BACnet/IP Connector - Coreflux Documentation

Connect Coreflux to Building Automation

The BACnet connector connects Coreflux to building automation controllers (ASHRAE 135) using the unified OT TAG system. Define the BACnet configuration, add Tags for continuous polling or COV subscriptions, and handle alarm operations.

BACnet is the dominant protocol for building management systems. If your controller supports BACnet/IP, this connector maps each data point to an MQTT topic using the same TAG model as every other Coreflux industrial connector.

When to use this

Use the BACnet connector when you need to integrate HVAC, lighting, metering, or access-control controllers that expose BACnet/IP — read live values on a schedule, subscribe to change notifications, write setpoints from MQTT, receive intrinsic alarms, or run ad-hoc reads and writes triggered by MQTT commands.

Key capabilities

BACnet/IP over UDP — standard port 47808 (0xBAC0) with broadcast or direct-IP discovery
TAG-based polling — per-point MQTT topics with a configurable polling interval
Change-of-Value (COV) — push subscriptions per tag (WITH COV true) without polling
Event alarms — BACnet Event-Notifications to MQTT with per-tag or device-wide streams
Bidirectional writes — MQTT-triggered writes to analog, binary, and value objects
On-demand events — ADD EVENT with READ, WRITE, and ACK queries triggered by any MQTT publish
Operator ACK workflow — auto-registered ACK handler per alarming tag
Direct IP mode — connect to controllers that do not respond to Who-Is/I-Am
Docker and hostname support — resolve container service names before opening the BACnet socket

Quick Start

Pick the starting point that matches what you need. Each tag publishes to {SOURCE_TOPIC}/{tagName} unless the tag sets its own SOURCE_TOPIC.

Connect to a controller and read a room temperature every five seconds:

DEFINE CONNECTOR BMS WITH TYPE BACNET
    ADD BACNET_CONFIG
        WITH IP "192.168.1.10"
        WITH DEVICE_ID 1234
    ADD MAPPING RoomSensors
        WITH SOURCE_TOPIC "bacnet/bms"
        WITH EVERY 5 SECONDS
        ADD TAG RoomTemp
            WITH ADDRESS "AI:0"
            WITH DATA_TYPE "FLOAT"
            WITH UNIT "degC"

Read a setpoint and allow MQTT writes back to the device:

DEFINE CONNECTOR HVAC WITH TYPE BACNET
    ADD BACNET_CONFIG
        WITH IP "10.0.0.50"
        WITH DEVICE_ID 2000
        WITH WRITE_PRIORITY 8
    ADD MAPPING Setpoints
        WITH SOURCE_TOPIC "bacnet/hvac"
        WITH EVERY 10 SECONDS
        ADD TAG CoolingSetpoint
            WITH ADDRESS "AV:1"
            WITH DATA_TYPE "FLOAT"
            WITH UNIT "degC"
            WITH WRITABLE true
            WITH DESTINATION_TOPIC "bacnet/hvac/CoolingSetpoint/set"

Subscribe to Change-of-Value so the device pushes updates only when values change — no polling interval needed:

DEFINE CONNECTOR BMS WITH TYPE BACNET
    ADD BACNET_CONFIG
        WITH IP "192.168.1.10"
        WITH DEVICE_ID 1234
        WITH COV_LIFETIME 600
    ADD MAPPING CovPoints
        WITH SOURCE_TOPIC "bacnet/bms/cov"
        ADD TAG RoomTempCov
            WITH ADDRESS "AI:0"
            WITH DATA_TYPE "FLOAT"
            WITH COV true

When the controller does not answer Who-Is/I-Am, connect straight to its IP address:

DEFINE CONNECTOR BMS WITH TYPE BACNET
    ADD BACNET_CONFIG
        WITH IP "10.0.0.50"
        WITH PORT 47808
        WITH DEVICE_ID 1234
        WITH DIRECT_IP true
    ADD MAPPING RoomSensors
        WITH SOURCE_TOPIC "bacnet/bms"
        WITH EVERY 5 SECONDS
        ADD TAG RoomTemp
            WITH ADDRESS "AI:0"
            WITH DATA_TYPE "FLOAT"
            WITH UNIT "degC"

Trigger a single BACnet read or write by publishing to an MQTT command topic:

DEFINE CONNECTOR BMS WITH TYPE BACNET
    ADD BACNET_CONFIG
        WITH IP "192.168.1.10"
        WITH DEVICE_ID 1234
    ADD EVENT ReadProperty
        WITH SOURCE_TOPIC "bacnet/cmd/read"
        WITH DESTINATION_TOPIC "bacnet/cmd/read/result"
        WITH QUERY "READ:AI:0:PRESENT_VALUE"
    ADD EVENT WriteProperty
        WITH SOURCE_TOPIC "bacnet/cmd/write"
        WITH DESTINATION_TOPIC "bacnet/cmd/write/result"
        WITH QUERY "{payload}"

Each alarming point gets its own MQTT alarm stream and auto-registered ACK topic:

DEFINE CONNECTOR BMS WITH TYPE BACNET
    ADD BACNET_CONFIG
        WITH IP "192.168.1.10"
        WITH DEVICE_ID 1234
        WITH LOCAL_DEVICE_ID 4194300
    ADD MAPPING LimitPoints
        WITH SOURCE_TOPIC "bacnet/bms"
        ADD TAG RoomTemp
            WITH ADDRESS "AI:0"
            WITH DATA_TYPE "FLOAT"
            WITH COV true
            WITH ALARM true

Protocol Overview

BACnet (Building Automation and Control networks) is an open protocol for building automation, standardized as ANSI/ASHRAE 135 and ISO 16484-5. It enables interoperability between devices from different manufacturers in HVAC, lighting, fire detection, access control, and energy management.

