The turn of the second and third decades of the 2000s and until now is a period of rapid development of ICT network and cloud services. During this period, the widespread use of server resources (cloud) for storing and processing large amounts of data have been developing basically in all areas of industry, science and social life. In the building automation industry, there are subsequent years of progressive integration of field-level networks with ICT networks and a trend of implementing advanced control, monitoring and management functions of an increasing number of building infrastructure elements. Moreover, the progressive implementation of energy management algorithms, energy media and the operation of local microgrids with RES and smart grid services.
3.1. Service Oriented IoT and Edge and Fog Computing in BACS and BMS
Such a significant development of functional concepts indicating new development trends in BACS systems in smart home and building applications. Simultaneously the continuous development of IoT techniques and microcontrollers, determine the need for organizational changes in BACS networks. In particular, this concerns the expansion of the ability to perform most of the analyzing and data processing functions for monitoring and controlling the building infrastructure directly in the local network (within the building, campus of buildings etc.). This is made possible by the computing power and memory resources of many modern distributed embedded electronics modules (automation servers, advanced routers and gateways), integrated in the
Automation level of IoT network. These modules, usually located at the junction of the
Field and
Automation (middle) layers, create the so-called
edge computing in the modern BACS with IoT network nomenclature [
35].
Edge computing can be defined as a computing approach that is using resources at the periphery of a network. In this way it brings the computation closer to the nodes of the BACS at the network’s edge to provide a minimal delay and lower latency period between the moments that data are acquired by sensors and then send as control signals for actuators within the BACS [
29,
60,
61]. The ongoing development of this layer of the BACS network, in particular the exchange of data in TCP/IP channels between distributed embedded electronics modules and their performance of local, advanced analytical and data processing functions at the
Automation level, has led to the creation of a new paradigm and term
fog computing in the modern BACS with IoT networks.
Fog computing is a distributed network resource that performs functions using local network resources but is also open to external services outside the local network – in the cloud [
34,
35].
Fog computing therefore operates at the
Automation and
Management levels, which are still supported the local network as well as external resources. Hence the fog element in the name, indicating a kind of blurring of the integrated network layers [
37,
38,
40,
60]. The technical and organizational aspects of IoT networks presented in this subsection have significantly influenced the architecture of modern BACS and BMS systems in applications for smart homes and buildings. The general structure of such a network, highlighting the most important elements and levels is shown in
Figure 2.
In addition, BACS and BMS networks with such a structure, using distributed modules with TCP/IP communication in the
edge and fog computing structure, create environment for a service oriented IoT [
36] and a new Building as a Service (BaaS) [
62] strategy. The first one is more general in nature, in the literature referred also as Fog of Everything (FoE) and Internet of Everything (IoE) and focuses on the abilities of using IoT technology in the implementation of services for four main areas: Processes, Data, People, Things. Formally, this approach refers to an ecosystem of edge modules, that autonomously share and self-manage their limited resources, in order to achieve the system goal (e.g. implementation of dynamic control, monitoring, management functions, etc.) [
63].
The second one is more detailed and refers directly to the development concepts of BACS and BMS systems, in particular in smart building applications. According to [
64,
65] buildings, in particular non-residential, equipped with BACS and IoT distributed networks integrated with fog and cloud computing, can be perceived in the BaaS convention, defined as demand-oriented deployment of resources respectively assets. With this approach, buildings become platforms of information for providers and consumers. The focus moves from functions and services available in a building with BACS, BMS to view the building as a service-dominant logic-based asset. In this way, facility management (FM) is in practice a process of dynamic data management and data mining in order to adjust the operating conditions of building infrastructure devices to the current needs of users and changing environmental parameters (e.g. temperature, daylight level, energy tariffs, etc.). Moreover, it opens the way to building a framework of open data processing platforms to provide specific services to users and infrastructure elements, based on measurement data and device operating parameters.
Wildenauer et al. [
64] also point to the inclusion of the BaaS and IoE approaches for enabling a Digital Twin (DT) tool based on Building Information Modeling (BIM), which is becoming mandatory in several European states. In this context, it should be emphasized that the latest Energy Performance of Buildings Directive (EPBD 2018) [
66] and the related technical report [
67] define the Smart Readiness Indicator (SRI) along with guidelines for verifying this readiness based on the services offered and possible to implement in the building. The first verification analyzes of the usability of this indicator and related services in buildings are carried out as part of research and engineering works in order to develop mechanisms for applying the indicator's guidelines in real applications of buildings as well as energy microgrids with RES and energy storages [
33,
68,
69,
70].
