5.27.5 5G System Bridge delay

This clause applies if 5GS is integrated as a bridge into an IEEE TSN network.

In order for the 5G System to participate as a TSN bridge according to transmission gate schedules specified, the 5GS Bridge is required to provide Bridge Delays as defined in IEEE Std 802.1Q [98] for each port pair and traffic class of the 5GS bridge to an IEEE 802.1 TSN system. In order to determine 5GS Bridge Delays, the following components are needed:

1. UE-DS-TT Residence Time.

2. Per traffic class minimum and maximum delays between the UE and the UPF/NW-TT that terminates the N6 interface (including UPF and NW-TT residence times), independent of frame length that a given 5GS deployment supports. The per-traffic class delays between the UE and the UPF/NW-TT are pre-configured in the TSN AF (see clause 5.28.4).

The TSN AF calculates the 5GS independentDelayMin and independentDelayMax values for each port pair and for each traffic class using the above components. If the UE-DS-TT Residence Time has not been provided by the UE, then the TSN AF uses a locally configured minimum UE-DS-TT Residence Time for the calculation of independentDelayMin and a locally configured maximum UE-DS-TT Residence Time for the calculation of independentDelayMax.

The dependentDelayMin and dependentDelayMax for 5GS Bridge specify the time range for a single octet of an Ethernet frame to transfer from ingress to egress and include the time to receive and store each octet of the frame, which depends on the link speed of the ingress Port as per IEEE Std 802.1Q [98].

NOTE: Further details how TSN AF determines dependentDelayMin and dependentDelayMax are up to implementation.

Since residence times may vary among UEs and per traffic class delay between the UE and the UPF/NW-TT may vary among UPFs, the 5GS Bridge Delay is determined after the PDU Session Establishment for the corresponding UPF and the UE by the TSN AF. The TSN AF deduces the related port pair(s) from the port number of the DS-TT Ethernet port and port number of the NW-TT Ethernet port(s) of the same 5GS Bridge when the TSN AF receives the 5GS Bridge information for a newly established PDU Session and calculates the bridge delays per port pair. Additionally, TSN AF deduces the port pair(s) consisting of two DS-TT ports connecting to the same 5GS bridge and determines the 5GS bridge delay as sum of bridge delays related to PDU Sessions of two DS-TT ports.