## 2 Materials and Methods Background
### Distributed Systems and Cloud Computing
* Microsoft 365 (SaaS) covering documents, websites, and video conferencing. * Amazon EC2 (PaaS) is part of Amazon Web Services (AWS, offering virtual machine rental). * IBM Cloud (SaaS, PaaS, IaaS), which mainly covers commercial services. Analysis of the Applied Protocols and Transmission Systems within IoT  
The Internet of Things uses a wide range of possible protocols to transfer data. These protocols have been derived from telecommunication protocols. The main feature of these protocols consists in the transmission of small data volume (in the order of tens to hundreds of bits), so they do not have large energy and memory requirements. These protocols belong to the TCP/IP protocol family. It contains four basic layers: the application layer, transport layer, network layer, and network-interface layer [35]. Figure 8 shows the protocols used in IoT. Let's take a closer look at four protocols belonging to the application layer and one that belongs to the adatlink layer. The most important protocols that are most used in IoT will be presented in the following section. These selected protocols try to work with the data in various ways, but standardizing allows for a \"thing\" to recognize how the data should be further used or displayed to the user. Therefore, these protocols allow for \"things\" to communicate seamlessly among various kinds of devices. Below, the basic protocols and transmission systems are listed:  
Figure 8: IoT protocols and standards. HTTP  
HTTP (Hypertext Transfer Protocol) is the most well-known protocol today. It allows communication between client and server via TCP (Transmission Control Protocol). It is the most widely used transport layer protocol in the TCP/IP suite of protocols used on the Internet. It is used to transfer hypertext documents in HTML, XML, and other formats. This protocol provides the transfer of information between endpoints. In 2015, a new version called HTTP/2 was released, featuring better compression and data transfer. This makes it much faster than the older version [35; 36]. 2. MQTT  
MQTT (Message Queuing Telemetry Transport) represents a standard protocol in IoT as well. It forwards messages between devices using a central point, called a broker. The message content can be arbitrary; however, it is limited by the size defined by the protocol version. The transfer in the protocol is carried out using TCP/IP and works with the publisher and subscriber models. The messages are sorted into topics and published on the given topic. Based on this, the device sends the message to the central point, which stores it and makes it available to other devices. Then, other devices subscribe to these messages. The protocol was created by IBM in 1999. In 2013, it was standardized by OASIS (Organization for the Advancement of Structured Information Standards) [35] and MQTT (undated). 3. AMQP  
AMQP (Advanced Message Queue Protocol) is a protocol for passing business messages between applications or organizations. It is considered an asynchronous addition to the HTTP protocol. It is not a normal publish/subscribe protocol; it rather works with MOM (Message-oriented middleware). Message oriented middleware (MOM) is a type of software product that enables message distribution over complex IT systems [37]. The protocol defines a set of rules that must be followed in order to transfer a certain amount of bytes. AMQP was founded in 2003 when the first version of the protocol was released. AMQP has been a member of OASIS since 2011. 4. CoAP  
CoAP (Constrained Application Protocol) is a protocol for constrained devices and constrained networks in IoT. Constrained devices are called nodes. It is based on the HTTP protocol but differs from it in many ways. It uses the UDP (User Datagram Protocol), which is a transfer protocol, unlike HTTP, which uses TCP. By this, the burden of maintaining a connection is removed; it is advantageous for smart devices having limited capabilities. To reduce overhead, CoAP uses a binary format instead of the text format used by HTTP.