## 1 Introduction  
In the last few years, urbanization has skyrocketed due to rapid population growth, UN-Habit [1] predicted that the world's populace would increase to approximately ten billion by 2050, almost thrice the status of the present global population. As a result, community safety, smart transit, clean energy, sustainable development, and productivity improvements are critical problems modern cities must address. An inadequate supply of clean water and a rapidly growing population has prompted the development of a new way of thinking about cities, called intelligent urbanization or smart city concept. As the density of population in metropolitan areas has grown at an extremely fast rate, the overall infrastructure and amenities are required to meet the needs of residents. As a result, many digitized components, such as smartphones, sensors, controllers, and smart gadgets, have emerged as massive business goals of the IoT because they can be interconnected via the Internet [2]. Additionally, wired networks are more complex and expensive to set up and manage than wireless ones. Therefore, modern networking systems prioritize wireless communication because of these realities. It is of primary importance for the smart infrastructure to gather and analyze information from the physical environment. Sensory information/records are generated through various sorts of sensors in multiple spots with diverse functionalities. In order to be smart, an environment has to be aware of what is going on both outside and within its service area, and it is enabled via a wireless sensor network (WSN) [3; 4]. Figure 1 represents the backbone elements of smart cities. WSN is a network of autonomous, multipurpose, and low-power sensing units embedded with communication units that are linked to access points or base stations (BS) [5; 6]. The utilization of generalized/conventional ad-hoc routing methods for data transmission in WSN is restricted by increased node density, limited data rates, and other resource limitations. WSN routing methods often emphasize adaptive routing and resource and service awareness [7; 8]. Figure 2 depicts the WSN-based communication architecture of smart cities. Smart cities are designed to process infrastructural systems such as water and sewage disposal management, urban and resource management, and transit, in addition to medical centers, transmission and distribution power grids, and several other operations. The delivery of goods and services from one place to another is a vital element of smart city design [9; 10] and an important service for everyday living. Routing mechanisms have to be flexible enough to meet the requirements of a large-scale network. Routing is perhaps  
Figure 1: Backbone elements of a smart city  
Figure 2: WSN-based communication architecture of smart cities. more difficult due to the frequent changes in data routing paths. Routing techniques should be developed in such a manner that they can handle unforeseen node failures. The classification of routing strategies depends on the functionality of the evolved protocols. Prominent routing strategies are query-based, multi-path, Quality of Service (QoS)-based, and negotiation (reactive) based routing, which are delineated as follows. In query-based, to fulfill the query and responses better, the transfer of data is performed. Next, the BS disseminates the required data across the network under the user's demand. The primary difficulty with query-based systems is receiving similar queries at the BS/sink side for several instances. It is therefore essential to eliminate unnecessary/excess ones. In multi-path routing, multiple paths are built between transmitter and receiver to better balance the load. In addition, the backup routes allow the system to continue running despite link failures/errors, which is referred to as fault tolerance. Thus, dependability is achievable.