PXF4333 Datasheet, PDF (78/361 Pages) Infineon Technologies AG – ABM 3G ATM Buf fer Manager

ABM-3G
PXF 4333 V1.1
Functional Description
3.4.2.2.2 Round Robin Scheduler
The round robin scheduler keeps all of its input queues, which have cells to send in a
FIFO structured list. The queue at the head of the list is allowed to send one cell and is
then rescheduled at the end of the list. Thereby, the available bandwidth is divided
equally among those queues which have cells to send.
3.4.2.2.3 Weighted Fair Queueing Scheduler
Rate guarantees for non real-time connections are achieved with the WFQ scheduler.
The WFQ scheduler has an arbitrary number of input queues with a weight factor
assigned to each of them. The absolute values of the weights are irrelevant, only the
relative values count. See Chapter 4.2.2.7 for a discussion on appropriate selection of
weight factors.
The WFQ scheduler has the following important properties:
• It is work conserving, i.e. the available bandwidth is always used completely as long
as any of the attached queues has cells to send.
• It provides a fair distribution of the available bandwidth in proportion to the assigned
weights under any load condition.
• It guarantees minimum rates to queues as long as the sum of the configured minimum
rates fits into the available bandwidth.
The properties above make the WFQ scheduler particularly useful for bursty connections
with start/stop behavior. The WFQ scheduler automatically deals with the varying load
situations and always distributes the bandwidth according to the weight factors.
Arrival Rate
Multiplexer Rate
Priority
Round
Robin
WFQ
Figure 3-23 Behavior of Different Scheduler Types
Data Sheet
78
2001-12-17