The Resource ReSerVation Protocol - RSVP - is a signalling mechanism used for network management of packets.
It uses a method where resources available to handle Quality Of Service traffic is broadcasted throughout the network.
Listening devices reply with a RESV (Reserve) message containing a flow specification for the traffic.
Devices on the route between sender and listener either accept the reservation and handle the flow, or send a reject message.
Reservations can end normally or time out as needed.