# A Reliable Routing Algorithm Based on Path Satisfaction in the Energy Internet
## 1 Introduction
Compared with the traditional distributed network, it facilitates improved network survivability, reduces response time, enhances resource utilization, and strengthens an effective coordination of the IP/Optical networks. In view of these features, the centralized communication architecture is employed in this study. Additionally, various routing algorithms in terms of service characteristics provide effective solutions to deal with such questions. We firstly reviewed typical service routing strategies in communication networks. Authors in [4] proposed a priority-based routing and wavelength algorithm for the Wavelength Division Multiplexing (WDM) networks to improve transmission reliability. Authors in [5] presented a dynamic wave-channel balanced routing and wavelength assignment algorithm for OTNs. However, it neglected the efficiency of resource utilization, which may lead to network congestion on certain shared links in the event of traffic bursts. Authors in [5] proposed a metric of betweenness centrality to the bandwidth ratio tree approach to ease network congestion. In recent years, with the aid of artificial intelligence (AI), more studies concerning cross-layer routing selection and resource utilization based on machine learning (ML) have been increasing rapidly. In [6], authors map the routing and wavelength assignment (RWA) into a supervised classification problem which can be handled with ML algorithms, for example, Logistic Regression or Deep Neural Networks. Other AI-based [7] studies leverage Genetic Algorithms or Reinforcement Learning [8] to tackle the RWA problem. Indeed, these AI-based models or algorithms are computationally costly and tough to converge within a few milliseconds. In contrast, most of the services in the EI are sensitive to transmission latency, especially control services that are required to be delivered in milliseconds. Therefore, developing AI-based algorithms further needs to be supported by powerful high-performance devices to guarantee computing or training time. In our previous work [9], we proposed a risk-aware dual-route planning method for control services in the system protection communication network in the smart grid. The above works have comprehensively studied routing strategies and rerouting mechanisms in communication networks. However, considering diverse service characteristics, the research on routing across different networks remains inadequately explored, which prompts us to develop more reliable service-aware routing algorithms to ensure the seamless operation of EI. Given this, we propose a service-aware cross-layer routing algorithm based on path satisfaction (PS) inspired by the literature [10], which formulated a link resource model based on the time and spectrum domains. To the best of our knowledge, this is the first study that comprehensively combines service features and network structure with the spectrum resources on the link. The goal is to search for a cross-over layer routing algorithm to satisfy service transmission needs. In summary, this paper makes the following contributions:  
* The indicator of path satisfaction in terms of the particular characteristics of the network and the utilization of spectrum resources on the link is proposed. At the same time, the system model and service model are constructed. * We abstract searching routing paths for services into a constrained optimization problem. The optimal objective is to maximize path satisfaction. At the same time, the metrics of service requirements concerning end-to-end latency, bandwidth, etc., should also be satisfied. * To reduce computational complexity, a heuristic path satisfaction-based service-aware routing algorithm (PSSRA) is designed to resolve it. The final results demonstrate its effectiveness. The rest of the paper is organized as follows: Firstly, Section 2 reviews related works in routing algorithms of the IP layer, and routing and spectrum algorithms of the optical layer.