IEC 60870-5-104 Integration Guide

IEC 60870-5-104 (IEC 104) is the telecontrol standard used by power utilities, substations, solar and wind parks, and other energy sites. MaestroHub connects as the controlling station (the SCADA master side) to an outstation: an RTU, a protection relay, or a gateway that concentrates many devices. This guide covers connection setup, the connect sequence, TLS, the five function types, and how the matching nodes and trigger slot into the Pipeline Designer.

Overview

The IEC 104 connector provides:

• A live process image: the latest report of every point the outstation sends, with its quality flags and device timestamp
• Monitor Points trigger: start a pipeline for every point the outstation reports, with no polling
• Read Points: the latest known value of the points you list, with quality and age, never a made-up 0
• Interrogation: station, group (1–16) and counter (1–4) interrogations on demand, on connect, and periodically
• Commands: single, double, regulating-step, set-point and bitstring commands with select-before-operate, sent at most once
• Clock synchronisation: on connect and on demand, written in the device's time zone
• TLS (IEC 62351-3): TLS 1.2+ with mutual authentication

How IEC 104 delivers data

An IEC 104 outstation pushes its data. It sends a point when the value changes (spontaneous), on a fixed cycle (periodic), or when it is asked for a snapshot (interrogation). MaestroHub keeps the latest report of every point in a process image for the connection, and pipelines use that image in two ways:

• Monitor Points is a trigger. It starts a pipeline for every point the outstation reports, with no polling.
• Read Points returns the latest known value of the points you list, with its quality and age.

Every point is addressed by its information object address (IOA), a number from 0 to 16,777,215, within one common address (the station address, 1 to 65,534).

What happens on connect

After the TCP (or TLS) connection is up and data transfer has started, MaestroHub runs up to three requests, in this order. Each one has its own switch and all three are on by default:

1. Clock synchronisation: sends the current time, written in the device's time zone. Turn this off for outstations whose clock comes from GPS or from another master.
2. Station interrogation: asks for the current value of every point, so the process image is complete straight away.
3. Counter interrogation: asks for every integrated total (energy counters).

MaestroHub also repeats the station interrogation when the outstation reports that it restarted (end of initialisation), and, if you set Periodic Interrogation, at that interval.

If the outstation refuses or does not answer one of these requests, the connection stays up, and the connection log says which request failed and what to change.

Connection Configuration

Creating an IEC 104 Connection

Navigate to Connections → New Connection → IEC 60870-5-104 and configure the form. The form is organized into seven tabs: Connection, Startup, Link Timers, Security, Functions, Scaling, and Health. The Functions, Scaling, and Health tabs unlock after the connection is saved.

1. Profile Information

Field	Default	Description
Profile Name	—	A descriptive name for this connection profile (required). Must be unique across all connections.
Description	—	Optional description for this IEC 104 connection
Labels	—	Key-value pairs to categorize and organize the connection

Example Labels

• site: substation-north — Site
• voltage: 110kv — Voltage level
• device: rtu-1 — Specific outstation
• environment: production — Deployment environment

2. Outstation

Field	Default	Meaning
Address	(required)	Outstation host name or IP address
Port	2404	2404 for plain IEC 104; 19998 is the port IEC 62351-3 assigns for IEC 104 over TLS
Common Address	1	The station address used in every request. Messages for any other common address are ignored
Originator Address	0	Identifies MaestroHub when several masters share the outstation. 0 = not used
Device Time Zone	UTC	The zone the outstation's clock runs in. Device timestamps carry no zone; MaestroHub converts them from this zone to UTC

3. Startup

The Startup tab holds the three on-connect requests described in What happens on connect, and the periodic interrogation.

Field	Default	Meaning
Synchronise Clock on Connect	on	See What happens on connect
Interrogate on Connect	on	See What happens on connect
Counter Interrogation on Connect	on	See What happens on connect
Periodic Interrogation	0s (off)	Repeat the station interrogation at this interval

4. Link Timers

These are the standard IEC 104 link parameters. Change them only to match what the outstation is configured with.

Field	Default	Meaning
Connection Timeout (t0)	30s	Time allowed to open the connection
Send / Test Timeout (t1)	15s	The link is closed if a sent frame is not acknowledged within t1. Also bounds waiting for a request's confirmation
Acknowledge Delay (t2)	10s	Received frames are acknowledged at the latest after t2. Must be shorter than t1
Idle Test Interval (t3)	20s	A test frame is sent when nothing has been received for t3
Send Window (k)	12	Maximum unacknowledged frames MaestroHub sends
Acknowledge After (w)	8	Received frames are acknowledged at the latest after w frames. Must not exceed k

5. Security: TLS (IEC 62351-3)

Turn on Enable TLS and, usually, set the port to 19998.

