Section: 4.4.8.2 Architecture to support IEEE Time Sensitive Networking
Content: The 5G System is integrated with the external network as a TSN bridge. This "logical" TSN bridge (see Figure 4.4.8.2-1) includes TSN Translator functionality for interoperation between TSN Systems and 5G System both for user plane and control plane. 5GS TSN translator functionality consists of Device-side TSN translator (DS-TT) and Network-side TSN translator (NW-TT). The TSN AF is part of 5GC and provides the control plane translator functionality for the integration of the 5GS with a TSN network, e.g. the interactions with the CNC. 5G System specific procedures in 5GC and RAN, wireless communication links, etc. remain hidden from the TSN network. To achieve such transparency to the TSN network and the 5GS to appear as any other TSN Bridge, the 5GS provides TSN ingress and egress ports via DS-TT and NW-TT. DS-TT and NW-TT optionally support: - hold and forward functionality for the purpose of de-jittering; - per-stream filtering and policing as defined in clause 8.6.5.2.1 of IEEE Std 802.1Q [98]. DS-TT optionally supports link layer connectivity discovery and reporting as defined in IEEE Std 802.1AB [97] for discovery of Ethernet devices attached to DS-TT. NW-TT supports link layer connectivity discovery and reporting as defined in IEEE Std 802.1AB [97] for discovery of Ethernet devices attached to NW-TT. If a DS-TT does not support link layer connectivity discovery and reporting, then NW-TT performs link layer connectivity discovery and reporting as defined in IEEE Std 802.1AB [97] for discovery of Ethernet devices attached to DS-TT on behalf of DS-TT. NOTE 1: If NW-TT performs link layer connectivity discovery and reporting on behalf of DS-TT, it is assumed that LLDP frames are transmitted between NW-TT and UE on the QoS Flow with the default QoS rule as defined in the clause 5.7.1.1. Alternatively, SMF can establish a dedicated QoS Flow matching on the Ethertype defined for LLDP (IEEE Std 802.1AB [97]). There are three TSN configuration models defined in IEEE Std 802.1Q [98]. Amongst the three models: - fully centralized model is supported in this Release of the specification; - fully distributed model is not supported in this Release of the specification; - centralized network/distributed user model is not supported in this Release of the specification. NOTE 2: This Release supports interworking with TSN using clause 8.6.8.4 of IEEE Std 802.1Q [98] scheduled traffic and clause 8.6.5.2.1 of IEEE Std 802.1Q [98] per-stream filtering and policy. Figure 4.4.8.2-1: System architecture view with 5GS appearing as TSN bridge NOTE 3: Whether DS-TT and UE are combined or are separate is up to implementation. NOTE 4: TSN AF does not need to support N33 in this release of the specification.