# 5G Physical Layer-Based Procedure to Support Time-Sensitive Networking
## 2 Literature Review  
### Configuration Methods in 3 GPP Standards  
Enabling wireless TSN for real-time communication presents a challenge in achieving dynamic industrial automation across diverse applications like collaborative robotics, precision manufacturing, and Industry 4.0 initiatives, where TSN-enforceable communications play a key role in providing reliable scheduling and synchronization for multiple Industrial IoT applications with system controllers. A significant milestone in this pursuit is represented by Release 16, which lays a robust foundation for the seamless integration of 5G and TSN [7]. Under the umbrella of this release, 3 GPP delineates the essential features of the 5G System designed to support TSN standards. Furthermore, it introduces novel entities that translate TSN protocols into internal 5G procedures. This development carries substantial practical implications, particularly in scenarios involving motion control and control-to-control communication. In the specific context of these scenarios, a controller assumes the role of transmitting a downlink timestamp--a critical component for synchronizing one or multiple actuators tasked with the execution of precise and coordinated tasks. This synchronization, underpinned by the fusion of TSN and 5G technologies, can revolutionize the landscape of dynamic industrial automation, opening new horizons for realizing agile and responsive industrial processes. Furthermore, Release 17 expands the integration of TSN to include uplink synchronization, where machine sensors transmit timestamps to a controller or monitoring device [8]. This use case holds significant importance, particularly in applications like smart grids, where accurate interpretation of sensor measurements is crucial. Release 18 includes new signaling messages that could allow the UE to synchronize over the air. Thus, 3 GPP has put forth three distinct configuration methods from Release 16 to Release 18 [9]:  
1. 5G as a PTP instance (Release 16): The 5 GS can be integrated with a PTP network as another PTP node that disseminates either the 5 GS clock or an external clock. In this case, the 5 GS can be configured as a PTP Boundary Clock where the 5 GS is used as the time source. The 5 GS maintains the timescale used in the PTP domain and synchronizes the connected PTP time receivers. Alternatively, the 5 GS can be configured as a PTP Transparent Clock, which measures the time taken for the PTP event messages to travel within the 5 GS, referred to as the residence time. Here, the 5 GS is used to correct PTP messages. 2. 5G as a Time-Aware System (Release 17): 5 GS acts as a bridge and \"time-aware system\" when integrated with IEEE TSN networks. In this scenario, the TSN domain uses its clock domain, and the Generalized Precision Time Protocol (gPTP) is used to distribute the time information from a Grand Master (GM)--the main source of time--to all the time receivers. 3. Over the Air Interface Synchronization (OAS) (Release 18): The 5G Next Generation-Radio Access Network (NG-RAN) can directly transmit epoch/Coordinated Universal Time (UTC) time to the UE via the air interface. To circumvent any confusion regarding the timing of transmission and reception, the network provides Reference Time Information (RTI) about a specific air interface event, such as a System Frame boundary, which the UE can easily identify. This RTI can be broadcast to the whole cell via the System Information Block 9 (SIB9) or dedicated Radio Resource Control (RRC) messages targeted for a single device. Methods (a) and (b) require the incorporation of the IEEE specifications into the 3 GPP; the support for (g)PTP is introduced at the edges of the 5 GS. This involves the introduction of two new functional entities--the Device-Side TSN Translator (DS-TT) on the UE (User Equipment) side and the Network-Side TSN Translator (NW-TT) on the 5G network side. In the 5G Core, the configuration of the DS-TT and the NW-TT is carried out by a newly introduced function, called the TSN Application Function (TSN AF).