Inalp Networks SmartWare Release 2.10, Software Configuration Manual

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Link Scheduler Configuration 125
Software Configuration Guide Release 2.10, Revision 1.00
transfers that last longer than simple web requests. In such a case there is a risk that TCP flow-
control might be ineffective. With RED configured the queue occasionally drops packets when the
Command Purpose
node (src)[ name ]#set ip dscp value
Defines the Differentiated Services Codepoint
value applied to packets of for the
selected
class or policy name . The range for value is from
0 to 63.
15.8.8 Specifying Layer 2 Marking
The IEEE ratified the 802.1p standard for traffic prioritization in response to the realization that
different traffic classes have different priority needs. This standard defines how network frames are
tagged with user priority levels ranging from 7 (highest priority) to 0 (lowest priority). 802.1p-
compliant network infrastructure devices, such as switches and routers, prioritize traffic delivery
according to the user priority tag, giving higher priority frames precedence over lower priority or
non-tagged frames. This means that time-critical data can receive preferential treatment over non-
time-critical data.
Under 802.1p, a 4-byte Tag Control Info (TCI) field is inserted in the Layer 2 header between the
Source Address and the MAC Client Type/Length field of an Ethernet Frame. Table 15-4 lists the tag
components.
Tag Control Field Description
Tagged Frame Type Interpretation Always set to 8100h for Ethernet frames (802.3ac tag
format)
3-Bit Priority Field (802.1p) Value from 0 to 7 representing user priority levels (7 is the
highest)
Canonical Always set to 0
12-Bit 802.1Q VLAN Identifier VLAN identification number
Table 15-4: Traffic Control Info (TCI) Field
802.1p-compliant infrastructure devices read the 3-bit user priority field and route the frame through
an internal buffer/queue mapped to the corresponding user priority level.
The command
set layer2 cos specifies the layer 2 marking applied to packets of this class by setting
the 3-bit priority field (802.1p). The no form of this command disables packet marking.
Procedure
Defining the 3-bit priority field (802.1p)
Mode
Source
Command Purpose
node (src)[ name ]#set layer2 cos value Defines the Class-Of-Service value applied to
packets of for the
selected class or policy name .
The range for value is from 0 to 7.
15.8.9 Defining Random Early Detection
The command random-detect is used random early detection (RED) for queues that carry lots of TCP