Feature History For Atm Vc Oversubscription; Oversubscription Factor And Unspecified Bit Rate Virtual Circuits - Cisco 10000 Series Configuration Manual

ATM Virtual Circuit Oversubscription
For optimal performance, configure the oversubscription factor as closely as possible to the sum of all
VCs. The system allows VCs to be added, provided the total subscribed rate is less than or equal to the
port speed times the over-subscription-factor. The CAC is based on the oversubscription factor you
specify and evaluated separately for both VCs and VP tunnels into the port, and VCs into VP tunnels.
Whenever you reduce the oversubscription factor, less bandwidth is available for VC creation. As a
result, a warning message appears indicating that some VCs might not be created. The router does not
explicitly remove the VCs from the configuration; the VCs remain up and functional until you reboot the
router or reset the slot. At this point, the VCs remain in the configuration but they are not up.
When the no atm pxf queuing command is configured on an interface for the PRE1 or PRE2, the router
allows unlimited oversubscription. The ATM oversubscription commands have no effect. For the PRE3,
the no atm pxf queuing command is not supported.

Feature History for ATM VC Oversubscription

Cisco IOS Release
Release 12.2(16)BX
Release 12.3(7)XI3
Release 12.2(28)SB
Release 12.2(31)SB2

Oversubscription Factor and Unspecified Bit Rate Virtual Circuits

Unspecified bit rate (UBR) virtual circuits (VCs) are not subject to a call admission check (CAC).
Therefore, by default the router allows unlimited oversubscription of UBR VCs.
For releases prior to Cisco IOS Release 12.3(7)XI1, if you use unshaped (no PCR specified) UBR VCs,
the router allocates bandwidth to the variable bit rate (VBR) and constant bit rate (CBR) VCs, and to the
VP tunnels before allocating the remaining bandwidth to the unshaped UBR VCs. For example:
The bandwidth the router allocates to the unshaped UBR VCs must be 64 kbps less than the total
bandwidth of the interface.
In Cisco IOS Release 12.3(7)XI1 and later releases, the oversubscription factor is used to evaluate the
amount of bandwidth allocated for unshaped UBR VCs. The CAC adjusts the bandwidth for unshaped
UBR VCs based on the oversubscription factor.
You can apply a hierarchical policy map to the main ATM interface to override this default equation and
Note
set a specific bandwidth for the aggregate UBR queues. For more information about hierarchical
policies, see
Cisco 10000 Series Router Quality of Service Configuration Guide
15-4
Description
The ATM VC oversubscription feature was introduced on
the PRE2 with an oversubscription factor from 1 to 50.
This feature was enhanced on the PRE2 with an
oversubscription factor from 1 to 500.
This feature was integrated in Cisco IOS
Release 12.2(28)SB for the PRE2.
This feature was introduced on the PRE3 with an
oversubscription factor from 1 to 500.
Port Speed – Sum of the VBR VCs = Aggregate UBR bandwidth
Chapter 13, "Defining QoS for Multiple Policy Levels."
Chapter 15 Oversubscribing Physical and Virtual Links
Required PRE
PRE2
PRE2
PRE2
PRE3
OL-7433-09