D Traffic Classification - 3Com SuperStack 3 3812 Implementation Manual

54 C 6: U
HAPTER SING
802.1D traffic
classification
T M
RAFFIC ANAGEMENT
802.1D (classification is done at layer 2 of the OSI model).
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DiffServ code point (classification is done at layer 3 of the OSI model).
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IP Port (classification is done at layer 4 of the OSI model).
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These methods can be used together. If a packet is prioritized differently
by the two methods then it will be tagged with the higher priority.
At layer 2, a traffic service class is defined in 802.1Q frame, which is able
to carry VLAN identification and user priority information. The
information is carried in a header field immediately following the
destination MAC address, and Source MAC address.
802.1D Priority Levels
The traffic prioritization feature supported by the Switch at layer 2 is
compatible with the relevant sections of the IEEE 802.1D/D17 standard
(incorporating IEEE 802.1p). Once a packet has been classified, the level
of service relevant to that type of packet is applied to it.
The 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
You cannot alter the mapping of priority levels 0 - 7 to the traffic queues.
These priority levels are fixed to the traffic queues as shown in
Figure 12 in order of increasing priority.
Figure 12.