In no doubt, IoT is network oriented – even the name IoT naturally relates to the Internet network. Communication is an essential part of IoT idea. Every IoT device must communicate somehow, even most simple, passive RFID tag – it responds with some data to the excitation. Communication is always performed with some rules known for both communicating parties. Like people have their different languages to use, devices have protocols. Communication protocol describes how to address the information to the remote device, how to encode the data, how to check the correctness of the incoming message. The physical layer of protocol description also tells how to transmit every bit of data, what is the frequency of radio waves, how fast we can send the data, what is the maximum range of the transmission.
Communication in IoT devices can be wired or wireless.
IoT networking is much different than typical, multilayered, stack-oriented TCP/IP or similar communication model; we know well while using our PC, MAC, server or Smartphone on a daily basis.
Indeed constrained IoT devices are usually unable to operate regular – full time on, ISO/OSI layered stack, because of constrained resources. In details it primary means, IoT devices are limited by the processor power, RAM and storage sizes and mainly because of limited power resources. IoT device is expected to be energy efficient, thus low powered, that in most cases excludes typical wireless connection standards, e.g. WiFi. On the other hand, IoT devices are expected to communicate over long distances – some couple or a dozen of kilometres – where wired infrastructure like Ethernet cables and related infrastructure is non-existent and most of the wired technologies, copper-based is out of range.
Also, IoT devices daily life-cycle is much different than, e.g. or PC life-cycle. We as humans used to switch on the notebook, work extensively on the web, then put it to the low power or off, making the machine to sleep, hibernate or just shutting it down. And we wake it up when needed. It barely makes network operation during sleep. IoT devices are expected to be sleeping providing low power mode whenever possible, and on the other hand, they're supposed to be fully operable, when only needed. Most performed IoT tasks related to the sensing have cyclical nature, i.e. measuring gases as a sensor-network node whereas period can be something like between seconds and months or even longer. Anyway, they're usually expected to trigger themselves to be awake from sleep, perform some operation and connect to the network.
Because of the existence of different IoT devices including those very constrained from 8-bit processors with some kB of the RAM to 32-bit multicore machines well-replacing PCs, IoT networking is very competitive on protocols, approaches and solutions. There are indeed some networking standards introduced by standardisation organisation like IEEE, yet they are competed by large manufacturers forcing their complex solutions including dedicated hardware, software and protocols. The third force driving this market are open solutions and enthusiasts, usually working with cheap equipment, providing de-facto standards for many hobbyists and also industry.
Following chapters explain some most popular concepts about how to organise network fulfilling the above constraints on communication between IoT devices (Machine-2-Machine) and how to let them communicate with the Internet: including hardware, software and human-users. We focus on the de-facto standards existing in the web, usually as open-source libraries and somewhat low-cost devices.
An interesting survey made by RS components [1] shows 11 wireless protocols used in IoT. Some of them you can use free, without having any license to purchase, while some others are proprietary, some of them need the subscription plan.