filipecalasans / databroker

Data Broker

Data Broker

It is a data broker that allows exchanging data between distributed modules. Modules are distributed entities able to exchange data and keep state synchnization between them. This broker is targetet to applications where data must be shared among modules and there must exist state consistence between them. Applications such as distributed simulation, simulators, multi-agent systems and multiplayer game may apply for use this broker.

How does it work ?

Modules provide and consume data periodically using the data connection interface. The broker builds data routes using the module configuration file, which describes the data needed by each module. The same principle is used in the Control communication channel, used to forward command packets between modules. Commands are a special kind of data, which are not produced periodically and may be used to module synchronization, module configuration or to delivery low rate data.

Configuration

Modules Configuration

Example of Module configuration file.

{
"id": "radio",
"name":"Radio Communication",
"description": "This module receives and send data throught RF to the robots",
"ip": "127.0.0.1",
"port_data":6002,
"port_control":6003,
"socket_type":"udp",
"mandatory": true

"data_published": [ 
   {
      "id": "vx0",
      "name": "Estimated position X",
      "description": "Measured Velocity X from robot 0",
      "unit": "m/s"
   },
   {
      "id": "vy0",
      "name": "measured velocity Y",
      "description": "Measeured velocity Y from Robot 0",
      "unit": "m/s"
   },
   {
      "id": "ball_sensor",
      "name": "Ball Pocession Sensor ",
      "description": "Indicates if the robot got the ball procession",
      "unit": "True of False"
   }
],

"data_consumed": [ 
   {
      "source": "ai",
      "id": "vx0" 
   },
   {
      "source": "ai",
      "id": "vy0" 
   }
],

"commands_consumed": [ 
   {
      "source": "ai",
      "command": "kick"
      }
   ]	
}

Following you can see the desciption of each parameter.

Parameter	Description	Data Type	Optional
id	Module Identification name. It must be unique.	String - Unique	No
name	Module name in human readable format.	String	yes
mandatory	Module must be connected to communication go to the Running state, otherwise it fails to start the communication.	Boolean	Yes - default value is True
description	Module description in human readable format.	String	Yes
port_data	Socket port for the Data Channel	Unsigned Integer 16-bits	No
port_control	Socket port number for the Control Channel	Unsigned Integer 16-bits	No
socket_type	Socket type for the Data Channel. Two values possible "tcp" or "udp"	String - "tcp" or "udp"	Yes: Default is "udp"
data_published	List of data descriptor objects. Data descrptors describes each data provided by the module.	JSON object list.	Yes
data_consumed	List of data consumed by the module.	JSON object list	Yes
commands_consumed	List of commands consumed by the module	JSON Object list	Yes

Data Published

Parameter	Description	Data Type	Optional
id	Data id. must be unique in the given module.	String	No
name	Data name in human readable format.	String	Yes
description	Data description in human readable format.	String	Yes
unit	Data Unit. It may be a pysical unit, such as m, m/s, degrees or something that represent the unit.	String	Yes

Data Consumed

Parameter	Description	Data Type	Optional
source	Module Id of the data provider.	String	No
id	Data Id	String	No

Commands consumed

Parameter	Description	Data Type	Optional
source	Module Id of the command provider	String	No
command	Command string	String	No

When no command consumed is provided, the module that is sending the command must specify the destination in the command packet. The explicit definition in-packet of the destinations has precedence over the pre-defined route table. More information can be found in the section Communication API.

Broker Configuration

Example of broker configuration file. Modules are a list of data paths to the module configuration files. The Path is relative to the config.json file.

{
"data_rate": 0,
"auto_start": false,
"master_module": "vision",
"modules": [
   "vision.json",
   "radio.json"
   ]
}

Parameter	Description	Data Type	Optional
data_rate	Minimum time between data packets in milliseconds (ms)	Unsigned Integer	Yes - default is 0
auto_start	Enable autostart process. If autostart is true the broker will try to go trhough the initialization process automatically until it reaches the RUNNING state	Boolean	True
connect_timeout	The broker will wait for <connect_timeout> milliseconds before verifying if all the mandatory modules are connected.	Unsigned Integer	No default - 2000 ms
ready_timeout	The broker will wait for <ready_timeout> milliseconds before verifying if all the mandatory modules are in READY state.	Unsigned Integer	No - default 2000 ms
running_timeout	The broker will wait for <running_timeout> milliseconds before verifying if all the mandatory modules are in RUNNING state.	Unsigned Integer	No - default 2000 ms
pause_timeout	The broker will wait for <pause_timeout> milliseconds before verifying if all the mandatory modules are in PAUSE state.	Unsigned Integer	No - default 2000 ms
autoconnect_timeout	The broker will wait for <autoconnect_timeout> milliseconds before trying to connected to the modules.	Unsigned Integer	No - default 2000 ms
retry_timeout	The broker will wait for <retry_timeout> milliseconds before retrying the autostart process again.	Unsigned Integer	No - default 2000 ms
modules	Path to the module descriptors. Paths are relative to the broker configuration directory.	Unsigned String	No

Communication API

Dependencies

• Qt >= 5.4
• Google Protobuffer