# MPResiSDN: Multipath Resilient Routing Scheme for SDN-Enabled Smart Cities Networks
## 1 Introduction and Motivations  
In the last few decades, the number of people who live in cities has increased dramatically. In 2018, 55% of the world's population lived in cities, and that percentage is expected to reach 68% by 2050 [1]. Rapid urban growth poses tangible challenges for the implementation of government development plans to deliver safe, resilient, and sustainable services to an increasing number of citizens [2]. In response, many governments have launched smart city projects to address urbanization issues and challenges [3]. According to the Cities In Motion Index, globally, more than 180 cities in more than 80 countries have been evaluated as smart cities [4]. These numbers increase each year as the number of people who live in urban areas increases. Keeping pace with this development, governments' interest and investments in smart city projects also increases. Smart cities are considered one of the most important applications of the vision of the Internet of Things (IoT) [5] The IoT connects physical items with embedded sensors and/or software to send or receive information over the Internet. Access to the Internet enables \"smart\" things, i.e., IoT objects, to make decisions and determine actions based on real-time information. The IoT vision may sound aspirational in view of the fact that connecting everything directly to the Internet is not technically feasible due to problems related to current Internet protocols and inadequate infrastructure. However, this is notthe complete story, because other existing technologies, such as Wireless Sensor Networks (WSN) could play a major role in achieving the vision. WSNs are considered suitable technology to enable the IoT [6; 7]. Ubiquitous sensing enabled by WSNs could help achieve the \"everything connected to the Internet\" vision [8] in smart cities. WSNs are preferable and play an important role in many smart city applications [9], because they are relatively inexpensive, scalable, and easy to implement [10]. Important smart city applications that utilize WSNs include disaster monitoring and management, surveillance applications, smart transportation systems, traffic management, and smart healthcare systems, as well as atmospheric monitoring, pollution reduction, and energy-saving applications [11; 12]. WSNs function effectively in ordinary stable environmental conditions; however, they have difficulty handling challenging environments [13]. In fact, WSNs are vulnerable to various challenges when implemented in real time in smart city environments. Here, a challenge is defined as any event that impacts the normal operation of the network [14]. Challenges trigger faults that may permanently or temporarily block the transmission of sensor information. Therefore, failure management is a significant aspect to be considered when developing any smart city project [5]. Challenges in a smart city environment include various natural disasters, such as severe storms, fires, floods, tornadoes, earthquakes, and volcanic eruptions. Such challenges can affect network connectivity due to fluctuations of wireless channel attenuation [15]. Some challenges, e.g., fires, can disrupt network services completely. However, some smart city services are critical and should remain available, particularly during disasters, to obtain the sensory information required to control them, limit their impact, and provide critical information for decision-making during rescue operations. Thus, improving the resilience of these underlying networks in smart cities is crucial [16]. Resilience refers to the ability of the network to adapt and retain basic functionality when errors, failures, and environmental changes occur [17]. Challenges to WSNs can cause link or node failures [18]. Under challenging conditions, the ability to respond quickly to changes in network topology can significantly improve data delivery. WSNs use a multi-hop routing mechanism; thus, alternative routes may be available.