Enhanced Red Support - Extreme Networks BlackDiamond 6800 Installation And User Manual

Configuring the ATM Module
Resetting DiffServ Code Point Mapping Tables
To reset the DSCP mapping tables for a specified ATM port to their default values, use
the following command:
unconfig diffserv dscp-mapping ports <portlist>
Replacing DiffServ Code Points
To replace DiffServ code points, you must use the following command to enable
DiffServ replacement:
enable diffserv replacement ports [<portlist> | all]
You then change the 802.1p priority to DiffServ code point mapping to any code point
value using the following command:
config diffserv replacement priority <vpri> code_point <code_point>
ports [<portlist> | all]
By doing so, the hardware queue used to transmit a packet determines the DiffServ
value replaced in the IP packet.
To verify the DiffServ configuration, use the command:
show ports <portlist> info detail

Enhanced RED Support

Random Early Detection (RED) is a congestion avoidance mechanism. The basic idea
behind RED is that most data transports detect packet loss and will, therefore, restrain
transmission—if only temporarily—when they detect dropped packets. Consequently, if
the switch needs to signal another device to slow transmission due to congestion, RED
provides a way of intelligently dropping packets.
This section describes the changes and additions to ExtremeWare to support RED in
conjunction with ATM modules that have IP frames encapsulated in bridged or routed
protocols. The Extreme implementation of RED combines the functions of the RED
algorithm with IP precedence to provide support for preferential traffic handling for
higher-priority packets. This implementation provides weighted RED (WRED)
functionality through two packet-drop probabilities (described below), so that a device
can selectively drop lower-priority traffic when an interface begins to show signs of
congestion. This capability is combined with DiffServ attributes to allow you to tailor
performance characteristics for different classes of service.
3-36 Asynchronous Transfer Mode (ATM) Module Installation and User Guide