Section: 4.15.3 Time synchronization
Content: Two types of synchronization processes are supported by the 5GS: 5GS synchronization and (g)PTP domain synchronization (see 3GPP TS 23.501[ System architecture for the 5G System (5GS) ]  [8]). For 5GS synchronization, the lower layers provide the 5G internal system clock signalled via the NG-RAN (see 3GPP TS 38.331[ NR; Radio Resource Control (RRC); Protocol specification ]  [30]) and the UE forwards the 5G internal system clock to the DS-TT(s). For (g)PTP domain synchronization, the UE supports forwarding (g)PTP messages (see 3GPP TS 23.501[ System architecture for the 5G System (5GS) ]  [8], 3GPP TS 23.502[ Procedures for the 5G System (5GS) ]  [9], and 3GPP TS 24.535[ 5G System (5GS); Device-Side Time Sensitive Networking (TSN) Translator (DS-TT) to Network-Side TSN Translator (NW-TT) protocol aspects; Stage 3 ]  [19A]). For all (g)PTP domains associated with a PDU session: a) if the UE receives (g)PTP message via the PDU session, the UE forwards the (g)PTP messages to the DS-TT associated with the PDU session; or b) if the UE receives (g)PTP messages from the DS-TT associated with the PDU session, the UE forwards the (g)PTP messages via the PDU session. Depending on the 5G access stratum-based time distribution or (g)PTP-based time distribution, the network timing synchronization status of the nodes involved in the operation (e.g., NG-RAN nodes, NW-TTs) may change. Using the 5GMM protocol, the network can request a supporting UE to reconnect to the network upon receiving an indication of a change in the RAN timing synchronization status.