> For the complete documentation index, see [llms.txt](https://docs.iotcore.omnicore.korewireless.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.iotcore.omnicore.korewireless.com/overview/universal-device-broker/mqtt-and-http-devices/resources/requirements.md).

# Requirements

This page lists OmniCore requirements and related information.

### Regions and versions[​](https://docs.omnicore.korewireless.com/docs/Universal%20Device%20Broker/MQTT%20&%20HTTP%20Devices/Resources/requirements#regions-and-versions) <a href="#regions-and-versions" id="regions-and-versions"></a>

#### Transport Layer Security (TLS)[​](https://docs.omnicore.korewireless.com/docs/Universal%20Device%20Broker/MQTT%20&%20HTTP%20Devices/Resources/requirements#transport-layer-security-tls) <a href="#transport-layer-security-tls" id="transport-layer-security-tls"></a>

OmniCore requires TLS version 1.2 or higher.

#### MQTT bridge[​](https://docs.omnicore.korewireless.com/docs/Universal%20Device%20Broker/MQTT%20&%20HTTP%20Devices/Resources/requirements#mqtt-bridge) <a href="#mqtt-bridge" id="mqtt-bridge"></a>

MQTT version 3.1.1 is required. The following features are not supported:

* MQTT QoS 2
* Arbitrary MQTT topics and subscriptions. For topic requirements, see the section on connecting devices using MQTT
* Last Will and Testament (LWT)
* Retained messages
* Persistent sessions

#### HTTP bridge[​](https://docs.omnicore.korewireless.com/docs/Universal%20Device%20Broker/MQTT%20&%20HTTP%20Devices/Resources/requirements#http-bridge) <a href="#http-bridge" id="http-bridge"></a>

Secure communication (HTTPS) is required. OmniCore supports HTTP 1.1 only (not 2.0).

### Permitted characters and size requirements[​](https://docs.omnicore.korewireless.com/docs/Universal%20Device%20Broker/MQTT%20&%20HTTP%20Devices/Resources/requirements#permitted-characters-and-size-requirements) <a href="#permitted-characters-and-size-requirements" id="permitted-characters-and-size-requirements"></a>

Registries and device identifiers, and their associated fields, are limited to certain characters. These fields are also limited in size (either length or byte size). The following table lists the permitted characters and sizes for each resource:

| Resource               | Limitations                                                                                                                                                                                                                                                                               |
| ---------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Registry IDs           | <ul><li>Permitted characters: \[a-zA-Z]\[-a-zA-Z0-9.\_+\~%]+</li><li>First character must be a letter (\[a-zA-Z])</li><li>Minimum length: 3 characters</li><li>Maximum length: 255 characters</li></ul>                                                                                   |
| Device metadata keys   | <ul><li>Permitted characters: \[a-zA-Z]\[-a-zA-Z0-9.\_+\~%]+</li><li>First character must be a letter (\[a-zA-Z])</li><li>Minimum length: 1 character</li><li>Maximum length: 128 characters</li><li>Maximum combined total size of all device metadata key-value pairs: 256 KB</li></ul> |
| Device metadata values | <ul><li>Minimum size: 0KB</li><li>Maximum size: 128KB</li><li>Maximum combined total size of all device metadata key-value pairs: 256 KB</li></ul>                                                                                                                                        |
| Subfolders\*           | <ul><li>Permitted characters: \[a-zA-Z]\[-a-zA-Z0-9.\_+\~%]+</li><li>First character must be a letter (\[a-zA-Z])</li></ul>                                                                                                                                                               |