15-5
Cisco 10000 Series Router Quality of Service Configuration Guide
OL-7433-09
Chapter 15 Oversubscribing Physical and Virtual Links
ATM Virtual Circuit Oversubscription
ATM VC Oversubscription and ATM Line Cards
ATM VC oversubscription controls the allocation of resources that are managed on a line card. If you
enable oversubscription on one port alone, other ports might use more resources than they are supposed
to use, which could result in resource starvation of other ports, causing VC creation to fail. Therefore,
we recommend that you apply VC oversubscription to all ports of an ATM line card.
Table 15-1
lists the number of active VCs the ATM line cards support in atm pxf queuing
mode for Cisco
IOS Release 12.3(7)XI2 and later releases.
You can configure the maximum number of VCs across the ports in any fashion, provided that you do
not exceed the per-port maximum.
Although the maximum number of VBR, CBR, and shaped UBR VCs per E3/DS3 and OC-3 ATM line
card is 28,672 VCs, the router supports a maximum of 22,204 VBR, CBR, and shaped UBR VCs per line
card that you can place within virtual path (VP) tunnels. If you attempt to bring up more than 22,204
VCs in a configuration that includes VP tunnels and VCs (hierarchical traffic shaping configuration), the
VCs might not assign traffic correctly or the VCs might not come up at all. Be sure to limit the number
of configured VBR, CBR, and shaped UBR VCs on an ATM card to less than 22,204 VCs if you place
the VCs in VP tunnels.
For the OC-12 ATM line card, the router supports 16,384 VCs in VP tunnels.
atm over-subscription-factor Command
To oversubscribe ATM virtual circuits (VCs), use the
atm over-subscription-factor
command in
interface configuration mode. To prevent oversubscription of an ATM VC, use the
no
atm
oversubscribe
command. By default, oversubscription of ATM interfaces and tunnels is enabled.
atm over-subscription-factor
{
factor
}
no
atm over-subscription-factor
{
factor
}
Table 15-1
Active VCs on ATM Line Cards
Line Card
Max. VCs per Port
Maximum VCs per Module
No. VBR, CBR, Shaped UBR VCs
E3/DS3
4,096
32,768
1
1.
For 32,768 VCs per module, 4096 of them must be unshaped UBR VCs.
28,672
2
2.
For 28,672 VBR, CBR, and shaped UBR VCs, no VCs can be in shaped VP tunnels. If VCs are in shaped VPs, the number of VBR, CBR, and shaped
UBR VCs is 22,204.
OC-3
8,191
32,764
3
3.
For 32,764 VCs per module, 4096 of them must be unshaped UBR VCs.
28,672
4
4.
For 28,672 VBR, CBR, and shaped UBR VCs, no VCs can be in shaped VP tunnels. If VCs are in shaped VPs, the number of VBR, CBR, and shaped
UBR VCs is 22,204.
OC-12
16,384 (previously 14,436)
16,384
16,384