em-udpclient.rb

#--------------------------------------------------------------------------- 
# The first one receives and prints a datagram: 
#--------------------------------------------------------------------------- 

require 'rubygems' 
require 'eventmachine' 

module A 
  def receive_data a 
    p a 
  end 
end 

EM.run { 
  p "Listening on 9600" 
  EM.open_datagram_socket "localhost", 9600, A 
} 

em-udpinitiator.rb

#--------------------------------------------------------------------------- 
# The third one sends a datagram to start off the process: 
#--------------------------------------------------------------------------- 

require 'rubygems' 
require 'eventmachine' 

module G 
  def post_init 
    send_datagram "AAA", "localhost", 9601 
  end 
end 

EM.run { 
  EM.open_datagram_socket "localhost", 0, G 
} 

em-udpserver.rb

#--------------------------------------------------------------------------- 
# The second one waits to receive a datagram, then sends it to a different 
# port.
#--------------------------------------------------------------------------- 

require 'rubygems' 
require 'eventmachine' 

module A 
  def receive_data a 
    p a 
    send_datagram "<#{a}>", "localhost", 9600 
  end 
end 

EM.run { 
  p "Listening on 9601, sending to 9600" 
  EM.open_datagram_socket "localhost", 9601, A 
}