3Com 3C17203 - SuperStack 3 Switch 4400, Implementation Manual

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68 C
HAPTER
6: U
SING
T
RAFFIC
P
RIORITIZATION
not the egress port is tagged for that VLAN. If it is, then the new 802.1p
tag is used in the extended 802.1D header.
By default, the SuperStack 3 Switch 4400 SE supports a basic level of
QoS. To make advanced traffic prioritization available on the Switch 4400
SE, upgrade the product to the Switch 4400 SE Enhanced Software
Upgrade (3C17207).
The IEEE 802.1D standard specifies eight distinct levels of priority (0 to 7),
each of which relates to a particular type of traffic. The priority levels and
their traffic types are shown in
Figure 15 in order of increasing priority.
The mapping from 802.1p level to traffic queue in the Switch is
proprietary and is slightly different to the recommended IEEE mapping.
Figure 15 IEEE 802.1p priority levels and recommended IEEE 802.1D traffic
types
The number of queues and their mappings to the 8 levels is proprietary
and can even vary between Switches from the same vendor.
You cannot alter the mapping between the IEEE 802.1p priorities and the
traffic queues. These are calculated to be the most efficient, and are fixed
as illustrated in
Figure 15 .
Low Priority (Queue 1)
Ingress Port
High Priority (Queue 4)
Traffic Queues
Priority (Queue 2)
Priority (Queue 3)
Best Effort (Default)
Video and Business Critical
Voice
Network Control
Network Control 7
Voice 6
Video 5
Multimedia 4
Business Critical 3
Spare
2
Background 1
Best Effort 0
802.1D
Switch 4400
Egress Port
802.1p
Service Levels
Traffic
Classification