This paper presents the essence of IoT (Internet of Things) works and design challenges, discusses its principles of operation, and presents IoT development concepts. WSN (Wireless Sensor Network) was characterized in detail as an essential component of IoT infrastructure. The various faults that can occur at all levels of the IoT architecture, such as sensor nodes, actuators, network links, as well as processing and storage components clearly demonstrate that fault-tolerance (FT) has become a key issue for IoT systems. A properly applied routing algorithm has a direct impact on the power consumption of sensors, which in extreme cases is the reason why nodes shut down due to battery degradation. To study the fault tolerance of IoT infrastructure, a ZigBee network topology was created, and various node failure scenarios were simulated. Furthermore, the results presented showed the impact and importance of choosing the right routing scheme, based on the correlation of throughput to the number of rejected packets, as well as the proportionality of the value of management traffic to the other including the ratio of rejected packets.