-
Notifications
You must be signed in to change notification settings - Fork 2
Designing your Scenario
Your scenario model consists of your network topology and the messages that communicate across it. To define your scenario, identify the ROS2 messages that flow between robots and the configuration of robot network. Then construct your scenario model by creating your communication and network components:
We model communication flows between robots by defining ROS2 messages that flow between network nodes using the DDS communication protocol. Communication is sent from publishers and is received by registered subscribers. A publication consists of the publisher's role, the subscription topic name, the size and frequency of the publication of the publication, and QoS properties of the publication. A subscription consists of the subscriber's role, the subscription topic name, and QoS properties of the subscription.
We define communication flows in two steps to reflect the role-based organization of swarms. First we define role-based publications and subscriptions that our Scenario will model. Then we assign robots to these roles, where a given robot runs on a specific network node.
These publisher, subscriber, and robot properties are defined using comma-separated (CSV) entries in Scenario files.
We define publisher, subscriber, and robot properties in a CSV file, where properties consist of role-based publication definitions, role-based subscription definitions, and the names of robots and their role:
-
Publisher - Define publisher subscriptions by role. Also defines the QoS policy (defined below) for publishing the subscription. Publisher entries have this format:
Publisher, Role, Subscription, Frequency, Size, History, Depth, Reliability, Durability
This example defines a publisher role for a
red_team
robot whereodometry
messages are simulated by transmitting 10 bytes at 500 Hz using a QoS policy ofkeep_last, 0, reliable, volatile
:Publisher, red_team, odometry, 10, 500, keep_last, 0, reliable, volatile
-
Subscriber - Define subscriber subscriptions by role. Also defines the QoS policy (defined below) for the subscription. Subscriber entries have this format:
Subscriber, Role, Subscription, History, Depth, Reliability, Durability
This example defines a subscriber role for Ground Station
GS
"robots" for receivingodometry
data using a QoS policy ofkeep_last, 0, reliable, volatile
:Subscriber, GS, odometry, keep_last, 0, reliable, volatile
-
Robot - Define robot names and the role the robots will take:
Robot, Name, Role
This example assigns robot
R1
to theGS
role:Robot, R1, GS
The QoS policy consists of settings for History, Depth, Reliability, and Durability, see https://index.ros.org/doc/ros2/Concepts/About-Quality-of-Service-Settings/. Here is the QoS syntax for scenario files:
-
History
controls history depth. Modes arekeep_all
andkeep_last
. Forkeep_last
, useDepth
. -
Depth
defines history depth whenHistory
mode iskeep_last
. -
Reliability
regulates reliability of data received. Modes arereliable
andbest_effort
. Forreliable
, DDS will track transmissions and attempt to repair lost transmissions. Forbest_effort
, DDS will not track transmissions and will not attempt to repair lost transmissions. -
Durability
provides durability by transmitting previously transmitted data to readers that join late. Modes aretransient_local
andvolatile
.
Several GUI tools are available for defining complex network configurations, https://dl.acm.org/doi/10.5555/2685617.2685639, https://ieeexplore.ieee.org/document/7148414?reload=true&arnumber=7148414. We describe working with the miniedit
tool because it is packaged with mininet-wifi. We can also define simpler ad-hoc networks directly in the CSV configuration file as described later.
Here we show an example of using miniedit to define the ad-hoc network that is similar to the example at ~/gits/mininet-wifi/examples/adhoc.py
:
-
Start miniedit:
~/gits/mininet-wifi/examples/miniedit.py
-
Build the adhoc example:
- Click the station (laptop) icon
- Click three places to drop three stations. You may need to adjust their positions later so they are in range of each other.
- Click the link (line) icon
- For each station, click down on one station, drag the cursor, and release the click on another station to connect stations with a link.
- Click the selection (arrow) icon
- Right click each link to define the connection type as ad-hoc and to set the source and destination properties for wlan0.
- Save the network as a Python script by selecting the File menu and selecting Export level 2 script.
-
Make the saved script compatible with the mininet_runner tool:
-
Using an editor, comment out the lines near the bottom which start the command line interpreter and then stop the network (older mininet-wifi 2.4.3 used
CLI_wifi(net)
):# CLI(net) # net.stop()
and add this line in its place:
return net
-
Save this modified file.
-
In the future this option may be removed because everything here can be done with miniedit
and having this option adds complexity.
For ad-hoc networks, we can define stations, links, radio propagation, robot mobility and some other properties directly within the CSV file instead of using miniedit by adding CSV entries as described here. These entries are ignored when using GUI-generated code:
-
Stations - Station definitions for each robot such as location for fixed-location stations:
Station, Name, param=value, ...
For example settings, see
addStation
in the examples in the mininet-wifi repository. -
Links - Radio link information for the network link on each robot:
Link, Name, param=value, ...
