RSVP can be used with multicast and unicast traffic. RSVP is not a routing protocol, but it does use routing protocols and consults the local router tables for routes. A typical reservation flow is initiated by sending a PATH message downstream to the receiver. Each node in the data path establishes a PATH state, to maintain the appropriate QoS. A PATH message states the flow ID, reservation information, and the source and destination address. Once the PATH message reaches its destination, the receiver passes the request to the local RSVP process, which passes the request to admission control and policy control.
Admission control determines whether the node has the available resources to satisfy the request.
Policy control determines whether or not the user has permission to request the reservation. If either of these is not successful, the RSVP process sends an error response to the sending program. If Admission control and Policy control succeed, parameters are set in the packet classifier and packet scheduler to implement the appropriate QoS. A RESV message is then sent upstream from the receiver to each node in the reverse data path. The RESV message uses the same flow information used in the PATH message. Routers along the path commit to the reservation and then store the information in a flow table.