50: Link Control

Control a link to the internet to send and receive messages. Used to control a remote device link, such as connecting to a UDP server, and using the V3 messaging protocol to communicate with it. Once initiated, messages can be forwarded to the link directly using the forwarding headers. Enable is a common keep-open override: it applies to Link2 when Link2 is configured and available, otherwise to Link1. IP Address, Port, and FQDN configure Link2 only. They do not change Link1's protected endpoint and are unsupported when Link2 is compiled out.

Header

Field	Name	Description	Type
5	Method	Request a service to be perform an action Possible values: 1: SET— Set one or more values that are provided in the message payload. 2: GET— Get values for the associated message type. 3: SUBSCRIBE— Subscribe to values for the associated message type. Can be used in conjunction with other header fields to define the subscription parameters, such as Interval, Duration, Timeout, Storage Level and Message Level. If no interval is provided, messages will be sent as and when new data is available. Some data, such as GPS position, may require a set interval to be provided. 5: UNSUBSCRIBE— Unsubscribe from a previous subscription.	uint8

This is an extract of header fields that are relevant to this message type, you can find them all documented in the Headers section.

Payload

Field	Name	Description	Type	Unit
1	IP Address	IP address of Link2, if not using FQDN	ascii
2	Port	UDP port for Link2	uint16
3	Enable	Enable or disable the keep-open override; Link2 when configured and available, otherwise Link1	bool
4	FQDN	FQDN of Link2, if not using IP address	ascii

Examples

Set a link to a server using FQDN

📡 Real example from Generate tool on 2025-10-16This example was generated using the generate tool, and tested against an RH2 device, sent from Toit.

ACK for setting a link to a server using FQDN

📡 Real example from RH2 P1 v2300 on 2025-10-16This example is captured from an RH2 device as part of normal communications over I2C with the ESP32 co-processor, where P1 responses to a request from Toit on the ESP32.

GET request for link settings

📡 Real example from Generate tool on 2025-10-16This example was generated using the generate tool, and tested against an RH2 device, sent from Toit.

Code

For convenience, the following constants can be used to reference this message type.