Menus and Parameters
Operation and Administration
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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.
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 0) after reaching a decision that the medium has become free.
DIFS equal SIFS plus AIFS, where AIFS can be configured to a value from 1 to 50
time slots. A unit with a lower AIFS has an advantage over units with a higher
AIFS, since it has a better chance to gain access to limited wireless link
resources. 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 0) parameter in both units is
configured to 0 to disable the contention window back-off algorithm.
NOTE
The AIFS parameter is not applicable when the Wireless Link Prioritization Option is enabled.
The available range is from 1 to 50 (time slots).
The default is 2 time slots.
CAUTION
An AIFS value of 1 should only be used in point-to-point applications (when the Wireless Link
Prioritization Option is enabled). Otherwise the default value of 2 must always be used. In a point-
to-point link, only one unit should be configured to an AIFS value of 1. When both units need to
transmit, the unit with an AIFS value of 1 will have an advantage over the unit with AIFS of 2. In this
case, the Minimum Contention Window parameter in both units must be configured to 0 to disable
the contention window back-off algorithm.