There's a multiplying grab bag of software, hardware and support technologies that blaze the alternative trails for moving data from operations to decision-makers. The trick is picking the right combination that's most efficient and useful for each application. Here are some of the major networking thoroughfares:
Ethernet—Whether it's communicating open or proprietary protocols/languages, Ethernet is defined in its IEEE 802.3 standard as the physical cables, connectors and support technologies used in local area networks (LAN) and wide area networks (WAN). The entire Internet and IIoT pretty much rides on this infrastructure.
Wireless—Several earlier wireless methods and standards have coalesced over the years, mostly around WiFi and Bluetooth. WiFi is detailed in the IEEE 802.11 stanadards, and consists of a set of media access control (MAC) and physical layer (PHY) specifications for implementing wireless local area network (WLAN) communication in the 900 MHz and 2.4, 3.6, 5, and 60 GHz frequency bands. Bluetooth is governed by its IEEE 802.15.1 standard.
Internet—Though it's grown to include the Internet of Things (IoT) and the Industrial IoT (IIoT), all of these are just more Internet, which is the global system of interconnected computer networks that use the Internet protocol suite (TCP/IP) to link devices worldwide.
HART—Defined long ago as the Highway Addressable Remote Transducer (HART) protocol, HART is a hybrid analog plus digital industrial automation protocol that can communicate over legacy 4-20 mA analog instrumentation current loops, sharing the pair of wires used by the analog only host systems. It's administered by the FieldComm Group.
OPC-UA—OPC Unified Architecture (OPC-UA) is a machine-to-machine communication protocol for industrial automation developed by the OPC Foundation. It concentrates on communicating with industrial equipment and systems for data collection and control; is freely available and can be implemented without restrictions or fees; operates across platforms and isn't tied to one operating system or programming language; uses a service-oriented architecture (SOA); maintains robust security; and uses an integral information model for information integration.
MQTT—Message Queue Telemetry Transport (MQTT) is an ISO standard (ISO/IEC PRF 20922) publish-subscribe-based, lightweight messaging protocol for use on top of the TCP/IP protocol. It's designed for connections with remote locations where a small code footprint is required or network bandwidth is limited. The publish-subscribe messaging pattern requires a message broker. The broker is responsible for distributing messages to interested clients based on the topic of a message.
AMQP—Advanced Message Queuing Protocol (AMQP) is an open standard application layer protocol for message-oriented middleware. The defining features of AMQP are message orientation, queuing, routing—including point-to-point and publish-and-subscribe—reliability and security.
IO-Link—IO-Link is the first standardized I/O technology worldwide (IEC 61131-9) for the communication with sensors and also actuators. Its point-to-point communication is based on the long established three-wire sensor and actuator connection without additional requirements regarding the cable material.
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