Beta Draft Confidential
Configuring ATM PVCs
Configuring Frame Relay-to-ATM Interworking Circuits
ATM Services Configuration Guide for CBX 3500, CBX 500, GX 550, and B-STDX 9000 1/19/0510-47
Frame Relay-to-ATM Parameters Conversion Formula
When you configure Frame Relay traffic parameters on the Frame Relay endpoint, the
NMS automatically converts the Frame Relay CIR, Bc, and Be fields to the ATM
PCR, SCR, and MBS fields and displays these ATM parameters on the screen. You
should use these values as a guideline in order to provision a PVC with roughly
symmetric traffic parameters. Optionally, you can enter these converted values into the
appropriate fields on the ATM endpoint, or enter new ATM parameter values for the
ATM endpoint.
The NMS uses the following formula to convert the entered Frame Relay traffic
parameters:
IOH represents the Interworking Overhead factor; it is a fixed number based on an
average frame size of 256 bytes with additional factors for the AAL5 trailer size and
the cell padding overhead.
PCR = (CIR + EIR) * IOH / 8
SCR = CIR * IOH / 8
MBS = Bc * IOH / 8
EIR = Be * CIR /Bc
IOH = .0234375
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