This document addresses the problem of providing a bi-directional multicast protocol in an Intranet environment. A protocol named Switched Bi-directional Multicast Protocol (XMP) is proposed. Participants(Sender, S, or Receivers, Rs)signal their will to join the group sending a START(G) packet toward a Focal Point Router(FP). To take control of transmission a receiver application receives permission from the master application (the master transmitter)and sends a START(G) packet re-labeling the involved routers interfaces from R to S. The master Sender resumes transmission by means of his application commanding the receiver's application to go back to the receiver mode and emitting a START(G)packet to FP. ns-2 has been used to simulate it.