---
title: "Protocols"
description: "Overview of supported communication protocols"
source_url: https://ai-ops.com/docs/protocols/introduction
---

# Protocols

A **protocol** defines how Koios communicates with an external device or data source. When you create a device, you choose a protocol — this determines the connection settings you'll need to provide and the types of tags you can create.

> [!WARNING] Protocol cannot be changed after creation
> The protocol is locked once a device is created. If you need a different protocol,
> create a new device and recreate the tags.

## Supported Protocols

| Protocol | Use Case | Configuration Guide |
|----------|----------|---------------------|
| **OPC-UA** | PLCs, SCADA systems, historians, and modern industrial equipment | [OPC-UA Device](https://ai-ops.com/docs/devices/creating-opc-ua.md) |
| **Modbus TCP** | Sensors, meters, and simple controllers using register-based addressing | [Modbus TCP Device](https://ai-ops.com/docs/devices/creating-modbus-tcp.md) |
| **EtherNet/IP** | Allen-Bradley Logix controllers and generic CIP-compliant devices | [EtherNet/IP Device](https://ai-ops.com/docs/devices/creating-ethernet-ip.md) |
| **SOAP** | RDM HVAC controllers via web services | [SOAP Device](https://ai-ops.com/docs/devices/creating-soap.md) |
| **REST** | HTTP-based APIs (e.g. CAREL BOSS systems) | [REST Device](https://ai-ops.com/docs/devices/creating-rest.md) |
| **Microsoft SQL** | Querying data directly from SQL Server databases via ODBC | [Microsoft SQL Device](https://ai-ops.com/docs/devices/creating-mssql.md) |

## Protocol Details

### OPC-UA

OPC Unified Architecture is the modern standard for industrial data exchange. It provides a platform-independent, service-oriented architecture for communicating with PLCs, SCADA systems, historians, and other industrial equipment.

Koios connects as an OPC-UA client and supports:
- **Server discovery** — browse your network for available OPC-UA servers and endpoints
- **Security modes** — None, Sign, or Sign & Encrypt
- **Security policies** — Basic128Rsa15, Basic256, Basic256Sha256
- **Authentication** — Anonymous or Username/Password
- **Node browsing** — explore the server's address space to find and select tags

### Modbus TCP

Modbus TCP is a widely-used protocol for communicating with sensors, meters, and simple PLCs over Ethernet. It uses a register-based addressing model where data points are identified by register type and address number.

### EtherNet/IP

EtherNet/IP (Ethernet Industrial Protocol) uses the Common Industrial Protocol (CIP) to communicate with industrial devices over standard Ethernet. Koios supports two device types under this protocol:

- **Logix Controller** — connects to Allen-Bradley ControlLogix and CompactLogix controllers using tag-based addressing. Includes a tag browser for exploring the controller's tag database.
- **Generic CIP** — connects to any CIP-compliant device (variable frequency drives, I/O modules, non-Allen-Bradley equipment) using assembly-based addressing. Supports EDS file upload for structured browsing of device data.

### SOAP

The SOAP (Simple Object Access Protocol) implementation in Koios is designed for **RDM** (Resource Data Manager) controllers. RDM devices expose a SOAP-based API for reading and writing HVAC parameters.

### REST

The REST protocol connects to HTTP-based APIs, such as **CAREL BOSS** building management systems. Koios sends HTTP requests to the configured endpoint and parses the response to extract tag values.

### Microsoft SQL

Microsoft SQL devices allow Koios to query data from SQL Server databases using ODBC. Each tag on an SQL device executes a SQL query on every scan cycle and stores the result as a live value. This is useful for integrating data from business systems, energy management platforms, or external historians.

## Certificates

Some OPC-UA servers require certificate-based trust in addition to (or instead of) username/password authentication. See [OPC-UA Certificates](https://ai-ops.com/docs/protocols/opc-ua-certificates.md) for details on managing certificates in Koios.