# Cross-Layer MAC/Routing Protocol for Reliability Improvement of the Internet of Things
## 1 Introduction
The authors show that the resulting graph is highly disconnected and comprises up to 25% isolated nodes, using propagation models corresponding to 2.4 GHz IEEE 802.15.4 technology and considering 52 city maps extracted from OpenStreetMap. One of the largest test beds related to smart cities is the Smart Santander [10], with approximately 3000 IEEE 802.15.4 devices deployed. The effects associated with these applications are not limited to economic aspects, but are also the ability to construct and use capillary wireless networks that reach all locations with smart streetlights. Through this, the following new services can be provided. * Smart Parking: Real-time monitoring of parking lots (parking/user) [11; 12; 13; 14; 15; 16; 17; 18]
* Waste Management: Detecting waste levels in containers to optimize waste collection paths and schedules [19; 20; 21]
* Air Quality: Air Pollution Monitoring [22; 23; 24; 25]
* Structural integrity: monitoring vibration and material conditions of buildings, bridges, and historical monuments [26; 27; 28]
* Traffic monitoring and control: traffic jam detection and alternate path notification [29; 30; 31; 32; 33; 34]. Recently, an Zigbee S2C module that expands the communication distance of Zigbee has been released. The Zigbee S2C has a range of 1.2 km and the Zigbee Pro S2C model is 3.2 km. The data transmission rate is 250 kbit/s for RF and the serial portion is 1 Mbit/s. There are 16 communication channels of Zigbee S2C and 15 communication channels of Zigbee Pro S2C [35]. The Zigbee S2C module is a very low-cost communication module suitable for streetlights installed at tens of meters apart. Although existing Internet-related technologies on wireless network protocol can be applied to the IoT, many limitations have been expressed in technical applications as related applications have become remarkably diverse. In particular, various medium access control (MAC) and routing technologies have been proposed considering the IoT requirements. For example, IoT applications with low-power requirements use the IEEE 802.15.4 standard or associated extensions of it as the physical or media access control layer [36]. The IEEE 802.15.4 standard, a wireless personal area network (WPAN) standard, uses frequencies in the 2.4 GHz unlicensed band and has the advantage of being able to communicate at low power and low cost. Applications--such as building and industrial automation systems--use network technologies based on the IEEE 802.15.4 standard, such as ZigBee and WirelessHART. Recent market research shows that these standards account for approximately 50% of the building and industrial automation systems market [1]. By contrast, routing protocol technology still has no dominant solution. To address this problem, the IETF is working on standardizing routing protocols based on IEEE 802.15.4 MAC. A crucial challenge for wireless MAC and routing protocols is to simultaneously satisfy the diverse network requirements of the IoT, interlayer interoperability, and standardization requirements [37]. In particular, the complex interactions between these MAC and routing layers must be considered in depth for critical IoT applications that have high-performance requirements, as traditional layer-separated research and development inevitably has many performance limitations [38]. For example, when the IoT is applied to a control system, the information at the source node must be delivered smoothly to the target node to ensure the stability of the overall control system. Consequently, performance measures such as the reliability, delay, and power consumption of the wireless network should be considered in depth. A fundamental consideration of the interaction between network layers is essential to satisfy these performance requirements. Figure 1 shows the relationships between the MAC and routing layers using a block diagram. Information such as the topology of the application layer and the volume of traffic generated by the node becomes the input data to the entire system.