As shown in b, the
c.802.1Q tag header
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| TPID (Tag protocol identifier) |
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| TCI (Tag control information) |
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1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | Priority |
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| VLAN ID |
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7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
The priority in the 802.1Q tag header is called 802.1p precedence, because its use is defined in IEEE 802.1p. 4 presents the values for 802.1p precedence.
4.Description on 802.1p precedence
802.1p precedence (decimal) | 802.1p precedence (binary) | Description |
0 | 000 | |
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1 | 001 | background |
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2 | 010 | spare |
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3 | 011 | |
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4 | 100 | |
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5 | 101 | video |
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6 | 110 | voice |
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7 | 111 | |
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Queue scheduling
In general, congestion management adopts queuing technology. The system uses a certain queuing algorithm for traffic classification, and then uses a certain precedence algorithm to send the traffic. Each queuing algorithm is used to handle a particular network traffic problem and has significant impacts on bandwidth resource assignment, delay, and jitter.
In this section, two common hardware queue scheduling algorithms Strict Priority (SP) queuing and Weighted Round Robin (WRR) queuing are introduced.
SP queuing
SP queuing is specially designed for
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