PXF4336 Datasheet, PDF (107/425 Pages) Infineon Technologies AG – ABM Premium ATM Buf fer Manager

ABM-P
PXF 4336 V1.1
Functional Description
The algorithm is designed to control the queue length around a given operating point,
which can be chosen with parameter QL0 (see Table 3-55) to be one of 256, 512, 1024,
2048 cells.
3.5.1.8 Reactive Switch Control
Reactive Switch Control (RSC) is an extension to the Explicit Rate Marking mechanism.
A switch with RSC behavior enabled is intended to adjust connection specific rates to not
exceed the current explicit rate value from the incoming BRM cells (see Figure 3-45).
The ABM-P supports RSC by extracting the ER from incoming BRM cells in the ERC unit
(see Section 3.5.2) and dynamically adjusting the PCR limiter of the corresponding
logical queue to the value of the ER.
Example:
Imagine that a connection crosses 2 bottlenecks called ABM-P (a) and ABM-P (b). At a
certain moment ABM-P (a) serves the connection with 10 Mbit/s, ABM-P (b) with 5 Mbit/
s. Hence, ABM-P (b) will have to store the difference of 5 Mbit/s incoming cells. In such
a situation the BRM cells flowing backwards from ABM-P (b) towards ABM-P (a) will
carry the ER=5 Mbit/s. The ABM-P (a) has calculated an ER=10 Mbit/s and hence will
not modify the ER field of the backward RM cells. Depending on the loop length (round
trip time until BRM cells arrive at the source and source reduces the emit rate), ABM-P
(b) is likely to overflow with cells for this connection. To shorten the control loop, Reactive
Switch Control (RSC) immediately updates the emit rate of ABM-P (a) to the lower ER
value extracted from the BRM cells.
Symmetric, but de-coupled control loops are foreseen by the standard to control both
source-destination flows. For simplification, only one flow is shown in this example.
Source
ABM-P (a)
ABM-P (b)
Destination
adjust
ACR
Source and
sink RM cells
adjust
ACR to
5Mbit/s
ä ER=
10Mbit/s
No update
ä ER=
5Mbit/s
update RM
ER=5Mbit/s
user and RM cell flow
RM cell flow
Figure 3-45 Reactive Switch Control Example
Data Sheet
107
ä
update RM
Turn-around
RM cells
2001-12-17