User's Manual

HAPTER

| Introduction

Overview

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There are four priority levels labeled TC0, TC1, TC2 and TC3. The untagged

packets and the eight IEEE 802.1p priority tags (defined by the standard) are

mapped to the four priority queues on the switch. TC3 has the highest priority of

the four priority queues while TC0 has the lowest priority. The untagged packets

and eight priority tags, specified in IEEE 802.1p, are mapped to the switch’s

priority tags as follows:

◆ Untagged packets, and packets with priority tag 1 and 2 are assigned to the

switch’s TC0 level queue.

◆ Packets with priority tag 0 and 3 are assigned to the switch’s TC1 level

queue.

◆ Packets with priority tag 4 and 5 are assigned to the switch’s TC2 level

queue.

◆ Packets with priority tag 6 and 7 are assigned to the switch’s TC3 level

queue.

The SMCGS1601 switch uses Weighted Fair Queuing (WFQ) for scheduling. The

WFQ scheduling algorithm assigns bandwidth to all the queues based on default

weight values. The queue with the highest weight value has the largest

bandwidth of the four queues. And the SMCGS2401 Switch uses Weighted Robin

Round (WRR) for scheduling. The WRR queue-scheduling algorithm schedules all

the queues in turn with every queue assured a certain service time. For both

WFQ and WRR mode, the default weight values of TC0, TC1, TC2 and TC3 are

1:2:4:8.