20-19
ATM Switch Router Software Configuration Guide
OL-7396-01
Chapter20 Configuring Frame Relay to ATM Interworking Port Adapter Interfaces
Configuring Frame Relay to ATM Resource Management
You can also use the following generic formula to calculate Frame Relay to ATM traffic conversion:
•PCR = Peak Cell Rate (cells/sec)
•SCR = Sustained Cell Rate (cells/sec)
•MBS = Maximum Burst Size (cells)
•Bc = Committed Burst size (bits)
•Be = Excess Burst Size (bits)
•CIR = Committed Information Rate (bits/sec),
•PIR = Peak Information Rate (bits/sec),
•OHB(n)= Overhead Factor for frame-size(n)
•h1 = Frame Relay Header Size (octets), 2-octet
•h2 = AAL Type 5 PDU Trailer Size (8 octets)
•n = configured frame size
–
OHB(n) = [((n+h1+h2)/48) / n ]
where
((n+h1+h2)/48) value is to be rounded to the nearest integer
–
Peak Cell Rate (PCR) (0+1) (Cells Per Second)(0+1) (Cells Per Second) = PIR/8 [OHB (n)]
–
Sustainable Cell Rate (SCR) (0) (Cells Per Second) = CIR/8 [OHB (n)]
–
Maximum Burst Size (MBS)(0) (Cells) = [Bc/8 ( 1/(1 –(CIR/PIR))) + 1 ] [OHB (n)]
Example
Using the following values and example generic formula, MBS equals 47 cells:
•CIR=32000
•PIR=64000
•Bc=4000
•frame-size=64bytes
OHB(n) = [((n+h1+h2)/48) / n ] = [((64 + 2 + 8) / 48) / 64]
= (74/48) / 64
= 1.541 / 64
ROUNDING 1.541 TO 2
OHB(64) = 2/64
PCR = PIR/8 [OHB (n)] = 64000/8 [2/64]
= 250
Converting Cells/sec to Kbps
= 250 * 424 / 1000
PCR = 106 kbps
SCR = CIR/8 [OHB (n)] = 32000/8 [2/64]
= 125
Converting Cells/sec to Kbps
= 125 * 424 / 1000
SCR = 53 kbps
1. In bits per second
2. In bits