# Virtual Replication of IoT Hubs in the Cloud:
## 1 Introduction
Although IP-based IoT would make it possible to address smart objects directly, the following potential drawbacks exist: (i) in order to extend their battery lifetime, smart objects may be duty-cycled devices and, thus not always accessible; (ii) smart objects might be unable, to handle a large number of concurrent requests, thus leading to service disruption and becoming possible targets for Denial-of-Service (DoS) attacks; (iii) under some circumstances (for instance, to minimize memory footprint when the available in-device memory is critically low), smart objects may play the role of clients rather than servers. In all the above cases, the presence of an intermediate network element operating at the application layer, which may typically coincide with the border router, is desirable. Such a node could integrate several functionalities which may reduce the processing load on smart objects and help overcome some of the problems discussed above (e.g., caching). This resourceful node, denoted as \"IoT Hub\" and shown in Figure 1, helps moving some of the processing load towards the edge of the network, following the emerging paradigm of \"Fog Computing\" [6]. Fog Computing, also referred to as Edge Computing, is a novel paradigm, which has been introduced to meet several requirements such as mobility support, low latency, and location awareness [6]. Fog Computing aims at distributing and moving some Cloud-based computation and storage to the edge of the network. While Cloud-only architectures can provide a solution to scalability and flexibility issues by distributing resources among multiple servers, this approach presents some weaknesses, such as: (i) latency; (ii) availability/dependence on Internet connectivity for operations; (iii) flexible networking; (iv) quality of service/experience; (v) security and privacy. Due to its benefits over Cloud-based architectures, especially if time is a critical issue or Internet connectivity is poor or absent, Fog Computing is expected to play a key role in the deployment of IoT applications. The Fog is not intended to replace the Cloud, but rather to complement it, in order to provide location-aware and real-time services, thus enabling new applications that could have not been deployed otherwise. Characteristics features of Fog Computing are the following:  
* Geographically distributed, in contrast with a fully Centralized solution associated with Cloud-based architectures;
* Low latency and high performance to support real-time applications;
* Support for mobility. According to the principles of Fog Computing and the fact that it will represents the reference architecture for IoT, the IoT Hub represents a critical building block for the deployment and manageability of complex IoT scenarios. The IoT Hub will allow Smart Objects to interoperate at a local level and to enable the design of new applications and interaction patterns of the Edge (e.g., analytics, machine learning, and human-to-machine interactions). In this context and architectural vision, the role of the IoT Hub becomes central in the foreseen IoT architecture, since it should process all requests providing the following functionalities and benefits:  
* Independence from Internet Connectivity allows to guarantee continuous service operation at the local level with no disruption in case of unreachability of Cloud. In case Internet Access is temporarily unavailable, the IoT Hub will keep the state of all Smart Objects and will automatically synchronize with the Cloud as soon as the connection resumes;
* Controlled and secure access to things.