# IoT-Based Solid Waste Management Solutions: A Survey
## 4 Available IoT Architecture Reference Models for Waste Management Systems  
To standardize this IoT segment or vertical, being supported by a reference architecture model is very important, so in the future, these waste management devices, which are called objects in IoT, can be connected (and the interoperability challenge is solved). The Internet is supported by the Transmission Control Protocol/Internet Protocol (TCP/IP) architecture so that communication between network hosts is possible as it is known today. Similarly, an architecture for IoT-based applications is also necessary, always addressing factors such as scalability, interoperability, reliability, Quality of Service (QoS), etc. According to the author of [51], there are several models and reference architectures available for IoT. Each group or company describes its own, which often causes conflicts of ideas and makes the task of standardization more complex. Among the predominant reference models, it is possible to mention some initiatives, such as RAMI 4.0, a reference architecture for intelligent factories applied to IoT standards, which began in Germany and later became relevant through the direction of companies from large industrial sectors. Another initiative was launched by a consortium formed by AT&T, Cisco, General Electric, International Business Machines Corporation (IBM) and Intel, called Industrial Internet Reference Architecture (IIRA), and provided a reference architecture that involves broad discussions and considerations, while Internet of Things Architecture (IoT-A) is an initiative that stimulates an architecture model which covers detailed system requirements [52]. Many project models focus on a typical architecture based on needs analysis or on some layers that form a basic model of a reference architecture. Figure 2 illustrates the basic layered architecture. The most basic approach only considers a three-layer architecture composed by application, network, and perception layers [10]. There are also, in recent literature, some other models that add more abstraction to an IoT architecture, such as the Service Oriented Architecture (SOA) model, the middleware model [51; 53; 54], and the five-tier model [55; 11; 56]. Even with a flexible architecture, there are still relevant challenges, especially related to security and privacy. Therefore, to overmatch these challenges, new standard architectures need to be proposed with a focus on critical factors, such as QoS, sustainability, data integrity, confidentiality, and reliability. Next, there is a brief discussion about these layers that, in turn, alternate between the presented models. * **Perception Layer**. The IoT architecture perception layer is similar to the physical layer of the Open Systems Interconnection (OSI) model, because it is based on the hardware level and has the responsibility of collecting physical information, processing it, and transferring it to the upper layers through secure channels. It applies technologies for the detection of parameters of physical characteristics through specific sensors, such as weight, temperature, humidity, etc., in addition to the collection of object identification data, such as Quick Response codes (QR codes) and RFID. * **Network Layer. ** The network layer is responsible for transferring the measured information in the perception layer to the upper layers, where the processing systems are located. and uses ZigBee, Z-wire, GSM, UMTS, Wi-Fi, Infrared, 6 LoWPAN. In addition to the basic assignments, the network layer also performs the cloud computing process and the data management process. * **Middleware Layer. ** The middleware layer is a layer of software or even a set of sublayers that work to interconnect components of the IoT that would not be possible to communicate otherwise, that is, an interpreter. In addition to providing concurrency so that the application layer can interact with the layer of perception and ensure effective communication, it plays an important role in the development of new technologies.