Concept	Description
Object model	Every data point is a typed object (Analog Input, Binary Value, etc.) identified by instance number, accessed by properties (Present Value, High Limit, Event State, …)
Service model	Clients read and write properties using BACnet services (ReadProperty, WriteProperty, SubscribeCOV, AcknowledgeAlarm)
Device discovery	Who-Is/I-Am broadcast locates devices by Device Instance without knowing the IP address
Intrinsic alarming	Controllers generate Event-Notifications when values cross configured limits — alarm logic lives in the device

BACnet variants

Variant	Transport	Port / Layer	Notes
BACnet/IP	UDP/IP	47808 (0xBAC0)	Most common; fully supported
BACnet MSTP	Serial RS-485	N/A	Not supported
BACnet over Ethernet	Ethernet (Annex H)	—	Not supported
BACnet/SC	TLS/WebSocket	—	Not currently implemented

Coreflux supports BACnet/IP (UDP). MS/TP parameters are parsed but the transport is not validated. Use BACnet/IP for all production deployments.

Supported controllers and platforms

Category	Examples
HVAC controllers	Siemens Desigo, Johnson Controls Metasys, Honeywell WEBs, Carrier i-Vu
DDC / field panels	Distech Controls ECB, Alerton Ascent, Delta Controls ORCAview
Meters and sensors	Veris BMeter, Onset HOBO, Accuenergy Acuvim
Gateways	Contemporary Controls BASRT-B, Babel Buster (Modbus→BACnet)
Simulators	IOTech BACnet device simulator (Docker); VTS (Visual Test Shell)
Integration platforms	Niagara (Tridium), EBO (Schneider)

Configuration

Only DEVICE_ID is strictly required. For a working connector, also set IP and add at least one ADD MAPPING with tags.

DEFINE CONNECTOR BMS WITH TYPE BACNET
    ADD BACNET_CONFIG
        WITH IP "192.168.1.10"
        WITH DEVICE_ID 1234
    ADD MAPPING RoomSensors
        WITH SOURCE_TOPIC "bacnet/bms"
        WITH EVERY 5 SECONDS
        ADD TAG RoomTemp
            WITH ADDRESS "AI:0"
            WITH DATA_TYPE "FLOAT"
            WITH UNIT "degC"

All configuration options

DEFINE CONNECTOR BMS WITH TYPE BACNET
    ADD BACNET_CONFIG
        WITH IP "192.168.1.10"
        WITH PORT 47808
        WITH LOCAL_PORT 0
        WITH DEVICE_ID 1234
        WITH TIMEOUT 3
        WITH DISCOVERY_TIMEOUT 5
        WITH DIRECT_IP false
        WITH WRITE_PRIORITY 8
        WITH RETRIES 3
        WITH MAX_APDU 1476
        WITH COV_LIFETIME 300
        WITH COV_CONFIRMED false
        WITH LOCAL_DEVICE_ID 4194300
        WITH ALARMS false
        WITH ALARMS_TOPIC "bacnet/bms/alarms"

Configuration parameters

Setting	Required	Default	Description
`DEVICE_ID`	Yes	`1`	Target BACnet device instance (Who-Is/I-Am and ReadProperty)
`IP` / `HOST` / `ADDRESS`	Conditional	`192.168.1.1`	Remote device IPv4 or hostname. Required when `WITH DIRECT_IP true`; strongly recommended for Docker and routed networks
`PORT`	No	`47808`	Remote device BACnet/IP UDP listen port
`LOCAL_PORT`	No	`0`	Local UDP port the broker binds on this host (`0` = OS ephemeral)
`TRANSPORT`	No	`IP`	`IP` or `MSTP` (MS/TP not validated — use BACnet/IP)
`TIMEOUT`	No	`3`	Read/write timeout in seconds
`DISCOVERY_TIMEOUT`	No	`5`	Who-Is/I-Am wait in seconds
`DIRECT_IP`	No	`false`	Skip discovery; connect to `IP:PORT` and verify with ReadProperty
`WRITE_PRIORITY`	No	`8`	BACnet command priority (1 = highest, 16 = lowest)
`RETRIES`	No	`3`	Retry count on failure
`MAX_APDU`	No	`1476`	Maximum BACnet/IP frame size in bytes; this is not a string-size setting
`COV_LIFETIME`	No	`300`	Default COV subscription lifetime in seconds (`0` = infinite)
`COV_CONFIRMED`	No	`false`	Request confirmed COV notifications by default
`LOCAL_DEVICE_ID`	Conditional	`0`	Local device instance for directed I-Am. Required when `WITH ALARMS true` or any TAG has `WITH ALARM true`
`ALARMS`	No	`false`	Publish all device Event-Notifications to `ALARMS_TOPIC`
`ALARMS_TOPIC`	No	`bacnet/{routeName}/alarms`	MQTT topic for device-wide alarms when `WITH ALARMS true`
`ALARM_TOPIC`	No	—	Alias for `ALARMS_TOPIC` on `BACNET_CONFIG`

After 3 failed read cycles in a row on the current connection, the route goes to Reconnecting. Reads and writes still queued on a replaced connection give way at once and don’t count against the new one. See Connection status.

