17-14 Riverstone Networks RS Switch Router User Guide Release 8.0
RSVP Configuration MPLS Configuration
17.3.1 Establishing RSVP Sessions
RSVP includes the following types of messages:
•Path messages travel from the potential sender of the data flow to the receiver and include traffic
specifications and QoS requirements provided by the sender. Path messages establish the RSVP path
between the sender and the path flow destination, storing a path state in each router along the way.
The path state includes the unicast IP address of the previous hop.
•Resv messages travel from the intended receiver of the data flow to the sender and identify the
session for which the reservation is being made, the level of QoS required by the receiver, and the
label binding for the session. Resv messages use the path state information in each router to follow
exactly the reverse path (or paths) that the data packets will use, creating and maintaining a
reservation state in each router along the path(s).
•Teardown messages delete the reservation. Although RSVP uses session timeouts, teardown
messages are a more efficient way to release network resources. Either the sender or receiver of a
data flow can initiate a teardown request: PathTear messages are sent by the sender of the data flow,
and ResvTear messages are sent by the data flow receiver.
Figure17-7 illustrates the flow of RSVP Path and Resv mess ages.
Figure 17-7 RSVP Path and Resv messages
With RSVP, the potential receiver of a data flow is responsible for initiating and maintaining the resource reservation
for that flow. The receiver passes a QoS request to the local RSVP process. The RSVP protocol then carries the request
to all routers upstream to the data sender(s).
During reservation setup, RSVP determines:
•whether the router has sufficient available resources to supply the requested QoS, and
•whether the requestor has the administrative permission required to make the reservation
If either of the above checks fail, RSVP returns an error notification to the requestor. Otherwise, if both checks
succeed, the reservation is made at the link layer and the request is propagated upstream toward the appropriate sender.
RSVP uses a soft state approach to managing the reservation state in routers, that is, the state is created and periodically
refreshed by Path and Resv messages. When a path or reservation state times out, the reservation is deleted or torn
down. An explicit teardown message, either PathTear or ResvTear, can also delete the reservation.
Table 1 7-3 is a summary of the RSVP parameters on the RS and their default values. The commands that you use to
enable an RSVP operation or change a default value are also listed.
Sender Receiver
Path messages
Resv messages
12
Transit
Router
Transit
Router