Egress Queue vs Packet Priority Mapping
AT-GS950/16PS Switch Web Interface User’s Guide
Each port has four egress queues, labeled Q0, Q1, Q2, and Q3. Q0 is the lowest priority queue and Q3 is the highest. A packet in a high priority egress queue is typically transmitted sooner than a packet in a low priority queue.Table 3 lists the default mappings between the eight CoS priority levels and the four egress queues of a switch port.
Table 3. Default Mappings Priority Levels to Priority Queues
IEEE 802.1p | Port Priority |
Priority Level | Queue |
|
|
|
|
0 | Q0 |
|
|
1 | Q0 |
|
|
2 | Q0 |
|
|
3 | Q0 |
|
|
4 | Q0 |
|
|
5 | Q0 |
|
|
6 | Q0 |
|
|
7 | Q0 |
|
|
You can change these mappings. For example, you might decide that packets with a priority of 6 and 7 need to be handled by egress queue Q3 and packets with a priority of 2 and 3 should be handled in Q1. The result is shown in Table 4.
Table 4. Customized Mappings Priority Levels to Priority Queues
IEEE 802.1p | Port Priority |
Priority Level | Queue |
|
|
|
|
0 | Q0 |
|
|
1 | Q0 |
|
|
2 | Q1 |
|
|
3 | Q1 |
|
|
4 | Q2 |
|
|
5 | Q2 |
|
|
6 | Q3 |
|
|
7 | Q3 |
|
|
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