pxf4333 Infineon Technologies Corporation, pxf4333 Datasheet - Page 82

• Manufacturer Part Number: pxf4333
• Description: Abm 3g Atm Buf Fer Manager
• Manufacturer: Infineon Technologies Corporation

The ABM-3G contains two basic shaping mechanisms, which can be activated per
logical queue: PCR limitation and leaky bucket shaping. In particular it is possible to
enable both mechanisms simultaneously on the same logical queue, a necessary
feature to implement true VBR shaping as explained below.
3.4.2.4.1 PCR Limitation
For all logical queues a rate limitation can be enabled, which controls the peak cell rate
(PCR) from this queue. In other words, cells from a PCR limited queue are always
spaced by at least TP=1/PCR seconds. Cell clumping within the network is thereby
eliminated. Traffic passing through a PCR limiter is conforming to any PCR traffic
contract, since the tolerance of the PCR limiter is zero.
3.4.2.4.2 Leaky Bucket Shaping
A leaky bucket shaper controls a given sustainable cell rate (SCR) within the limits of a
given Burst Tolerance (BT).
The Burst Tolerance and the SCR determine the Maximum Burst Size (MBS) (in cells)
that may be transmitted at an arbitrary PCR according to the following formula (refer to
[ 2 ] ):
Vice versa, when the MBS is received (via signalling), the corresponding BT can be
calculated according to the following formula:
In the ABM-3G leaky bucket shaping can be enabled for up to 2048 PCR limited logical
queues. In addition to the parameter TP = 1/PCR, the cell spacing for TS = 1/SCR and
the burst tolerance tauS = BT must be specified.
Figure 3-27
conditions when loaded with a burst.
Data Sheet
MBS
BT
shows the outcome of the ABM-3G leaky bucket shaper under ideal
=
=
(
MBS 1
1
+
–
-------------------------------- -
------------ -
SCR
1
)
⋅
BT
æ
è
–
------------ -
SCR
------------ -
PCR
1
1
–
------------ -
PCR
1
82
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ø
[
cells
s [ ]
]
Functional Description
PXF 4333 V1.1
2001-12-17
ABM-3G
(1)
(2)