# From Brown-Field to Future Industrial Networks, a Case Study
## 1 Introduction  
The future industrial networks are expected to accommodate both Internet technology (IT) and operational technology (OT) traffic in a unified infrastructure. The expectation begun with the vision of Industry 4.0 and efforts towards digitization in industries to increase productivity and to enable innovation. In order to reach these visions, it is needed to facilitate the availability of data from everywhere to anywhere, which requires effort to unlock the data in automation pyramid communication. Furthermore, IT and OT systems need to be integrated to have a bridge for utilizing the unlocked data. Many research works and under development technologies, such as Time Sensitive Networking, are trying to predict the requirements of converged IT-OT networks and provide a collection of mechanisms to address requirements of various traffic classes. Despite these efforts, there is still a lack of insight and results from the existing systems, brown-fields, that can be used for a smooth transition from today's system toward the digitalized industries and Industry 4.0 vision. The importance of IT-OT convergence for IIoT systems has been discussed during recent years, and it is considered a mandatory element of future industries. Nonetheless, the progress in developing IT-OT networks has been difficult to advance because of several challenges that need to be overcome to reap the benefits of IT-OT integration [1, 2]. From a practical perspective, these challenges can roughly be categorized into three groups. The first challenge set concerns with different characteristics of IT and OT traffic and their diverse, and sometimes contradicting, performance requirements. OT systems are the combination of communication and control components with a relatively long life-cycle, whereas the IT technological spectrum commonly has a shorter life-cycle and areexpected to go through more changes in shorter periods of time [3]. From the performance perspective, OT networks focus on availability, reliability, real-time and determinism, whereas IT networks emphasize privacy, confidentiality, authentication and integrity, with reduced emphasis on real-time and determinism [2,4]. IT-OT converged networks are yet to become de facto infrastructure in the industrial environment and have a long path to reach technological maturity. The existing research and development efforts still lack the knowledge for configuration and performance management purposes. Hence, another challenge set hindering the development progress is concerned with uncertainties surrounding characteristics and performance requirements that IT-OT networks need to address. Among the more discussed challenges, complexity, flexibility and scalability of the converged networks are standing out. The increased number of smart devices and their demand for communication resources both in vertical and horizontal integration pose serious difficulties on configuration and performance management, and require more investigations for identifying what would be the vital parameters to consider. Another challenge set, adjacent to the ones stated, is that the new network infrastructure cannot be realized in one revolutionary act. In practice, this approach faces a two-fold problem. Firstly, there are no preliminary information or data that can be used to build and to configure the system from scratch, known as green-field implementation, with parameters that can ensure essential performance criteria. Secondly, it is unexpected that a whole functioning system with ongoing processes is stopped and replaced by a new system with a high risk of downtime. There needs to be considerations for integration with legacy systems, the machinery and infrastructure that already exist, also known as brown-field [5]. The limited knowledge of IT-OT consolidated networks' performance and configuration requirements partially derives from a lack of understanding about the characteristics as well as the complexity of configuration, resources and performance managements of IT-OT converged system of systems.