User's Manual

Chapter 4 - Operation and Administration
BreezeACCESSS VL System Manual
4-56
Fairness Factor
The Fairness Factor enables to define the level of fairness in providing
services to different SU. When set to 100%, all SUs have the same
probability of getting services when competing for bandwidth. If set to
X%, than SUs located up to X% of the maximum distance from the AU
will have advantage in getting services over SUs located farther than
this distance.
The range is 0 to 100 (%)
The default is 100 (%).
Show Cell Distance Parameters
Select Show Cell Distance Parameters to view the Cell Distance
parameters. In addition, the Measured Maximum Cell Distance and the
MAC address of the unit that the mechanism found to be the farthest
from the AU are displayed. A distance of 1 km means any distance
below 2km.
Arbitration Inter-Frame Spacing (AIFS)
The time interval between two consecutive transmissions of frames is
called Inter-Frame Spacing (IFS). This is the time during which the unit
determines whether the medium is idle using the carrier sense
mechanism. The IFS depends on the type of the next frame to be
transmitted, as follows:
! SIFS (Short Inter-Frame Spacing) is used for certain frames that
should be transmitted immediately, such as ACK and CTS frames.
The value of SIFS is 16 microseconds.
! DIFS (Distributed coordination function Inter-Frame Spacing) is
typically used for other frame types when the medium is free. If the
unit decides that the medium is not free, it will defer transmission
by DIFS plus a number of time slots as determined by the
Contention Window back-off algorithm (see Minimum Contention
Window on page 4-77) after reaching a decision that the medium
has become free.
DIFS equal SIFS plus AIFS, where AIFS can be configured to one or two
time slots. Typically AIFS should be configured to two time slots. A
value of 1 should only be used in one of the two units in a point-to-
point link, where in the other unit the AIFS remains configured to two
time slots. This ensures that the unit with AIFS configured to one has
an advantage over the other unit, provided that the Minimum
Contention Window parameter (see page 4-77) in both units is
configured to 0 to disable the contention window back-off algorithm.