PM7326 datasheet(91/238 Pages) PMC

91 / 238 page

PM7326 S/UNI APEX

DATA SHEET

PMC-1981224

ISSUE 6

ATM/PACKET TRAFFIC MANAGER AND SWITCH

PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE

It is possible to mix VCs that have FCQ and WFQ scheduling within the same

class, and ClassPacket enabled. Non FCQ VCs and non-user cells (as defined

in Table 8) are treated as single cell packets.

All counters, control and limit fields for the class scheduler are located in the

class scheduler context memory. As stated earlier, memory is only allocated for

classes one, two, and three. Class zero does not require any class scheduler

context information.

10.9.3.2

Partial Packet Scheduling

A per-Port parameter, ClassFragEn, is provided to support packet fragmentation.

In this fragmentation mode, classes are selected on a strict priority basis. Once

a class is selected, the packet at the head of the class queue is transmitted up to

a programmable length or until the EOM is encountered, whichever comes first.

Non FCQ VCs and non-user cells (as defined in Table 8) are treated as single

cell packets. When the length/EOM is reached, the classes are evaluated once

again in a strict priority. The transmission of the original packet will resume once

the original class regains transmission rights. Note that by virtue of the strict

priority scheduling, Class0 will always have its packets transmitted in their

entirety.

10.9.4 Congestion Control

The congestion control decides whether to permit a cell to enter the queue

structure. The objective is to provide a minimum reserved buffer allocation to all

active VCs and to fairly allocate shared buffer resources to eligible VCs. The

algorithm is applied to both frame and non-frame traffic. The objectives of the

algorithm are as follows:

• provide guaranteed resources to all active VCs

• share available buffer resources to eligible VCs with excess buffering

requirements

• restrict resource allocation on a per-VC, per-Class, per-Port, and per-

Direction basis to those levels that have exceeded their allotment of

resources.

• avoid global synchronization

• Provide interrupts and ID of the last maximum threshold discard invoked.

These objectives are achieved by having several thresholds and hierarchical

count values, at the per-Device, per-Direction, per-Port, per-Class, and per-VC

PM7326 Datasheet(PDF) 91 Page - PMC-Sierra, Inc