# Low Power Multi-Hop Networking Analysis in Intelligent Environments
## 6 Selection of the Most Suitable Low Power Mode
So, since there are no known interoperability problems with sniff mode (the specification for sniff mode is very simple compared to the one for park mode), and the system is less complex (which reduces its cost), such alternative solution provides better performance. All in all, the focus of this paper is set on the time performance of the multi-hop networks and the subsequent power consumption reduction of the low power modes under test, sniff and park. It is out of the scope the way to handle more than seven slaves in a single piconet. Then, the power consumption in both modes is almost the same [51]. In fact, the sniff mode uses a little less power because of two facts: the sniff mode does not require regular Link Management Protocol (LMP) negotiations, and the beacon channel signaling in park mode requires more bandwidth. Figure 8 shows the reduction of the current consumption when the inactivity interval in sniff mode, \(T_{sniff}\), increases [52]. It shows a general trend where small values of \(T_{sniff}\) provide minimal power savings, but larger values show diminishing returns. As \(T_{sniff}\) becomes longer, the slave must expand its uncertainty window to allow for clock drift, so it uses more power. Then, in the situation depicted in Figure 8, the best choice to set \(T_{sniff}\) that provides the best latency-power consumption trade-off is about 100 ms, because there is a rapid power increase for shorter intervals, and the little additional power savings for longer intervals do not justify the decrease in the responsiveness of the system. Then, the main factors that must be taken into account to select the most suitable Bluetooth low power mode deployments in intelligent environments are the power consumption of the network and the latency QoS metric. Both sniff and park low power modes provide almost the same power saving when the inactivity interval increases. So the key difference between these modes must be found in terms of QoS, i.e., latency. [PERSON] and [PERSON] looked for the best mode power-wise for a link under particular traffic conditions [53]. Sniff mode was found to be particularly indicated in piconets when data duration is small compared to data period while park mode results effective when data duration is longer. [PERSON] et al., showed that sniff offers low power consumption and low transmission delay inside a piconet [54]. Furthermore, in multi-hop communications along a scatternet, the experiments in this paper demonstrate that sniff provides smaller latency than park when the inactivity interval is about 1 s or less. Such inactivity interval optimizes not only the responsiveness of the system for most of the applications that can be found in the real world, but also the latency-power consumption trade-off of the system. The only issue to take into account when operating in sniff mode is the amount of slaves that would simultaneously need to participate in each one of the piconets of the multi-hop network. Generally speaking, sniff low power mode is the best choice when compared to park low power mode for multi-hop communications with Bluetooth standard with burst pattern data traffic, i.e., short data packets. Such data packets usually are in many applications for the Internet of Things (IoT) [55]. Actually, the latest version of the Bluetooth specification is focused on applications for IoT and it does not support the park low power mode. Then, each application must evaluate their specific needs and determine a suitable value for the sniff interval through experiment running. Moreover, the value set in all of the sniff mode parameters depends on the use case and the role assignments for the nodes involved. Therefore, the best way to set these values is to carry out interoperability tests and try different combinations of values. Then, it will be easy to find out which set of parameters works best when considering the trade-off between power consumption and latency.