High Performance Two Port 10/100 Managed Ethernet Switch with 32-Bit Non-PCI CPU Interface
Datasheet
6.4.3
Transmit 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.
Packet is from Host
Packet is Tagged
Packet is IPv4
Packet is IP
VL Higher Priority
Use Precedence
Use IP
VLAN Enable
ALR Static Bit
DA Highest Priority
6b
IPv4(TOS)
IPv6(TC)
programmable
DIFFSERV table
3b
3b
programmable
Traffic Class
table
IPv4 Precedence
2b
priority
calculation
static DA
override
priority queue
3b
programmable
port default
table
2b
Source Port
3b
programmable
Priority
Regeneration
3b
VLAN Priority
ALR Priority
table
per port
2b
Figure 6.4 Switch Engine Transmit Queue Selection
SMSC LAN9312
Revision 1.2 (04-08-08)
DATA6S7HEET
SMSC [ SMSC CORPORATION ]
