# Survey on Quality of Experience Evaluation for Cloud-Based Interactive Applications
## 4 Architecture of CIAs  
Researchers and industry are continuously exploring different strategies to quantify QoE in CIAs. Studies obtain different metrics from the infrastructure and evaluate their relevance and the relationship between them. First, we offer a general view of how CIAs work and what differences exist compared to other services and applications. Second, we explore the components of the architecture to understand which ones the researchers focus on. Unlike local computing systems, the experience perceived by users of cloud services is influenced by the fact that the server executing the applications is not physically located in their vicinity. This requires the dissection of the infrastructure into the components that influence the final service (Figure 2): client, network, and cloud server. The client is the first component, and it is the display device with which the user interacts. The client can be a thin client, desktop computer, laptop, game console, smartphone, or tablet. The client has to perform less computational work compared to that carried out by the infrastructure in the cloud since its main purpose is to capture the interactions of the users via the peripherals (keyboard, mouse, gamepad, etc.). The client sends the interactions to the cloud server through the network (the second component), as shown in Figure 2. The client and the cloud implement a request-response scheme that generates the network traffic to be carried by the network. Some CIAs require high-speed and low-latency networks in addition to the best possible availability. The last component is the cloud server. The cloud server is in charge of processing client requests and sending the answers back through the network. The responses could be screen updates according to a player's movement in cloud gaming or window movement in remote desktop CIAs. Additionally, they could be the result of a database query or data processed in the cloud server in an interactive web application, prompting a screen update for the client. In CIAs, users interact expecting near-real-time responses. Hence, the server updates the graphical representation on the client so fast that the user does not notice that the application is not running locally. Figure 2 depicts the common operation of the three types of CIAs. However, the three types of CIAs present differences at a logical level. The common aspect that encompasses remote desktop and cloud gaming CIAs is the fact that the user interface logic is shared between the cloud server and the client's device. The application processing logic, however, is exclusively located on the cloud server, and the client becomes a device oriented to graphical representation and network communication (see Figure 3). In an interactive web application, the client can perform part of the application processing logic without interacting with the cloud server. The bulk of the application logic continues to run on the cloud server. However, the client's browser JavaScript can execute small parts of the  
Figure 2: The three components of the architecture of a CIA’s services provision. service, such as graphical animations of a photographic carousel or simple mathematical operations in a spreadsheet (see Figure 3). Figure 4 depicts in detail the components involved in CIAs: the client, network, and cloud server. Throughout this survey, we explore the metrics researchers use related to these components, how they use these metrics, and why they chose them. On the client side, device usability, usage context, and user expectations and personalities determine the final QoE [30]. The research and tools we analyse seek to identify user insights when using CIAs. However, as direct user opinion is not always available, some measurement strategies obtain performance metrics from the components, evaluating the relationship between these metrics and the QoE. Figure 4 illustrates the three basic subcomponents common to computers, laptops, smartphones, tablets, and video consoles: hardware, operating system (OS), and application.