3Com NJ220 - IntelliJack Switch Features Manual - Page 9

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3Com NJ220 - IntelliJack Switch Features Manual
3 C O M
®
N J 2 0 5 I N T E L L I J A C K
Traffic Prioritization
Configuration and Setup
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.
How the LAN port handles traffic coming from the LAN
NO
802.1 Priority Tag Set?
Do not modify
Do not modify
tag information
tag information
Forward frame
to PAN port
™
S W I T C H — 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

Setting Priority Tag Values

The first step in configuring a traffic prioritization scheme is to ensure that the NJ205
IntelliJack Switch 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. NJ205 IntelliJack Switch 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
0 or 1
2 or 3
4 or 5
6 or 7
Inspect
Ethernet
frame
YES
NO
YES
Ingress rule set
to add tag?
Remove all tag
information
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.)
Priority Value
0
2
4
6
How the LAN port handles traffic coming from the PAN
Inspect
Ethernet
frame
NO
802.1 Priority Tag Set?
YES
NO
Egress rule set
to add tag?
Add priority tag
Do not modify
information
tag information
YES
Do not modify
tag information
Forward frame
to PAN port
9