Network setup: IP, PORT, and LOCAL_PORT

BACnet/IP is UDP. Three settings control two different endpoints — the BACnet device (remote) and the Coreflux broker (local).

Setting	Side	What it is	Typical value
`IP`	Remote	IPv4 address or hostname of the BACnet controller	`192.168.1.10`, `coreflux-connector-bacnet`
`PORT`	Remote	UDP port where the device accepts BACnet/IP traffic	`47808`
`LOCAL_PORT`	Local	UDP port the broker binds on before sending/receiving	`0` (OS-assigned)

Scenario	`IP`	`PORT`	`LOCAL_PORT`
Sandbox simulator on the same host	`127.0.0.1`	`47808`	`0`
Simulator in Docker, broker in another container	`coreflux-connector-bacnet` (docker container name)	`47808`	`0`
Device on non-standard port	`10.0.0.5`	`47809`	`0`
Firewall requires fixed source port	`10.0.0.5`	`47808`	`47808`

WITH IP accepts hostnames and Docker service names (for example coreflux-connector-bacnet, host.docker.internal). The broker resolves them to IPv4 before opening the BACnet socket.

Direct IP mode

Use when the controller does not respond to Who-Is/I-Am but accepts ReadProperty at a known UDP endpoint:

DEFINE CONNECTOR BMS WITH TYPE BACNET
    ADD BACNET_CONFIG
        WITH IP "10.0.0.50"
        WITH PORT 47808
        WITH DEVICE_ID 1234
        WITH DIRECT_IP true

Write priority

Commandable objects (analog, binary and multi-state outputs and values) keep a 16-slot priority array. The device uses the value in the highest slot that holds one (1 = highest, 16 = lowest). If every slot is empty, it falls back to RELINQUISH_DEFAULT.

Default: every write from the connector goes to slot 8.
Set it: WITH WRITE_PRIORITY <1-16> in the connector config. It applies to every write on that connector, and there is no per-tag override. A value outside 1–16 is refused when the connector is added.
Higher slots win: a write at 8 doesn’t change the present value while a BMS or operator holds slot 1–7.
Relinquish isn’t supported: the connector can’t write NULL to free its slot. Its last value stays in that slot until you overwrite it, or until another tool relinquishes it.
Inspect it: set a tag’s ADDRESS_TYPE to PRIORITY_ARRAY or RELINQUISH_DEFAULT to see which slot is active.

The IOTech sandbox profile seeds AO:0 at priority 1. Use WITH WRITE_PRIORITY 1 for that test device.

If a write appears to succeed but the present value does not change, the device may be holding the value at a higher priority. Try WITH WRITE_PRIORITY 1 and check whether a BMS already owns the point.

TAG System

Mapping parameters

    ADD MAPPING RoomSensors
        WITH SOURCE_TOPIC "bacnet/bms"
        WITH EVERY 5 SECONDS
        ADD TAG RoomTemp
            WITH ADDRESS "AI:0"
            WITH DATA_TYPE "FLOAT"
            WITH UNIT "degC"
            WITH WRITABLE false
            WITH COV false
            WITH ALARM false

Parameter	Required	Default	Description
`SOURCE_TOPIC`	Yes*	—	Base MQTT topic; each tag publishes to `{SOURCE_TOPIC}/{tagName}` unless the tag sets its own
`EVERY`	Conditional	—	Polling interval (e.g. `1 SECONDS`, `200 MILLISECONDS`). Required when the mapping has polled tags; omit for COV-only mappings
`ADD TAG`	Yes	—	At least one tag per mapping

* You may set SOURCE_TOPIC on each tag instead of on the mapping, but one of the two is required.

Tag parameters

ADD TAG RoomTemp
    WITH ADDRESS "AI:0"
    WITH DATA_TYPE "FLOAT"
    WITH UNIT "degC"
    WITH WRITABLE false
    WITH COV false
    WITH ALARM false

Parameter	Required	Default	Description
`ADDRESS`	Yes	—	BACnet object `TYPE:INSTANCE` (e.g. `AI:0`, `AV:3`, `BI:0`)
`DATA_TYPE`	Yes	—	`BOOL`, `INT16`, `UINT16`, `INT32`, `UINT32`, `FLOAT`, `DOUBLE`, `STRING`
`SOURCE_TOPIC`	Conditional	`{mapping SOURCE_TOPIC}/{tagName}`	MQTT topic for tag data. Required on the tag or on the parent mapping
`DESTINATION_TOPIC`	Conditional	—	MQTT topic to subscribe for writes. Required when `WITH WRITABLE true`
`ADDRESS_TYPE`	No	`PRESENT_VALUE`	BACnet property to read/write (e.g. `OBJECT_NAME`, `HIGH_LIMIT`)
`LENGTH`	No	`256`	Maximum string size in bytes when `DATA_TYPE` is `STRING`. Alias: `STRING_SIZE`.
`WRITABLE`	No	`false`	Allow MQTT writes to this object
`SCALING`	No	`1.0`	Multiply raw value
`OFFSET`	No	`0.0`	Add after scaling
`UNIT`	No	`""`	Engineering unit label (e.g. `degC`, `%RH`)
`DECIMAL_PLACES`	No	`2`	Rounding precision
`DEADBAND`	No	`0.0`	Minimum change before republishing
`MIN_VALUE` / `MAX_VALUE`	No	—	Clamp published values
`PUBLISH_MODE`	No	`VALUE_ONLY`	`VALUE_ONLY` or `JSON`
`DESCRIPTION`	No	`""`	Documentation string only
`COV`	No	`false`	Subscribe to BACnet Change-of-Value instead of polling
`COV_LIFETIME`	No	connector `COV_LIFETIME`	Per-tag COV subscription lifetime in seconds
`COV_CONFIRMED`	No	connector `COV_CONFIRMED`	Request confirmed COV for this tag
`ALARM`	No	`false`	Enable MQTT alarm stream on `{tag_topic}/alarms`
`ALARM_TOPIC`	No	`{tag_topic}/alarms`	Override alarm MQTT topic (only when `WITH ALARM true`)

