5.27.0 General

This clause describes 5G System features that can be used independently or in combination to enable time-sensitive communication, time synchronization and deterministic networking:

• Delay-critical GBR;
• A hold and forward mechanism to schedule traffic as defined in IEEE Std 802.1Q [98] for Ethernet PDU Sessions in DS-TT and NW-TT (see clause 5.27.4) to de-jitter flows that have traversed the 5G System if the 5G System is to participate transparently as a bridge in a TSN network;
• TSC Assistance Information: describes TSC flow traffic characteristics as described in clause 5.27.2 that may be provided optionally for use by the gNB, to allow more efficiently schedule radio resources for periodic traffic and applies to PDU Session type Ethernet and IP.
• Time Synchronization: describes how 5GS can operate as a PTP Relay (IEEE Std 802.1AS [104]), as a Boundary Clock or as Transparent Clock (IEEE Std 1588 [126]) for PDU Session type Ethernet and IP and how 5GS can detect and report the status of the time synchronization.
• RAN feedback for BAT offset and adjusted periodicity describes a mechanism supported by NG-RAN and 5G CN that enables AF to adapt to received BAT offset and adjusted periodicity from NG-RAN for a given traffic flow.

The 5G System integration as a bridge in an IEEE 802.1 TSN network as described in clause 5.28 can make use of all features listed above.

To support any of the above features to enable time-sensitive communication, time synchronization and deterministic networking, during the PDU Session establishment, the UE shall request to establish a PDU Session as an always-on PDU Session and the PDU Sessions are established as Always-on PDU session as described in clause 5.6.13. In this release of the specification, to use any of the above features to enable time-sensitive communication, time synchronization and deterministic networking:

• Home Routed PDU Sessions are not supported;
• PDU Sessions are supported only for SSC mode 1;
• Service continuity is not supported when the UE moves from 5GS to EPS .i.e. interworking with EPS is not supported for a PDU Session for time synchronization or TSC or deterministic networking.