# Survey on Quality of Experience Evaluation for Cloud-Based Interactive Applications
## 6 Stages of the Quantification of QoE in CIAs
### Input Stage  
We present a classification of the information extracted from the proposals in the literature with respect to the sources of information or starting metrics extracted from the elements of the CIA's infrastructure. In particular, some researchers aimed to extract information related to the human perceptions discussed in Section 2. In some cases, these were the inputs used directly in the next stage of processing, whereas in others, the tools performed transformations of the metrics to obtain other input metrics. In Figure 6, the 21 metrics or sources of input information collected from the state of the art are grouped into four main categories. The four main sources of information are as follows:  
* Audiovisual content: The tools extract the input information about the graphic or audio content from the CIA the user is consuming. Figure 5: Sequential process of QoE evaluation. Figure 6: Grouping of input stage metrics into four types of information sources. * Device resources: The input information comes from the computational resources of the elements of the CIA architecture. * Network information: Incoming information comes from network traffic. * User feedback: Tools extract input information directly from user impressions. Table 5 summarises the proposals we discussed in Section 5 and identifies the different types of input sources used, along with the specific metrics. Each proposal may use several sources of input information simultaneously. The table categorises the proposals into two broad types: specific or general scores. This categorisation distinguishes works that are generalizable to any type of CIA (general scope) from those in which the authors specialise in quantifying QoE in specific CIAs (specific scope). In the case of remote desktops, proposals that use input metrics independent of the remote desktop protocol used by the CIA are part of the general scope group. Conversely, proposals that dissect any given remote desktop protocol to obtain the input metrics are part of the specific application scope. Audiovisual content allows researchers to obtain sources of information and metrics related to the visual and audio perceptions of the CIA user. To obtain metrics or sources of information on visual perception, the source can be the graphic content represented by the CIA. Some proposals attempted to obtain measurements in a timely manner, opting to obtain screenshots of specific elements of the architecture as a source of information. Other proposals chose to obtain measurements continuously, using screen streams as a source of information. To obtain screenshots or screen streams, researchers either instrumented the architecture or externally recorded some display elements. When proposals obtained screenshots or screen streams on the client side, they obtained metrics related to the user's final receipt. However, proposals that obtained their source information from the cloud server extracted information prior to any visual degradation generated by the infrastructure. As discussed in Section 5, some researchers used graphical content to obtain metrics such as visual quality or frames per second (FPS). These tools can obtain these metrics from graphical content by passively monitoring the connections between graphical representation elements (e.g., a screen monitor). Strategies that instrument the wiring require additional custom hardware. In remote desktop or cloud gaming CIAs, the cloud server can send compressed or uncompressed graphical content over the network. Additionally, the cloud server may be able to communicate with the client by employing graphical primitives of the operating system. In such a case, the cloud server indicates how and which regions of the client's screen it will update. Graphical primitives save bandwidth but require an understanding of the client's graphical libraries and the cloud server. Even when the graphical content was not accessible in real time, some proposals used graphical update primitives.