Object address format

Shorthand	Full name	Example
`AI`	`ANALOG_INPUT`	`AI:0`
`AO`	`ANALOG_OUTPUT`	`AO:1`
`AV`	`ANALOG_VALUE`	`AV:0`
`BI`	`BINARY_INPUT`	`BI:0`
`BO`	`BINARY_OUTPUT`	`BO:0`
`BV`	`BINARY_VALUE`	`BV:0`
`MSV`	`MULTISTATE_VALUE`	`MSV:0`

ADDRESS_TYPE is the BACnet property (e.g. PRESENT_VALUE, OBJECT_NAME), not the object type.

String sizing

For STRING tags, WITH LENGTH is the maximum string size in bytes and defaults to 256. STRING_SIZE is accepted as an alias for the same field. Connector-level MAX_APDU limits the BACnet/IP frame size — it does not size strings. Read an object’s name property as a STRING. WITH LENGTH 64 overrides the 256-byte default to match a shorter BACnet property allocation:

DEFINE CONNECTOR BMS WITH TYPE BACNET
    ADD BACNET_CONFIG
        WITH IP "192.168.1.10"
        WITH DEVICE_ID 1234
    ADD MAPPING DeviceInfo
        WITH SOURCE_TOPIC "bacnet/bms"
        WITH EVERY 30 SECONDS
        ADD TAG RoomName
            WITH ADDRESS "AI:0"
            WITH ADDRESS_TYPE "OBJECT_NAME"
            WITH DATA_TYPE "STRING"
            WITH LENGTH 64
            WITH SOURCE_TOPIC "bacnet/bms/RoomName"

Change-of-Value (COV)

Tags with WITH COV true subscribe to BACnet Change-of-Value notifications instead of polling. A mapping with only COV tags does not need WITH EVERY. Mixed mappings poll non-COV tags on EVERY and receive COV tags via push.

COV requires support on the device side. If you receive no change notifications, confirm the controller supports COV and that WITH COV true is set on the tag.

Alarms and Event Notifications

The broker receives BACnet Event-Notification messages from the field device and publishes them to MQTT. Alarm limits and Notification Class membership are configured on the controller — the broker only needs the device to send events to its LOCAL_DEVICE_ID.

Alarm message format

Every time the BACnet device reports an alarm or state change, the broker publishes one JSON object to the alarm topic. Subscribe to that topic to see events as they happen, or subscribe to {alarm_topic}/active for a retained snapshot of alarms that are still open. Example — a room temperature crosses its high limit (bacnet/bms/RoomTemp/alarms):

{
  "connector_name": "BMS",
  "device_id": 1234,
  "address": "AI:0",
  "tag_name": "RoomTemp",
  "tag_topic": "bacnet/bms/RoomTemp",
  "alarm_topic": "bacnet/bms/RoomTemp/alarms",
  "object_type": "ANALOG_INPUT",
  "instance": 0,
  "event_type": "EVENT_OUT_OF_RANGE",
  "from_state_short": "NORMAL",
  "to_state_short": "HIGH_LIMIT",
  "fundamental_state": "OFFNORMAL",
  "transition": "TO_OFFNORMAL",
  "event_state_to_ack": "HIGH_LIMIT",
  "ack_required": true,
  "present_value": 28.5,
  "bacnet_timestamp": "2026-06-10T15:28:21.000Z",
  "timestamp": "2026-06-10T16:28:21.003Z"
}

Fields to know:

Field	What it tells you
`address`	Which BACnet point raised the alarm (e.g. `AI:0` = Analog Input 0)
`tag_name` / `tag_topic`	The connector TAG and MQTT topic for live values on that point
`from_state_short` → `to_state_short`	State change just reported (e.g. `NORMAL` → `HIGH_LIMIT`)
`transition`	Direction of the change: `TO_OFFNORMAL` (new alarm), `TO_NORMAL` (cleared), or `TO_FAULT`
`fundamental_state`	Overall condition: `OFFNORMAL` (limit alarm), `FAULT`, or `NORMAL`
`present_value`	Value on the device when the event fired (when provided)
`ack_required`	If `true`, an operator must acknowledge the alarm on the device
`event_state_to_ack`	State to send when acknowledging — use this in ACK payloads
`bacnet_timestamp`	When the device recorded the event — include when acknowledging

Common to_state_short values:

Value	Meaning
`HIGH_LIMIT`	Value rose above the configured high limit
`LOW_LIMIT`	Value fell below the configured low limit
`FAULT`	Device reported a fault condition
`NORMAL`	Point returned to normal (alarm cleared)

Setting Alarms on BACnet ROUTE

Mode	Configuration	Default MQTT topic	Coverage
Device-wide	`WITH ALARMS true` on `BACNET_CONFIG`	`bacnet/{routeName}/alarms` (+ retained `…/active`)	Every Event-Notification from the device
Per-tag	`WITH ALARM true` on TAG	`{tag_topic}/alarms` (+ retained `…/active`)	Only events matching the TAG’s `ADDRESS`

Both modes can coexist. When both are enabled for the same object, the event is published to both topics.

