Specifying Layer 2 Marking; Defining Random Early Detection - Patton electronics SmartNode Series Software Configuration Manual

13 • Link scheduler configuration
The command set ip dscp sets the DS field applied to packets of the class name. Shaping may be applied to
make the class conformant. The no form of this command disables packet marking.
This procedure describes defining the codepoints in the DS field
Mode: Source
Command
node (src)[ name ]#set ip dscp value

Specifying layer 2 marking

The IEEE ratified the 802.1p standard for traffic prioritization in response to the realization that different traf-
fic 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 pref-
erential 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 11 lists the tag components.
Tag Control Field
Tagged Frame Type Interpretation
3-Bit Priority Field (802.1p)
Canonical
12-Bit 802.1Q VLAN Identifier
802.1p-compliant infrastructure devices read the 3-bit user priority field and route the frame through an inter-
nal 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.
This procedure describes defining the 3-bit priority field (802.1p)
Mode: Source
Command
node (src)[ name ]#set layer2 cos value Defines the Class-Of-Service value applied to packets of for the
Defining random early detection
The command random-detect is used random early detection (RED) for queues that carry lots of TCP trans-
fers that last longer than simple web requests. In such a case there is a risk that TCP flow-control might be inef-
fective. With RED configured the queue occasionally drops packets when the queue has grown over half the
154
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.
Table 11. Traffic control info (TCI) field
Always set to 8100h for Ethernet frames (802.3ac tag format)
Value from 0 to 7 representing user priority levels (7 is the highest)
Always set to 0
VLAN identification number
selected class or policy name . The range for value is from 0 to 7.
SmartWare Software Configuration Guide
Purpose
Description
Purpose
Link scheduler configuration task list