Internet of Things – Architecture © - 89 -
In this figure above: (left) compared to the ISO/OSI communication stack
(right): dashed lines have been used for the IoT aspects to make them
graphically different from stack layers.
The model, as depicted in Figure 20 on the left-hand side, stresses the
relevance of the wide range of interoperability aspects that characterise IoT
systems. In fact, instead of focusing on a specific realisation of the
communication stack, the IoT Communication Model provides a transversal
approach from which one or more communication stacks can be derived: in fact
a single interoperability aspect can be used to describe the interactions of
stacks belonging to different communicating systems. Once a system is
modelled according to the IoT Communication Model it is easy to derive a set of
ISO/OSI interoperable stacks in order to provide the needed interoperability
features.
Below, the different interoperability aspects are described:
Physical aspect: This interoperability aspect concerns the physical
characteristics of the communication technologies used in the system. It
is similar to the OSI Physical Layer. This is necessary in order to neither
exclude any available technology, and to prevent emerging solutions
from being integrated into the Reference Model. This aspect does not
force the adoption of any specific technology, but it uses the adopted
technologies as a base to model the remaining of the system. In fact, as
per the recurring example the Mote Runner Node can communicate
using some low-power radio transceiver such as ZigBee, while the
AndroidApp can be hosted in an IoT-Phone connected to the Internet
either via WiFi or 3G cellular networks; Link aspect: In order to address the heterogeneousness of networking
technologies represented in the IoT field, the Link aspect requires special
attention. In fact, most networks implement similar, but customised
communication schemes and security solutions. In order for IoT systems
to achieve full interoperability, as well as the support of heterogeneous
technologies and a comprehensive security framework, this layer must
support solution diversity. At the same time, it needs to provide upper
layers with standardised capabilities and interfaces. Therefore, this layer
needs to abstract a large variety of functionalities, enabling direct
communication. IoT systems do not have to restrict the selection among
data link layers, but must enable their coexistence; Network and ID aspects: This interoperability aspect combines two
communication aspects: networking, which provides the same
functionalities as the correspondent OSI layer; and identifiers, which are
provided using resolution functionalities between locators and IDs. In