PXF4336 Datasheet, PDF (87/425 Pages) Infineon Technologies AG – ABM Premium ATM Buf fer Manager

ABM-P
PXF 4336 V1.1
Functional Description
The ABM-P 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 ] ):
MBS = 1 + -------------^B----^T---------------
[cells]
(1)
-----¹------- – ------¹------
SCR PCR
Vice versa, when the MBS is received (via signalling), the corresponding BT can be
calculated according to the following formula:
BT
=
(MBS
–
1)
⋅
æ
è
-----¹-------
SCR
–
P^-----C^-1---R^---øö
[s]
(2)
In the ABM-P 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 shows the outcome of the ABM-P leaky bucket shaper under ideal
conditions when loaded with a burst.
Data Sheet
87
2001-12-17