3Com CoreBuilder 3500, Implementation Manual

Page: 476 / 592

476 C
HAPTER
17: Q
O
S
AND
RSVP
QoS Overview
Quality of Service (QoS) is an advanced 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 focuses on differentiating
traffic into classes and prioritizing those classes.)
Features Your system supports the following QoS features:
■
QoS Classifiers — Define how your system groups packets in order
to schedule them with the appropriate service level.
■
QoS Controls — A ssign rate limits and IEEE 802.1p priorities, and/or
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.
Benefits You can use QoS on your system to provide the following benefits:
■
Control a wide variety of Ethernet or FDDI network traffic by:
■
Classifying traffic based on packet attributes such as protocol type,
class type (802.1p), IP address, and/or TCP/UDP socket.
■
Assigning priorities to traffic (for example, to set higher priorities to
time-critical or business-critical applications).
■
Applying security policy through traffic filtering.
■
Using the connection-oriented RSVP for bandwidth reservation
(reserving and policing an RSVP session to make sure the session
uses only as much bandwidth as it needs).
■
Provide constant delay/jitter for multimedia applications such as video
conferencing or voice over IP.