• CA Certificate: the CA that signed the outstation's certificate. Leave it empty to use the host's system roots.
• Client Certificate / Client Private Key: MaestroHub's certificate for mutual authentication. Most utilities require one. Both are stored encrypted.
• Server Name: the name expected in the outstation's certificate. It defaults to the address.
• Skip Certificate Verification: accepts any certificate. Use it only while commissioning.

TLS 1.2 is the minimum. MaestroHub accepts a renegotiation started by the outstation but cannot start one itself, so it covers the IEC 62351-3 transport profile without claiming full conformance.

If TLS fields are filled in while Enable TLS is off, the connection is refused rather than silently connecting without TLS.

Testing the Connection

Click Test Connection at the bottom of the form to try the current settings before saving. Once the connection runs, its health probe sends an IEC 104 test frame and reports the round trip; a test frame the outstation does not answer drops the session, and the connection reconnects.

Function Builder

Creating IEC 104 Functions

After the connection is saved:

1. Open the connection and navigate to the Functions tab
2. Click New Function to open the function type selection dialog
3. Choose Monitor Points, Read Points, Interrogate, Send Command, or Synchronise Clock
4. Fill the Basic tab (name, description, labels) and the Configuration tab (operation-specific parameters)
5. Use the Test button to run the function against the live outstation before saving

Monitor Points (iec104.monitor)

Purpose: Starts a pipeline for each point the outstation reports. This function type is a pipeline trigger: see Pipeline Integration and the IEC 104 Trigger node.

Parameter	Meaning
Information Object Addresses	Addresses and ranges to watch, e.g. 1001, 2000-2999. Empty = every point
Include Interrogation Responses	On (default): points that arrive as interrogation responses also fire the trigger. Off: only spontaneous and periodic changes do

Each event's payload:

{
  "commonAddress": 1,
  "ioa": 1001,
  "type": "M_DP_TB_1",
  "value": 2,
  "detail": { "state": "on" },
  "quality": "good",
  "flags": { "invalid": false, "notTopical": false, "substituted": false, "blocked": false, "overflow": false, "timeInvalid": false },
  "cause": "spontaneous",
  "sourceTimestamp": "2026-09-30T10:14:03.221Z",
  "serverTimestamp": "2026-09-30T10:14:03.240Z"
}

Every point has the same top-level keys, whatever its type; what only some types carry sits in detail.

• sourceTimestamp is the device's own timestamp, in UTC. It is null for types that carry none, and when the device marked its time tag invalid (then flags.timeInvalid is true).
• serverTimestamp is when MaestroHub received the point.
• quality is the platform's band: bad when the device marked the value invalid; uncertain when it is blocked, substituted, not topical, has overflowed, or is a counter with carry or adjustment; otherwise good. The individual flags stay in flags.

When the link to the outstation drops, the trigger fires once per outage with quality bad and the cause under error; see the IEC 104 Trigger node.

How value is written depends on the type:

Types	value
Single point (M_SP_*)	true / false
Double point (M_DP_*)	0–3; detail.state is intermediate, off, on or faulty
Step position (M_ST_*)	-64–63; detail.transient
Bitstring (M_BO_*)	32-bit unsigned number
Normalized (M_ME_NA_1, M_ME_TD_1, M_ME_ND_1)	-1.0 to just under 1.0
Scaled (M_ME_NB_1, M_ME_TE_1)	whole number, -32768–32767
Short float (M_ME_NC_1, M_ME_TF_1)	number
Integrated totals (M_IT_*)	whole number; detail.counterSequence, detail.carry, detail.adjusted

Types this connector does not decode (for example protection events, types 38–40) are skipped. The connection log names each such type once.

Read Points (iec104.read)

Purpose: Returns the latest value of each listed point, for example 1001-1004, 2001 (at most 10,000 addresses). Each entry is the payload above plus status: "ok" and ageMs, the time since the point was received. A point the outstation has not reported since the connection came up is returned as { "ioa": 1003, "status": "noValueYet" }, never as 0.

The process image starts empty on every new connection, so a read never returns a value from a link that has since dropped.

Interrogate (iec104.interrogate)

Purpose: Asks the outstation for a snapshot and returns every point it sends until it reports the interrogation finished.

Parameter	Meaning
Kind	station = process values; counter = integrated totals
Group	0 = all. Station groups are 1–16; counter groups are 1–4
Timeout	Bound on the whole interrogation (default 30m)

The interrogation also updates the process image and fires any matching Monitor Points triggers.

Send Command (iec104.command)

Purpose: Operates one information object and waits for the outstation's confirmation.

