## 5 Experiments and Evaluation
### Response Time  
In the first experiment, external sensor applications concurrently gathered the temperature data of three rooms with two cases; a conventional WSN and TinyONet. To examine the response time of concurrent applications, we performed the test ten times by increasing the number of sensor applications one by one. To emulate conventional WSN, the URGENT and GET packets were used to provide the synchronous communication. For the case of TinyONet, the REGISTER and GET packets were used as usual.  
Response time, \(T_{response\_time}\), is defined as the amount of time that the last sensor application takes to get the response when several external sensor applications issue a request simultaneously. As shown in Equation (1), \(T_{response\_time}\) is composed of three factors; \(T_{transmission}\), \(T_{process}\), and \(T_{wm}\). \(T_{transmission}\) is the transmission time between a sensor application and TinyONet. \(T_{process}\) is the processing time within TinyONet. \(T_{wm}\) is the elapsed time to complete gathering sensing data on WSN.  
\[T_{response\_time}=T_{transmission}+T_{process}+T_{wm} \tag{1}\]  
The graph in Figure 11 shows the response time of two cases. The graph indicates that the response time of the conventional WSN is linearly increased according to the number of sensing applications. Comparing to this, the response time of TinyONet is nearly constant value regardless of the number of sensor applications. We identified that the difference is caused from \(T_{wm}\). Both cases have similar \(T_{\textit{transmission}}\) and \(T_{\textit{process}}\), but they have totally different \(T_{\textit{vem}}\). In ordinary WSN, only a single packet can be transmitted at a time over radio due to the lack of the channel multiplexing. That is, multiple requests from concurrent sensor applications have to be queued and processed one by one on WSNs. For this reason, in the conventional WSN, the response time of the n-th sensor application, \(T_{\textit{response\_time}}(n)\), can be modeled as Equation (2).  
\[T_{\textit{response\_time}}(n)=T_{\textit{transmission}}(n)+T_{\textit{process}}( n)+\sum_{k=1}^{n}T_{\textit{vem}}(k) \tag{2}\]  
While the \(T_{\textit{vem}}\) of the conventional WSN is affected by the number of sensor applications, the \(T_{\textit{vem}}\) of TinyONet is nearly regular because the elapsed time for completing the report session is independent of the number of external sensor applications. Since the data packets on WSN are asynchronously transmitted independent of the external sensor applications' request, \(T_{\textit{vem}}\)  is considered as a constant value. Therefore, the response time of the n-th sensor application in TinyONet can be modeled as Equation (3). As shown in the equation, all the applications share the same elapsed time, \(T_{\textit{vem\_common}}\)  for communicating with WSN.  
\[T_{\textit{response\_time}}(n)=T_{\textit{transmission}}(n)+T_{\textit{process}}( n)+T_{\textit{vem\_common}} \tag{3}\]  
Generally, \(T_{\textit{transmission}}\)  and \(T_{\textit{process}}\)  are much smaller than \(T_{\textit{vem\_common}}\), therefore the response time of TinyONet seems a constant value regardless of the number of sensor applications.