User's Manual
Menus and Parameters
Operation and Administration
139
The range is 0 to 100 (%)
The default is 100 (%).
4.2.6.2.10.4 Per SU Distance Learning
The Per SU Distance Learning option defines the mode in which SUs calculate the
ACK timeout: based on the maximum cell distance or on the actual distance from
the AU.
When this feature is disabled, all SUs in the cell use for the calculation of the
ACK timeout the maximum cell distance; when enabled, each SU uses instead its
actual distance from the AU.
The options are Disable or Enable.
The default is Disable.
4.2.6.2.10.5 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 2 km.
4.2.6.2.11 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
section 4.2.6.5.2
) 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
(section 4.2.6.5.2) parameter in both units is
configured to 0 to disable the contention window back-off algorithm.