that the local service is also maintaining an information database of the data
gathered in the house; database, which is only accessed by the service in the
cloud.
Finally, the system integrator must make decisions about connectivity and data
management: since the time requirements of the application are quite loose, low
power devices can be chosen and low data rate connection can be selected for
the sensing devices.
The first and foremost requirement is the addressability of every Service /
Resource regardless of the Device hosting it. This can be achieved by
supporting IP addressing and its compressed version defined by 6LoWPAN is
currently the most feasible way to implement this in constrained devices. In
addition, to make Resources and Services unambiguously addressable, unique
identifier must be provided. To this extent many solutions have been proposed,
but, in order to obtain the widest interoperability, it is preferable HTTP mappable
solutions, such as CoAP. In such a way it is possible to implement very simple
Services on the most constrained Device by providing web-service like
interaction capabilities to every resource and functionality offered.
However, if the above baseline solution is not realizable, it is important to mimic
its behaviour as close to the source device is located. To this extent Resources,
Services or both can be deployed on other devices such as aggregator servers,
gateways and proxies of the network. In such a way, it is the more powerful
Device providing Resource and Service in the correct format that will interact
with Services and Users on behalf of the final Device; also, this device must
ensure the synchronization between the mimicked functionalities and their
actual counterparts. This workaround allows for the integration of any possible
technologies in the IoT, however it does not grant the full compliance to all the
IoT-A unified requirement list.
However, in order to make the sensing devices interoperable with both the local
and the cloud services, connectivity gateways or proxies must be considered. A
few possible realizations are the following:
Cabled sensors with Ethernet/xDSL gatewayo Pros: reliable, possibility to use the same cable for connectivity
and power.o Cons: high installation costs. Wireless sensors (802.15.4) with Ethernet/xDSL gatewayo Pros: low cost, easy and cheap installation, moderate robustness,
good lifetime.o Cons: may suffer from data losses. Low power WiFi sensors with WiFi/xDSL gateway