Category Archives: Communication Protocols

MQTT 5 Topic Aliases Explained: Per-Connection Bandwidth

A factory floor PLC publishes temperature data to the topic factory/site-A/line-3/station-5/conveyor-7/motor/temperature every 100 milliseconds. That’s a 65-byte topic name sent 10 times per second, every second of every day. Over 24 hours, the topic name alone consumes 56 megabytes of bandwidth — not the payload, just the topic string. Multiply by hundreds of similar sensors and you have… Read More: MQTT 5 Topic Aliases Explained: Per-Connection Bandwidth »

MQTT 5 Flow Control Explained: Receive Maximum

In MQTT 3.1.1, the question “how many QoS 1 messages can I have in flight at once?” had no clear answer. The spec didn’t say. Implementations varied — some Servers accepted thousands of pipelined PUBLISH packets; others would only process one in-flight message per client. Clients that wanted predictable behavior had to assume the worst (one in-flight message… Read More: MQTT 5 Flow Control Explained: Receive Maximum »

MQTT 5 Negative Acknowledgements: Reason Codes Explained

For two decades MQTT 3.1.1 gave you one of two answers to every operation: it worked, or it didn’t. When a PUBLISH failed, you got nothing actionable back — just silence or a disconnect. When a SUBSCRIBE half-failed (one topic accepted, one rejected), you couldn’t tell which was which. When the Server kicked you off the network, you… Read More: MQTT 5 Negative Acknowledgements: Reason Codes Explained »

Enhanced Authentication in MQTT 5 Explained

For two decades, MQTT clients authenticated to the Server the same way: send a username, send a password, hope the Server accepts. That worked for the IoT prototypes of the 2000s. It does not work for modern industrial systems where credentials rotate, identities federate, and a plain-text password traveling over the wire is a security incident waiting to… Read More: Enhanced Authentication in MQTT 5 Explained »

CIP Security Explained: TLS, X.509, and OT Cybersecurity

Ten years ago, OT cybersecurity meant “air gap the control network.” That model failed. Modern industrial systems need controllers talking to MES systems, drives reporting to cloud analytics, engineering tools accessing devices remotely. The air gap is gone — and with it, the security model that depended on physical isolation. CIP Security is the ODVA-defined answer for CIP… Read More: CIP Security Explained: TLS, X.509, and OT Cybersecurity »

CIP Device Profiles Guide: Interoperability Framework

You buy an EtherNet/IP AC drive from Rockwell Automation. It works with your ControlLogix PLC. You later buy a different AC drive from a different manufacturer — say, Yaskawa or ABB — and it works with the same PLC too. Why? Because both drives implement the CIP AC Drive Device Profile (Device Type 0x02). They expose the same… Read More: CIP Device Profiles Guide: Interoperability Framework »

CIP Motion Explained (Class 0x42 Motion Axis Object)

Twenty years ago, synchronized motion across multiple servo drives required a dedicated motion bus — SERCOS, MACRO, FireWire, or a proprietary fieldbus. The motion network ran separately from the control network because standard Ethernet couldn’t deliver the deterministic microsecond timing motion needs. Today, with CIP Motion running over standard EtherNet/IP, the motion bus and the control network are… Read More: CIP Motion Explained (Class 0x42 Motion Axis Object) »

CIP Sync Explained: IEEE 1588 PTP for Industrial Networks

When a six-axis servo system has to coordinate moves across drives that may be sitting in different cabinets, on different switches, in different rooms — sub-microsecond timing matters. When a sequence-of-events recorder needs to log which fault tripped first across a network of distributed I/O — microsecond timing matters. When a process control application needs to correlate data… Read More: CIP Sync Explained: IEEE 1588 PTP for Industrial Networks »

CIP Path Segments Explained: EPATH Encoding for Engineers

Open any CIP packet in Wireshark and you’ll see paths encoded as hex bytes — 20 04 24 66 2C 67 2C 68, 20 06 24 01, 34 04 01 00 0C 00 B8 00 04 01. These are CIP path segments — the universal addressing format that tells every CIP service where to go. Class IDs, Instance… Read More: CIP Path Segments Explained: EPATH Encoding for Engineers »

MQTT 5 User Properties Explained: Custom Metadata

If you have ever built a system on MQTT 3.1.1 and ended up encoding metadata into topic names or stuffing JSON envelopes inside payloads to carry information about the message, you have already felt the gap that user properties fill. MQTT 3.1.1 had no place for application-defined metadata in a message; the protocol’s headers were rigidly defined, and… Read More: MQTT 5 User Properties Explained: Custom Metadata »