setup problem for a publisher/subscriber running on different PCs

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Hi,

I am really a ROS and Baxter beginner, and I am experiencing strange behaviour of the ROS communication layer that I do not understand. Consider two trivial scripts, a publisher and a subscriber:

publisher.py:

import rospy
from std_msgs.msg import String

pub = rospy.Publisher('foo', String)
rospy.init_node('publisher_test')
r = rospy.Rate(10)
while not rospy.is_shutdown():
    pub.publish("hello world")
    r.sleep()

subscriber.py:

import rospy
from std_msgs.msg import String

def callback(data):
    rospy.loginfo("I heard %s",data.data)

rospy.init_node('subscriber_test')
rospy.Subscriber("foo", String, callback)
rospy.spin()

The ROS_MASTER is running in the Baxter internal PC.

I have 4 different shell opened: two shells in my PC, both configured launching the script baxter.sh, and two SSH shells - both configured launching the script baxter.sh. I have done 4 different experiment:

1. If I launch both the publisher and the subscriber from my PC, no problem arises.

2. If I launch both the publisher and the subscriber from the Baxter PC, no problem arises.

3. If I launch the publisher in from my PC and the subscriber from Baxter PC, no problem arises.

4. If I launch the publisher in the Baxter internal PC and the subscrber in my PC, the subscriber does not receive any message. If I launch "rostopic echo /foo" from my PC, it does not print anything. However, if I launch "/robot/joint_states" from my PC, no problem arises.

The PC and the baxter are direct connected with a twisted cable.

Some ideas?

Many thanks,

Sincerely Nicola