Hi all,
I made a proof of concept, meaning still experimental, of the UDP Broadcast transport layer and how it could work.
The final aim is to make a multimaster implementation with UDP Broadcast to avoid WiFi struggle.
I would like some advice of what is wrong and how to improve.
Architecture:
- Topic negotiation - Both the Subscriber/Publisher uses a TCP service to get the publishing port from the
organizer.py - Publisher serialize the packets into a Msg message then broadcast the packets to the port given by the organizer.
- The subscriber binds to the port, deserialize packets and either send it to the callback or publish it on the local master
Known limitations:
- Not secure (publisher ip not checked, not crypted)
- 64k maximum packet size (from IP protocol), tested only for non fragmented packets of less than 1k
- ROS Indigo
- Python 2.7
Usage:
roscore &
rosrun multimaster_udp organizer.py
# in another terminal
rosrun multimaster_udp smallest_subscriber_udp.py
# in another terminal
rosrun multimaster_udp smallest_publisher_udp.py
UDP Subscriber:
#!/usr/bin/env python
import rospy
from multimaster_udp.transport import UDPSubscriber
from std_msgs.msg import String
def callback(data, topic):
global counter
counter += 1
print data, "\n received",counter, "UDP messages from \n", topic
def main():
global counter
counter = 0
rospy.init_node("smallest_subscriber_udp")
# if the callback is not defined (None), it will publish locally
# to the equivalent topic.
sub = UDPSubscriber("hello", String, callback=None)
rospy.spin()
if __name__ == '__main__':
main()
UDP Broadcast Publisher
#!/usr/bin/env python
import rospy
from multimaster_udp.transport import UDPPublisher
from std_msgs.msg import String
def main():
rospy.init_node("smallest_broadcast_publisher_udp")
msg = String("World")
pub = UDPPublisher("hello", String)
rate = rospy.Rate(100)
while not rospy.is_shutdown():
pub.publish(msg)
rate.sleep()
if __name__ == '__main__':
main()
