PXF4336 Datasheet, PDF (84/425 Pages) Infineon Technologies AG – ABM Premium ATM Buf fer Manager

ABM-P
PXF 4336 V1.1
Functional Description
For a given arrival rate Figure 3-23 shows the repartition of the output rate. The priority
scheduler simply cuts off the low priority traffic assumed in the white bar. The RR
scheduler iteratively divides the output rate into equal shares among the active inputs.
The WFQ scheduler divides the output rate in proportion to the assigned weights
assumed to be proportional to the respective arrival rates.
3.4.2.3 Quality of Service Support
In the context of ATM service categories, it is useful to introduce the concept of guaran-
teed rate. This is the rate which the network must guarantee to the user in order to fulfill
the QoS demands.
Table 3-24 Guaranteed Rates for each ATM Service Category
ATM Service
Category
Guaranteed Rate Comment
CBR
PCR
rt-VBR
SCR...PCR
Guaranteed rate is calculated with “effec-
tive bandwidth formulas” assuming small
buffers and taking into account statistical
multiplexing gain.
nrt-VBR
SCR
ABR
MCR
GFR
MCR
Guaranteed rate is delivered in complete
uncorrupted AAL5 frames.
UBR+
MCR
UBR
none
Guaranteed rate is always > 0 with queue
connected to the WFQ scheduler, can be 0
for arbitrary long times in low priority RR
scheduler.
Mapping of connections to stage 1 schedulers depends on the ATM service category of
the connection (also shown in Figure 3-22) as follows:
– Priority 1 RR:
– Priority 2 WFQ:
– Priority 3 RR:
real-time connections (CBR, rt-VBR).
non real-time connections with guaranteed rate
(nrt-VBR, ABR, GFR, UBR+)
best effort connections UBR
An example of a scheduler with one priority 1 real-time queue (Queue 1) and nine priority
2 non-real-time queues (Queue 2 through Queue 10) is shown in Figure 3-25. Queue 1
is shared by a number of connections with different bit rates.
Data Sheet
84
2001-12-17