## 3 Selected Elements of IoT System Architecture
### Programmable Networks and Virtualization Techniques  
In the context of real-time IoT tasks, new developments in Software-Defined Networking (SDN) and mass-scale Network Function Virtualization (NFV) methods are important elements to consider. SDN networks are commonly associated with IoT technology because the architecture provides a more flexible and manageable environment. In addition, more and more research (for example, on blockchain) is focused on implementing solutions that combine SDN and IoT technologies with NFV methods. Therefore, it is anticipated that NFV will be a very important tool to support the automation of network solutions, including in real-time transmission issues. In SDN, management tasks are separated from data transmission tasks. In this approach, network devices solely act as relays that transmit sequentially routed packets from the source to the destination, with all policies in place for both communication and security [71]. The management space in SDN is a highly centralized area, while the data space operates on a distributed plane. Potential SDN applications related to real-time transmission are shown in [72], where a four-tier cloudlet architecture (based on SDN) in combination with a WBAN (Wireless Body Area Network) architecture was described. The paper described a cloudlet--a mobile, cloud-based data center system that is located at the edge of the network. This approach was shown to enable efficient traffic processing, optimal resource utilization, and reduced latency, which is of great importance for real-time systems. The approach proposes that all network controllers be located in a cloudlet, resulting in better optimization in terms of QoS mechanisms, as well as a complete view of the network. On the other hand, the authors of [73] proposed the concept of a three-layer SDN application based on a WBAN scheme called an SDWBAN (Software-Defined Wireless Body Area Network). In this solution, network traffic prioritization is performed. Higher-priority packets are analyzed and sent through the network first, which is made possible by optimal resource allocation (e.g., throughput), path allocation and the use of cloud computing. In this case, transmission latency is reduced by formulating a heuristic allocation model for minimizing the service time of individual services. Security issues for IoT systems are also an important issue. In this area, solutions using SDN are known, such as artificial intelligence mechanisms that automatically analyze network traffic while taking real-time transmission requirements into account [74]. In today's vast IT world, technology is beginning to play an increasingly important role in the move away from physical infrastructure building and solutions based on dedicated physical network devices to virtualization technology. An example of virtualization technology in relation to the IoT area is the NFV solution. The implementation of virtualization technology in IoT solutions provides flexibility for applications regardless of the platform on which this solution is based or built while maintaining the full management of logical network functions and the modeling of the full technology stack. An additional advantage of implementing NFV technology in IoT solutions is the ability to fully manage and configure individual virtualized network elements at all levels (from physical machines to virtualized machines to sublime network services) [75]. From the point of view of the IoT and real-time requirements, the use of NFV virtualization technology has begun to play a key role due to the requirements of real-time transmission, i.e., transmission with the shortest possible packet delivery and processing time while maintaining an appropriate QoS and meeting the deadline value requirements of individual packets [76].