3Com 4007, Руководство по внедрению, Страница: 566 / 684

566 C
HAPTER
22: Q
O
S
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RSVP
QoS Overview
Quality of Service (QoS) is a Layer 3 feature that allows you to establish
control over network traffic. QoS provides
policy-based services , which
establish various grades of network service to accommodate different
types of traffic, such as multimedia, video, protocol-specific, time-critical,
and file-backup traffic. Although QoS and Class of Service (CoS) are
closely related, QoS has more features and addresses bandwidth, delay,
loss, and jitter control. (CoS tends to focus on differentiating traffic into
classes and assigning prioritization to those classes.)
QoS is crucial in the wide area network (WAN) environment to guarantee
quality of service without escalating WAN bandwidth costs. In the LAN
environment, QoS implementations are growing.
Features The Multilayer Switching Modules that are available on the Switch 4007
support the following QoS features:
■
QoS Classifiers — Define how the Multilayer Switching Module
groups packets to schedule them with the appropriate service level.
■
QoS Controls — A ssign rate limits and IEEE 802.1p priorities, as well
as prioritize packets that are associated with one or more classifiers.
Using the QoS Excess Tagging feature, you can also select an IEEE
802.1p priority for packets that exceed the control’s rate limit.
■
Settable QoS Bandwidth — Controls the weighting of high-priority
and best-effort traffic.
■
Resource Reservation Protocol (RSVP) — A building block of QoS
that implements QoS characteristics in your LAN environment. RSVP is
an end-to-end signaling IP protocol that allows an end station to
request the reservation of bandwidth across the network. RSVP
provides admission control. QoS can operate at Layer 2 and Layer 3;
RSVP operates at Layer 3 only.