6LowPAN (IPv6 in Low-Power Wireless Personal Area Networks) for IEEE 802.15.4 networks

The Internet of Things profoundly alters the usual vision of protocols, as the constraints are different from conventional computing environments. In particular, energy constraints are significant, as objects would have non-continuous power sources, either batteries or recovery of ambient energy (temperature changes, vibrations, radio wave energy...). Fortunately, today's processors are relatively energy-efficient, and transmission is the criterion to be optimized. However, equipment must be kept inactive for as long as possible to avoid transmitting data too regularly, as listening is just as costly as transmitting, due to the complex operations involved in decoding signals. It is also important to avoid a situation in which one piece of equipment is constantly tapping into all the traffic to retrieve the data intended for it. This last criterion runs counter to protocols based on broadcast networks such as Wi-Fi. Another consequence of energy conservation is the low power of transmitted signals, which means that either data must be relayed if the distances to be covered are great, or sophisticated coding must be used to cover long distances, but at the expense of throughput.

Finally, another difference comes from the low computing power compared with that of a computer, as well as the low memory resources which will impose strong constraints on the size of the embedded program and on the contexts imposed for dialoguing with its environment (neighborhood tables...). This will require a much more integrated protocol approach than that offered by the ISO (International Organization for Standardization) reference model, which tends to separate functionalities and insist on interfaces between layers. So, in the Internet of Things, even if the model is respected in its philosophy, its implementation will require optimizations, such as the sharing of information between layers. Moore's Law, on the evolution of computing power, is to be interpreted differently when it comes to the Internet of Things, since, given the massive diffusion expected in the years to come, cost criteria will be decisive. This law will therefore tend towards a reduction in costs, rather than a drastic increase in power.

Finally, the Internet of Things will have to take into account object lifecycles that are totally different from IT developments. The lifespan of an electricity (or gas) meter is around twenty years, and although Internet Protocol has remained stable over similar periods, the means of transmitting packets have evolved considerably. There are two possible scenarios:

• integrate into the Internet of Things existing equipment that lacks communication capacity or uses proprietary methods incompatible with Internet protocols;

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