Connect an IIoT Platform (Unified Namespace)

Use this class of northbound application when the plant runs an IIoT platform such as Ignition or Cogent DataHub, or when a unified namespace (UNS) is being built to the Sparkplug B specification.

How it differs from plain MQTT

MQTT defines which topic a message goes to, not how the message is structured. Three problems follow: the field names and data types of the payload have to be agreed between both sides in advance, so a format change on the gateway requires a parser change on the platform; the platform cannot know which tags a newly connected device has and must be modelled by hand; and the platform cannot distinguish a current value from a stale one — an absence of data may mean the device stopped, the gateway dropped off, or that the tag simply does not report.

Sparkplug B is an industrial IoT data transfer specification built on MQTT 3.1.1 that addresses these with four mechanisms:

Mechanism	Purpose
BIRTH message	On connect, a device declares its tag list, data types, and initial values. The platform models it automatically, and adding a device requires no platform-side configuration change
DEATH message	Published by the broker through the MQTT will mechanism when the gateway disconnects unexpectedly, so the platform knows at once that the device's data is no longer trustworthy
Sequence and bdSeq numbers	Every message carries an incrementing sequence number, letting the platform detect a gap and request a re-BIRTH to keep its model consistent with the field
Aliases	A short integer replaces the full tag name in transit, materially reducing payload size when tag counts are high

Together these give an MQTT network state awareness and a self-describing structure — the basis of a unified namespace, in which the plant maintains a single source of data that every upper-level system reads from and writes to, rather than integrating point to point.

Namespace structure

EMQX Neuron joins as a Sparkplug B edge node and maps each southbound driver to one device beneath it:

spBv1.0 / {group id} / DDATA / {node id} / {southbound driver}
              ↑                    ↑               ↑
        plant or workshop     this gateway     one device

Field	Source
Group ID	An application parameter; the top-level grouping of the namespace, usually a plant or workshop
Node ID	An application parameter; the unique identifier of this EMQX Neuron instance
{southbound driver}	The name of the subscribed southbound driver node — one driver is one device

Group Path is enabled by default, which prefixes the metric name with the collection group name so that the tree the platform sees matches how the line is organized.

Changing the Group ID or Node ID triggers a re-BIRTH, so settle the naming convention for both before rolling out at scale.

For the full topic list, see Sparkplug B · Topic Structure.

Writing back to devices

Upper-level platforms write tags on a southbound driver through DCMD commands; NCMD carries edge-node-level commands. The target tag must have the write attribute configured in the southbound driver — see Groups and Tags · Tag attributes.

Selecting an application

Application	When it applies
Sparkplug B	The first choice whenever the platform supports the Sparkplug B specification. Connection parameters — broker address, port, credentials, SSL, offline caching — match the MQTT application; only Group ID and Node ID come from the Sparkplug B specification itself

Connection examples

• Integration with EMQX: publish to EMQX and decode the payload with its codec functions
• Ignition
• Cogent DataHub