Extreme Networks PoS Installation And User Manual page 100

Configuring the PoS Module
The drop probability is specified as a percentage, where the
integer in the range from 1 to 100.
Weighted RED (WRED) functionality is supported through two different drop
probabilities: a low-drop-probability and a high-drop-probability. The DiffServ code
points of IP packets indicate whether the packet should be dropped with low
probability or high probability, and the appropriate percentage is then applied if WRED
is active.
WRED is applied only to IP packets. The
command gives you complete flexibility in assigning DSCPs to the
code-point
two different drop-probability levels. This configured mapping of DSCPs to
drop-probability levels is used by WRED even if
disabled on the port.
The
drop-probability
for both the low and high drop-probabilities. This effectively disables WRED and
reverts to standard RED operation. For SONET ports, both the low and high
drop-probabilities default to 10%.
The role of the configured drop probability in RED operation on SONET ports is
illustrated in Figure 3-8A. RED is active when the average queue length is between the
minimum and maximum thresholds. In this region, the probability that a given packet
is dropped increases in a straight line up to the configured drop probability at the
maximum threshold. All packets are dropped when the average queue length exceeds
the maximum threshold.
The operation of WRED on SONET ports is depicted in Figure 3-8B. In this case, the
drop probability depends not only on the average queue length, but also upon whether
the DSCP indicates that the packet should be dropped with a low or high probability,
which is to say, the DSCP of the packet controls which curve is used.
3-52
keyword indicates that the specified percentage should be used
parameter is an
percent
config diffserv examination
diffserv examination
Packet Over SONET Module Installation and User Guide
is