3Com CoreBuilder 3500, Implementation Manual, Page: 477 / 592

QoS Overview 477
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Improve performance for specific types of traffic and preserve
performance as the volume of traffic grows.
■
Reduce the need to constantly add bandwidth to the network.
■
Manage network congestion.
Methods of Using
QoS
Your system’s implementation of QoS focuses on traffic classification,
policy-based management, and bandwidth. It provides multiple service
levels (mapped to several transmit queues), classification of traffic types,
and weighted fair queueing of priority-queued traffic.
If you use QoS and simply opt to broadly classify traffic, you are using a
subset of QoS called
network class of service . To simplify your
classification of traffic, the system provides a set of predefined traffic
classes. You can also specify your own classes of traffic with applied
controls to:
■
Create a to/from classifier with address/port patterns that isolate
traffic based on source and destination.
■
Block traffic (for example, prevent certain traffic from one workgroup
from seeing another workgroup).
■
Assign priorities to traffic.
See “Examples of Classifiers and Controls” later in this chapter.
If you use QoS with RSVP, you are opting for a more complex type of
end-to-end QoS that aims for a “guaranteed” quality of service. To use
RSVP, you must be routing. In addition, RSVP is required at the desktop,
which may present issues of desktop control and upgrade issues
concerning the resident operating-system and applications.