# Multi-Layer QoE Learning System Implemented by Fiberhost
## 3 Multi-Layer QoE Metric Nature
### Iv Service Layer
The stream bandwidth can be affected by the codec used, resolution, frame rate and other parameters related to the video. Commonly, streams with lower bitrates are established for mobile devices, since they have a smaller screen size and may struggle with less efficient network access. On the other hand, streams with the highest bitrates are targeted at larger screens, such as those of TV sets. If the network is not efficient enough, it is also possible to play intermediate streams that provide video content of average quality. Continuous stream adaptation allows for video stream playback in degraded network environments. The linear TV service tends to target consumers who play their content on TV sets. In that case, set-top boxes are expected to strive to display the highest quality available. In pure OTT applications, it is usually possible to change the bitrate manually, while in a TV service such a feature seems not to be relevant. From the perspective of a TV operator, any playback of a stream with the quality other than the maximum should be treated as video degradation within a given set-top box. This is particularly true when TV services are provided along with Internet access by the same operator, because it is directly associated with the operator's managed network degradation. Figure 5 demonstrates the percentage of intermediate stream playbacks compared to playbacks of the highest quality streams over 30 days of observation in the Fiberhost TV system. We found that for a given linear TV, the playback of non-maximum streams was more or less constant, constituting about 35% of all playbacks. A significant change occurs when the content delivery network (CDN) servers are close to saturation or there is an increased level of degradation, e.g., due to a system failure or CPU overload of the server streaming Unicast content. When the decoder begins playback, its goal is to play the highest quality stream, but it can accomplish this only when the video buffer reaches a certain level. In the meantime, the decoder will start playback from the lowest video stream, which in this case is 800 kbps. Optimally, the streams with bitrates other than the maximum and other than 800 kbps would not appear in the described chart. In that case, customers could experience stalls that would impact QoE much more strongly than while playing the quality slightly worse than the maximum. Increasing the percentage of the intermediate streams significantly affects the QoE level of individual customers, and is also an indication of the health of the TV service as a whole. On the operator's side, improvements could be made in the area of streaming servers and the access network used for content distribution. On the customer/CPE site, improvements could be made in the area of the Wi-Fi connectivity to ensure the highest possible signal quality and strength. Rebufferings are related to video player buffer saturation. During a stall event, the black screen or loading animation is displayed on the video player. When the playback begins, the CPE represented by the OTT decoder burst downloads video chunks to feed the buffer. After the specified threshold is reached, the STB plays the video content. When a network impairment occurs, the STB does not download new video chunks, so the buffer gets empty, and as a result the stall occurs. It is these occurrences of stalls that were investigated during the 30 days of observation period in Fiberhost TV system. The highest number of errors occurred when two CDN servers malfunctioned and the decoders needed a certain amount of time to download more video segments from other available streaming servers. Table 2 indicates the number of stalls from the hour in which the described event occurred, along with the number of all decoders connected to each aggregation router. The names of the routers have been anonymized at the operator's request.