High Performance Two Port 10/100 Managed Ethernet Switch with
Datasheet
6.4.3Transmit Priority Queue Selection
The transmit priority queue may be selected from five options. As shown in Figure 6.4, the priority may be based on:
the static value for the destination address in the ALR table
the precedence bits in the IPv4 TOS octet
the DIFFSERV mapping table indexed by the IPv4 TOS octet or the IPv6 Traffic Class octet
the VLAN tag priority field using the per port Priority Regeneration table
the port default
The last four options listed are sent through the Traffic Class table which maps the selected priority to one of the four output queues. The static value from the ALR table directly specifies the queue.
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| Packet is from Host |
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| Packet is Tagged |
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| Packet is IPv 4 |
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| Packet is IP |
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| VL Higher Priority |
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| Use Precedence |
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| Use IP |
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IPv4(TOS) | 6b |
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| VLAN Enable |
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| ALR Static Bit |
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| programmable |
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| DA Highest Priority |
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IPv6(TC) |
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| DIFFSERV table |
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IPv4 Precedence |
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| 3b |
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| priority |
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| 3b |
| calculation |
| Traffic Class |
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Source Port |
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| programmable |
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| port default |
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| table |
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| 3b |
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VLAN Priority |
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| Priority |
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| Regeneration |
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| table |
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| per port |
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ALR Priority |
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Figure 6.4 Switch Engine Transmit Queue Selection
SMSC LAN9312 | 67 | Revision 1.4 |
| DATASHEET |
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