# A New Bit Repair Fast Reroute Mechanism for Smart Sensors IoT Network Infrastructure
## 1 Introduction  
IoT architectures operate many types of different smart devices. The most used smart devices in the IoT are sensors that can be connected to the network using several technologies. In most cases, they are connected via wireless sensor networks (WSNs) [1; 2; 3; 4]. With the growing popularity of the Internet of Things solutions, the number of WSN deployments is growing, as is the number of sensors connected in them, which of course leads to an increase in the amount of data generated by these sensors. Such devices are no longer used only for simple tasks, but also in comprehensive scenarios and services. Consequently, from the communication point of view, new challenges arise here. The whole communication chain must meet new requirements not only for simple data deliverybut also must guarantee some reliability parameters of different data transfers such as availability, reliability, and network fault tolerance [5; 6; 7; 8]. For example, if there is a connectivity loss or a change of network topology within the delivery chain, routing protocols of external base stations (BS) networks [9; 10], in analogy to the Open Shortest Path Free (OSPF), respond to this change by re-converging the network [7; 8; 11; 12; 13]. During this process, routing protocols must update their routing information. Therefore, routers affected by the failure begin to send update messages to other routers that include recorded changes in the network topology. Receiving routers can then respond to topological changes and adjust their routing decisions. The time of the network convergence process depends mainly on the size and complexity of the network (number, density of nodes and links), as well as the routing protocol used. In a period of network convergence, network routers do not have valid routing information needed to deliver data properly. The loss, duplication, or other negative effects on data flows may significantly increase, and applications, services, or hosts may be unreachable, interrupted, or may provide unsatisfactory quality. This may be unacceptable for the quality of some services, such as critical or real-time. To address this issue and limit the impact of different network convergence times on the correct delivery of transmitted data, the FRR mechanisms have been developed [14; 15; 16; 17]. The primary feature of many existing FRR mechanisms is the proactive calculation of alternative routes for each expected failure scenario. Alternative paths are calculated in advance on each individual router locally and before an unexpected specific network failure occurs. Once a connectivity failure is detected, the FRR mechanism of a local router quickly uses the pre-calculated alternative path to bypass a faulty connection. A simplified example is illustrated in Figure 1. Here, in the event of a connection failure of the link between the routers S and E, the S router uses a pre-prepared alternative path through the router N1 to bypass the failure and successfully deliver critical data during the convergence period. The alternative path is active and used at least until the network convergence process will complete. Thus, the main idea of FRR is that their recovery time of the affected communication is much faster than the convergence time of a routing protocol. This reduces the negative impact of failure on data delivery (loss, delay). To further limit the effects of the error and to speed up the process of using the alternative route, FRR mechanisms may use other enhancement mechanisms, such as those for rapid detection of connection failure or neighbor unavailability (for example, bidirectional forwarding detection-BFD). These specialized mechanisms offer significantly faster detection of local failure than mechanisms built-in into current routing protocols (e.g., OSPF, IS-IS, EIGRP Hello mechanisms). Figure 1: An example of the Fast ReRoute protection. When using the FRR technology, the specific terms and definitions need to be introduced for denoting routers with unique FRR behavior [18; 19; 20; 21; 22].