# Route Availability as a Communication Quality Metric of a Mobile Ad Hoc Network
## 5 Evaluation of the RA Calculation Method and Verification of Usefulness of RA
### Usefulness of RA as a QoE Metric  
We made a subjective quality assessment test of streaming video to verify whether RA is useful as a QoE metric. In the evaluation environment described in Section 4, videos transmitted from the sender PC were captured by the receiver PC, and the quality of each captured video was assessed by subjects. The test was based on the degradation category rating method (DCR) [22] which has been standardized by ITU-T (International Telecommunication Union--Telecommunication Standardization Sector). Each subject first watched the reference video, then viewed a video to be assessed (test video), and rated the test video using a 5-point degradation scale. There were 40 subjects, men and women aged 10 to 30 years. Many of them were around 20 years old. It was anticipated that subjects aged about 20 tended to be more critical than people in other age groups because they often watch videos on the Internet. Therefore, before starting the test, the subjects were asked to assess test videos considering that the reference video was the highest quality video. The length of assessment time per subject was around 75 min. Since the ratings by the subjects can vary, the rating values by 10 subjects were collected for each scenario. The average of these values was used as the degradation mean opinion score (DMOS). The assessment results are shown in Figures 13-15. Figure 13 shows the relationship between RA and DMOS for videos having different video quality levels. When RA increased beyond a certain value, DMOS rose rapidly, indicating that there is a positive correlation between RA and QoE. While a subject was viewing a test video, the video stopped when the route used was disconnected. When a route was re-established, the test video the subject began to view did not start at the point it stopped. The video that was played during the disconnected  
Figure 12: Relationship between RA and throughput (when video quality was varied). time was skipped. When the test video was played again, block noise arose. If disconnections occurred in rapid succession, the video became seriously corrupted. The fact that DMOS for low-quality videos was higher than that for high-quality videos in Figure 13 can be attributable to the more serious block noise that arose when a high-quality video was replayed after a disconnection. Figure 14 shows the relationship between packet loss rate and DMOS. As the packet loss rate increased, DMOS decreased rapidly up to the point where the packet loss rate was about 0.3. After that, DMOS stayed around 1 even when the packet loss rate increased. Thus, it can be stated that there is a negative correlation between packet loss rate and QoE when the packet loss rate is between 0 and 0.3. Packet loss rate is more loosely correlated with QoE than RA is, as shown in Figure 13, because RA did not reflect the packet loss caused by degradation in the transmission quality in wireless sections. Thus, RA is a metric more sensitive to QoE than is the packet loss rate. Figure 15 shows the relationship between RA and DMOS for the two different routing protocols. The relationship did not differ greatly between the two routing protocols. Although some disconnections may not be detected in the measurement method described in Section 3.2.2 for OLSR, its effect was negligible and did not produce results that were much different from those for AODV, which is sensitive to disconnections. However, the way streaming videos degraded differed between AODV and OLSR. Since AODV is more sensitive to disconnections caused by link disconnections than OLSR is, instantaneous disconnections can occur more frequently with AODV. As a result, block  
Figure 14: Relationship between packet loss rate and DMOS (when video quality was varied). Figure 13: Relationship between RA and degradation mean opinion score (DMOS) (when video quality was varied). noise, which arose when a video was replayed or when key frames were lost, tended to occur more frequently.