TCP/IP Tutorial and Technical Overview - IBM Redbooks

Figure 8-6 shows the reservation process in an RSVP router.
RESV Message
Data
Packet
Classifier
Figure 8-6 RSVP reservation process
2. Forwarding of the reservation request
After a successful admission and policy check, a reservation request is
propagated upstream toward the sender. In a multicast environment, a
receiver can get data from multiple senders. The set of sender hosts to which
a given reservation request is propagated is called the scope of that request.
The reservation request that is forwarded by a node after a successful
reservation can differ from the request that was received from the previous
hop downstream. One possible reason for this is that the traffic control
mechanism may modify the flowspec hop-by-hop. Another more important
reason is that in a multicast environment, reservations from different
downstream branches, but for the same sender, are merged together as they
travel across the upstream path. This merging is necessary to conserve
resources in the routers.
A successful reservation request propagates upstream along the multicast
tree until it reaches a point where an existing reservation is equal or greater
than that being requested. At this point, the arriving request is merged with
the reservation in place and does not need to be forwarded further.
300 TCP/IP Tutorial and Technical Overview
Flow Descriptor
Flowspec Filterspec
Determine route
and QoS class
Packet
Scheduler
Application
Authority?
Routing
Resources?
Prioritize
and
schedule
packet link
RESV Message
Policy
Control
Admission
Control