3.2. Big Data Processing and Cloud Computing
An aforementioned approach to BACS with IoT as a framework of open data processing platform requires the integration of numerous sensor and actuator modules as well as automation servers at the
Field and
Automation layers. Moreover, it is necessary to organize network connections of edge modules and computing infrastructure with external resources in the cloud. This entails the need to ensure efficient transmission and processing of large data resources, while maintaining the time regime (real-time), so that the implementation of BACS and BMS functions and services takes place essentially unnoticed by the building users. At the same time, in recent years there has been a rapid increase in the popularity of data collection and processing services in the cloud - external servers usually operated by external entities or at the disposal of suppliers of smart home and smart building systems. This situation also affects designers and integrators of BACS systems with IoT, who often decide to implement cloud-centric systems, where there are basically only two levels of network structure:
Field and
Management (Cloud) layers, and all more advanced functions and services in system are implemented in external cloud resources [
71,
72]. At the same time, they rely largely on data processing and protection tools offered by external administrators of such cloud services. However, this is not always beneficial, especially considering that many advanced services can be provided by modern BACS and IoT modules directly at the
Automation layer, close to the
Field layer modules. This solution naturally increases data security and reduces the load on network communication channels. Therefore, in concept research and application case studies of modern BACS and BMS with IoT, solutions based on more advanced, multi-level structures of system networks are considered and developed. The key element of these analyzes is the development of guidelines regarding the areas of implementation of BACS and BMS functions and services in the network structure (what levels, between levels) and the methodology for the effective organization of network variables and data objects binding (interoperability, integration) to provide control and monitoring services. Considering the possibility of moving away from a cloud-centric organizational strategy, Chen et al. [
73] propose an original cloud-fog computing architecture for information-centric IoT applications providing classification of IoT applications and scheduling computing resources. Moreover, a developed scheduling mechanism optimizes the dispatch of cloud and fog resources regarding minimum cost in a cloud-fog computing environment. In turn, Sahil and Sood [
74] discuss cloud-fog architecture implemented in a specific application - the panic-oriented disaster evacuation system in smart cities, with a particular analysis of the effectiveness of the proposed system data processing algorithms for various functional priorities (e.g. accuracy, sensitivity) in a very demanding time regime.
Research and development work are also carried out from a second perspective focused on the lowest levels of the network structure. In the paper [
4], the authors proposed a model and algorithms for handling modules with video cameras distributed at the
Field layer, with identification and classification services of recognized objects implemented at the
Automation layer in edge modules and a local workstation with Microsoft Azure IoT Platform. Research focused on the functional capabilities of this solution and measurements of the system's effectiveness was carried out with results discussion. In other studies, Huang et al. [
36] propose an edge intelligence framework for building smart IoT applications. The project they developed is based on an extensive
Automation layer, with many edge modules cooperating to support local groups of field devices. A characteristic element of the concept is virtualized IoT services, which enable hardware-independent application design and simplify IoT services composition using different
Field layer (physical) devices without redefining applications. This is an element of the ongoing strategy of organizing
fog computing at the
Automation layer, within local system network. Further development of the concept is proposed by Nasir et al. [
28] employing edge devices as a computational platform in terms of reducing energy costs and providing security, as well as remote control all field devices and appliances behind a secure gateway. Moreover, at the
Automation layer, in addition to edge modules (nodes), they define fog nodes based on the powerful device Jetson Nano [
75]. The platform is open for integration with external cloud services but considered only as an additional tool to perform the most advanced processing, data analysis and machine learning services.
In turn, in the paper [
29] Lacatusu et al. analyze several design variants of the monitoring and control system for the infrastructure of a smart buildings complex, based on
edge computing and containers with additional cloud computing services. Importantly, the authors conducted a comprehensive performance evaluation of design concepts using testing environments with two architectural options: (i) centralized (a cluster hosted in a public cloud), and (ii) decentralized (a similar cluster deployed in a local datacenter). They executed tests considering different numbers of edge nodes, corresponding to real application cases: a small apartment, a house, a small residential building, an office building, and a complex of smart buildings.
