666 Configuring Quality of Service
Differentiated Services
DiffServ Overview
The QoS feature contains Differentiated Services (DiffServ) support that allows traffic to be classified
into streams and given certain QoS treatment in accordance with defined per-hop behaviors.
Standard IP-based networks are designed to provide “best effort” data delivery service. “Best effort”
service implies that the network delivers the data in a timely fashion, although there is no guarantee that
it will. During times of congestion, packets may be delayed, sent sporadically, or dropped. For typical
Internet applications, such as e-mail and file transfer, a slight degradation in service is acceptable and in
many cases unnoticeable. Conversely, any degradation of service has undesirable effects on applications
with strict timing requirements, such as voice or multimedia.
Defining DiffServ
To use DiffServ for QoS, the web pages accessible from the Differentiated Services menu page must first
be used to define the following categories and their criteria:
1.
Class: create classes and define class criteria
2.
Policy: create policies, associate classes with policies, and define policy statements
3.
Service: add a policy to an inbound interface
Packets are classified and processed based on defined criteria. The classification criteria is defined by a
class. The processing is defined by a policy's attributes. Policy attributes may be defined on a per-class
instance basis, and it is these attributes that are applied when a match occurs. A policy can contain
multiples classes. When the policy is active, the actions taken depend on which class matches the packet.
Packet processing begins by testing the class match criteria for a packet. A policy is applied to a packet
when a class match within that policy is found.
The Differentiated Services menu page contains links to the various Diffserv configuration and display
features.
To display the page, click Quality of Service
→
Differentiated Services in the tree view. The
Differentiated Services menu page contains links to the following features:
• Diffserv Configuration
• Class Configuration
•Class Criteria
• Policy Configuration
• Policy Class Definition
• Service Configuration
• Service Detailed Statistics
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