PXF4336 Datasheet, PDF (151/425 Pages) Infineon Technologies AG – ABM Premium ATM Buf fer Manager

ABM-P
PXF 4336 V1.1
Operational Description
4.2.7 Support of Standard ATM Service Categories
The following sections provide some insight into how the ABM-P supports connections
belonging to the well known ATM Forum service categories.
4.2.7.1 CBR Connections
These connections should use the real-time bypass of the respective scheduler block.
However, if two priority levels for real-time connections must be offered, a slightly lower
real-time performance can be achieved by using the WFQ scheduler with maximum
weight. In this case, the bandwidth must fit into the WFQ scheduler (conditions (1) and
(2) in “Bandwidth Reservation” on Page 149).
4.2.7.2 rt-VBR Connections
These connections can be treated like CBR connections with a guaranteed cell rate less
than or equal to the Peak Cell Rate (PCR). Depending on the behavior of the sources, a
statistical benefit could be obtained by reserving less than PCR.
As an example, assume 1000 connections with compressed voice are multiplexed on a
link. PCR is 32 Kbps, but on average only 16 Kbps. SCR is 8 Kbps. Hence, instead of
reserving 32 Mbit/s for the ensemble of connections, only 16 Mbit/s must be reserved.
The large number of connections guarantees that the mean sum rate of 16 Mbit/s is ex-
ceeded only with a negligible probability.
4.2.7.3 nrt-VBR Connections
For these connections, the three parameters PCR, SCR, and MBS are given. One queue
is reserved for each nrt-VBR connection with SCR programmed as the weight of the re-
spective Scheduler queue. The maximum queue size is set to MBS plus approximately
100 cells for cell level bursts. If the buffer space reserved for nrt-VBR connections is set
to the sum of all MBS, it is guaranteed that no cell is lost. However, with a large number
of nrt-VBR connections, the total reserved buffer can be smaller with a negligible number
of cell losses.
For the PCR, no adjustment is necessary as the rates of the queues of a Scheduler al-
ways adjust automatically to the maximum possible values.
As an option for network endpoints, for both rt-VBR and nrt-VBR the PCR and SCR may
be shaped by the PCR limiter and SCR leaky bucket shaper as described in
Chapter 3.4.2.4. This is useful at network boundaries (UNI/NNI) to provide conforming
traffic to the subsequent policer.
4.2.7.4 ABR Connections
It is recommended that ABR connections be configured with per VC queueing and with
the peak rate limiter for the queue enabled. Further on, ABR logical queues are always
Data Sheet
151
2001-12-17