Configuring ATM VC Classes

As an alternative to configuring individual parameters for ATM data PVCs, you can access ATM VC Class Configuration mode to configure a class of attributes for an ATM data PVC. A VC class is a set of attributes for a virtual circuit (VC) that can include the service category, encapsulation method, F5 OAM options, and Inverse ARP.

After you configure the VC class, you then apply the attributes in the class as a group by assigning the VC class to one of the following:

• An individual PVC
• All PVCs created on a specified static ATM major interface
• All PVCs created on a specified static ATM 1483 subinterface
• A base profile from which bulk-configured VC ranges are created on a dynamic ATM 1483 subinterface

VC class assignments are valid only for ATM data PVCs created with the pvc command. Assigning a VC class to a PVC created with the atm pvc command, or to a control (ILMI) PVC, has no effect. For information about creating a data PVC by using the pvc command, see Creating Data PVCs.

Note: For information about the total number of VC classes supported on the router, see JunosE Release Notes, Appendix A, System Maximums.

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:
   1. Attribute value specified in the VC class assigned to this PVC
   2. Attribute value specified in the VC class assigned to the ATM 1483 subinterface on which this PVC is created
   3. Attribute value specified in the VC class assigned to the ATM major interface on which this PVC is created
3. If no PVC attributes are explicitly specified and no VC class assignments exist, the router applies the default values for the commands listed in Table 8. For information about the default value for each command, see the command descriptions in Configuring VC Classes.

Precedence Levels for Dynamic PVCs

For PVCs that are dynamically created, the router determines the PVC attribute values according to the following precedence levels, in order from highest precedence to lowest precedence:

1. The attribute value specified in the VC class assigned in the base profile always has the highest precedence.
2. If no VC class is assigned in the base profile, the router takes the value for that attribute from the VC class assigned to the associated ATM major interface.
3. If neither the base profile nor the ATM major interface has a VC class assigned, the router takes the value for that attribute from the individually specified attributes in the base profile.
4. If neither the base profile nor the ATM major interface has a VC class assigned, and no attributes are individually specified in the base profile, the router applies the default values for the commands listed in Table 8. For information about the default value for each command, see the command descriptions in Configuring VC Classes.

Precedence Level Examples

For examples that illustrate how precedence levels affect the assignment of VC classes, see Precedence Level Examples for Assigning VC Classes.

To help you better understand these examples, we recommend that you first read the following sections to learn how to configure and assign VC classes:

Upgrade Considerations

The following considerations apply to using ATM VC classes when you upgrade to the current JunosE Software release from a lower-numbered JunosE Software release:

• It is possible to use VC classes for PVCs created in a lower-numbered release with the atm pvc command. In such cases, the router uses the following rules to determine the PVC attribute values:
  • Nondefault values explicitly specified for PVC attributes with the atm pvc command take precedence over the attribute values specified in the associated VC class. As a result, the router takes the values for these attributes from the atm pvc command settings.
  • Default values implicitly specified for PVC attributes with the atm pvc command have a lower precedence than the attribute values specified in the associated VC class. As a result, the router takes the values for these attributes from the assigned VC class.
• The output of the show configuration command uses either the pvc command format or the atm pvc command format to display ATM PVCs. The display format of configuration information for ATM PVCs created with the atm pvc command depends on the JunosE Software release from which you are upgrading, as follows:
  • When you upgrade to the current JunosE Software release from a JunosE release numbered lower than Release 7.3.x, the output of the show configuration command uses the pvc command format (pvc vcd vpi/vci) to display configuration information for all ATM PVCs. This occurs even if those PVCs were created in a JunosE release numbered lower than Release 7.3.x with the atm pvc command. For example, assume that you created a PVC in JunosE Release 7.2.x by issuing the command atm pvc 2 0 33 aal5snap 0 0 0. The show configuration command in the current JunosE Software release displays the identifier for this PVC as follows:

    pvc 2 0/33

  • When you upgrade to the current JunosE Software release from JunosE Release 7.3.x or a higher-numbered release, the output of the show configuration command uses the atm pvc command format to display configuration information for ATM PVCs created with the atm pvc command. For example, assume that you created a PVC in JunosE Release 7.3.x or Release 8.0.x by issuing the command atm pvc 2 0 33 aal5snap 0 0 0. The show configuration command in the current JunosE Software release displays the identifier for this PVC as follows:

    atm pvc 2 0 33 aal5snap 0 0 0

    For PVCs previously created in the lower-numbered release by using the pvc command, the show configuration command displays configuration information using the pvc command format, as described previously.

