# Networking for Cloud Robotics: The DewROS Platform and Its Application
## 6 Experimental Evaluation
### Analysis of Response Time  
Factors influencing the response time of CVI are investigated in this section. CVI was selected for this analysis because it presents the best results in terms of the detected labels. Results related to the time required by CVI as a function of the label detection mode requested are analyzed first. Figure 10 reports the relationship between the response time of _Shot&Frame_ and _Unspecified_ detection modes, respectively. A single sample in this figure represents the response time of CVI for a particular video, with a particular combination of all test parameters (e.g., _video location_, _video size_, _video length_). The scatter plot compares the response time of CVI under the two label detection modes conditions, fixing all the other variables. As shown in Figure 10, the requested label detection mode has no significant impact on the response time of the request. The observations are close to the bisector of the first quadrant (grey line in Figure 10) and distributed around (over and under) it. Therefore, it can be assumed that there is no significant difference between the response times for these label detection modes. For this reason, in the following experiments, the label detection mode will not be considered. Figure 9: Empirical cumulative distribution function of the confidence level associated with the labels at different video resolutions for AR in three different videos: A, B and C.  
We now analyze the impact of the video length on the response time of an annotation request. Figure 11 (left) reports such time using the three networks under test and videos with very different lengths (3 s and 71 s) and the same size (about 2 MB). Two important behaviors can be seen in this figure: (i) the lower the connection speed, the higher the response time, and (ii) the two lengths are processed in about the same time by CVI. The former behavior is more expected and mainly due to the time required to upload the video on the Cloud. The latter is less expected. This may suggest that the response time is not strongly impacted by the video length. A scatter plot to validate the last consideration was considered, in which observations with the same combination of variables, except the video length, are coupled together. The resulting plot of Short vs. Long is reported in Figure 11 (right). The figure shows that the points are generally very close to the bisector and randomly distributed around it. This confirms that there is no significant difference between the time required for the annotation of videos of different lengths but the same size. In the following, consideration of the video size will be made. In Figure 12, the response time obtained for the three Internet connections, using Small, Medium, and Large videos, all located at the client side, is reported. The figure evidences very large differences among the Internet connections and video sizes. The variation in the samples (e.g., the extension of the box plots) is interesting, as it tends to decrease with the increase in the response time. The mean of such a parameter, instead, is in clear inverse proportion to the nominal upload speeds of the Internet connections under test (see Table 3 for reference values). The lower the upload speed and the larger the file size, the larger the response  
Figure 11: Response time using the UNI, HOME and SAT network connections, in case of video files hosted locally on the client, with different video lengths (short and long) and the same size. Figure 10: Scatter plot of the CVI response time of two label detection modes, Unspecified and Shot&Frame, fixing all the other variables. time (and its variation). This could easily be due to the fact the video file must be sent to Google servers first and then annotated. To further investigate this important issue, the contribution of the file upload has been isolated.