Finally, research and engineering works of the last few years are focused on the development of various, comprehensive concepts for organizing smart home and building systems with the IoT-edge-fog-cloud architecture. For instance, in [
3,
40,
76] the authors propose similar structures and frameworks for BACS and BMS networks with IoT, using in particular the new capabilities of
edge and
fog computing modules. In all cases, regardless of the application area, the structures of the
Automation layer are expanded, where operations are carried out providing services such as data aggregation and analytics, security, access control or self-healing, self-managing. The general diagram of such a network layer structure is shown in
Figure 3.
For these solutions, the use of various communication technologies and the possibility of building network nodes based on universal modules with microcontrollers (e.g. Arduino, ESP) or a class of microcomputers (e.g. Raspberry Pi, BeagleBone) are analyzed. Using the results of these analyses, engineering teams carry out tests aimed primarily at improving efficiency and reliability, while rationalizing costs and resources used.
With this approach and the clear development trends of
edge and
fog computing in BACS and BMS systems, the issues of selecting communication protocol techniques and implementing data security mechanisms, certainty and unambiguity of communication become very important. In the context of the variety of available communication protocols, both wired and wireless, a comprehensive analysis of their usefulness and application potential was carried out in [
60]. Additionally, a broader analysis of security issues and data transmission reliability in BACS and IoT
edge computing networks in smart city applications was carried out in [
7].
3.3. Cybersecurity, Privacy and Blockchain Solutions for Distributed IoT in Buildings
It should be noted that the aforementioned developments of new structural concepts of BACS and BMS networks in smart home and building applications, in particular the progressive distribution of IoT nodes and edge modules at the
Automation layer cooperating with external cloud services, resulted in a greater “openness” of the BACS network structure for new threats related to their inclusion and progressive integration into commonly used TCP/IP networks. Moreover, new structures of communication and access to data in the
fog computing networks have been created, generating completely new categories of threats. According to [
77] traditional, conventional security mechanisms will not design or develop to secure such technology as IoT. Therefore, it is necessary to develop and introduce innovative solutions in the field of data security and reliable, trusted communication in such organized structures of smart home and building network. These issues are the subject of numerous research and technical analyses.
One of the most generalized analyzes is presented in [
78], where the authors indicate the most important issues related to the security and privacy in IoT networks. They discuss: (i) confidentiality (data secrecy which guarantees the reliable transfer of data); (ii) data integrity (prevents corruption or alteration of data during transmission); (iii) availability/disposability (ability to provide sufficient network and data processing resources when necessary) and (iv) authenticity (unique identification of users and resources authorized to operate on a given network). Moreover, they indicate significant challenges resulting from the development of IoT networks affecting security and safety issues. According to the authors, there are five main ones [
78]:
Heterogeneity of devices and communication, resulting from the coexistence of various modules/nodes in one network structure (from small sensors, relays, to large modules of automation servers, data servers) and the fact that they are produced by various manufacturers, often with different hardware architectures, supporting various types of software tools;
Integration of physical devices, the result of aforementioned “openness” is that an attacker is potentially able to communicate with more devices than before. If he breaks the home/building/local network protection, he is able to manipulate the lighting system, lock doors, control HVAC etc.;
Constrained devices, the feature of many IoT devices resulting from a tendency to reduce the cost of their production. As a consequence, IoT devices have limited resources, memory space, low bandwidth etc. and these considerably reduce the possibility to implement conventional security techniques;
Large scale, since currently there are more computers and other IoT devices connected to the Internet than number of humans on the globe and management of so large number of smart devices is very demanding task as well as inevitably raise the security risks;
Privacy, IoT devices by their nature operate in a distributed structure, allowing communication in various wired and wireless technologies. This approach allows interaction everywhere, data communication with many other BACS network nodes, edge modules, in order to provide various services with different scope and resource use. The openness and flexibility of this structure generates additional privacy risks.
