Specification

IoT is not one technology, so no single specification defines it. The radio, the network, the application protocol and the service layer each come from a different body, such as 3GPP, ETSI, IEEE, IETF or an industry alliance. This page lists the main documents for each of them, and then the consortia that work on IoT above the protocol level.

Which documents define each IoT technology ?

The table has five groups: IoT, M2M, MTC, D2D and LTN. Inside the IoT group, the rows are split into Unlicensed radio, Licensed radio and Application protocols. For the 3GPP NB-IoT rows, the table also gives the relevant sections of each specification. NB-IoT was added into the existing LTE specifications rather than written as new ones, so you need these section numbers to find it.

IoT
Unlicensed	6LowPAN	IPv6 over Low Power Wireless Personal Area Network (RFC 4944)
	IEEE 802.15.4	Wireless PAN (IEEE 802.15.4)
	RPL	Routing Protocol for Low Power and Lossy Networks
	LoRa	LoRa Specification
	SigFox	SigFox Home
	ZigBee	ZigBee Smart Energy 2.0
	PLC	Powerline Communication
Licensed	LTE	Category 1, Category 0, LTE-M (M1, M2)
	NB-IoT (NB-LTE)	3GPP TR 45.820 V13.1.0 (2015-11)
		3GPP 36.133 - Requirements for support of radio resource management (search 'NB' in the document)
		3GPP 36.211 - Physical channels and modulation, section 10.2.3, 10.2.5, 10.2.6,10.2.7,10.2.9
		3GPP 36.212 - Multiplexing and channel coding, section 6.4.3
		3GPP 36.213 - Physical layer procedures, chapter 16
		3GPP 36.306 - 4.1C UE Category NB
		3GPP 36.302 - Services provided by the physical layer (search 'NB' in the document)
		3GPP 36.321 - MAC Protocol, section 3.1,3.2,4.4,5.1,5.3,5.4,5.7
		3GPP 36.322 - RLC Protocol (Search 'NB' in the document. It is everywhere)
		3GPP 36.331 - RRC Protocol, section 4.2.1,4.4,5.1.3,5.2.2,5.2.3
		3GPP 36.401 - Architecture description, section 6.1,6.2.1,6.2.4,6.4, 7.2.5,7.2.7,7.2.11,7.2.12,9.1,9.2,11.2
Application	MQTT	MQ Telemetry Transport
	CoAP	RFC 7252
	WebSocket	RFC 6455
M2M
	OneM2M	ETSI OneM2M, OneM2M Home
	ETSI TS 102.690	Machine-to-Machine communications (M2M); Fuctional Architecture
	ETSI TS 102.921	Machine-to-Machine communications (M2M); mla, dla and mld interface
MTC (Machine-Type Communications)
	RP-141865	Further LTE Physical Layer Enhancements for MTC
	TR 36.888	Study on provision of low-cost MTC UEs
D2D (Device to Device)
	TR 22.803	Feasibility study for Proximity Services(ProSe)
	TS 22.278	Service Requirements for the Evolved Packet System (EPS)
	TR 23.703	Study on Architecture Enhancements to support Proximity-based Services(ProSe)(Release 12)
	TS 23.303	Proximity-based services(ProSe); Stage 2(Release 12)
	TR 33.833	Study on Security Issues to support Proximity Services
	TR 36.843	Study on LTE Device to Device Proximity Services-Radio Aspects
	TS 24.333	Proximity-services Management Object(MO)
LTN (Low Throughput Network)
	ETSI GS LTN 001	Low Throughput Network (LTN);Use Cases for Low Throughput Networks
	ETSI GS LTN 002	Low Throughput Network (LTN);Functional Architecture
	ETSI GS LTN 003	Low Throughput Network (LTN);Protocol and Interfaces

Keep the date of this table in mind, because it reflects the state of 2015 and 2016. Some names in it have changed since then. In the LTE row, "LTE-M (M1, M2)" follows the early naming, where M2 was sometimes used for the narrowband solution. In Release 14, 3GPP used Cat-M2 for a wider LTE-M category of up to 5 MHz, and NB-IoT got its own categories, Cat-NB1 and Cat-NB2. The NB-IoT specifications also kept growing after Release 13, so the section numbers in the table point to the Release 13 versions.

The M2M group has changed too. ETSI moved its M2M service layer work into oneM2M, so the ETSI TS 102 690 architecture now continues in the oneM2M Technical Specifications. On the unlicensed side, the ZigBee Alliance renamed itself the Connectivity Standards Alliance in 2021, and it now also publishes Matter for smart home devices.

Each layer has its own standards body : The radio comes from 3GPP, IEEE or an alliance. The IP adaptation and the application protocols come from IETF, and the service layer comes from ETSI and oneM2M.
NB-IoT lives inside the LTE specifications : Search for "NB" in 36.211, 36.212, 36.213, 36.321 and 36.331, as the table suggests.
Check the category names against the release : Cat-M2 in a 2016 document and Cat-M2 in Release 14 are not the same thing.

Standard Bodies

Besides the formal standards bodies such as 3GPP, ETSI, IEEE and IETF, industry consortia also write IoT specifications. They work above the radio, on device interoperability, data models and reference architectures. The two below were both founded in 2014, and both have changed their names since then.

OIC, Open Interconnect Consortium, became OCF, Open Connectivity Foundation, in 2016. OCF defines how IoT devices discover each other and exchange data, and IoTivity is its open source implementation. IIC, Industrial Internet Consortium, became the Industry IoT Consortium in 2021. It works on reference architectures and testbeds for industrial IoT rather than on protocols. So the two groups answer different questions. OCF asks how two devices talk to each other, and IIC asks how an industrial system is built from many of them.

Several alliances in the table above also act as standards bodies for their own technology. The LoRa Alliance publishes the LoRaWAN specification, and the Connectivity Standards Alliance publishes ZigBee and Matter. They are missing from this list only because the table already links to their specifications.

Consortia work above the radio : They define device models and architectures, and they rely on 3GPP, IEEE and IETF for the transport.
Both names on this list have changed : Search for OCF and the Industry IoT Consortium to find their current documents.