RSVP (Resource Reservation Protocol) is a protocol used in VoIP to manage QoS (Quality of Service).

RSVP works by requesting that required bandwidth and latency be “reserved” for the VoIP telephone call by every network device between the two endpoints.

RSVP is defined in RFC 2205: Resource ReSerVation Protocol (RSVP).

RSVP is a unicast and multicast signaling protocol, designed to install and maintain reservation state information at each router along the path of a stream of data.

The RSVP protocol is used by a host to request specific qualities of service from the network for particular application data streams or flows. RSVP is also used by routers to deliver quality-of-service (QoS) requests to all nodes along the path(s) of the flows and to establish and maintain state to provide the requested service. RSVP requests will generally result in resources being reserved in each node along the data path.