icast protocol is being used; PIM does not require any particular unicast protocol. Sparse-mode PIM is optimized for environments with intermittent multicasts in with many multipoint data streams, and for senders and receivers that WAN segments separate. It works by defining a Rendezvous Point. When a sender wants to send data, it first sends to the Rendezvous Point. When a receiver wants to receive data, it registers with the Rendezvous Point. Once the data stream begins to flow from sender to Rendezvous Point, the routers in the path will optimize the path automatically to eliminate superfluous hops. PM-DM is simpler because it does not require the control overhead that is necessary for a Rendezvous Point, which is often not needed when leveraging the data-handling capacity in the switch infrastructure, and one is not running a connection oriented network (e.g., ATM). Another difference between PIM-SM and PIM-DM is that the latter does not transmit periodic joins, only explicitly triggered grafts/prunes. Although PIM-DM is not yet a RFP, it does work, and it is interoperable. Sparse-mode PIM assumes that no hosts want the multicast traffic unless they specifically ask for it. It works well in corporate environments where multiple groups may need to multicast across WANs, but only occasionally. Conferencing and the Internet Enterprises will continue to seek networks that facilitate the transmission of every type of data, including Real-Time multimedia. A debate has subsided for now, and the enterprise network of choice is a refined set of IP protocols that runs over fat pipes. Some companies circumvented IP's best-effort design limitations by adopting ATM cell switching for LAN and WAN, but ATM's demise finally seems imminent. Deterministic ATM-based networks currently have the advantage in service quality, Standards for Conferencing over IP Networks but IP protocols are widely implemented and are constantly evolving. Moreover, it is very difficult to find skilled resources with an ATM background (or to pay for 