Chapter 12: Configuring Quality Of Service - Cisco SGE2000 Reference Manual

Configuring Quality of Service
Network traffic is usually unpredictable, and the only basic assurance that can be offered is best effort
traffic delivery. To overcome this challenge, Quality of Service (QoS) is applied throughout the network.
This ensures that network traffic is prioritized according to specified criteria, and that specific traffic
receives preferential treatment. QoS in the network optimizes network performance and entails two basic
facilities:
• Classifying incoming traffic into handling classes, based on an attribute, including:
– The ingress interface
– Packet content
– A combination of these attributes
• Providing various mechanisms for determining the allocation of network resources to different
handling classes, including:
– The assignment of network traffic to a particular hardware queue
– The assignment of internal resources
– Traffic shaping
The terms Class of Service (CoS) and QoS are used in the following context:
• CoS provides varying Layer 2 traffic services. CoS refers to classification of traffic to traffic-classes,
which are handled as an aggregate whole, with no per-flow settings. CoS is usually related to the
802.1p service that classifies flows according to their Layer 2 priority, as set in the VLAN header.
• QoS refers to Layer 2 traffic and above. QoS handles per-flow settings, even within a single traffic
class.
The QoS facility involves the following elements:
• Access Control Lists (ACLs) — Used to decide which traffic is allowed to enter the system, and
which is to be dropped. Only traffic that meets this criteria are subject to CoS or QoS settings. ACLs
are used in QoS and network security.
• Traffic Classification — Classifies each incoming packet as belonging to a given traffic class,
based on the packet contents and/or the context.
• Assignment to Hardware Queues — Assigns incoming packets to forwarding queues. Packets are
sent to a particular queue for handling as a function of the traffic class to which they belong, as
defined by the classification mechanism.
• Traffic Class-Handling Attributes — Applies QoS/CoS mechanisms to different classes,
including: Bandwidth Management
The Quality of Service section contains the following section:

Chapter 12: Configuring Quality of Service

SGE2000/SGE2000P Gigabit Ethernet Switch Reference Guide
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