# Low Power Multi-Hop Networking Analysis in Intelligent Environments
## 4 Methodology  
In order to come near the intelligent home environment network deployment, the tests presented in this paper were carried out in the test bench deployed in the laboratory of the research group. The nodes were spread in the laboratory and the corridor nearby. Firstly, it was checked that the medium range distances considered in the following tests had no significant influence in the latency of the communication. After that, it was applied the methodology to analyze the performance of master-slave gateways in scatternets described in [48]. The proprietary middleware in the nodes of the test bed considers the Basic Data Rate, as well as some specific values to define the parameters for the low power modes under test. For instance, the sniff low power mode is defined by the amount of desired slots for the _Sniff_Max_Interval_, two slot less for the _Sniff_Min_Interval_, one slot for the \(N_{\mathit{sniff\_attempt}}\) and eight slots for \(N_{\mathit{sniff\_timeout}}\) parameters. In addition, the park low power mode is defined by the amount of desired slots for the _Beacon_Max_Interval_, and two slots less for the _Beacon_Min_Interval_ parameters. The scheme of interconnection of nodes in the test bench is shown in Figure 3 for the case of four hops in the communication. It included a computer connected to the end nodes, i.e., the first and last ones of the network, to ease the monitoring process. The NW tester and the addressed node emulator (ANE) functionalities were built-in the computer. All the functionalities, i.e., NW tester, DS and ANE, were synchronized because they shared the computer. Thus, the time that the data packets took hopping from slave to master nodes could be measured, in addition to the time taken from master to slave nodes. So, the tests were carried out as explained next. First, the NW tester functionality sends _ping_ type data packets to the last node of the wireless test network, i.e., node N6 in Figure 3. The halfway nodes receive the packets, process and resend them towards the addressed node. The ANE functionality in the computer receives the _ping_ packet, logs the reception moment and sends the answer packet while logging the transmission moment. The answer consists of a _pingback_ type data packet. Since the communication follows the TDM scheme, both the _ping_ and _pingback_ packets, fit in a time slot defined in the Bluetooth standard (625 \(\upmu\)s). So, the _pingback_ packet flows along the network, going from slaves to masters of the piconets and in the end, it reaches the computer connected to the first node of the network. The DS functionality included in the computer logs the reception moment of the _pingback_ packet. The latencies for both the _ping_ packets (master-to-slave communication) and the _pingback_ packets (slave-to-master) are obtained as the differences between the logs in both ends of the network. Therefore, each _ping_ packet went hopping from node to node until it reached the destination node. Similarly, the _pingback_ packets went back to the source node following the same path. The following _ping_ packets were sent right after the _pingback_ packet reached the source node. This way, the _ping_ packets were randomly sent, as the sending interval was defined by the latency of the network, which turned to be not constant and with some deviation in the tests. The tests were repeated numerous times (a total amount above 12,000 samples were taken in park mode and almost 11,000 samples in sniff mode). The 95% percentile of the latency distribution for each one of the situations considered was chosen to be analyzed because it provides us with the upper limit of the latency. This statistic datum helps the network engineers to design the management of limited response time systems or intelligent environments with the latency limit estimation of multi-hop communications over Bluetooth Asynchronous Connectionless Links (ACL) in park and sniff mode.