Work on ROS2

communication.md

@@ -75,6 +75,54 @@ For example:
 - roscombridge/dji0/a/ext/unit_info/ALL
 - roscombridge/dji0/a/ext/tf/op0
 
+## Unreliable Communication
+
+Messages not arriving can in some cases be handled on the application level.
+
+For example to distribute a TST tree to all possible agents we have a service call
+TSTDistributeTreeFromUuid.srv:
+```bash
+string[] units      # List of units to distribute to.
+                    # If empty distribute to everybody in possible units
+string uuid         # Root node node_uuid of the TST to distribute
+---
+string com_uuid     # Used to check if tree have been distributed.
+bool success
+int32 error
+string reason
+```
+
+And GetResponse.srv:
+```bash
+string cuuid        # Identifier for the thing we need an response for
+---
+bool have_response  # True if there is a response
+string name
+string[] need_response_from # List of units we need response from
+string[] have_response_from # List of units we have response from
+bool success        # If true the thing was OK.
+```
+
+So we make a service call to distribute the tree and get com_uuid as
+response. We use com_uuid in the GetResponse service call to check if
+we have gotten a response from every receiver of the tree.
+
+The actual distribution of the tree is done by sending a TSTDistributeTreeInfo.msg message on a topic:
+```bash
+string uuid         # Use this uuid for confirmation that the tree have been distributed
+string sender       # Namespace for the sender
+string tree_json    # The TST tree to distribute
+```
+
+And the message confirming reception Response.msg:
+```bash
+string uuid
+string cuuid        # uuid for the command this is a response to
+string responder    # Namespace for the responder.
+bool success        # If true the command was OK.
+string fail_reason  # If fail, this is if given the reason.
+```
+
 
 ## UNSTRUCTERED MISC