User manual

Chapter Three Operation
Page 35 March 2010
improvement in overall throughput rate can be achieved by reducing
MTU size. This improvement is achieved through a reduction in the
retry holdoff time required for units in the system. As packets in the
system are smaller, units will holdoff for shorter periods of time and
be confident that their retry transmission will not cause interference
with other units.
RSSI Threshold
The received signal
strength level at which
beacons from Access
Points are to be ignored.
This should be used to prevent Clients and Access Points
establishing links beyond a sustainable range.
The default value is set below the noise floor at -150 dBm. This
allows all messages received to be processed.
If a value of –90 is entered, any beacons weaker than –90dBm will
be ignored, resulting in the link eventually resetting if the radio path
continues at less than –90.
Contention Window Size This configurable parameter was introduced in firmware V1.18
This field sets the number of transmission slots available for usage
by Clients. Each Client in the system has an individual time slot, to
reduce radio communications clash. This field can be set to optimise
throughput for particular applications.
When set to zero, this field is automatically adjusted by the Access
Point. When there is only one Client connected to an Access Point,
this is automatically set to 1. Contention Window Size will increase
with each additional Client in the system. Contention Window size
will increase to a maximum size of 7 - for more than 7 Clients, slots
are reused.
If making adjustment to this field, leave Clients set to automatic, and
adjust the value at the Access Point. If traffic within the system is
usually only directed at a single Client at a time (such as a master
device polling slave devices), there is some advantage in overall
system speed by setting the Contention Window Size low to perhaps
1 or 2.
Frequency Fallback
Probation Counter
When data rate is reduced automatically on a particular frequency
due to poor signal, the module may attempt to increase back to the
higher rate after the specified number of successful transmissions has
been made on that particular frequency. Before increasing rate on a
particular frequency, the Global Fallback Probation Counter must be
met also.
Global Fallback
Probation Counter
When data rate is reduced automatically due to poor signal, the
module may attempt to increase back to the higher rate after the
specified number of successful transmissions have been made.
Before increasing rate on a particular frequency, the Frequency