S/UNI®-ATLAS-3200 Telecom Standard Product Data Sheet
Preliminary
1
I =
SCR
(
∆t
)
1
1
æ
ç
ö
(
MBS −1
)
−
BT
∆t
SCR PCR
∆t
è
L =
=
where
SCR = Sustaned Cell Rate (cells/s)
MBS = Maximum Burst Size at the Peak Cell Rate (cells)
BT = Burst Tolerance (s)
In order to compensate for the potentially large CDV and Burst Tolerance limits anticipated in
ATM networks, the Limit fields, L1 and L2 are encoded as floating-point values, in the same
manner as the Increment fields:
m
512
e æ
ö
L = 2 1+
where 0 ≤ e ≤ 31
0 ≤ m ≤ 511
ç
÷
è
where e is the 5-bit exponent and m is the 9-bit mantissa. The Limit fields are formatted as
follows:
MSB
4
LSB
0
0 8
e
m
The Theoretical Arrival Time (TAT1 and TAT2) are encoded as fixed-point values with an integer
and fraction portion. The integer portion of the TAT field is a 31-bit value, and the fractional
portion is a 3-bit value. The TAT fields are formatted as follows:
33
3
2
0
Integer Portion
Fractional Portion
The fractional portion of the TAT field is measured in fractions of the clock period, ∆t . For a 8
ns clock period, the accuracy of the policing algorithm can be measured as follows:
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-1990553, Issue 4
94
PMC [ PMC-SIERRA, INC ]
