Internet of Things Architecture

Internet of Things – Architecture © - 94 -

Figure 24 : Channel model for the current Internet.

To proceed in modelling the channel in IoT it is important to give a definition of
what we call constrained and unconstrained networks:

 Unconstrained networks are characterised by high-speed

communication links (e.g., offering transfer rates in the Mbit/s range or

higher) like, for instance, the wired Internet of today. Link-level transfer

latencies are also small and mainly impacted by congestion events in the

network rather than by the physical transmission technology;

 Constrained networks are characterised by relatively low transfer rates,

typically smaller than 1 Mbit/s, as offered by, e.g., IEEE 802.15.4. These

networks are also characterised by large latencies. These are due to

several factors including: (1) the involved low-bitrate physical layer

technology and (2) the power-saving policy of the terminals populating

these networks, which may imply the periodic power off of their radios for

energy-efficiency reasons.

According to this, heterogeneous networks can be seen as the combination of
constrained and unconstrained networks linked together via gateways and/or
proxies.

The picture is much different in the IoT. As can be seen in the scenarios
depicted in [Rossi 2013], in the simplest IoT case the channel consists of a
single constrained network (e.g. a WS&AN island), as depicted in Figure 25.

Figure 25 : IoT channel for a single constrained network.

In a slightly more complicated case, the IoT channel can consist of several
constrained networks, which can rely on different network technologies (see
Figure 26 ).

Figure 26 : IoT channel for communication over two constrained networks.

A different case consists of a channel embodied by a constrained network and
an unconstrained one (see Figure 27 ).