## 2 Background
### 5G Support for Industrial Networks  
Nowadays, the communication between industry machines, end devices, controllers, as well as production cells/lines is based on legacy fieldbus technologies or industrial Ethernet technology (e.g., different real-time Ethernet variants), while the larger subnetworks are interconnected on the Internet Protocol (IP) level. Due to the fragmented market of industrial networking technologies, numerous different technologies can be deployed in particular factory premises. However, over recent years, there has been intensive work to develop a converged, standardized networking technology, which can fulfill the strict requirements of the Industry 4.0 use cases. The result is the set of time-sensitive networking (TSN) standards specified by the IEEE 802.1, which extend the bridged Ethernet to provide a future-proof solution for time-sensitive applications and is expected to replace the different fieldbus technologies and the various legacy real-time Ethernet variants [2]. The corresponding TSN standards specify the details of deterministic communication, time synchronization, high reliability, as well as enhanced resource management by enabling the support of a wide range of applications that require robust data transport with bounded, ultra-low latency, low jitter, and extremely low loss. From Release 15, 3 GPP focuses on several technology enablers aiming at how 5G can support industrial use cases, and such a way facilitates the seamless integration of 5G systems with industrial networks. On the one hand, the \"Ethernet\" type packet data unit (PDU) session was introduced by enabling the 5G network to handle Ethernet frames directly. Then, a set of radio- and architecture-level features are defined that enhance the ultra-reliable low latency communication (URLLC), ensuring the bounded latency data transmission on a redundant path over the 5G segment. Furthermore, in Release 16, the support of TSN is introduced, where the 5G system is modeled as a logical TSN bridge on per a user plane function (UPF) base. By enabling the interconnection of the 5G system with the legacy TSN network segment in a seamless way and ensuring the handling of TSN streams, 3 GPP introduced the TSN translator function in the user plane at the User Equipment (device TSN translator) and the UPF side (network TSN translator) that acts as a gateway functionality. In the control plane, a TSN application function (TSN AF) is defined by enabling the 5G control plane to interact with the centralized network configuration (CNC) entity of the TSN segment according to the IEEE 802.1 Qcc. The TSN AF reports the capabilities of the 5 GS bridge towards the CNC, and based on this information, the CNC configures the 5 GS bridge as well as calculates the traffic paths and schedule of a specific TSN stream. Then, the CNC pushes the corresponding bridge configuration (e.g., scheduled traffic, per-stream filtering and policing (PSPF) according to IEEE 802.1 Qci, traffic forwarding information) to the 5 GS. In order to provide sufficient quality of service (QoS) for the TSN streams in the 5 GS segment, the TSN traffic streams are mapped to the corresponding 5G QoS flows. Furthermore, to optimize the transmission over the 5G radio, the detailed traffic pattern of the TSN streams can optionally also be obtained from the PSPF information by the TSN AF, and it is forwarded to the 5G base stations by allowing more efficient scheduling of the TSN traffic. 5 GS also supports the TSN time synchronization feature according to IEEE 802.1 AS by enabling the time synchronization of end devices that connects to the TSN system via the 5 GS segment. The 5G Alliance for Connected Industries and Automation (5G-ACIA) published a white paper about the integration of 5G with time-sensitive networking for industrial communication [3]. The paper extensively discusses and validates the different 5 GS-TSN integration options in a factory environment.