Using the Resource Reservation Protocol
.. RSVP does not provide QoS directly to applications, but instead,
coordinates an overall service level by making reservation requests across
the network. It is up to other QoS mechanisms to actually prevent and
control congestion, provide efficient use of links, and classify and police
traffic.
.. End-to-end resource reservation can only be accomplished by using
RSVP on every router end-to-end, but it is not mandatory that RSVP
be enabled everywhere on a network. RSVP has the built-in capability
to tunnel over non-RSVP aware nodes.
.. Because of the resources required for each reservation, RSVP has some
distinct scaling issues that make it doubtful it will ever be implemented
successfully on a very large network, or on the Internet, in its current
revision.