Intel 480T, Руководство пользователя

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C H A P T E R 8 Quality of Service (QoS)
137
Explicit Class of Service (802.1p and
Differentiated Services) Traffic Groupings
This category of traffic groupings describes what is sometimes
referred to as
explicit packet marking, and refers to information
contained within a packet that is intended to explicitly determine a
class of service. This includes the following:
• IP Differentiated Services (DiffServ) code points, also known as
IP TOS bits
• Prioritization bits used in IEEE 802.1p packets
An advantage of explicit packet marking is that the class of service
information can be carried throughout the network infrastructure,
without repeating what may be complex traffic grouping policies at
each switch location. Another advantage is that end stations can
perform their own packet marking on an application-specific basis.
The 480T switch can observe and manipulate packet marking
information with no performance penalty.
The documented capabilities for 802.1p priority markings or
DiffServ capabilities are not impacted by the switching or routing
configuration of the switch. For example, 802.1p information may
be preserved across a routed switch boundary and DiffServ code
points may be observed or overwritten across a layer 2 switch
boundary.
Configuring 802.1p Priority
The switch supports the standard 802.1p priority bits that are part of
a tagged Ethernet packet. The 802.1p bits can be used to prioritize
the packet, and assign it to a particular QoS profile.
When a packet arrives at the switch, the 802.1p priority field is
examined, and can be mapped to a specific hardware queue when
subsequently transmitting the packet. The 802.1p priority field is
located directly following the 802.1Q type field, and preceding the
802.1Q VLAN ID, as shown in Figure 14.