# Heuristic Routing Algorithms for Time-Sensitive Networks in Smart Factories
###### Abstract  
Over recent years, traditional manufacturing factories have been accelerating their transformation and upgrade toward smart factories, which are an important concept within Industry 4.0. As a key communication technology in the industrial internet architecture, time-sensitive networks (TSNs) can break through communication barriers between subsystems within smart factories and form a common network for various network flows. Traditional routing algorithms are not applicable for this novel type of network, as they cause unnecessary congestion and latency. Therefore, this study examined the classification of TSN flows in smart factories, converted the routing problem into two graphical problems, and proposed two heuristic optimization algorithms, namely GATTRP and AACO, to find the optimal solution. The experiments showed that the algorithms proposed in this paper could provide a more reasonable routing arrangement for various TSN flows with different time sensitivities. The algorithms could effectively reduce the overall delay by up to 74% and 41%, respectively, with promising operating performances. time-sensitive network; smart factory; industrial internet; routing; heuristic algorithm +
Footnote †: These authors contributed equally to this work. However, incompatible network protocols lead to problems such as incompatible applications, a lack of interoperability, difficulty in portability, and expensive costs for development, deployment, and maintenance. With the relentless efforts of the AVnu Industry Alliance and the IEEE TSN Working Group (formerly the AVB Working Group), TSNs [3] have emerged as a brand new industrial communication technology that are now being actively promoted by industrial communities. TSNs allow both periodic and non-periodic data to be transmitted within the same network, giving standard Ethernet communication the ability for deterministic transmission. TSNs are constructed on the standard 802.1 Ethernet protocol stacks, which naturally have the advantage of interconnection and can achieve open Layer 2 Forwarding while ensuring deterministic latency bounds and bandwidth guarantees [4]. Therefore, TSNs are able to interconnect mutually isolated information technology (IT) networks and OT networks to achieve the co-networked converged transmission of multiple data flows with varying time sensitivities [5]. In recent years, TSNs have received continuous attention from both academia and industry and have been identified as a key technology for the next generation of industrial communication systems [6; 7; 8]. With this continuous attention and the efforts of standardization organizations, including the IEEE and IEC, a series of amendments and standards to improve TSN protocols [9; 10; 11] have been released. The continuous improvement of TSN-related standardization has become a research trend in the building of a comprehensive industrial internet communication system that is based on a TSN with deep integration of IT and OT [12]. Among many application directions, smart factories, a key component of Industry 4.0, comprise an important application scenario for TSN communication technology. A smart factory is a comprehensive production system with multiple intelligent subsystems at different levels [13], with each subsystem having different needs for industrial communication. While ensuring real-time control data communication for smart factories, only TSNs can realize barrier-free communication with other the subsystems mentioned above within the smart factory architecture [14; 15]. For TSNs in smart factories, a novel routing mechanism needs to be established that considers their unique characteristics. Currently, research on TSNs is still in the development stage and existing data flow route planning mechanisms are relatively simple.