Hermes OSIndustrial Intelligence Platform
Back to the library

Industrial Protocols

MQTT

Pub/sub topics, QoS, and edge telemetry patterns.

OT Network

Overview

MQTT is publish/subscribe telemetry for the edge: lightweight clients push topic-organized data through a broker, decoupling producers from consumers.

Engineering purpose

Move sensor and edge data to platforms and dashboards efficiently over unreliable links, with state recovery via retained messages and Last Will.

How it works

Clients connect to the broker with keep-alive supervision; topic hierarchies (site/area/device/signal) enable selective subscription; QoS levels trade delivery guarantees against throughput; retained messages give late subscribers current state.

  • Topic hierarchies (site/area/device/signal) enable selective subscription — design them before deployment.
  • QoS 1 can duplicate and QoS 2 costs throughput — choose per signal criticality.
  • Retained messages and Last Will provide state recovery and device-loss detection.

Common faults

Keep-alive exceeding firewall NAT idle timeouts causing periodic drops; QoS 2 throttling throughput unnecessarily; topic sprawl without a designed hierarchy; open brokers on OT networks.

Diagnostic checks

  1. 1Verify broker authentication and TLS — never run open brokers on OT networks.
  2. 2Monitor client reconnect counts; flapping indicates network or keep-alive issues.
  3. 3Monitor client reconnect counts at the broker — connection flapping localizes network and keep-alive problems.

Safety notes

MQTT is telemetry, not control: never close protective loops over a broker, and never run unauthenticated brokers on OT segments.

Commissioning notes

Design the topic tree before deployment, enforce TLS and authentication, and verify Last Will behavior for every device class.

Related concepts

Pub/sub decoupling, topic design, QoS levels, retained messages and Last Will, broker security.

mqtt · broker · topic · publish · subscribe · qos · بروکر · ام‌کیوتی‌تی

Related engineering cases

Related articles

Industrial Protocols

Fieldbus and industrial Ethernet selection and diagnostics.

OPC UA

Information modeling, sessions, and security in OPC UA.

Modbus TCP

Register model, function codes, and polling behavior.

Siemens S7 Communication

PUT/GET, ISO-on-TCP (port 102), and data exchange between Siemens CPUs.

When Hermes Brain uses this article

Cited for edge telemetry architecture, broker disconnect patterns, QoS selection, and IIoT data movement.

…