The RSVP protocol allows applications to reserve bandwidth for thier data flows. It is used by a host, on the behalf
of an application data flow, to request a specific amount of bandwidhth from the network. RSVP is also used by the routers
to forward bandwidth reservation requests. RSVP software must be present in the receivers, senders, and routers.
The two principal characteristics of RSVP are:
It provides reservations for bandwidth in multicast trees.
It is receiver-oriented: that is, the receiver of a data flow initiates and maintains ther resources reservation used
for that flow.
When a router forwards a reservation message upstream toward the sender, the router may merge the reservation message
with other reservation meddages arriving from downstream.
A session can consist of multiple multicast data flows. Each sender in a session is the source of one or more data
flows; for example, a sender might be the source of a video data flow and an audio data flow. Each data flow in a session
has the same multicast address. To keep the discussion concrete, we assume that routers and hosts identify the session
to which a packet belongs by the paclet's multicast address.
What RSVP Is Not
RSVP standard does not specify how the network provides the reservedd bandwidth to the data flows. It is merely
a protocol that allows the application to reserve the neccessary link bandwidth. Once teh reservations are in place,
it is up to the routers in the Internet to actually provide reserved bandwidth to the data flow.
It is also important to understand that RSVP is not a routing protocol--it does not determine the links in which the
reservations are to be made. Insteadd it depends on an underlying routing protocol to determine the routers for the
flows.