For example settings, see
addLink
in the examples in the mininet-wifi repository. -
Propagation Model - The radio signal propagation model:
Propagation Model, param=value, ...
See
setPropagationModel
in the examples in the mininet-wifi repository. -
Mobility Model - The mobility model:
Mobility Model, param=value, ...
See
setMobilityModel
in the examples in the mininet-wifi repository.Alternative to Mobility Model, we can define start and stop points for individual robots using
Start Mobility
,Mobility
, andStop Mobility
, see example usage in the mininet-wifi repository. -
Plot Graph - How to plot the real-time mobility graph:
Plot Graph, param=value, ...
See
plotGraph
in the examples in the mininet-wifi repository.
Publisher and subscriber roles are defined for ground station GS and team red_team for robots sta1, sta2, and sta3 in these lines of scenarios/adhoc.csv
:
# Publisher, Role, Subscription, Frequency, Size, History, Depth, Reliability, Durability
Publisher, red_team, odometry, 10, 500, keep_last, 0, best_effort, volatile
# Subscriber, Role, Subscription, History, Depth, Reliability, Durability
Subscriber, GS, odometry, keep_last, 0, best_effort, volatile
# Robot, Name, Role
Robot, sta1, GS
Robot, sta2, red_team
Robot, sta3, red_team
File scenarios/adhoc.py
was created as shown above, with station coordinates modified so the stations are in range.
This is then run by typing the following:
cd ~/gits/mininet_testbed
./mininet_runner.bash -s scenarios/adhoc.py scenarios/adhoc.csv adhoc_output_log
where the -s
option instructs mininet_runner.py
to only use publisher, subscriber, and robot definitions and to take network setup instructions from the Python setup script.
Once enough data is collected, analysis may be performed by typing
cd ~/gits/mininet_testbed
./plot_analytics.py adhoc_output_log adhoc_example
In the future this option may be removed because everything here can be done with miniedit
and having this option adds complexity.
Because the ad-hoc network only has station nodes, it can be defined completely in CSV file scenarios/adhoc.csv
:
# Publisher, Role, Subscription, Frequency, Size, History, Depth, Reliability, Durability
Publisher, red_team, odometry, 10, 500, keep_last, 0, best_effort, volatile
# Subscriber, Role, Subscription, History, Depth, Reliability, Durability
Subscriber, GS, odometry, keep_last, 0, best_effort, volatile
# Robot, Name, Role
Robot, sta1, GS
Robot, sta2, red_team
Robot, sta3, red_team
# Station, Name, param=value, ...
Station, sta1, position=10;10;0, range=100
Station, sta2, position=50;10;0, range=100
Station, sta3, position=90;10;0, range=100
# Link, Name, param=value, ...
Link, sta1, cls=adhoc, intf=sta1-wlan0, ssid=adhocNet, mode=g, channel=5, ht_cap=HT40+
Link, sta2, cls=adhoc, intf=sta2-wlan0, ssid=adhocNet, mode=g, channel=5
Link, sta3, cls=adhoc, intf=sta3-wlan0, ssid=adhocNet, mode=g, channel=5, ht_cap=HT40+
Propagation Model, model=logDistance, exp=4
Because scenarios/example1
only has station nodes, it is defined completely in a CSV file. It defines one ground station that publishes odometry data and four red team robots that subscribe to odometry data:
# Publisher, Role, Subscription, Frequency, Size, History, Depth, Reliability, Durability
Publisher, GS, odometry, 10, 500, keep_last, 0, reliable, volatile
# Subscribers, Role, Subscription, History, Depth, Reliability, Durability
Subscriber, red_team, odometry, keep_last, 0, reliable, volatile
# Robot, Name, Role
Robot, R1, GS
Robot, R2, red_team
Robot, R3, red_team
Robot, R4, red_team
Robot, R5, red_team
# Station, Name, param=value, ...
Station, R1, range=100, position=0;0;0
Station, R2, range=100, position=1;0;0
Station, R3, range=100, position=0;1;0
Station, R4, range=100, position=-1;0;0
Station, R5, range=100, position=0;-1;0
# Link, Name, param=value, ...
Link, R1, cls=adhoc, intf=R1-wlan0, ssid=adhocNet, mode=g, channel=5, ht_cap=HT40+
Link, R2, cls=adhoc, intf=R2-wlan0, ssid=adhocNet, mode=g, channel=5, ht_cap=HT40+
Link, R3, cls=adhoc, intf=R3-wlan0, ssid=adhocNet, mode=g, channel=5, ht_cap=HT40+
Link, R4, cls=adhoc, intf=R4-wlan0, ssid=adhocNet, mode=g, channel=5, ht_cap=HT40+
Link, R5, cls=adhoc, intf=R5-wlan0, ssid=adhocNet, mode=g, channel=5, ht_cap=HT40+
Propagation Model, model=logDistance, exp=4
Plot Graph, min_x=-2, min_y=-2, max_x=2, max_y=2