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How Is Quality of Service Performed on the
Cisco Catalyst 4500 Series?
The Cisco® Catalyst® 4500 Series performs all quality
of service (QoS) on the supervisor engine. This enables
the Cisco Catalyst 4500 Series line cards to expand their
QoS feature set and capabilities by simply upgrading
one piece of hardware, the supervisor engine. This is
investment protection at its best, enabling all line cards
purchased as far back as 1999 to perform enhanced
QoS capabilities built into the new Cisco Catalyst 4500
Series Supervisor Engine 6-E. QoS on the Supervisor
Engine 6-E has been greatly enhanced over that on
previous Cisco Catalyst 4500 Series supervisor engines.
Through CenterFlex technology, the Supervisor Engine
6-E has several new functions and capabilities that
enable the network administrator to provide better QoS
in the same chassis construct. This flexibility is a function
of the centralized architecture provided by the Cisco
Catalyst 4500 Series, the most widely deployed modular
Ethernet switch to date.
What Problems Need to Be Solved?
Today's networks contain a larger variety of advanced
applications that require more bandwidth than ever.
Unfortunately, providing more bandwidth is not the
solution to the advancement and use of today's networks.
Bandwidth solves only the initial problem of application
starvation. It does not, however, address the requirement
to prioritize these applications based on their specific
needs. Certain applications require large amounts of
bandwidth, but timely data delivery is not a requirement.
These applications can hinder voice or video traffic, for
which timely data delivery is required. The combination
of proper bandwidth utilization as well as the use of QoS
is needed to protect time-sensitive and delay-sensitive
applications during times of congestion (for example, a
worm attack).
Main QoS Features of the Cisco Catalyst 4500
Series Supervisor Engine 6-E
The Supervisor Engine 6-E with CenterFlex technology
offers a rich suite of QoS features for small, medium, and
large enterprise customers. In its most basic form the
QoS features provide:
Traffic classification
Policing and marking
Congestion avoidance
Queueing and scheduling
(based on the priority of traffic)
Traffic classification: The use of classification provides a
way for the switch to identify specific traffic so that it can
determine what level of service needs to be applied to
that data. Identification can be achieved by a number of
means, such as inspecting primary fields in the packet
header or looking at the port of arrival. The main set of
classification tools provided by the Cisco Catalyst 4500
Series Supervisor Engine 6-E includes access control
lists (ACLs) and table maps. The classification can be
based on several fields in an IPv4, IPv6, or Multiprotocol
Label Switching (MPLS) packet. These fields include but
are not limited to Layer 2 or Layer 3 fields, Layer 2 and
Layer 3 fields, QoS groups, packet size, and IP.
Policing and marking: The act of policing in the switch
provides a means to limit the amount of bandwidth traffic
traveling through a given port, virtual L AN (VLAN), or
collection of ports in a VL AN can use. Policing works by
defining an amount of data that the switch is willing to
send or receive. The Supervisor Engine 6-E can dynamically allocate the number of policers to either ingress or
egress, unlike other platforms. It also supports several
different policer types, allowing the Cisco Catalyst 4500
Series to be used for several different applications.
These policer t ypes include 1Rate 2Color, 1Rate 3Color,
2Rate 3Color, packet policers, Metro Ethernet Forum
(MEF) and IETF policers.
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Marking is the action of changing the priority setting
of the packet. This can be incorporated with policers
or table maps to modify traffic based on the actions
in either the policer or table map. The overall goal is
to provide the most flexible policing possible with an
extremely accurate granularity.
Congestion avoidance: Managing queues and buffers
is the primary goal of congestion avoidance. As a queue
starts to fill up with transient data, it is important to try
to make sure that the available memory in the queue
does not fill up completely. If this happens, subsequent
packets coming into the port will simply be dropped,
irrespective of the priority that they could have received.
This could have a detrimental effect on the performance
of critical applications. Dynamic Buffer Limiting (DBL) is a
flow-based algorithm that is used on the Cisco Catalyst
4500 Series Supervisor Engine 6-E. This algorithm
inhibits belligerent flows from consuming large amounts
of buffers and bandwidth. These flows typically include
worm traffic, Spanning Tree loops, and denial-of-service
attacks, which are all dynamically removed from your
network simply by enabling DBL.
Figure 1. The Supervisor 6-E QoS Pipeline
Cisco Catalyst 4500 Series Supervisor Engine 6-E
Quality of Service
At-A-Glance
Ingress QoS
Actons
Egress QoS
Actons
Egress
Policing
Egress
Marking
Conditional
Dynamic
Buffer
Limiting
Queue 1
Queue 2
Queue 3
Queue 4
Queue 5
Queue 6
Queue 7
Queue 8
Egress
Marking
Unconditional
Egress
Classification
Ingress
Classification
Ingress
Policing
Ingress
Marketing
Unconditional
Ingress
Marking
Conditional
Ingress
Scheduling
Shaping
Sharing
Egress
Scheduling
Shaping
Sharing
Strict
Priority
RX
TX
Future Release
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Queueing and scheduling: Queueing is the QoS mechanism used to empty the queues of data and send the
data onward to its destination. The scheduling options
available in the Supervisor Engine 6-E are per port, per
queue virtual time shaping and sharing (VTSS) and
strict priority queuing. The per port, per queue shaping
and sharing provide flexible options for enterprise
networks with diversified traffic. The Supervisor Engine
6-E includes as many as eight egress queues for traffic
placement, including the option of a priority queue.
Dynamic buffer allocation in the Supervisor Engine 6-E
provides the ability to modify buf fering assignments
throughout the chassis regardless of the port. Also, the
scheduling algorithm provides dynamic bandwidth
allocation, such that no bandwidth ever goes unused if a
queue is empty.
QoS Innovations on the Cisco Catalyst 4500
Series Supervisor Engine 6-E Enabled by New
CenterFlex Technology
CenterFlex technology enables many Supervisor Engine
6-E QoS enhancements, including increased configuration flexibility and ease of use with the Modular QoS CLI
(MQC)-compliant command-line interface (CLI). Cisco's
MQC CLI is a company standard for QoS that provides
configuration simplicity for the network administrator; it
is no longer necessar y to understand switch-specific
configurations. This CLI flexibility extends to all current
chassis and line cards and provides them with a larger
number of queues, configurable thresholds per queue,
configurable per port buffering, dynamic bandwidth
allocation, per port and per queue shaping and sharing,
and configuration tools such as QoS groups, and table
maps. All of these features in the Supervisor Engine 6-E
provide the network administrator with a QoS toolkit far
more advanced than those of the previous generation of
supervisor engines in the Cisco Catalyst 4500 Series.
Deliver a Robust Network with the Cisco
Catalyst 4500 Series Supervisor Engine 6-E QoS
Feature Toolkit
The Supervisor Engine 6-E also provides Auto QoS, a set
of Cisco best-practice predefined macro commands.
The architecture helps enable all QoS features with no
switching performance degradation.
These features provide what is needed in today's converged networks by allowing a highly customized QoS
profile configuration applied to the ports or VLANs for
maximum flexibility.
Cisco Catalyst 4500 Series Supervisor Engine 6-E
Quality of Service
At-A-Glance
© 2007 Cisco Systems, Inc. All rights reserved. Cisco, the Cisco logo, and Cisco Systems, are registered trademarks or trademarks of Cisco Systems, Inc. and/or its affiliates in the United States and certain other countries . C45-438302-00 10/07
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