Internet of Things – Architecture © - 87 -
3.6.2 Communication interoperability aspects
The model we are going to propose in this section takes its roots from the
ISO/OSI [ISO 1994] stack, the US Department of Defense 4 - layer model
(DoD4) [Darpa 1970] and, the Internet stack, but it puts its focus on IoT
specific features and issues. All the previous models have a great value, going
beyond any discussion, but simply they have not been conceived with the IoT
issues and features in mind.
Figure 19 : 4 layers Internet stack (left) and DoD4 stack (right).In Figure 19 we can see Internet and the DoD4 stacks. it is evident how towel
they map onto each other, thus in what follows we will address the 4 layers
Internet model only.
The 4-layer Internet stack abstracts from the underlying Physical Layer; in fact
its lowest layer is represented by the Link Layer. This choice is indeed the right
one for the Internet, as the Link Layer is not visible from the Application Layer,
and the same can be be applied to fully homogeneous networks, since
applications can be totally agnostic of the underlined common physical
technology. However, the Physical Layer rises to a great importance when
talking about the IoT; in fact the IoT is characterized by a high heterogeneity of
hardware and technologies and the necessity of making different system
interoperable. Moreover, this is a clear statement on the fact that IP is
conceived in order to be implemented on top of any hardware networking
technologies, while in the IoT there exist technologies that do not dispose of the
needed resources to manage a complete IP compliant communication. Thus,
solutions such as 6LoWPAN, are needed to extend IP communication to
constrained networks.
Moreover the main objective of the 4-layer Internet model is to let Internet
applications communicate, having intermediate devices understanding the
communication at IP level, without meddling with upper layers. This model is
Internet DoD4