Alcatel-Lucent 7450 Quality Of Service Manual page 61

A RED slope itself is a graph with an X (horizontal) and Y (vertical) axis. The X-axis plots
the percentage of shared buffer average utilization, going from 0 to 100 percent. The Y-axis
plots the probability of packet discard marked as 0 to 1. The actual slope can be defined as
four sections in (X, Y) points
Plotting any value of shared buffer average utilization will result in a value for packet discard
probability from 0 to 1. Changing the values for start-avg, max-avg and max-prob allows the
adaptation of the RED slope to the needs of the access or network queues using the shared
portion of the buffer pool, including disabling the RED slope.
Quality of Service Guide
Figure 7: RED Slope Characteristics
Probability
1. Section A is (0, 0) to (start-avg, 0). This is the part of the slope that the packet discard
value is always zero, preventing the RED function from discarding packets when the
shared buffer average utilization falls between 0 and start-avg.
2. Section B is (start-avg, 0) to (max-avg, max-prob). This part of the slope describes a
linear slope where packet discard probability increases from zero to max-prob.
3. Section C is (max-avg, max-prob) to (max-avg, 1). This part of the slope describes
the instantaneous increase of packet discard probability from max-prob to one. A
packet discard probability of 1 results in an automatic discard of the packet.
4. Section D is (max-avg, 1) to (100%, 1). On this part of the slope, the shared buffer
average utilization value of max-avg to 100% results in a packet discard probability
of 1.
1
Max-Avg
.75
.50
Start-Avg
.25
A
0
0% 25% 50%
Average Utilization
(Figure 7):
QoS Policies
D
C
B
Max-Prob
75% 100%
OSSG020
61