The Receiver sends reservation messages to routers along the path. The routers check the path message and if all conditions are met, resources are reserved. The Sender application receives a reservation message. The Sender starts sending data packets. RSVP is uni-directional.
Receivers initiate and maintain the resource reservation for a flow.
RSVP is not a routing protocol, but relies upon routing protocols for delivering flows. RSVP supports IPV4 and IPV6. Though RSVP clearly has many advantages for voice and video applications, several issues have been raised that are delaying its wide-scale deployment. To date, the IETF committee has addressed the limitations of RSVP through a series of guidelines on deployment. The general message of the Applicability Statement is to urge caution about the immediate large-scale deployment to the general Internet.