  3GPP has recently introduced NB-IoT, a new mobile communication standard
offering a robust and energy efficient connectivity option to the rapidly
expanding market of Internet of Things (IoT) devices. To unleash its full
potential, end-devices are expected to work in a plug and play fashion, with
zero or minimal parameters configuration, still exhibiting excellent energy
efficiency. We perform the most comprehensive set of empirical measurements
with commercial IoT devices and different operators to date, quantifying the
impact of several parameters to energy consumption. Our campaign proves that
parameters setting does impact energy consumption, so proper configuration is
necessary. We shed light on this aspect by first illustrating how the nominal
standard operational modes map into real current consumption patterns of NB-IoT
devices. Further, we investigate which device reported metadata metrics better
reflect performance and implement an algorithm to automatically identify device
state in current time series logs. Then, we provide a measurement-driven
analysis of the energy consumption and network performance of two popular
NB-IoT boards under different parameter configurations and with two major
western European operators. We observed that energy consumption is mostly
affected by the paging interval in Connected state, set by the base station.
However, not all operators correctly implement such settings. Furthermore,
under the default configuration, energy consumption in not strongly affected by
packet size nor by signal quality, unless it is extremely bad. Our observations
indicate that simple modifications to the default parameters settings can yield
great energy savings.