Device-wide
Per-tag

Publish every Event-Notification from the device to a single MQTT topic — useful for commissioning and catch-all monitoring:

DEFINE CONNECTOR BMS WITH TYPE BACNET
    ADD BACNET_CONFIG
        WITH IP "192.168.1.10"
        WITH DEVICE_ID 1234
        WITH LOCAL_DEVICE_ID 4194300
        WITH ALARMS true
        WITH ALARMS_TOPIC "bacnet/bms/alarms"
    ADD MAPPING CovPoints
        WITH SOURCE_TOPIC "bacnet/bms"
        ADD TAG CovCounter
            WITH ADDRESS "AV:0"
            WITH DATA_TYPE "FLOAT"
            WITH COV true

Alarm events appear on bacnet/bms/alarms. Operator ACK via bacnet/bms/alarms/ack.

Each alarming point gets its own MQTT alarm stream and ACK topic:

DEFINE CONNECTOR BMS WITH TYPE BACNET
    ADD BACNET_CONFIG
        WITH IP "192.168.1.10"
        WITH DEVICE_ID 1234
        WITH LOCAL_DEVICE_ID 4194300
    ADD MAPPING LimitPoints
        WITH SOURCE_TOPIC "bacnet/bms"
        ADD TAG RoomTemp
            WITH ADDRESS "AI:0"
            WITH DATA_TYPE "FLOAT"
            WITH COV true
            WITH ALARM true
        ADD TAG ChillerPressure
            WITH ADDRESS "AI:2"
            WITH DATA_TYPE "FLOAT"
            WITH EVERY 5 SECONDS
            WITH ALARM true

Data topic	Alarm topic	ACK topic
`bacnet/bms/RoomTemp`	`bacnet/bms/RoomTemp/alarms`	`bacnet/bms/RoomTemp/alarms/ack`
`bacnet/bms/ChillerPressure`	`bacnet/bms/ChillerPressure/alarms`	`bacnet/bms/ChillerPressure/alarms/ack`

On connect, when alarms are enabled and LOCAL_DEVICE_ID is set, the broker sends a directed I-Am so Notification Class recipients learn the broker’s UDP endpoint.

Set a non-zero WITH LOCAL_DEVICE_ID before enabling alarms. Without it, Event-Notifications are unlikely to arrive because the field device does not know where to send them.

Active alarm list

In addition to live events on {alarm_topic}, the broker maintains a retained snapshot on {alarm_topic}/active. Subscribe here to build an alarm panel — late subscribers receive the current state immediately without waiting for the next transition.

Topic	Retain	Use for
`{alarm_topic}`	No	Live transitions as they happen (logging, notifications)
`{alarm_topic}/active`	Yes	Current open alarms (dashboards, alarm panels)

How the list updates:

Event	Effect on `/active`
`TO_OFFNORMAL` or `TO_FAULT`	Add or update the entry for that BACnet `address`
`TO_NORMAL`	Remove the entry for that `address`
Successful ACK on `{alarm_topic}/ack`	Remove the entry matching `address` + `event_state_to_ack`

Per-tag lists usually hold 0 or 1 entry (one BACnet object per tag). Device-wide lists hold one entry per alarming object on the device. Example — device-wide active list on bacnet/bms/alarms/active:

{
  "connector_name": "BMS",
  "device_id": 1234,
  "alarm_topic": "bacnet/bms/alarms",
  "active_topic": "bacnet/bms/alarms/active",
  "updated_at": "2026-06-16T12:00:00.000Z",
  "count": 2,
  "alarms": [
    {
      "address": "AI:0",
      "tag_name": "RoomTemp",
      "to_state_short": "HIGH_LIMIT",
      "fundamental_state": "OFFNORMAL",
      "transition": "TO_OFFNORMAL",
      "event_state_to_ack": "HIGH_LIMIT",
      "ack_required": true,
      "present_value": 28.5,
      "bacnet_timestamp": "2026-06-10T15:28:21.000Z"
    },
    {
      "address": "AI:2",
      "tag_name": "ChillerPressure",
      "to_state_short": "HIGH_LIMIT",
      "fundamental_state": "OFFNORMAL",
      "transition": "TO_OFFNORMAL",
      "event_state_to_ack": "HIGH_LIMIT",
      "ack_required": false,
      "present_value": 95.2,
      "bacnet_timestamp": "2026-06-10T15:30:05.000Z"
    }
  ]
}

Each object in the alarms array uses the same fields as a single live alarm event. When no alarms are active, count is 0 and alarms is [] — the broker still publishes valid retained JSON.

Acknowledging alarms

When a BACnet device raises an alarm, the broker publishes it to MQTT. To clear or acknowledge it on the device, an operator publishes to the ACK topic. The broker sends AcknowledgeAlarm to the controller and replies with a result. How it works:

Subscribe to the alarm topic (live events) or {alarm_topic}/active (current alarm list).
Publish your acknowledgement to {alarm_topic}/ack.
Check {alarm_topic}/ack/result for success: true or false.

No additional configuration is needed for ACK — the broker registers the handler automatically when you enable device-wide alarms or per-tag WITH ALARM true.

