The Resource ReserVation Protocol (RSVP) is a resource reservation setup protocol. It is a protocol by which applications can request end-to-end, per-conversation, QoS from the network, and can indicate QoS requirements and capabilities to peer applications. RSVP is a layer-3 protocol, suited primarily for use with IP traffic.
Since RSVP is a layer-3 protocol, it is largely independent of the various underlying network media over which it operates. Therefore, RSVP can be considered an abstraction layer between applications (or host operating systems) and media-specific QoS mechanisms.
There are two significant RSVP messages, PATH and RESV. Transmitting applications send PATH messages towards receivers. These messages describe the data that will be transmitted and defines the path that the data will take. Receivers send RESV messages. These follow the path seeded by the PATH messages, back towards the senders, indicating the profile of traffic that particular receivers are interested in. In the case of multicast traffic flows, RESV messages from multiple receivers are 'merged', making RSVP suitable for QoS with multicast traffic.
As defined today, RSVP messages carry the following information:
Classification information is conveyed using IP source and destination addresses and ports. Policy information is typically a secure means for identifying the user and/or the application requesting resources. Network administrators use policy information to decide whether or not to allocate resources to a conversation.