For information about how to use the show configuration command, see Managing the System in JunosE System Basics Configuration Guide.

To make the most efficient use of the VC class feature when you upgrade to the current JunosE Software release, we recommend that you follow these steps:

1. Delete any PVCs created with the atm pvc command and recreate them by using the pvc command. For information about creating a data PVC by using the pvc command, see Creating Data PVCs.
2. Configure the VC class as described in Configuring VC Classes.
3. Assign the VC class in one of the following ways:
   • Assign the VC class to the individual PVC when you create or modify the PVC.
   • Assign the VC class to the associated ATM major interface or ATM 1483 subinterface before you create the PVC.

Configuring VC Classes

To configure a VC class, you issue the vc-class atm command to create and name the VC class. The vc-class atm command accesses ATM VC Class Configuration mode, from which you configure a set of attributes to apply to an ATM data PVC.

Table 8 lists the commands that you can use in ATM VC Class Configuration mode to configure a set of attributes for a data PVC. These commands are identical to the commands in ATM VC Configuration mode described in Configuring Individual ATM PVC Parameters. For more information about the syntax of each command, see the JunosE Command Reference Guide.

For example, the following commands configure two VC classes: premium-subscriber-class and dsl-subscriber-class. You must issue the exit command from ATM VC Class Configuration mode for each VC class configuration to take effect.

In premium-subscriber-class:

• The encapsulation command sets the encapsulation method to aal5autoconfig.
• The cbr command sets the service category to CBR with a PCR of 200 Kbps.
• The oam-pvc command enables generation of F5 OAM loopback cells and F5 OAM VC integrity.
• The oam ais-rdi command configures the alarm down count for successive AIS and RDI alarm cells to 5.

In dsl-subscriber-class:

• The encapsulation command sets the encapsulation method to aal5autoconfig.
• The ubr command configures the UBR service category without a PCR.

To configure an ATM VC class with systemwide default values, you can issue the vc-class atm command followed immediately by the exit command. For example, the following commands create a VC class named default-vc-class. Because no attribute values are explicitly specified in default-vc-class, the router applies the default values for the commands listed in Table 8. For information about the default value for each command, see the command descriptions in this section.

To verify the VC class configuration, use the show atm vc-class command. For information about how to use this command, see show atm vc-class.

Assigning VC Classes to Individual PVCs

To assign a previously configured VC class to an individual ATM data PVC, you use the class-vc command from ATM VC Configuration mode. Issuing this command applies the set of attributes configured in the specified VC class to the ATM data PVC.

Note: The class-vc command is valid only for a data PVC created with the pvc command. It has no effect for data PVCs created with the atm pvc command, or for control (ILMI) PVCs. For information about creating a data PVC by using the pvc command, see Creating Data PVCs.

For example, the following commands assign the VC class named premium-subscriber-class to the ATM data PVC with VCD 2, VPI 0, and VCI 200.

For those attributes that you do not explicitly specify for the ATM PVC, the router applies the values specified in the VC class. As explained in Precedence Levels, the values in a VC class assigned to an individual PVC take precedence over both of the following:

• Values in a VC class assigned to an ATM 1483 subinterface
• Values in a VC class assigned to an ATM major interface

For examples that illustrate how precedence levels affect the assignment of VC classes, see Precedence Level Examples for Assigning VC Classes.

Assigning VC Classes to ATM Major Interfaces

To assign a previously configured VC class to an ATM major interface, you use the class-int command from Interface Configuration mode. Issuing this command applies the set of attributes in the specified VC class to the ATM data PVCs statically or dynamically created on this interface.

For example, the following commands assign the VC class named dsl-subscriber-class to an ATM major interface configured on slot 5, port 0.

For those attributes that you do not explicitly specify for an ATM PVC, the router applies the values specified in the VC class. As explained in Precedence Levels, the values in a VC class assigned to an ATM major interface have a lower precedence than both of the following:

• Values in a VC class assigned to an individual ATM PVC
• Values in a VC class assigned to an ATM 1483 subinterface

This means that if a VC class is assigned to an individual PVC or ATM 1483 subinterface configured on the major interface, the attribute values configured in the VC class assigned to the PVC or subinterface override the attribute values configured in the VC class assigned to the major interface.

For examples that illustrate how precedence levels affect the assignment of VC classes, see Precedence Level Examples for Assigning VC Classes.

