Microsoft KB Archive/244910

= Description of Reservation State in RSVP =

Article ID: 244910

Article Last Modified on 3/2/2007

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APPLIES TO


 * Microsoft Windows 2000 Server
 * Microsoft Windows 2000 Advanced Server
 * Microsoft Windows 2000 Professional Edition
 * Microsoft Windows 2000 Datacenter Server

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This article was previously published under Q244910



SUMMARY
This article describes how the Quality of Service (QoS) Resource Reservation Protocol (RSVP) manages the path state in nodes along a data path. This is accomplished by periodically using PATH and RESV refresh messages to maintain the path/reservation state for a data flow. The absence of these refresh messages results in the deletion of the state.



MORE INFORMATION

 * Soft State

RSVP is used to reserve resources in routers or hosts in the data path of a traffic flow. "Soft state" is used o maintain this condition in the devices in the data path. When Soft state is established, nodes send PATH and RESV messages periodically (usually about every 30 seconds) to refresh the reservation and path state. If no matching refresh messages arrive before a certain cleanup interval elapses, the state is deleted. The state can also be deleted by issuing an explicit "Teardown" message (RESVTEAR, PATHTEAR). After the expiration of the refresh time-out period, or after a state change, RSVP scans its state and issues the RESV, PATH refresh messages to the next hops.

Soft state is necessary because RSVP does not associate the data path to a static route throughout a network. It is possible for a route to change, so it is important that the reservation state be periodically refreshed. Because RSVP maintains a dynamic state, changes in QoS requests are allowed by simply permitting revised PATH or RESV messages from hosts. Devices along the data path receive the changes in the QoS parameters and make the appropriate adjustments to the RSVP state. The unused state is be terminated explicitly, or eventually times out.
 * Hard State

Hard state is used by other technologies when they are setting up some sort of virtual circuit for data transfers. The connection is then broken after the transfer is complete.
 * Steady State

Using Steady state allows a state to be refreshed "hop-by-hop" to allow the merging of flows. If a received state is different from the stored state, the stored state is updated. This warrants refresh messages to be generated and sent out immediately to update state changes on devices in the end-to-end data path. If a point is reached in which merging flows results in no change in state, propagation of the change stops. This is important when you are scaling large multicast groups and also reduces RSVP control traffic caused by any state changes.

For additional information, click the article number below to view the article in the Microsoft Knowledge Base:

227261 Description of the Resource Reservation Protocol (RSVP)

Additional query words: Soft State, QoS, RSVP, PATH, RESV

Keywords: kbenv kbinfo kbnetwork KB244910

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