Quality of Service (QoS): Managing Bandwidth More Effectively
Using QoS Classifiers to Configure Quality of Service for Outbound Traffic
TableOutbound Port |
| ToS Option: |
| 802.1p (Value = 0 - 7) | Differentiated Services |
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IP Packet Sent Out | Depending on the value of the IP | For a given packet carrying a ToS codepoint that the switch |
an Untagged Port | Precedence bits in the packet’s ToS | has been configured to detect: |
in a VLAN | field, the packet will go to one of four | • Change the codepoint according to the configured policy |
| outbound port queues in the switch: | and assign the 802.1p priority specified for the new |
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| • Do not change the codepoint, but assign the 802.1p priority | |
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| specified for the existing codepoint in the DSCP Policy | |
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| Depending on the 802.1p priority used, the packet will leave | |
| the switch through one of the following queues: | |
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| 1 - 2 = low priority (queue 1) | |
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| 0 - 3 = normal priority (queue 2) |
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| 4 - 5 = medium priority (queue 3) |
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| 6 - 7 = high priority (queue 4) |
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| If |
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| specified codepoint, then the packet is not prioritized by ToS |
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| and, by default, is sent to the “normal priority” queue. |
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IP Packet Sent Out | Same as above, plus the IP Prece- | Same as above, plus the Priority value (0 - 7) will be used to |
an Untagged Port | dence value (0 - 7) will be used to set | set a corresponding 802.1p priority in the VLAN tag carried by |
in a VLAN | a corresponding 802.1p priority in the | the packet to the next downstream device. Where |
| VLAN tag carried by the packet to the | ride is the assigned priority, the VLAN tag carries a “0” (normal |
| next downstream device. Refer to | priority) 802.1p setting if not prioritized by other QoS classi- |
| table | fiers. |
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ToS Byte IP | Corresponding | Service Priority Level |
Precedence Bits | 802.1p Priority |
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000 | 1 | Lowest |
001 | 2 | Low |
002 | 0 | Normal |
003 | 3 |
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004 | 4 |
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005 | 5 |
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006 | 6 |
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007 | 7 | Highest |
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