Topic	What you see
`{alarm_topic}`	Live alarm events as they happen
`{alarm_topic}/active`	Retained list of alarms that are still active
`{alarm_topic}/ack`	Publish here to acknowledge
`{alarm_topic}/ack/result`	Success or failure of your acknowledgement

Recommended — echo the alarm
Explicit command

Copy the alarm JSON you received, add an ack_text note, and publish it to the ACK topic. This is the safest approach because you keep all fields the device expects (event_state_to_ack, bacnet_timestamp, and so on).1. An alarm arrives on bacnet/bms/RoomTemp/alarms:

{
  "address": "AI:0",
  "tag_name": "RoomTemp",
  "to_state_short": "HIGH_LIMIT",
  "event_state_to_ack": "HIGH_LIMIT",
  "ack_required": true,
  "present_value": 28.5,
  "bacnet_timestamp": "2026-06-10T15:28:21.000Z"
}

2. Publish to bacnet/bms/RoomTemp/alarms/ack — same JSON, plus your note:

{
  "address": "AI:0",
  "tag_name": "RoomTemp",
  "to_state_short": "HIGH_LIMIT",
  "event_state_to_ack": "HIGH_LIMIT",
  "ack_required": true,
  "present_value": 28.5,
  "bacnet_timestamp": "2026-06-10T15:28:21.000Z",
  "ack_text": "Checked by operator — HVAC team notified"
}

Use any MQTT client (such as MQTT Explorer) to publish the payload above to the ACK topic.3. Result on bacnet/bms/RoomTemp/alarms/ack/result:

{
  "success": true,
  "connector_name": "BMS",
  "operation": "ACK",
  "address": "AI:0",
  "event_state": "HIGH_LIMIT",
  "timestamp": "2026-06-10T16:30:00.000Z"
}

If success is true, the device accepted the acknowledgement. The alarm is removed from {alarm_topic}/active.

For scripts or integrations that do not store the full alarm JSON, publish a short text command to the ACK topic.Publish to bacnet/bms/RoomTemp/alarms/ack:

ACK:AI:0:HIGH_LIMIT:Checked by operator

Format: ACK:OBJECT:INSTANCE:STATE:optional note

Part	Example	Meaning
Object	`AI`	Analog Input
Instance	`0`	Object instance number
State	`HIGH_LIMIT`	Active alarm state to acknowledge
Note	`Checked by operator`	Optional operator comment

Use the state name from the alarm (HIGH_LIMIT, LOW_LIMIT, FAULT, or NORMAL) — not labels like OFFNORMAL.Result on bacnet/bms/RoomTemp/alarms/ack/result:

{
  "success": true,
  "connector_name": "BMS",
  "operation": "ACK",
  "address": "AI:0",
  "event_state": "HIGH_LIMIT",
  "timestamp": "2026-06-10T16:30:00.000Z"
}

If success is false, the state or timestamp may not match what the device expects. Prefer the recommended method when possible — echo the alarm JSON and add ack_text.

Field device prerequisites

Before expecting MQTT alarms, confirm on the BMS or engineering tool:

Notification Class — recipient list includes LOCAL_DEVICE_ID
Intrinsic alarming on each object — NOTIFICATION_CLASS, HIGH_LIMIT / LOW_LIMIT, EVENT_ENABLE, LIMIT_ENABLE
Present value actually crosses a configured limit

COV working does not guarantee alarms — they use separate BACnet services.

On-Demand Events

Use ADD EVENT when you need a single read, write, or alarm acknowledgement triggered by an MQTT publish — instead of continuous TAG polling.

Parameter	Required	Description
`SOURCE_TOPIC`	Yes	MQTT topic that triggers the BACnet operation
`DESTINATION_TOPIC`	Yes	MQTT topic where the JSON result is published
`QUERY`	Yes	BACnet operation: `READ:…`, `WRITE:…`, `ACK:…`, or JSON
`EVERY`	No	Not supported on BACnet events — use TAG polling instead

Query formats

Style	Example	Notes
Colon-separated read	`READ:AI:0:PRESENT_VALUE`	Shorthand or full type name
Colon-separated write	`WRITE:AV:0:PRESENT_VALUE:72.5`	Value is everything after the property
JSON	`{"operation":"READ","object_type":"AI","instance":"0","property":"PRESENT_VALUE"}`	Also supports `"operation":"WRITE"` with `"value"`
Topic placeholder	`READ:{topic[0]}:0:PRESENT_VALUE`	`{topic[0]}` replaced from the matched MQTT topic segment
Dynamic payload	`{payload}`	Use the MQTT message body as the query (e.g. `WRITE:AV:0:PRESENT_VALUE:21.5`)

Supported operations: READ, WRITE, and ACK (alarm acknowledgement).

DEFINE CONNECTOR BMS WITH TYPE BACNET
    ADD BACNET_CONFIG
        WITH IP "192.168.1.10"
        WITH DEVICE_ID 1234
    ADD EVENT ReadProperty
        WITH SOURCE_TOPIC "bacnet/cmd/read"
        WITH DESTINATION_TOPIC "bacnet/cmd/read/result"
        WITH QUERY "READ:AI:0:PRESENT_VALUE"

Publish any message to bacnet/cmd/read and the result appears on bacnet/cmd/read/result:

{
  "success": true,
  "connector_name": "BMS",
  "operation": "READ",
  "address": "AI:0",
  "property": "PRESENT_VALUE",
  "value": 22.5,
  "timestamp": "2026-05-31T10:00:00.000Z"
}

The connector must be connected before events run. If an event returns "success": false, check that the device is reachable and that the object and property in the query are correct.

