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8-15
Cisco 10000 Series Router Software Configuration Guide
OL-2226-23
Chapter 8 Configuring ATM Permanent Virtual Circuit Autoprovisioning
Variable Bit Rate Non-Real Time Oversubscription
The VBR-nrt Oversubscription feature is described in the following topics:
• Feature History for VBR-nrt Oversubscription, page 8-15
• Restrictions for VBR-nrt Oversubscription, page 8-15
• Configuration Tasks for VBR-nrt Oversubscription, page 8-17
• Configuration Example for ATM PVC Oversubscription, page 8-18
Feature History for VBR-nrt Oversubscription
Restrictions for VBR-nrt Oversubscription
The VBR-nrt Oversubscription feature has the following restrictions:
Congestion
• Due to congestion on the physical interface, the accuracy of priority queuing (PQ) and class-based
weighted fair queuing (CBWFQ) on individual VCs degrades. For example, if you configure each
of three queues at a distribution of 50, 30, and 20 percent, the actual distribution might be 45, 40,
and 15 percent.
• The distribution of bandwidth for each VC might be less than expected based on the speed of the
VC. Typically, low speed VCs are allocated the expected bandwidth while high speed VCs share the
remaining bandwidth equally.
• The amount of bandwidth allocated for the PQ or latency might be less than expected.
Oversubscription Feature
• Oversubscription of the ATM interfaces is off by default. Oversubscription of the tunnels (the
number and bandwidth of VCs that can be in a tunnel) is on by default and is not subject to any
oversubscription factor. Oversubscription of the tunnels cannot be adjusted or turned off.
• Use the atm over-subscription-factor command to enable the oversubscription feature for a
particular interface or tunnel.
Note Do not use the atm oversubscribe command to enable oversubscription, as this can cause
undesirable results.
Cisco IOS Release Description Required PRE
12.2(16)BX3 This feature was introduced on the Cisco 10000 series
router.
PRE2
12.3(7)XI1 This feature was integrated into Cisco IOS Release
12.3(7)XI1.
PRE2
12.2(28)SB This feature was integrated into Cisco IOS Release
12.2(28)SB.
PRE2