Allied Telesis AT-S62 - Manual (Page 269)

AT-S62 Management Software Menus Interface User’s Guide
Section II: Advanced Operations 269
The QoS functionality described by this chapter sorts packets into various
flows, according to the QoS policy that applies to the port the traffic is
received on. The switch then allocates resources to direct this traffic
according to bandwidth or priority settings in the policy. Each policy is built
up out of traffic classes, flow groups and classifiers. In summary, to
configure QoS:
ˆ Create classifiers to sort packets into traffic flows.
ˆ Create flow groups and add classifiers to them. Flow groups are
groups of classifiers which group together similar traffic flows. You can
apply QoS prioritization to flow groups and/or replace the traffic’s
DiffServ Code Point.
ˆ Create traffic classes and add flow groups to them. Traffic classes are
groups of flow groups and are central to QoS. You can apply
bandwidth limits and QoS prioritization to traffic classes, and/or replace
the traffic’s DiffServ Code Point.
ˆ Create policies and add traffic classes to them. Policies are groups of
traffic classes. A policy defines a complete QoS solution for a port or
group of ports.
ˆ Associate policies with ports.
Note
These steps are listed above in a conceptually logical order, but the
switch cannot check a policy for errors until the policy is attached to
a port. You can simplify error diagnosis by determining your QoS
configuration on paper first, and then entering it into the switch
starting with classifiers.
Policies, traffic classes, and flow groups are created as individual entities.
When a traffic class is added to a policy, a logical link is created between
the two entities. Destroying the policy will only unlink the traffic class,
leaving the traffic class in an unassigned state. Destroying a policy will not
destroy any of the underlying entities. Similarly, destroying traffic classes
will simply unlink flow groups and destroying flow groups will simply unlink
classifiers.
Classifiers
Classifiers are used to identify a particular traffic flow, and range from
general to specific. (See Chapter 13, “Classifiers” on page 233 for more
information.) Note that a single classifier should not be used in different
flows that will end up, via traffic classes, assigned to the same policy. A
classifier should only be used once per policy. Traffic is matched in the
order of classifiers. For example, if a flow group has classifiers 1, 3, 2 and
5, that is the order in which the packets are matched.