The DDS Device

A DDS device is a collection of topics on which information flows.

Specifically:

<topic-root>/
- notification — server notifications, responses, etc.
- control — client requests to server
- metadata — optional stream information
rt/<topic-root>_ — ROS2-compatible streams
- <stream-name> — Image/Imu streams

The Topic Root

Note that topics are all using the same <topic-root> that is specified in the device-info. I.e., if the topic-root is known, all other topics can be found.

As long as the <topic-root> is a valid topic path, it can be anything and is entirely determined by Discovery.

Currently, the topic root as used by rs-dds-adapter is built as:

realsense/ <device-model> _ <serial-number>

Settings

On the client, device behavior with librealsense can be fine-tuned with JSON settings passed through the participant (and therefore from the librealsense context's dds settings), inside a device object:

{
  "dds": {
    "device": {
      "control": { "reply-timeout-ms": 2000 },
      "metadata": { "reliability": "reliable" }
    }
  }
}

The above overrides the default reply timeout to 2 seconds and makes the metadata topic use reliable QoS rather than the default best-effort.

Standard topic QoS settings

control, notification, and metadata topics all can have their own objects to override default QoS and other settings. See the above for an example. They all share common settings:

reliability can be a string denoting the kind, or an object:
- kind is best-effort or reliable
durability can be a string denoting the kind, or an object:
- kind is volatile, transient-local, transient, or persistent
history can be a number denoting the depth, or an object:
- kind is keep-last or keep-all
- depth is the number of samples to manage with keep-last
data-sharing is a boolean: true to automatically enable if needed; false to turn off
endpoint is an object:
- history-memory-policy is preallocated, preallocated-with-realloc, dynamic-reserve, or dynamic-reusable

Note that these settings are overrides. The default values may be different depending on the topic for which they're intended (for example, metadata uses best-effort by default while control and notification use reliable).

Other Settings

Field	Default	Type	Description
`control`/
`reply-timeout-ms`	2000	size_t	Reply timeout, in milliseconds

Device Options

To use device-level options, the control-reply needs to be used. The server publishes device options as part of the initialization sequence, in the device-options message. If available, the query-option and set-option controls can be used (no stream-name) to retrieve or update the values. Setting these options will not take effect until the device is reset.

The following device options may be available:

Setting	Default	Type	`option-name`	Description
Domain ID	0	int, 0-232	`domain-id`	The DDS domain number to use to segment communications on the network
IP address	empty	string "#.#.#.#"	`ip-address`	The static IP that the server uses for itself (empty=DHCP on)
Multicast IP	-	string "#.#.#.#"	`multicast-ip`	The IP address to use for multicasting (empty to disable)

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