300+ SCADA Protocol Articles & Guides
Deep dives on Modbus, DNP3, IEC 60870-5-101/104, IEC 61850, OPC UA, Profinet, MQTT, IEC 62443, and substation automation — written for practicing engineers.
MQTT 5 Session & Message Expiry Intervals Explained
How MQTT 5 session and message expiry intervals work: bounding stored session lifetime and per-message TTL, with the values, defaults, and broker behavior explained.
MQTT Keep Alive & Client Take-Over Explained
How MQTT keep alive works: PINGREQ and PINGRESP packets, the half-open connection problem, the 1.5x detection rule, and client take-over on ClientId reconnect.
MQTT Last Will and Testament (LWT) Explained
How MQTT Last Will and Testament works: the will message, will topic, will QoS and retain, when the broker publishes the will, and the will + retained pattern.
MQTT Persistent Sessions & Message Queuing Explained
How MQTT persistent sessions and message queuing work: clean session flag, session present flag, what the broker stores, client state, and MQTT 5 changes.
MQTT Topics and Wildcards Explained
How MQTT topics and wildcards work: topic levels, single-level (+) and multi-level (#) wildcards, $SYS topics, matching rules, and topic naming best practices.
MQTT Clients, Brokers & Connection Establishment Explained
How MQTT clients and brokers work and how a connection is established: the CONNECT and CONNACK packets, every field, return codes, NAT and keep alive.
MQTT Publish, Subscribe & Unsubscribe: Packets Explained
How MQTT publish, subscribe and unsubscribe work: the PUBLISH, SUBSCRIBE and UNSUBSCRIBE packets, every field, and the SUBACK and UNSUBACK acknowledgements.
MQTT Publish/Subscribe Pattern Explained: How Pub/Sub Works
How the MQTT publish/subscribe pattern works: decoupling, the broker's role, message filtering, scalability, and how pub/sub differs from message queues.
What Is MQTT? Protocol Architecture, Packets & How It Works
MQTT is a lightweight publish/subscribe protocol for IoT. Learn its architecture, packet structure, QoS, sessions, security and how the protocol works.