Problems about mono-directional communication (yarp -> ROS)

[randaz81]

This is a tricky issue: a yarp machine (A) is able to subscribe to a ros topic and receive data correctly sent by a ros machine (B). But the data that (A) publishes on a ros topic are not received by the ROS machine (B). (*)

These are the things to check when this issue is observed:

• check that yarp server has been started with the --ros option
• check the existence of the /ros port with a yarp name list command. Be extremely careful when working with a wireless network: if you use the yarp clean --timeout xx.xx there exists the risk to remove the /ros port if your system is affected by delay issues! See also: About address conflict, yarp clean etc #181
• Use the yarp plugin --all command to check that the following yarp carrier plugins rossrv, tcpros, xmlrpc are compiled and can be found by the system. If they are not compiled, check if they are enabled in yarp cmake (ENABLE_yarpcar_XXX flags). If they are compiled but not found, check the $YARP_DATA_DIRS environment variable.
• Check the firewall settings.
• This is a very common source of problems and most likely the cause of the issue that you are experiencing now. Check the /etc/hosts on all the machines of your setup. Verify that all the machines are registered with their correct hostnames and ip addresses. If change an entry in this file, it's recommended to restart roscore and yarpserver. (**)
  On windows the host names are stored in the file: C:\Windows\System32\drivers\etc\hosts

PS:
(*) indeed rqt tool shows that there are not connections from A to B.
(**) it may be possible that this behavior is caused by a bug in either yarpserver or roscore. Currently under investigation.