[ros-users] Remote processes cannot communicate in ros-hydro

[Sietse Achterop]

    Dear list,

Having trouble communicating between two simple ROS processes when they are on 2 different hosts.
Networking as such is working as proved by netcat. I also turned off the firewall to be sure.

One process publishes on a topic and another process subscribes to it.
When that process receives a message, it sends a messsage to the first process via another topic.
Running both processes on the same machine as roscore works perfectly, but fail otherwise.

Both machines are Ubuntu 12.04, 64-bit, with ROS software (hydro) from the repository.
To get it to work, on each machine I do next to the regular catkin sourcing:

export HOSTNAME=`hostname`
export ROS_IP=<IP-number of this host>
export ROS_MASTER_URI=http://<ip-number-of-the-master>:11311

So for example we get (for the lcal machine):
HOSTNAME=fwn-nb4-16-202
ROS_IP=129.125.16.202
ROS_MASTER_URI=http://129.125.16.202:11311

We have two machines: local (running master) and remote.
When one process is on the remote somehow I only see
that the first process is publishing (via INFO) and on the other nothing is seen.

rostopic list
   works on the both machines
roswtf
    no errors on the local machine
    but hangs on the remote machine.
      every 5 seconds we see:
         unknown network error contacting node: timed out

What can be wrong?

For completeness below the code of the 2 processes.

      Thanks in advance,
            Sietse

Node1.cpp:
#############################################################
#include "ros/ros.h"
#include "std_msgs/String.h"
#include <sstream>

void T2Callback(const std_msgs::String::ConstPtr& msg)
{ ROS_INFO("What?: [%s]", msg->data.c_str()); }

int main(int argc, char **argv)
{
  ros::init(argc, argv, "node1");
  ros::NodeHandle n;
  ros::Publisher T1_pub = n.advertise<std_msgs::String>("T1", 1000);
  ros::Subscriber sub = n.subscribe("T2", 1000, T2Callback);
  ros::Rate loop_rate(2);

  int count = 0;
do {

  std_msgs::String msg;
  std::stringstream ss;
  ss << "hello world " << count;
  msg.data = ss.str();

  ROS_INFO("%s", msg.data.c_str());
  T1_pub.publish(msg);
  ros::spinOnce();
  loop_rate.sleep();
  ++count;
} while (ros::ok());

  return 0;
}


Node2.cpp:
###############################################################
#include <ros/ros.h>
#include "std_msgs/String.h"
#include <sstream>

class SubscribeAndPublish
{
public:
   SubscribeAndPublish()
   { //Topic you want to publish on
     T2_pub = n.advertise<std_msgs::String>("T2", 1000);
     //Topic you want to subscribe to
     sub = n.subscribe("T1", 1000, &SubscribeAndPublish::callback, this);
   }

   void callback(const std_msgs::String& msg)
   {	//msg contains data from subscribed topic 	
	//Output contains data which is published
	ROS_INFO("Massage received");
	std_msgs::String output;
	std::stringstream ss;
	ss << "You are listening to SublimeFM";
	output.data = ss.str();
	T2_pub.publish(output);
   }

private:
   ros::NodeHandle n;
   ros::Publisher T2_pub;
   ros::Subscriber sub;

};//End of class SubscribeAndPublish

int main(int argc, char **argv)
{
   //Initiate ROS
   ros::init(argc, argv, "subscribe_and_publish");
   SubscribeAndPublish SAPObject;
   ros::spin();
   return 0;
}