PXF4336 Datasheet, PDF (108/425 Pages) Infineon Technologies AG – ABM Premium ATM Buf fer Manager

ABM-P
PXF 4336 V1.1
Functional Description
3.5.1.9 VS/VD Behavior
The VS/VD behavior is very similar to the terminal source and destination behavior.
VS/VD source behavior performs two different tasks:
• Calculation of the ACR and appropriate adjustment of the sending rate.
• Multiplexing of user cells, FRM cells and BRM cells.
Calculation of ACR is done by using the CI/NI and ER conveyed in the BRM cells and
taking into consideration some further constraints:
• ACR must stay between MCR and PCR.
• In the absence of received BRM cells the source assumes heavy congestion in the
network and reduces ACR by a factor.
• After time-outs, the ACR is reduced to ICR.
According to the standards, after connection setup, the ICR must be adapted as
follows:
ICR
=
max
æ
è
MCR
,min
æ
è
I
CR_Se
t
up
,_F---^T-_R---^B--_T--^E--_T-- _øö
ö
ø
(3)
In the ABM-P, the ACR is programmed to the peak rate limiter of a queue. Then the rule
is fulfilled that the actual sending rate shall never be higher than ACR. If the queue is
served at a lower rate than ACR - due to resource contention - the unused bandwidth will
be consumed by the network (“use-it-or-lose-it” principle). Using the WFQ scheduler and
assigning an appropriate weight assures that ACR is not falling below MCR.
Multiplexing user cells and FRM cells occurs under control of the ERC unit according to
the behavior defined in the standards.
VS/VD destination behavior is basically to convert the received FRM cells into BRM
cells. The CI/NI and ER fields of the outgoing BRM cells are updated to reflect the
congestion situation of the VD side buffers. The received BRM cells are evaluated and
the ACR is conveyed to the companion virtual source.
In a switch, the VS/VD function is distributed, as shown in Figure 3-46.
Data Sheet
108
2001-12-17