# A Review on Internet of Things for Defense and Public Safety
## 5 Building IoT for Tactical and Emergency Environments
### Computation
#### 5.4.3 Fog Computing
Another Eclipse IoT project is Krikkit [154] that comes with a RESTful API that allows a developer to acquire data in edge devices such as sensor gateways. It uses a publish/subscribe model by which data acquiring rules or policies are registered on edge devices. [PERSON] et al. [155] use Software Defined Radio (SDR) technology as part of their platform to sense and transform the wireless signals in the frequency spectrum. An approach based on software-defined networking (SDN) for IoT tasks is presented in [156]. They develop a middleware with a layered SDN controller to manage dynamic and heterogeneous multi-network environments. Therefore, a new intelligent IoT gateway is needed. An intelligent ruled-based gateway should allow programmers to control the wire protocol traffic to optimize performance based on the specific needs of the given application [11]. The rules that pertain to autonomic management and data aggregation services can result in the generation and transmission of new data and management packets by the gateway itself. It will result in a lighter protocol stack that relies on uIP/lwIP (with no need for TCP/UDP, TLS or other security protocols on resource-constrained devices). On resource-rich devices that support the TCP/IP protocol suite, IoT applications are implemented on top of a variety of application level protocols and frameworks including REST, CoAP, MQTT, and AMQP, among others. On the other hand, devices that do not have the resources required to support TCP/IP have a myriad of interoperability issues that limit the potential applications of the IoT. The fulfillment of complex requirements such as ubiquity, scalability and high-performance lead to a convergence between the IoT and cloud through federation and multi-cloud architectures. Cloud federation is one of the core concepts for the design, the deployment and the management of decentralized edge cloud infrastructures. Since federated systems inherit all of the fundamental aspects of distributed computing, they can certainly leverage many existing standards that have been developed in this arena over the past years. The near-future evolution of IoT clouds is discussed in [157]. There the authors describe a three-stage evolution towards the creation of an IoT federation. The first of such stages is called monolithic and involves embedded devices that would be connected to IoT cloud systems to provide basic IoTaaS (the services would be developed either with stand-alone pieces of software or by means of container virtualization technology). The next stage is named vertical supply chain. In such a stage the IoT cloud providers leverage IoTaaS offered by other providers. Finally, the third stage corresponds to the real IoT cloud federation, where IoT cloud providers will federate to extend their sensing capabilities, adopting the container virtualization technology massively in order to create more flexible IoTaaS. Likewise, numerous research projects and initiatives [158; 159] are focused on the realization of innovative architectures for the Cloud-IoT, enabling features such as autonomous service provisioning and management. Indicatively, such a concept may be applicable to 5G technological solutions [160], such as SDN. For example, cloud-based mechanisms will enable the incorporation of resources and services independent of their location across distributed computing and data storage infrastructures. The challenge will be the integration of these different standardized capabilities into a coherent end-to-end federation model. According to the cloud federation's organization, access and scale, six federation deployment models can be identified [161]: simple pairwise federation, hierarchical federation, peer-to-peer federation, brokers or interclouds.