Traffic Management for the Available Bit Rate (ABR) Service in ...

Figure 6.4: Linear functions for ERICA+
A step function which reduces the capacity in steps (down to the cuto value)
as the queueing delay exceeds thresholds is a possible choice. This is shown in g-
ure 6.3. Linear segments as shown in gure 6.4 can be used in place of step functions.
Hysteresis thresholds ( gure 6.5) can be used in place of using a single threshold to
increase and decrease the capacity. Hysteresis implies that we use one threshold to
increase the capacity and another to decrease the capacity. However, these functions
require the use of multiple thresholds (multiple parameters). Further, the thresholds
are points of discontinuity, i.e., the feedback given to the source will be very di erent
if the system is on the opposite sides of the threshold. Since queueing delay is a highly
variant quantity, the thresholds and experience is required to choose these di erent
parameters.
However, it is possible to have a function with just 2 parameters, one for the
two ranges: (0, Q0) and (Q0, in nity) respectively. The rectangular hyperbolic and
the negative exponential functions are good choices to provide the aggressive control
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