15-6
Cisco 10000 Series Router Quality of Service Configuration Guide
OL-7433-09
Chapter 15 Oversubscribing Physical and Virtual Links
ATM Virtual Circuit Oversubscription
Syntax Description
atm over-subscription-factor Command History
Usage Guidelines for the atm over-subscription-factor Command
An ATM variable bit rate (VBR) VC uses the sustained cell rate (SCR) to define the VC’s average
transmission rate. Therefore, use the
atm over-subscription-factor
command to specify the ATM VC
oversubscription, not the
service-policy
command.
Use the
atm over-subscription-factor
command for each ATM interface that you want to oversubscribe.
Because the oversubscription of VBR-nrt VCs requires resources from the entire line card, apply the
atm over-subscription-factor
command on all ports of the ATM card (for example, the 4-port OC-3
ATM line card). If you enable the oversubscription on only one port, the other ports can use more
resources than they were configured to use. As a result, some ports do not receive adequate resources,
which results in VC creation failures.
Unlike other Cisco routers, the Cisco 10000 series router uses the
atm oversubscribe
command in
conjunction with the
atm over-subscription-factor
command to enable or disable oversubscription for
a particular interface or tunnel. When enabling ATM oversubscription for a particular interface or tunnel,
specify the
atm over-subscription-factor
command. Do not use the
atm oversubscribe
command to
enable oversubscription as this can cause undesirable results. Instead, leave it to the default value.
For example, the following configuration enables the oversubscription feature and configures the
interface with an oversubscription factor of 500.
Router(config)#
interface atm 4/0/0
Router(config-if)#
atm oversubscribe
Router(config-if)#
atm over-subscription-factor 500
Router(config-if)#
end
factor
Specifies the amount of oversubscription. The default value is 1, which
indicates no oversubscription. Valid values are:
•
1 to 500 on the PRE2—Requires Cisco IOS Release 12.3(7)XI3 or later
releases, or Cisco IOS Release 12.2(28)SB
•
1 to 500 on the PRE3—Requires Cisco IOS Release 12.2(31)SB2 or
later releases
Cisco IOS Release
Description
Release 12.2(16)BX
The
atm over-subscription-factor
command was introduced on the PRE2
with an oversubscription factor from 1 to 50.
Release 12.3(7)XI3
This command was enhanced on the PRE2 with an oversubscription factor
from 1 to 500.
Release 12.2(28)SB
This command was integrated in Cisco IOS Release 12.2(28)SB for the
PRE2.
Release 12.2(31)SB2
This command was introduced on the PRE3 with an oversubscription
factor from 1 to 500.
