Industrial IoT gateway

01

Match protocols, data points and buffering

USR IoT's N720 edge gateway, as an example of the class, collects data over Modbus RTU, Modbus TCP and DL/T645-2007 from two RS485 ports and one Ethernet port, decodes and computes up to 1,000 data points, and reports them as JSON over MQTT or TCP, with up to 2 MQTT and 2 TCP connections and optional SSL encryption. It caches data to an SD card when the internet link is lost and sends it when the link returns, runs from 9–36 V DC, and is rated for –40 to 85 °C operation. [1]

The OASIS MQTT 5.0 standard defines three delivery levels — QoS 0 'at most once', QoS 1 'at least once' and QoS 2 'exactly once'. A client's keep-alive is the longest interval allowed between its control packets; if the server hears nothing within one and a half times that period it must close the connection, and a stored 'will' message can then be published to tell others the gateway has dropped off. [2]

Editorial calculation: with a 60 s keep-alive, the broker closes a silent gateway's connection after 90 s. A gateway reading 1,000 points every 10 s produces 1,000 × 6 × 60 × 24 = 8.64 million values per day, which is what its local buffer must hold for each day of outage. The keep-alive and poll interval are assumed examples. [2] [1]

Give the supplier the field devices and protocols (Modbus RTU/TCP, others), number of points and poll rates, upstream platform and protocol (MQTT broker, OPC UA server, cloud), required QoS and buffering time, network links (Ethernet, cellular), security requirements, power supply, mounting, and ambient temperature.

02

Check the OPC UA TCP connection settings

Where the gateway serves or reads OPC UA rather than MQTT, the OPC Foundation's Part 6 mapping sets the transport rules. Endpoints using OPC UA TCP take the URL scheme 'opc.tcp'. When a client opens a connection, its Hello message states a ReceiveBufferSize and SendBufferSize, the largest message chunk it can receive or will send, which shall be at least 8192 bytes, or at least 1024 bytes if it intends to use an ECC security policy. MaxMessageSize and MaxChunkCount limit a response, with zero meaning no limit, and a server returns Bad_ResponseTooLarge when a response exceeds them. The EndpointUrl in the Hello message shall be less than 4096 bytes, and the specification says it "is used to allow multiple Servers to share the same endpoint on a machine". [4]

Editorial note: a gateway that maps 1,000 points, as the USR N720 example does, can return large read responses, so test reading all points in one request against the gateway's message size limits during acceptance, and confirm which security policies it supports before placing it behind the DMZ that NIST describes. [1] [3]

03

Place the gateway in a segmented OT network

NIST's Guide to Operational Technology Security (SP 800-82 Rev. 3, September 2023) describes a proximity network that "typically connects these edge nodes as one or more clusters to a gateway" that bridges to other networks, over a corporate network, a private overlay on the internet or 4G/5G. In its example architecture, traffic from the IIoT platform is routed through the DMZ border firewall, and it recommends a DMZ separating OT from the enterprise network so that connections pass through DMZ services. [3]

NIST also describes unidirectional gateways or data diodes as an alternative to firewalls that permit authorised communication in only one direction — for example between Purdue layers 2 and 3, protecting layers 0–2 from an incident at layers 3–5 — advises making outbound firewall rules as stringent as inbound ones, and asks that routers, gateways and other devices log events to a central platform. [3]

Editorial note: a gateway that only publishes data outwards can be placed so that no inbound connection from the enterprise or internet is needed; ask suppliers whether remote management requires inbound access, and how certificates, passwords and firmware updates are handled.

04

From Modbus-to-MQTT boxes to cellular routers and ARM edge computers

Listings range from protocol-specific gateways (Modbus, MQTT, OPC UA, BACnet, IEC 104, IEC 61850) to cellular routers with edge computing and ARM-based edge computers; ask each for the protocols, point count, buffering and security features of the exact model.

05

Processor, buffer storage, RS485 and Ethernet ports, cellular uplink and DIN-rail supply

06

Temperature rating, DC input, ports, buffer storage and protocol list for a gateway order

The USR N720 example supplies the published figures in this table (–40 to 85 °C, 9–36 V DC, two RS485 ports, one Ethernet port); CPU, RAM and Wi-Fi rows have no published value and must come from the offered model. [1]

07

Send the device, protocol and network data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Field: [devices; protocols; points; poll rates]
Upstream: [MQTT broker; OPC UA; cloud; QoS]
Buffering: [outage time to cover]
Network: [Ethernet; cellular; DMZ placement]
Security: [TLS; certificates; logging; updates]
Power: [voltage]
Environment: [temperature; humidity; mounting]
Management: [remote access method]

See manufacturer records Send an enquiry through CNFX