# Enhanced Multicast Repair Fast Reroute Mechanism for Smart Sensors IoT and Network Infrastructure
## 1 Introduction  
The Internet of Things (IoT) model allows the connection and exchange of data between various types of smart devices. These smart devices, usually sensors, can be connected in the Wireless Sensor Network (WSN) [1; 2; 3; 4] creating a unique sensor architecture [5; 6]. With increasing numbers of sensors in the environment and the importance of measured data, the network platform must guarantee the reliability of connection.  
Historically, Internet Protocol (IP) networks have been focused mainly on time-tolerant communication services, such as e-mail, file transfer and access to web content. However gradually, IP networks have evolved into converged platforms supporting several different types of services, including time-consuming and real-time applications such as voice transmission over IP, Internet of Things platform, sensors, streaming and multimedia services [7; 8]. These services have higher network performance requirements, such as delay, availability, or packet loss, and are also negatively affected by unexpected link or node failures in the network. In case of network failures, network routing protocols (IGP), such as Open Shortest Path First (OSPF), respond to network failures by flooding topology updates and calculating new routes [7; 8; 9; 10; 11]. This process is also known as the network convergenceprocess. Thus, in a period of network convergence, network routers have outdated information that can cause data loses and outages.  
For this reason, IP networks must meet specific qualitative and quantitative parameters in order to ensure an acceptable quality of service, e.g., availability and short repair time after a specific network failure. To do this, network providers must deploy appropriate technologies to ensure uninterrupted customer service. One such significant technology is a group of mechanisms for rapid network recovery, also known as Fast ReRoute (FRR) [12; 13; 14; 15]. A key principle of FRR mechanisms is that the backup path for possible failure scenarios is calculated in advance before the failure occurs. This principle presumes that the switching to a precomputed backup path is faster than waiting for the network convergence process to complete. FRR mechanisms that are designed to work on IP networks are known as Internet Protocol Fast ReRoute (IP FRR) mechanisms.  
The paper presents an enhanced version of Multicast Repair (M-REP) FRR mechanism (hereinafter EM-REP) that does not require pre-calculation of alternative routes in advance. At the same time, EM-REP is capable of finding an alternative path even in the case of multiple network failures. These features make EM-REP a unique IPFRR mechanism which can be also used in IoT architecture providing reliable connection for various types of sensor networks.  
The rest of this paper is organized as follows. Section 2 provides an insight into the issues of Fast ReRoute, the purpose, and terminology used. Section 3 provides state-of-the-art analysis, where existing FRR solutions and identified problems are discussed. Section 4 presents the specification of the original M-REP FRR mechanism and Section 5 proposes its enhanced version, the EM-REP FRR mechanism. Section 6 focuses on the evaluation of the EM-REP mechanism and compares its features with the predecessor, the M-REP algorithm, as well as with the other FRR solutions. Finally, Section 7 presents the conclusions and directions for future research work.