Laboratory
10
RSVP: Resource Reservation Protocol
Providing QoS by Reserving Resources in the Network
Objective
The objective of this lab is to study the Resource Reservation Protocol (RSVP) as a part of
the Integrated Services approach to providing Quality of Service (QoS) to individual
applications or flows.
Overview
For many years, packet-switched networks have offered the promise of supporting
multimedia applications, that is, those that combine audio, video, and data. Audio and
video applications are examples of real-time applications. The best-effort model, in which
the network tries to deliver your data but makes no promises and leaves the “cleanup
operation” to the edges, is not sufficient for real-time applications. What we need is a new
service model—one in which applications that need better assurances can request such
service from the network. The network may then respond by providing an assurance that it
will do better, or perhaps by saying that it cannot promise anything better at the moment. A
network that can provide different levels of service is often said to support QoS.
Two approaches have been developed to provide a range of QoS: Integrated Services
and Differentiated Services. The Resource Reservation Protocol follows the Integrated
Services approach, whereby QoS is provided to individual applications or flows. The
Differentiated Services approach provides QoS to large classes of data or aggregated
traffic.
While connection-oriented networks have always needed some sort of setup protocol to
establish the necessary virtual circuit state in the routers, connectionless networks like the
Internet have had no such protocols. One of the key assumptions underlying RSVP is that
it should not detract from the robustness that we find in the Internet. Therefore, RSVP
uses the idea of soft state in the routers. Soft state—in contrast to the hard state found in
connection-oriented networks—does not need to be explicitly deleted when it is no longer
needed. Instead, it times out after some fairly short period if it is not periodically refreshed.
RSVP adopts the receiver-oriented approach—the receivers keep track of their own
resource requirements, and they periodically send refresh messages to keep the soft state
in place.
In this lab you will set up a network that carries real-time applications and that utilizes
RSVP to provide QoS to one of these applications. You will study how RSVP contributes
to the performance of the application that makes use of it.
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