5.27.1.3 Support for multiple (g)PTP domains

This clause describes support for multiple domains for gPTP and PTP and for GM clocks connected to DS-TT and NW-TT and only applies if DS-TT and NW-TT support the related functionality. PTP support and support of gPTP for GM clocks connected to DS-TT by DS-TT and NW-TT may be determined as described in clause K.2.1.

Each (g)PTP domain sends its own (g)PTP messages. The (g)PTP message carries a specific PTP "domainNumber" that indicates the time domain they are referring to. The PTP port in ingress TT makes ingress timestamping (TSi) using 5G internal system clock for the (g)PTP event messages of all domains and forwards the (g)PTP messages of all domains to the UPF/NW-TT that further distributes the (g)PTP messages to the egress TTs as specified in clause 5.27.1.2.2.

The PTP port in the egress TT receives the original PTP GM clock timing information and the corresponding TSi via (g)PTP messages for one or more (g)PTP domains. The PTP port in the egress TT then makes egress timestamping (TSe) using 5G internal system clock for the (g)PTP event messages for every (g)PTP domain. Ingress and egress time stamping are based on the 5G internal system clock at NW-TT and DS-TT.

NOTE 1: An end-station can select PTP timing information of interest based on the "domainNumber" in the (g)PTP message.

The process described in clause 5.27.1.2.2 is thus repeated for each (g)PTP domain between a DS-TT and the NW-TT it is connected to.

NOTE 2: If all (g)PTP domains can be made synchronous and the synchronization can be provided by the 5G internal system clock, the NW-TT or DS-TT(s) generates the (g)PTP event messages of all domains using 5G clock as described in clause 5.27.1.7.

NOTE 3: This Release of the specification supports multiple gPTP domains as defined in IEEE Std 802.1AS [104]. If a 5GS TSN bridge supports stream gates and/or transmission gates as defined in IEEE Std 802.1Q [98], then they operate based on a single given gPTP domain.