The Resource ReSerVation Protocol (RSVP) is a Transport layer protocol designed to reserve resources across a network for an integrated services Internet. RSVP provides receiver-initiated setup of resource reservations for multicast or unicast data flows with scaling and robustness.

RSVP can be used by either hosts or routers to request or deliver specific levels of Quality of Service (QoS) for application data streams or flows. It also defines how applications place reservations and how they can relinquish the reserved resources once the need for them has ended. RSVP operation will generally result in resources being reserved in each node along a path.

RSVP is not itself a routing protocol and was designed to interoperate with current and future routing protocols.


Main attributes

  1. Requests resources for simplex flows: a traffic stream in only one direction from sender to one or more receivers.
  2. RSVP is not a routing protocol but works with current and future routing protocols.
  3. It is receiver oriented: in that the receiver of a data flow initiates and maintains the resource reservation for that flow.
  4. RSVP maintains soft state (the reservation at each node needs a periodic refresh) of the host and routers' resource reservations, hence supporting dynamic automatic adaptation to network changes.
  5. Provides several reservation styles (a set of reservation options) and allows for future styles to be added to protocol revisions to fit varied applications.
  6. Transports and maintains traffic and policy control parameters that are opaque to RSVP.


Messages

There are two primary types of messages:
  • Path messages (path)

    The path message is sent from the sender host along the data path and stores the path state in each node along the path.The path state includes the IP address of the previous node, and some data objects:
    1. sender template to describe the format of the sender data
    2. sender tspec to describe the traffic characteristics of the data flow
    3. adspec that carries advertising data.


  • Reservation messages (resv)

    The resv message is sent from the receiver to the sender host along the reverse data path. At each node the IP destination address of the resv message will change to the address of the next node on the reverse path and the IP source address to the address of the previous node address on the reverse path. The resv message includes the flowspec data object that identifies the resources that the flow needs.
The data objects on RSVP messages can be transmitted in any order.

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