# TETES: Trust Based Efficient Task Execution Scheme for Fog Enabled Smart Cities
## 1 Introduction  
The concept of smart cities has been emerging rapidly in the last few years as it provides a quality lifestyle by offering modern communication and information technologies. Smart cities provide home surveillance, intelligent transportation systems, smart industrial infrastructure, health care systems, agricultural farming, energy management, waste management and resource management [1, 2]. These applications demand secure data communication and reliable delivery of data to provide secure and successful communication. Internet of Things (IoT) applications in smart cities comprise of number of sensors that are required to forward their data to other nodes. With the evolution of 5G and 6G technologies, these nodes are required to adapt themselves to communicate with such base stations and also with their neighbouring nodes in transferring the data by using heterogeneous communication [3, 4, 5]. This heterogeneous communication makes it vulnerable and malicious nodes may attack it and disturb the communication channel. This becomes more serious when data comes from a health care system where unreliable datamight be life-threatening because treatment and suggestions from the specialist physician are based on this patient's data [6]. Smart cities comprise various applications that possess multiple networks with different service providers. In this scenario, trust with different service providers is a fundamental challenge and is required to be implemented by slicing a network over different infrastructures by considering the different service providers and different types of users [7; 8; 9]. Furthermore, virtual machines are susceptible to different types of security attacks so should be un-trusted during the communication operation, otherwise, it may disturb the network performance resulting in the QoS of the network being seriously compromised [10; 11]. There is also a possibility that the virtual networks are deployed by a third party and there are chances that it may become infected during network operation resulting in communication disturbances. The dramatic increase in the IoT heterogeneous network requires trust management in communicating their data to other devices is such a challenging job. IoT devices mostly comprise of large number of tiny sensors with limited computational and resource capabilities [12; 13]. Though limited resources reduce the cost of these sensors, at the same time they are more vulnerable to other networks and are under attack. This makes trust management an even bigger challenging job. Multiple smart city application such as healthcare and industrial applications are based on IoT networks, that are based on large number of wireless sensor nodes. These wireless sensor nodes generate vast amounts of raw data. Transmitting this huge amount of raw data to the central location makes it inefficient and it is required to be filtered and analyzed locally and only the relevant information needs to be forwarded to the concerned node. This may require sensor nodes to run complex analytic algorithms. Wireless sensors have limited processing capacity and are unable to execute such complex algorithms and need to offload their tasks to cloud servers. However, approaching cloud servers with multi-hop distances causes communication delays and the quality of services is compromised. To overcome these delays fog computing nodes are deployed in the near vicinity of these IoT nodes. Fog nodes consist of single or multiple data centres located at the edge of user networks without routing over the Internet backbone [14; 15; 16]. A fog node-based smart city IoT network is shown in Figure 1. Fog nodes with higher processing capacity than the IoT sensor nodes, execute these offloaded tasks in relatively much less time. The presence of malicious nodes compromises the performance of fog nodes by intentionally offloading the unwanted complex tasks to fog nodes.