
PM73487 QRT
PMC-Sierra, Inc.
PMC-980618
Issue 3
622 Mbps ATMTraffic Management Device
Released
Datasheet
36
causes congestion to be found for the limit when the queue depth is 31744. This allows a 15-bit
value to be used to store the state of each measurement except the device measurement, which has
a 1-bit value.
Three congestion management algorithms are available for use on a per-channel basis. In each
channel’s TX_CH_CONFIG word (refer to
section 9.3.1.7 “TX_CH_CONFIG” starting on
page 189
) are bits that enable EPD, CLP-based discard, and EFCI. These may be used in combi-
nation. In addition, Packet Tail Discard (PTD) is supported as a mode of the EPD operation.
Fig-
ure 35 on page 30
illustrates the operation of EPD/PTD. Figure 36 on page 30 illustrates the
operation of EPD/PTD with CLP.
As described in
“Transmit Resequencing Algorithm” on page 39
, there is an interaction between
EPD and the resequencing algorithm. Refer to that section for a complete description.
2.6.3
Transmit Queue Service Algorithm
The transmit queue controller supports 16 SCs for each of its 31 VOs (the per-VO structure is
shown in
Figure 42 on page 38
). As with the receive queue controller, the transmit queue control-
ler addresses the following key issues: QoS, CDV minimization, MCR guarantee, fairness maxi-
mization, and output isolation.
Figure 41. Transmit Maximum and Congested Threshold Checks
Per Service
Class (SC)
Per Queue
31 Virtual
Outputs (VOs)
16 Service
Classes (SCs)
Per Device
Per Virtual
Output (VO)
Per Channel