3 C O M
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N J 2 0 0 N E T W O R K J A C K — V L A N S & T R A F F I C P R I O R I T I Z AT I O N
9
Setting Priority Tag Values
The first step in configuring a traffic prioritization scheme is to ensure that the NJ200
Network Jack recognizes the priority tags as traffic passes through the switch. As with
the VLAN scheme, the switch can be configured to add tags, remove tags, or leave
frames unmodified.
As mentioned in the previous section, the IEEE 802.1D/p standard specifies eight dis-
tinct levels of priority (0 through 7), each of which relates to a particular type (class) of
traffic. The NJ200 Network Jack pairs up the eight tag values into four priority levels,
to match the available traffic queues. Each priority level is determined by the lower
value of each tag-value pair as follows:
Table 4.
IEEE 802.1D/p Tags and Switch Values
Tag Pair
Priority Value
0 or 1
0
2 or 3
2
4 or 5
4
6 or 7
6
Traffic Prioritization
Configuration and Setup
YES
YES
NO
NO
NO
NO
YES
YES
Inspect
Ethernet
frame
Inspect
Ethernet
frame
802.1 Priority Tag Set?
802.1 Priority Tag Set?
Egress rule set
to add tag?
Ingress rule set
to add tag?
Do not modify
tag information
Forward frame
to PAN port
Forward frame
to PAN port
Add priority tag
information
Remove all tag
information
Do not modify
tag information
Do not modify
tag information
Do not modify
tag information
Figure 6.
The ingress mode is applied to prioritized
traffic coming from the LAN before they are sent
downstream to the PAN ports. The egress mode is
applied to prioritzed traffic coming from the PAN
ports before they are sent upstream to the LAN.
The traffic prioritization process is similar to that of the VLAN scheme. The switch
applies ingress rules at the receiving-port buffer and egress rules at the transmitting
port buffer. (Figure 6.)
How the LAN port handles traffic coming from the LAN
How the LAN port handles traffic coming from the PAN