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ATM Switch Router Software Configuration Guide
OL-7396-01
Chapter9 Configuring Resource Management
Configuring Interface Overbooking
Switch#
In the previous example, ATM interface 1/1/1 is configured to allow any UBR traffic to passed while all
other traffic is policed.
Configuring Interface Overbooking
The interface overbooking feature allows the available equivalent bandwidth of an interface to exceed
the maximum cell rate (MaxCR) or physical line rate on ATM and inverse multiplexing over ATM (IMA)
interfaces. The available equivalent bandwidth is by default limited by the MaxCR. Increasing the
available equivalent bandwidth beyond the MaxCR allows the configuration of more connections on an
interface than its physical bandwidth would allow. Overbooking allows more flexibility when
configuring an interface when the traffic over the interface will be less than the MaxCR.
The following restrictions apply to interface overbooking:
•Regular VP tunnels do not support interface overbooking.
•You cannot add new hierarchical VP tunnels on a physical interface if the interface’s bandwidth
guarantees exceed the MaxCR regardless of any overbooking configured on that interface.
•On IMA interfaces, the available equivalent bandwidth for PVCs differs from the available
equivalent bandwidth for SVCs. The available equivalent bandwidth for PVCs is based on the
number of interfaces configured as part of the IMA group. The available equivalent bandwidth for
SVCs on an IMA interface is based on the number of interfaces that are active in the IMA group.
Overbooking increases both the available equivalent bandwidth values by the same configured
percentage.
•The MaxCR for transmit and receive flows might differ on output-paced physical interfaces.
Configuring overbooking on such interfaces results in different maximum guaranteed services
bandwidth values and available cell rates for service categories for transmit and receive flows.
Maximum guaranteed services bandwidth is the maximum e quivalent bandwidth allocated for
guaranteed services on the interface.
•When an interface is overbooked with traffic, cell flow through the well-known VCs might be
reduced.
•Although overbooking increases the available cell rates for various service categories on an
interface, various traffic parameters of a connection are still limited by the MaxCR.
•If the overbooking configuration results in a maximum guaranteed services bandwidth that is below
the currently allocated bandwidth guarantees on an interface, the configuration is rejected.
•Per class overbooking configuration and interface overbooking configuration cannot co-exi sts on the
same ATM and IMA interface. These two modes are mutually exclusive that are configurable on a
per interface basis (on an ATM or IMA interface). See the section, Configuring Service Class
Overbooking, page 9-39, for additional information.
Caution Overbooking can cause interface traffic to exceed the guaranteed bandwidth that the switch can provide.
Note Interface overbooking configuration is not supported on switc hes with feature card per-flow queuing
(FC-PCQ) installed.