This is, of course, a very general summary. More threads emerge in detailed analyses. Particularly noteworthy is the paper [
79], where Parikh et al. consider security and privacy risks for all three most important levels of IoT networks - cloud computing, fog computing and edge computing. The result of the analyzes is a classification of the complexity of problems and preliminary proposals for solutions, but without any technical or technological indications. In turn, the paper [
34] contains an overview of proposed solutions that increase the level of security and privacy in edge and fog computing structures. Laroui et al. provide a synthetic summary of the literature devoted to efforts to improve security and privacy in IoT networks, along with a brief discussion of proposed models, mechanisms, and tools. Moreover, they discuss future research directions in this area considering balance between openness and ease of use the IoT networks as well as need of high level of their security and reliability.
From the point of view of BACS and BMS systems with IoT, the most important are countermeasures dedicated to fog and edge computing, integrated at the
Automation layer, usually within a local subnet. Such countermeasures are described with detailed literature review by Alwakeel A. in [
80], in particular:
-
For fog computing
Encryption techniques;
Decoy technique for authentication of data;
Intrusion detection system for denial-of-service attack (DoS attack) [
81] as well as port scanning attacks;
Authentication schemes, where fog computing network enables users to access the fog services from the fog infrastructure if they are well authenticated from the system;
Blockchain strategy, it can prevent various malicious attacks in fog network including man-in-the-middle attack, DoS attack and data tampering.
-
For edge computing
Edge node security;
Full-time monitoring of edge nodes;
Encryption with secret keys and attribute-based [
82];
Intrusion detection system;
User behavior profiling;
Cryptographic techniques with smart, secret keys;
Data Confidentiality, for example with a privacy-preserving QueryGuard mechanism [
83].
One of the most frequently discussed and analyzed solutions that are intended to support the implementation of most advanced security and privacy elements is blockchain ledger technology [
34,
80]. In relation to the IoT paradigm it is explained in [
84] that blockchains, by definition, rely on a public directory acting as a common transaction information database for devices (nodes), edge modules as well as automation servers. Additionally, in [
85] Moniruzzaman et al. discuss the blockchain-based smart home ecosystem with framework presented in
Figure 4. According to them it is a four-layer conceptual framework consisting of four layers: (i) IoT data sources layer, (ii) blockchain network layer, (iii) smart home applications layer, and (iv) clients layer.
Sensors and actuators located in the first one generates and/or use data consolidated and stored in edge modules (servers) or a decentralized platform such as the second one – blockchain. All of the events and acts of the sensors and actuators became smart transactions, used to realize services. What is characteristic, time is an indestructible database that is placed in a new transaction and divided into a block hash chain. This way many copies of blocks are made and saved in the extracted nodes protocol. Moreover, hash values cryptographically connect blocks and edge modules (servers) may be considered as miners which are responsible for verifying and adding new transactions to new blocks while smart contracts follow predefined rules and facilitates the decentralized transactions [
84,
85]. This organization of data processing as a transaction with a trace in the block structure fits naturally into the framework of distributed BACS and BMS with IoT networks [
86]. Additionally, it opens the way to easier and reliable integration with external services for instance in community microgrid frameworks suggested in [
87].
Importantly, the more distributed network nodes in such a structure, the greater the security level due to blocking verification procedures in the nodes. Therefore, the distribution factor, previously identified as reducing data security, becomes an advantage with this approach. Pros and cons related to the implementation of blockchain technology in IoT networks in various application areas, including smart home and buildings are discussed in [
88,
89], considering security and privacy aspects as well and indicating the added value of such an approach. A detailed analysis of the transaction workflow along with the accompanying tools and methods of data protection in the fog and edge computing network structure is presented in [
90]. In the conclusion section, the authors also provide a comprehensive review of research work focused on the possibility of increasing the level of security and privacy in IoT networks, along with an indication of various limitations. Some of the latest research suggests innovations in the integration of blockchain technology in IoT networks, allowing for overcoming the limitations of classic approach: scalability, storage and bandwidth, transaction charges (checking by miners), data privacy (sharing every node), network size (all nodes within network). In [
77] Alshaikhli et al. introduce an IoT Application (IOTA) distributed ledger technology that can provide unlimited scalability specifically suitable for the IoT with fog and edge computing. In particular this technology provides fully distributed data transactions without central authority unit, micro-transactions in real-time with zero fees, new scalable distributed ledger mechanism as well as masked authentication messaging with advanced encryption of data.