Section: 5.27.1.4 DS-TT and NW-TT Time Synchronization functionality
Content: This clause describes the support of Time Synchronization functionality supported by the 5G System. Synchronization between UPF/NW-TT and NG-RAN is outside scope of 3GPP. DS-TT and NW-TT may support the following PTP instance types: - Boundary Clock as defined in IEEE Std 1588 [126] as described in clause 5.27.1.1; - End-to-End Transparent Clock as defined in IEEE Std 1588 [126] as described in clause 5.27.1.1; - Peer-to-Peer Transparent Clock as defined in IEEE Std 1588 [126] as described in clause 5.27.1.1; - PTP Relay instance as defined in IEEE Std 802.1AS [104]. Editor's note: Support for external networks operating with IEEE Std 1588-2008 [107] is for further study. DS-TT and NW-TT may support the following transports for PTP: - IPv4 as defined in IEEE Std 1588 [126] Annex C; - IPv6 as defined in IEEE Std 1588 [126] Annex D; IEEE Std 802.3 [131] (Ethernet) as defined in IEEE Std 1588 [126] Annex E. For operation as a Boundary clock or as a Transparent Clock, DS-TT and NW-TT may support the following path and link delay measurement methods: - Delay request-response mechanism as described in clause 11.3 of IEEE Std 1588 [126]; - Peer-to-peer delay mechanism as defined in clause 11.4 of IEEE Std 1588 [126]. DS-TT and NW-TT may support acting as a PTP grandmaster, i.e. may support generating (g)PTP Announce, Sync and Follow_Up messages. DS-TT and NW-TT supporting (g)PTP shall support one or more PTP profiles as described in clause 20.3 of IEEE Std 1588 [126], i.e.: - Default PTP Profiles in IEEE Std 1588 [126], Annex I; - IEEE Std 802.1AS [104] PTP profile for transport of timing as defined in IEEE Std 802.1AS [104] Annex F; - SMPTE Profile for Use of IEEE Std 1588 [126] Precision Time Protocol in Professional Broadcast Applications ST 2059-2:2015 [127]. TSN AF and TSCTSF may determine the PTP functionalities supported by DS-TT and NW-TT and may configure PTP instances in DS-TT and NW-TT using port and user plane node management information exchange as described in Annex K, clause K.2. NOTE: How the TSN AF or TSCTSF assigns NW-TT port(s) of one NW-TT to different PTP instances is up to implementation.