When to use what

Need	Recommended approach
Periodic telemetry	`ADD MAPPING` + `ADD TAG` + `WITH EVERY`
Write from MQTT	`WITH WRITABLE true` + `WITH DESTINATION_TOPIC` on a tag
Ad-hoc read/write on command	`ADD EVENT` + `WITH QUERY`
Alarm acknowledgement	Auto-registered handler on `{tag_topic}/alarms/ack`, or custom `ADD EVENT`

Examples

Simple polling
COV subscriptions
Device-wide alarms
Sandbox (Docker)

Reads two analog inputs and one analog value every five seconds:

DEFINE CONNECTOR BMS WITH TYPE BACNET
    ADD BACNET_CONFIG
        WITH IP "192.168.1.10"
        WITH DEVICE_ID 1234
    ADD MAPPING RoomSensors
        WITH SOURCE_TOPIC "bacnet/bms"
        WITH EVERY 5 SECONDS
        ADD TAG RoomTemp
            WITH ADDRESS "AI:0"
            WITH DATA_TYPE "FLOAT"
            WITH UNIT "degC"
        ADD TAG Humidity
            WITH ADDRESS "AI:1"
            WITH DATA_TYPE "FLOAT"
            WITH UNIT "%RH"
        ADD TAG Setpoint
            WITH ADDRESS "AV:0"
            WITH DATA_TYPE "FLOAT"
            WITH UNIT "degC"

Publishes to bacnet/bms/RoomTemp → 22.5, bacnet/bms/Humidity → 55.0, bacnet/bms/Setpoint → 21.0.

Subscribe to Change-of-Value for fast-changing points — no polling interval needed:

DEFINE CONNECTOR BMS WITH TYPE BACNET
    ADD BACNET_CONFIG
        WITH IP "192.168.1.10"
        WITH DEVICE_ID 1234
        WITH COV_LIFETIME 600
    ADD MAPPING CovPoints
        WITH SOURCE_TOPIC "bacnet/bms/cov"
        ADD TAG RoomTempCov
            WITH ADDRESS "AI:0"
            WITH DATA_TYPE "FLOAT"
            WITH COV true
        ADD TAG OccupancyStatus
            WITH ADDRESS "BI:0"
            WITH DATA_TYPE "BOOL"
            WITH COV true

DEFINE CONNECTOR BMS WITH TYPE BACNET
    ADD BACNET_CONFIG
        WITH IP "192.168.1.10"
        WITH DEVICE_ID 1234
        WITH LOCAL_DEVICE_ID 4194300
        WITH ALARMS true
        WITH ALARMS_TOPIC "bacnet/bms/alarms"
    ADD MAPPING CovPoints
        WITH SOURCE_TOPIC "bacnet/bms"
        ADD TAG CovCounter
            WITH ADDRESS "AV:0"
            WITH DATA_TYPE "FLOAT"
            WITH COV true

Alarm events appear on bacnet/bms/alarms. Operator ACK via bacnet/bms/alarms/ack.

Connects to the IOTech BACnet Docker simulator when the broker runs in another container:

DEFINE CONNECTOR Sandbox WITH TYPE BACNET
    ADD BACNET_CONFIG
        WITH IP "coreflux-connector-bacnet"
        WITH PORT 47808
        WITH DEVICE_ID 1234
        WITH DIRECT_IP true
    ADD MAPPING TestPoints
        WITH SOURCE_TOPIC "bacnet/sandbox"
        WITH EVERY 2 SECONDS
        ADD TAG RoomTemp
            WITH ADDRESS "AI:0"
            WITH DATA_TYPE "FLOAT"
        ADD TAG AnalogOut
            WITH ADDRESS "AO:0"
            WITH DATA_TYPE "FLOAT"
            WITH WRITABLE true
            WITH DESTINATION_TOPIC "bacnet/sandbox/AnalogOut/set"

Combining with Models and Actions

A BACnet connector publishes each point to its own MQTT topic, so the rest of LoT can use that data like any other topic.

Aggregate into a model
Monitor alarm streams

First, the connector publishes each point under bacnet/bms:

DEFINE CONNECTOR BMS WITH TYPE BACNET
    ADD BACNET_CONFIG
        WITH IP "192.168.1.10"
        WITH DEVICE_ID 1234
    ADD MAPPING RoomSensors
        WITH SOURCE_TOPIC "bacnet/bms"
        WITH EVERY 5 SECONDS
        ADD TAG RoomTemp
            WITH ADDRESS "AI:0"
            WITH DATA_TYPE "FLOAT"
        ADD TAG Humidity
            WITH ADDRESS "AI:1"
            WITH DATA_TYPE "FLOAT"
        ADD TAG Setpoint
            WITH ADDRESS "AV:0"
            WITH DATA_TYPE "FLOAT"

Then the model aggregates those topics into one object on bacnet/bms/Info:

DEFINE MODEL BacnetRoomSensors COLLAPSED WITH TOPIC "bacnet/bms/Info"
    ADD DOUBLE "RoomTemp" WITH TOPIC "bacnet/bms/RoomTemp" AS TRIGGER
    ADD DOUBLE "Humidity" WITH TOPIC "bacnet/bms/Humidity"
    ADD DOUBLE "Setpoint" WITH TOPIC "bacnet/bms/Setpoint"
    ADD STRING "TimeStamp" WITH TIMESTAMP "ISO"

An action can watch per-tag alarm topics and forward events:

DEFINE ACTION BmsAlarmMonitor
ON TOPIC "bacnet/bms/+/alarms" DO
    PUBLISH TOPIC "site/alarm/log" WITH PAYLOAD
    PUBLISH TOPIC "site/alarm/last" WITH PAYLOAD

Best Practices

Always set WITH IP explicitly

The default 192.168.1.1 is rarely correct. On Docker or routed networks, broadcast Who-Is may never reach the device. Set WITH IP to the controller’s address or hostname.

