseOriginTimestamp shall be set by NW-TT/UPF to the 5GS internal clock. When DS-TT(s) receive the Sync, Follow_Up messages, it modifies the payload of the Sync, Follow_Up message as described for the PTP port in the egress TT in clause 5.27.1.2.2.2. b) DS-TT generates the Sync, Follow_Up and Announce messages in this DS-TT. The OriginTimestamp or PreciseOriginTimestamp shall be set by DS-TT to the 5GS internal clock. In both options, the NW-TT generates the Sync, Follow_Up and Announce messages for the Leader ports on the NW-TT.