What RSVP Is Not
As mentioned before, RSVP is not a routing protocol. It relies on typical IP
routing protocols to forward the RSVP packets.The next section shows how
RSVP uses the routed path to create the setup messages that make the actual
reservations.
Because of its protocol-based nature, RSVP does not monitor reservations. It
is, therefore, not a resource manager. It is worth reiterating that it is simply a signaling
protocol—client talking to client, router talking to router. It does not actually
control what kinds of resources are reserved, either.That is up to the routers
and their particular capabilities.You can imagine the benefit to a network administrator
of knowing at any given moment how many reservations are made across
the network.This would help for bandwidth planning and provisioning. Although
it is possible to see what reservations are active in the routers, as we will see in
Chapter 9, the Resource Reservation Protocol has no capability of providing this
information directly.
Although RSVP is an important QoS mechanism, it is not an implementation
mechanism. It could be better thought of as a mechanism that requests QoS
from other mechanisms. It is not a packet scheduler, link-efficiency mechanism,
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or traffic classifier. It does, however, work with these mechanisms. Otherwise,
there would be no actual QoS—just a reservation!