Use Direct IP for unresponsive controllers

If a device does not answer Who-Is/I-Am, set WITH DIRECT_IP true to connect to IP:PORT and verify with ReadProperty. Otherwise the connector waits on discovery timeout every connect.

Use COV for fast-changing points

Polling at one-second intervals wastes bandwidth on BACnet/IP. Use WITH COV true for occupancy sensors, fast process variables, and alarm-related points.

Set LOCAL_DEVICE_ID before enabling alarms

The broker must announce itself as a BACnet device via directed I-Am so the field device knows where to send Event-Notifications.

Choose write priority deliberately

If a BMS holds a point at priority 1, a write at priority 8 will not change the present value. Match priority to your application and verify on the device.

Omit WITH EVERY from COV-only mappings

COV-only mappings do not need a polling interval. Adding WITH EVERY on a COV-only mapping adds confusion without benefit.

Use per-tag alarms for production points

Per-tag alarms (WITH ALARM true) give each monitoring point its own ACK topic. Use device-wide (WITH ALARMS true) as a catch-all or for commissioning.

Echo alarm JSON when acknowledging

Include event_state_to_ack and bacnet_timestamp from the received alarm message. Wrong state or missing timestamp causes ACK to fail.

Troubleshooting

Connection check

Publish -checkConnectorConnection BMS to $SYS/Coreflux/Command. The broker returns a JSON status for the named connector indicating whether the BACnet device was reached.

Discovery and connection issues

Symptom	Check	Solution
Connector never connects	`IP` and `DEVICE_ID` correct?	Verify device IP; use Wireshark to confirm Who-Is packet sent
Device not discovered	Device answers broadcast Who-Is?	Set `WITH DIRECT_IP true` if the device does not respond to Who-Is
Docker: connector cannot reach device	`WITH IP "127.0.0.1"` in Docker?	Use the container hostname (e.g. `coreflux-connector-bacnet`)
Discovery timeout on every connect	`DISCOVERY_TIMEOUT` too low?	Increase to 10+ seconds for slow devices

Data issues

Symptom	Check	Solution
No MQTT values	`DEVICE_ID` match device?	Sandbox default is `1234` — confirm with device profile
Wrong object value	Instance number correct?	Verify object index in device BACnet browser or profile
Write has no effect	Priority conflict?	Try `WITH WRITE_PRIORITY 1`; check if BMS holds a higher priority
COV notifications not arriving	Device supports COV?	Check device profile; simulator may require `--cov` flag

Alarm issues

Symptom	Check	Solution
No MQTT alarms (COV works)	`LOCAL_DEVICE_ID` set?	Add non-zero `LOCAL_DEVICE_ID`; verify device Notification Class recipient
Alarms on wrong topic	`SOURCE_TOPIC` or `ALARM_TOPIC` misconfigured?	Default is `{SOURCE_TOPIC}/{tagName}/alarms`
ACK returns `success: false`	Wrong `event_state_to_ack`?	Echo the received alarm JSON with `ack_text` field added
Events only after reconnect	Directed I-Am not sent?	Ensure `LOCAL_DEVICE_ID` is set and alarms are enabled before first connect

Networking issues

Symptom	Solution
`PORT` vs `LOCAL_PORT` confusion	`PORT` is the device’s listen port (47808). `LOCAL_PORT` is the broker’s bind port (leave `0`)
Event returns `success: false`	Connector not connected, or wrong object/property in `QUERY`; check broker logs
`LOCAL_DEVICE_ID is 0` warning	Set a non-zero device instance unique on the BACnet network

Additional resources

ASHRAE 135 Standard — official BACnet standard
BACnet International — conformance testing and product listings

Next Steps

Industrial Overview

Learn the patterns shared across all OT connectors.

OPC UA Client

Connect to cross-platform industrial servers with OPC UA.

​Connect Coreflux to Building Automation

​When to use this

​Key capabilities

​Quick Start

​Protocol Overview

​BACnet variants

​Supported controllers and platforms

​Configuration

​All configuration options

​Configuration parameters

​Network setup: IP, PORT, and LOCAL_PORT

​Direct IP mode

​Write priority

​TAG System

​Mapping parameters

​Tag parameters

​Object address format

​String sizing

​Change-of-Value (COV)

​Alarms and Event Notifications

​Alarm message format

​Setting Alarms on BACnet ROUTE

​Active alarm list

​Acknowledging alarms

​On-Demand Events

​Query formats

​When to use what

​Examples

​Combining with Models and Actions

​Best Practices

​Troubleshooting

​Connection check

​Additional resources

​Next Steps

Industrial Overview

OPC UA Client

Connect Coreflux to Building Automation

When to use this

Key capabilities

Quick Start

Protocol Overview

BACnet variants

Supported controllers and platforms

Configuration

All configuration options

Configuration parameters

Network setup: IP, PORT, and LOCAL_PORT

Direct IP mode

Write priority

TAG System

Mapping parameters

Tag parameters

Object address format

String sizing

Change-of-Value (COV)

Alarms and Event Notifications

Alarm message format

Setting Alarms on BACnet ROUTE

Active alarm list

Acknowledging alarms

On-Demand Events

Query formats

When to use what

Examples

Combining with Models and Actions

Best Practices

Troubleshooting

Connection check

Additional resources

Next Steps