Parameter	Meaning
Command Type	single (C_SC), double (C_DC), regulatingStep (C_RC), setpointNormalized (C_SE_NA), setpointScaled (C_SE_NB), setpointFloat (C_SE_NC), bitstring (C_BO)
Information Object Address	The object to operate
Value	single/double: on or off. regulatingStep: higher or lower. setpointNormalized: -1 to just under 1. setpointScaled: -32768 to 32767. setpointFloat: a number. bitstring: a 32-bit number, decimal or 0x hex
Select Before Operate	On (default): select first, execute only when the selection is confirmed. Bitstring commands have no select step, so for them it has no effect
Qualifier	single/double/regulatingStep: 0 = outstation default, 1 = short pulse, 2 = long pulse, 3 = persistent. Set-points: the QL value. Bitstring commands carry no qualifier: leave 0
Time Tag	Send the time-tagged variant (C_xx_TA_1)
Wait for Termination	Also wait for the outstation to report the command finished. Many outstations send none

Every parameter is checked before anything is sent; a bad value never reaches the outstation.

A command is sent at most once per call

If the outstation does not confirm it within t1, or the timeout ends the wait, the outcome is unknown: the outstation may have acted. MaestroHub then reports command outcome unknown and never sends it again on its own, not by the connector and not by a pipeline's Retry on Fail or ForEach retry. A refused command is reported as refused and is not retried either. Commands are never buffered for later delivery, and a pipeline started by a late (replayed) value does not execute them unless the node allows late input.

Synchronise Clock (iec104.clockSync)

Purpose: Sends the current time, written in the device time zone, and waits for the confirmation. The connection also does this on every connect unless Synchronise Clock on Connect is off.

Pipeline Integration

Use the IEC 104 functions you configure here as nodes inside the Pipeline Designer. Read Points, Interrogate, Send Command and Synchronise Clock are exposed as matching connector nodes, and Monitor Points functions drive the IEC 104 trigger node:

• IEC 104 Read Points (connected.iec104.read) — executes an iec104.read function
• IEC 104 Interrogate (connected.iec104.interrogate) — executes an iec104.interrogate function
• IEC 104 Send Command (connected.iec104.command) — executes an iec104.command function
• IEC 104 Synchronise Clock (connected.iec104.clockSync) — executes an iec104.clockSync function
• IEC 104 Trigger (trigger.iec104) — starts a pipeline for each point an iec104.monitor function matches

For node-level details (output structure, execution settings), see the IEC 60870-5-104 Nodes and IEC 104 Trigger pages.

For orchestration strategies that mix IEC 104 with other data sources, see the Connector Nodes page.

Common Use Cases

Substation Telemetry to a Historian or UNS

Author a Monitor Points function over the measured-value range (for example 2000-2999), then use the IEC 104 Trigger node to route every reported point to a historian, MQTT topic or the Unified Namespace. Each event carries the platform quality band and the device timestamp, so a UNS Publish node stores what the outstation said, not just the value.

Breaker and Alarm Events

Watch the single- and double-point addresses with Include Interrogation Responses off, so the pipeline fires only on spontaneous changes: a breaker opening, a protection alarm, a door contact. The device's own time-tagged timestamp (sourceTimestamp) orders events correctly even when they arrive in a burst.

Energy Metering

Read integrated totals with a counter Interrogate driven by a Schedule trigger, for example every 15 minutes, and forward the counter values with their counterSequence, carry and adjusted detail to billing or reporting.

Supervised Switching and Set-Points

Receive a switching order or set-point from an upstream system or operator UI, validate it with a Condition node, then issue a Send Command with select-before-operate on. Because a command whose outcome is unknown is never re-sent, confirm the device state with a Read Points before trying again.

Troubleshooting

Error Reference

What you see	Meaning	Retried?
the outstation refused C_IC_NA_1: unknown common address	The outstation rejected the request (also: unknown type, unknown cause, unknown IOA, or a negative confirmation)	No, it will not change on retry
no activation confirmation within t1	The request was sent but not confirmed in time	Reads and interrogations: yes. Commands: never (the outstation may have acted)
... was confirmed but not finished before the timeout (N points received)	The interrogation started but did not finish within the function's timeout	Yes
A certificate error on connect	The outstation's certificate does not match the CA or server name	No
not connected	The connection is not up	Yes, after reconnect

Connection Issues

Symptom	Possible Cause	Solution
No point ever arrives for a station	The Common Address does not match the outstation's	Messages for any other common address are ignored. Set the station address the outstation is configured with.
Connection refused with TLS fields filled in	TLS material is set while Enable TLS is off	Turn on Enable TLS, or clear the TLS fields.
Device timestamps are hours off	Device Time Zone does not match the outstation's clock	Set the zone the outstation's clock runs in; MaestroHub converts from it to UTC.
A read returns noValueYet for a point	The outstation has not reported it since the connection came up	Keep Interrogate on Connect on, or run an Interrogate, so the process image is filled.