PXB4330 Datasheet, PDF (61/201 Pages) Infineon Technologies AG – ICs for Communications

PXB 4330
Operational Description
In this case, the bandwidth must fit into the WFQ Multiplexer (conditions (1) and (2) in
"Bandwidth Reservation" on page 4-56).
4.11.2 VBR-rt 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 kbit/s, but on average only 16 kbit/s. SCR is 8 kbit/s. 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 nev-
er exceeded.
4.11.3 VBR-nrt Connections
For these connections, the three parameters PCR, SCR, and MBS are given. One queue
is reserved for each VBR-nrt connection with SCR programmed as the weight of the re-
spective Scheduler queue. The maximum queue size is set to MBS plus ~100 cells for
cell level bursts. If the buffer space reserved for VBR-nrt connections is set to the sum
of all MBS, it is guaranteed that no cell is lost. However, with a large number of VBR-nrt
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, the PCR may be shaped. The output rate of each queue may be limited indi-
vidually to a programmable value which results in PCR shaping. This could be useful at
points where a connection leaves one network and enters the next network which might
police the connection (NPC function).
4.11.4 ABR Connections
ABR connections must be setup in per-VC queuing configuration. The queue is assigned
a weight guaranteeing the MCR of the connection.
A backward direction connection must be setup. In Bi-directional Mode, the same queue
ID must be chosen in order to make the ABR functions work properly.
In Uni-directional Mode, the queue ID value with the toggled LSB must be setup for the
backward direction. EFCI marking in forward data cells or CI/NI marking in backward RM
cells can be enabled per traffic class.
Note: Also the LCI is toggled in the Uni-directional Mode (see "LCI Translation in Mini-
Switch Configurations" on page 1-27).
Data Sheet
4-61
09.99