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22 Differentiated Services
22
Differentiated Services
Differentiated Services (DiffServ) is one technique for implementing Quality of Service (QoS)
policies. Using DiffServ in your network allows you to directly configure the relevant
parameters on the switches and routers rather than using a resource reservation protocol. This
section explains how to configure the Unified Switch to identify which traffic class a packet
belongs to, and how it should be handled to provide the desired quality of service. As
implemented on the Unified Switch, DiffServ allows you to control what traffic is accepted
and what traffic is discarded.
Traffic to be processed by the DiffServ feature requires an IP header if the system uses IP
Precedence or IP DSCP marking.
How you configure DiffServ support on a DWS-3000 switch varies depending on the role of
the switch in your network:
•
Edge device
–
An edge device handles ingress traffic, flowing towards the core of the net-
work, and egress traffic, flowing away from the core. An edge device segregates inbound
traffic into a small set of traffic classes, and is responsible for determining a packet’s clas-
sification. Classification is primarily based on the contents of the Layer 3 and Layer 4
headers, and is recorded in the Differentiated Services Code Point (DSCP) added to a
packet’s IP header.
•
Interior node –
A switch in the core of the network is responsible for forwarding packets,
rather than for classifying them. It decodes the DSCP in an incoming packet, and provides
buffering and forwarding services using the appropriate queue management algorithms.
Before configuring DiffServ on a particular DWS-3000 switch, you must determine the QoS
requirements for the network as a whole. The requirements are expressed in terms of rules,
which are used to classify inbound traffic on a particular interface. The D-Link DWS-3000
switch does not support DiffServ in the outbound direction.
During configuration, you define DiffServ rules in terms of classes, policies and services:
•
Class –
A class consists of a set of rules that identify which packets belong to the class.
Inbound traffic is separated into traffic classes based on Layer 2, Layer 3, and Layer 4
header data. One class type is supported,
All,
which specifies that every match criterion
defined for the class must be true for a match to occur.
•
Policy –
Defines the QoS attributes for one or more traffic classes. An example of an attri-
bute is the ability to mark a packet at ingress. The D-Link DWS-3000 switch supports the
ability to assign traffic classes to output CoS queues.
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