Cisco Cisco IOS Software Release 12.4(15)T

ATM resources can be specified dynamically on a per-connection basis (per SVC). The ATM T3/E3 
network module supports four classes of service:

Constant Bit Rate (CBR): This class emulates circuit switching. CBR has the highest transport 
priority, which is 0. CBR can be used for connections such as voice and video. This bandwidth is 
characterized by peak cell rate (PCR). 

Variable Bit Rate (VBR): VBR is available in non-real-time (VBR-nrt) and real-time (VBR-rt). VBR 
has the second highest transport priority, which is 1. VBR sends traffic at a rate that varies with time, 
depending on the availability of user information.

Available Bit Rate (ABR): ABR has the transport priority of 2. ABR provides rate-based flow 
control and is aimed at data traffic. 

Unspecified Bit Rate (UBR): UBR has the transport priority of 3. UBR is a “best effort” class of 
service that uses the unutilized bandwidth for a connection. Traffic categorized as UBR+ is 
guaranteed a minimum line rate through the minimum cell rate (MCR) traffic parameter.

To configure the ATM T3/E3 network module, complete the following procedures:

To configure the ATM T3/E3 network module for T3 or E3 operation, perform the following tasks.

The ATM T3/E3 network module will not be operational until a card type is configured.

configure terminal

card type {t3 | e3} slot