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Chapter 1 An Introduction to Policy-Enabled Networks
Packet flow using QoS
Using DiffServ and QoS, a specific performance level for packets can be
designated. This system allows for network traffic prioritization. However, it
requires some thought to configure the prioritization. A number of policies
can be specified and each policy can match one or many flows, supporting
complex classification scenarios.
This section contains a very simplified introduction to the many ways to
prioritize packets using QoS. In simple terms, the methods of prioritizing
packets depend on the DSCP and the 802.1 priority level and drop
precedence.
The QoS class basically directs which group of packets receives the
best network throughput, which group of packets receives the next best
throughput, and so on. The level of service for each packet is determined
by the configurable DSCP.
The available levels of QoS classes are currently named Network, Premium,
Platinum, Gold, Silver, Bronze, and Standard. The level of service for each
packet is determined by the configurable DSCP.
Classifier elements, classifiers, and classifier blocks basically sort the
packets by various configurable parameters. These parameters include
VLAN IDs, IP source and subnet address, IP protocol, and many others.
The classifiers/classifier blocks are associated with policies, and policies
are organized into a hierarchy. The policy with the highest precedence is
evaluated first. The classifier elements, classifiers, and classifier blocks
are associated with interface groups, in that packets from a specific port
will have the same classification parameters as all others in the particular
interface group (role combination).
Meters, operating at ingress, keep the sorted packets within certain
parameters. A committed rate of traffic can be configured, allowing a certain
size for a temporary burst, as In-Profile traffic. All other traffic is configured
as Out-of-Profile traffic. If you choose not to meter the flow, you do not
configure meters.
Actions determine how the traffic is treated.
The overall total of all the interacting QoS factors on a group of packets
is a policy. Policies can be configured that monitor the characteristics
of the traffic and perform a controlling action on the traffic when certain
user-defined characteristics are matched.
"QoS Policy Schematic" (page 35)
provides a schematic overview of QoS
policies.
Nortel Ethernet Routing Switch 4500 Series
Configuration — Quality of Service
NN47205-504 (322816-
B
)
03.01
Standard
5.1
23 November 2007
Copyright © 2007, Nortel Networks
.