# Networking for Cloud Robotics: The DewROS Platform and Its Application
## 6 Experimental Evaluation
### Analysis of Response Time
Figure 13: Upload Time Distributions for each video type using the satellite (SAT) Internet connection  
We looked further into this unexpected outcome, examining the application protocol implemented by CVI. Using several Wireshark packet traces, varying the label detection mode, the length and size of our videos, all of which were already uploaded on GCS, were obtained. Then, the trace files were manually inspected to extract the client-server interaction pattern triggered after an annotation request. The application-level packets exchanged between client and server are encrypted with the TLSv1.2 protocol; their content is not accessible, so the sequence diagram notes rely on assumptions based on other information, such as domain names obtained from DNS responses. In the sequence diagram reported in Figures 17 and 18, the TLS conversations needed to extract relevant information regarding the communication delays are shown. Figure 16: Response time using the UNI, HOME and SAT network connections, in case of a pre-loaded video on Google Cloud Service server, with different size (small, medium and large). Figure 11:0 Coefficient of Variation calculated using all the video types and connections using locally hosted video files. Figure 11:1 Sequence Diagram: API RTTs Analysis, setup phase. In this context, two parallel TLS sessions are established between the client and the Google server. The first one is established with a web server, while the second one is established with an authentication server. Moreover, we focused on the request-response patterns, where the client must wait for the server response before sending the next message, called \"ping-pong\". In this context, there are several steps that need to be taken before the results are sent to the client in the form of labels. For every request-response, one or more RTT should be considered, which have a massive influence on the server response time. The total number of RTTs for one video annotation request is between 10 and 12. However, this fluctuation is related to the number of RTTs in the textit\"Waiting Phase\", which appears to be independent of the type of request. Moreover, some additional terms of client-side lag, which are not related to the network delay, and so are almost similar for every connection, are evidenced. This analysis led to expressing the annotation time \(T_{A}\), namely, the amount of time elapsed between the annotation request and the reception of the labels by the client, with this formula  
Figure 11:2  
where, as mentioned previously, the random variable \(X_{L}\) takes all the lag components into account, mostly client-side, not related to the network delay. At this point, the purpose is to validate the previous equation, comparing the differences between the response variables related to each connection under test with the ones  
Figure 11:3 Sequence Diagram: API RTTs Analysis, data exchange phase. coming from the formula, expressed in terms of RTTs. Thus, assuming that \"_HOME_\" and \"_UNI_\" connections are similar in terms of RTT, only the second one will be considered in the calculations  
\[ \begin{split} T_{A_{SAT}}-T_{A_{UNI}}=&\\ & X_{L_{SAT}}+(11\pm 1)*RTT_{SAT}-X_{L_{UNI}}+(11\pm 1)*RTT_{ UNI}=\\ &=(X_{L_{SAT}}-X_{L_{UNI}})+(11\pm 1)*(RTT_{SAT}-RTT_{ UNI})\approx\\ &\approx(11\pm 1)*(0.637-0.023)s=(11\pm 1)*0.614s\end{split}  \tag{2}\]  
If we consider the term \(X_{L_{SAT}}-X_{L_{UNI}}\) to be very close to zero on average, the result of the equation is a number in this range:  
\[T_{A_{SAT}}-T_{A_{UNI}}\in[6.14s\,,7.36s] \tag{3}\]  
In conclusion, the difference between the RTTs is reflected in the server response time, as well as when the video file is stored server-side. In addition, the SAT connection RTT is one order of magnitude higher than the other two connections, resulting in a slower server response time. Finally, how the video length impacts the response time in the case of videos which were already loaded on the Cloud has been considered.