Experimental Characterization of Mobile IoT Application Latency

The Internet of Things (IoT) emerges as a myriad of devices and services that interact to build complex distributed applications. Interoperability and standardization are imperative for the realization of this vision. Machine-to-machine (M2M) communications standards can be the middleware that glues together the IoT. However, standards are highly complex and require a large amount of interpretation, deployments are currently scarce, and performance evaluations simplistic or speculative. In this paper, we focus on the experimental evaluation of latency in IoT service composition with mobile gateways (GWs). We measure latency between system components and quantify application protocol overheads to assess the capabilities and limitations of a standard M2M middleware. We designed and implemented a mobile e-health use case on top of ETSI M2M and openEHR standards. We ran a pilot remote monitoring ten people for three weeks, collecting nearly 480 h of data. Our results show that while the latency added by a broker lies around 25 ms, the cellular network often exceeds 1 s, becoming a problem for interactive applications. Moreover, we observe that latencies between a smartphone GW and cloud hosted services vary largely depending on the user mobility, and on the promotion delay of the used wireless network.