Assigning VC Classes to Static ATM 1483 Subinterfaces

To assign a previously configured VC class to a static ATM 1483 subinterface, you use the class-int command from Subinterface Configuration mode. Issuing this command applies the set of attributes in the specified VC class to the ATM data PVCs statically or dynamically created on this subinterface.

For example, the following commands assign the VC class named premium-subscriber-class to an ATM 1483 subinterface configured on slot 5, port 0, subinterface 100.

For those attributes that you do not explicitly specify for an ATM PVC, the router applies the values specified in the VC class. As explained in Precedence Levels, the values in a VC class assigned to an ATM 1483 subinterface take precedence over the values in a VC class assigned to an ATM major interface, but have a lower precedence than the values in a VC class assigned to an individual ATM PVC.

This means that if a VC class is assigned to a PVC configured on the subinterface, the attribute values configured in the VC class assigned to the individual PVC override the attribute values configured in the VC class assigned to the subinterface.

For examples that illustrate how precedence levels affect the assignment of VC classes, see Precedence Level Examples for Assigning VC Classes.

Assigning VC Classes to Base Profiles for Bulk-Configured VC Ranges

To assign a VC class to a base profile for a dynamic ATM 1483 subinterface, you can use the atm class-vc command from Profile Configuration mode. Issuing this command applies the set of attributes in the specified VC class to all bulk-configured VC ranges that are dynamically created from this profile.

For more information, see Dynamic ATM 1483 Subinterfaces over Static ATM AAL5 Interfaces Overview in Configuring Dynamic Interfaces Using Bulk Configuration.

Precedence Level Examples for Assigning VC Classes

The examples in this section illustrate how the precedence level rules described in Precedence Levels affect the assignment of VC classes and PVC attribute values.

For all of these examples, assume that you have issued the following commands to configure a VC class named my-premium-class:

Example 1 and Example 2 illustrate the effect of precedence levels when you assign the VC class my-premium-class to an individual PVC with VCD 200, VPI 0, and VCI 200. Example 3 illustrates how using the atm pvc command affects VC class assignment. Finally, Example 4 illustrates how modifications to a VC class affect PVC attributes applied through RADIUS.

Example 1: Explicitly Changing the Service Category

Explicitly specified attribute values take precedence over attribute values specified in a VC class. As a result, the following commands cause the router to use the most recent explicitly specified value, UBR with a PCR of 200 Kbps, as the service category for this PVC instead of the service category specified in my-premium-class, CBR with a PCR of 200 Kbps. The router takes the values for the other attributes from the VC class my-premium-class.

The following commands change the service category for the PVC to VBR-RT because this is the most recent explicitly specified value for this attribute. The router takes the values for the other attributes from the VC class my-premium-class, which is still assigned to the PVC.

The following commands cause the router to retain the VBR-RT service category for the PVC because it is still the most recent explicitly specified value for this attribute. The router takes the values for the other attributes from the VC class my-premium-class.

Example 2: Changing the Encapsulation Method in the VC Class

The following commands change the value for the encapsulation method in the VC class my-premium-class from aal5autoconfig to aal5snap. As a result, the router now uses aal5snap instead of aal5autoconfig as the encapsulation method for the PVCs to which this VC class is assigned.

Example 3: Effect of Using the atm pvc Command

The following commands, which attempt to assign the my-premium-class VC class to a PVC originally created with the atm pvc command, have no effect. The router interprets all attribute values specified with the atm pvc command as explicitly specified values, and therefore takes the values for these attributes from the atm pvc command instead of from the VC class. As a result, the router continues to use aal5mux ip as the encapsulation method for this PVC instead of the encapsulation method specified in the VC class my-premium-class.

Example 4: Overriding RADIUS Values

If RADIUS is configured to provide traffic parameters for PVCs, a more recent, explicitly specified change in the VC class associated with that PVC overrides the PVC values applied through RADIUS.

In the following example, assume that RADIUS has been configured to apply a service category of CBR with a PCR of 400 Kbps to the PVC. Initially, the PVC uses the service category configured in my-premium-class, CBR with a PCR of 200 Kbps. However, when the subscriber logs in through RADIUS, the router applies the RADIUS-configured service category, CBR with a PCR of 400 Kbps.

While the subscriber is still logged in, my-premium-class is modified to change the service category to CBR with a PCR of 600 Kbps. Because this VC class modification results in the most recent, explicitly specified value for the service category, the router now uses CBR with a PCR of 600 Kbps as the service category for the PVC instead of the service category configured through RADIUS.