Beta Draft Confidential
Configuring SPVCs
Defining a Point-to-Point Offnet Circuit Connection
ATM Services Configuration Guide for CBX 3500, CBX 500, GX 550, and B-STDX 9000 1/19/0518-17
Table 18-6. Add Offnet Circuit: Traffic Type Tab Fields
Field Action/Description
QoS Class
(for Forward)
Select the QoS class for forward traffic. The QoS class determines 
which TDs you can select. The following pull-down menu options are 
available for ATM endpoints:
CBR – Constant bit rate (CBR) is used for applications that are 
represented by a continuous bit stream, such as video and digitized 
voice. CBR traffic requires guaranteed throughput rates and service 
levels.
VBR (Real Time) – VBR-RT is used for delay-sensitive applications, 
such as packet video, that require low cell delay variation between 
endpoints.
VBR (Non-Real Time) – VBR-NRT is used to transfer long, bursty data 
streams over a pre-established ATM connection. It is also used for 
short, bursty data such as LAN traffic. CPE protocols adjust for any 
delay or loss incurred.
UBR and ABR – Both ABR and UBR are used primarily for LAN 
traffic. The CPE should compensate for any delay or lost cell traffic.
Note: UBR and ABR are used only with the ATM Flow Control 
Processor (FCP).
The following pull-down menu options are available for Frame Relay 
endpoints:
VFR (Real-Time) – VFR-RT is used for packaging special 
delay-sensitive applications, such as packet video, which require low 
cell delay variation between endpoints.
VFR (Non-Real Time) – VFR-NRT handles packaging for transfer of 
long, bursty data streams over a pre-established ATM connection. This 
service is also used for short, bursty data, such as LAN traffic. CPE 
protocols adjust for any delay or loss incurred through the use of 
VFR-NRT.
UFR – Primarily used for LAN traffic. The CPE should compensate for 
any delay or lost cell traffic.
The Forward QoS Class does not have to be the same as the Reverse 
QoS Class.
For more information on QoS classes, see Table 12-1 on page 12-3.
Notes: For a CBX 500 that uses the FCP, resource management (RM) 
cells are sent in the backward direction. As a result, they assume the 
QoS class of the other direction. 
Due to hardware restrictions, you cannot dynamically modify the 
configured QoS class for ATM circuits with endpoints residing on BIO2 
modules. The NMS will not allow changes to the configured QoS for 
established BIO2 circuits. To modify the QoS class for a BIO2 circuit 
endpoint, delete the existing circuit and re-configure it using the new 
QoS class.