Juniper JUNOSE 11.2, Руководство по настройке

Страница: 85 / 772

Benefits
Using VC classes to configure and assign attributes to ATM data PVCs provides the
following benefits:
•
VC classes enable you to classify and group ATM PVCs based on the OAM and traffic
requirements of their associated subscribers.
In a typical scenario, you might group subscribers based on their OAM and traffic
requirements, and then create a VC class for each subscriber group. For example, you
might create two VC classes: premium-subscriber-class and economy-subscriber-class.
In premium-subscriber-class, you might enable F5 OAM VC integrity (with the oam-pvc
manage command), and configure a traffic class that has a higher scheduling priority,
such as CBR (with the cbr command). Conversely, in economy-subscriber-class, you
might retain the default setting that disables F5 OAM VC integrity, and configure a
traffic class that has a lower scheduling priority, such as UBR with or without a PCR
(with the
ubr command). By assigning each VC class to the appropriate interfaces or
individual circuits, you can group and manage the PVCs associated with the VC class
based on the network requirements of the subscribers they serve.
• VC classes facilitate modifications to PVC attributes.
If the OAM or traffic requirements change for a particular subscriber group, you can
simply reconfigure the VC class associated with the PVCs for that subscriber group.
This method is easier and less time-consuming than having to modify the attributes
for a large number of PVCs by using individual CLI commands.
Modifications to the attributes in a VC class affect PVCs that are already associated
with this VC class as well as PVCs subsequently created for this class.
Precedence Levels
Precedence levels play an important role in determining how the router assigns the
attribute values for statically created and dynamically created PVCs that have associated
VC classes.
Precedence Levels for Static PVCs
For PVCs that are statically created, the router determines the PVC attribute values
according to the following precedence levels, in order from highest precedence to lowest
precedence:
1.
The most recent explicitly set value for a PVC attribute always has the highest
precedence and overrides any settings in the VC class. Explicitly set values for PVC
attributes are those values configured with the CLI (by using the
atm pvc command
or commands in ATM VC Configuration mode), SNMP, or assigned by RADIUS.
2.
If an attribute value is not explicitly specified, the router takes the value for that
attribute from the assigned VC class, in the following order of precedence:
a. Attribute value specified in the VC class assigned to this PVC
b. Attribute value specified in the VC class assigned to the ATM 1483 subinterface
on which this PVC is created
53 Copyright © 2010, Juniper Networks, Inc.
Chapter 1: Configuring ATM