Allied Telesis 2.6.1 manual Quality of Service, Egress Rules

Layer 2 Switching 85

The Egress Rules

Once the Forwarding Process has determined which ports and transmission queues to forward a frame from, the Egress Rules for each port determine whether or not the outgoing frame is VLAN-tagged with its numerical VLAN Identifier (VID). (See “Virtual Local Area Networks (VLANs)” on page 72).

When a port is added to a VLAN, it is configured to transmit either untagged or VLAN tagged packets, using the command:

ADD VLAN={vlanname1..4094} PORT={port-listALL} [FRAME={TAGGEDUNTAGGED}]

This setting can be changed for a port which is already part of a VLAN, using the command:

SET VLAN={vlanname1..4094} PORT={port-listALL}

FRAME={UNTAGGEDTAGGED}

Quality of Service

The switch hardware has a number of Quality of Service (QOS) egress queues that can be used to give priority to the transmission of some frames over other frames on the basis of their user priority tagging. The user priority field in an incoming frame (with value 0 to 7) determines which of the eight priority levels the frame is allocated. When a frame is forwarded, it is sent to a QOS egress queue on the port determined by the mapping of priority levels to QOS egress queues. All frames in the first QOS queue are sent before any frames in the second QOS egress queue, and so on, until frames in the last QOS egress queue, which are only sent when there are no frames waiting to be sent in any of the higher QOS egress queues.

The mapping between user priority and a QOS egress queue can be configured using the command:

SET SWITCH QOS=P0,P1,P2,P3,P4,P5,P6,P7

The switch has four QOS egress queues. It has a default mapping of priority levels to QOS egress queues as defined in IEEE Standard 802.1Q (Table 14).

Table 14: Default priority level to queue mapping for four QOS egress queues

Priority level QOS Egress Queue

01

10

20

31

42

52

63

73

Software Release 2.6.1 C613-02039-00 REV A