Allied Telesis AT-GS950/8 manual Ieee 802.1p Priority Level Port Priority Queue

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AT-S82 Management Software User’s Guide

Table 1 lists the mappings between the eight CoS priority levels and the four egress queues of a switch port.

Table 1. Default Mappings of IEEE 802.1p Priority Levels to Priority

Queues

IEEE 802.1p Priority Level

Port Priority Queue

 

 

 

 

0

Q1

 

 

1

Q0

 

 

2

Q0

 

 

3

Q1

 

 

4

Q2

 

 

5

Q2

 

 

6

Q3

 

 

7

Q3

 

 

For example, if a tagged packet with a priority level of 2 entered a port on the switch, the switch would store the packet in Q11 on the egress port.

Note that priority 0 is mapped to CoS queue 1 instead of CoS queue 0 because tagged traffic that has never been prioritized has a VLAN tag user priority of 0. If priority 0 was mapped to CoS queue 0, this default traffic goes to the lowest queue, which is probably undesirable.

Scheduling A switch port needs a mechanism for knowing the order in which it should handle the packets in its four egress queues. For example, if all the queues contain packets, should the port transmit all packets from Q3, the highest priority queue, before moving on to the other queues? Or, should it instead just send a few packets from each queue and, if so, how many?

This control mechanism is called scheduling. Scheduling determines the order in which a port handles the packets in its egress queues. The AT-S82 management software uses weighted round-robin scheduling. This method functions as its name implies. The port transmits a set number of packets from each queue, in a round robin fashion, so that each queue has an opportunity to transmit traffic. This method guarantees that every queue receives some attention from the port for transmitting packets.

To set up scheduling, you need to specify the maximum number of packets a port should transmit from a queue before moving to the next queue. This is referred to as specifying the weight of a queue. In all likelihood, you will want to give greater weight to the packets in the higher priority queues over the lower queues. Table 2 provides a scheduling

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Contents Management Software Page Contents Contents Figures Figures Preface Where to Find Web-based Guides Contacting Allied Telesis Management Software UpdatesPreface Chapter Getting StartedStarting a Management Session Main Saving Changes Save Configuration Click ApplyQuitting a Management Session Getting Started Basic Switch Parameters Basic Switch Parameters AT-S82 Management Software User’s Guide Disabled EnabledDisabling or Enabling Ping Blocking Enabling or Disabling 802.1X Forwarding Control Changing the Administrator’s Password Rebooting the Switch Reset Click Apply Switch is reset Resetting the Switch and Retaining the IP AddressAT-S82 Management Software User’s Guide Download Status Message Downloading New FirmwarePort Configuration Configuring Port Parameters Port is enabled. This is the default Fiber CopperTrunking Trunking Guidelines Trunking Algorithm Trunking OverviewAT-S82 Management Software User’s Guide DAxorSA Configuring the Trunking AlgorithmPort Trunking Configuration Setting up the TrunkTrunking Port Mirroring Port Mirroring Overview Configuring Port Mirroring Port Mirroring VLANs Increased Performance Improved Manageability Security Vlan FeaturesAT-S82 Management Software User’s Guide Vlan Identifier Vlan Port Members Vlan OverviewIncoming Outgoing Tagged Untagged Frames Guidelines for Creating a Vlan Vlan Detail Working with VLANsClick Show All Static Vlan Entries Displaying all VLANsVlan Protected Ports Vlan Example Protected Ports VlanAT-S82 Management Software User’s Guide VLANs Class of Service Mapping Ports to Egress Queues Class of Service OverviewIeee 802.1p Priority Level Port Priority Queue Port Egress Queue Maximum Number Packets Mapping Priorities to Queues Setting Up the Schedule Assigning Priority to Ports Class of Service Spanning Tree Protocol STP Bridge Priority Root Spanning Tree OverviewIncrement Bridge Priority Path Costs and Port CostsPort Speed Port Cost Increment Port Priority Port PriorityHello Time and Bridge Protocol Data Units BPDUs Point-to-Point and Edge Ports Edge Port Spanning Tree and VLANs Spanning Tree Protocol STP Configuring Spanning Tree STP Compatible RstpDisabled Configuring STP Port Settings Auto YesFalse TrueSpanning Tree Protocol STP
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