Internet of Things – Architecture © - 85 -
This interaction is straightforward, as it is identical to typical Internet interactions
between Users and Services. In fact, in most of the application scenario the
User-Service connection can be established using standard Internet protocols.
However, two main exceptions to this general assumption apply when two
Services communicate one to each other and one or both of the communicating
elements belong to a constrained network.
The latter case, which applies when Services are deployed on constrained
Devices such as Sensor nodes and when the User of a given Service is
deployed on a constrained Device, requires for the use of constrained
communication protocols (see D3.3 [Rossi 2012]). Finally, when the two
elements belong to different sub-networks, gateway(s) and/or proxy(ies) must
be deployed for ensuring successful end-to-end communication. To this extent,
as a general rule, if a Service is constrained, or if it needs to provide access to
constrained Users, it must be accessible with constrained protocols (e.g.,
6LoWPAN, UDP, CoAP, etc.).
Service / Resource / Device interactions
Figure 18 illustrates the entities of the IoT Domain Model involved in the
interactions among Services, Resources and Devices. These interactions can
be exemplified with the communication among the Alarm Service, the Alarm
Resource and the Mote Runner Node of the recurring example. This Figure also
illustrates the interconnections of these entities.