ELPRO 805U-E Uživatelský manuál stáhnout pdf (Strana 32)

805U-E Wireless Ethernet User Manual

Man_805U-E Rev 1.5 Page 32

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

The number of time slots

allocated by the Access

Point.

The Access Point allocates a “time slot” to each Client, to minimise

transmission contention between Clients. Each Client can only transmit

during its allocated time slot. The width of each time slot varies from

7msec to 12 msec depending on the Beacon time – the time slot is

5msec at the shortest Beacon and 12 msec at the longest beacon.

The number of time slots can be manually set (1 to 8) or a value of zero

(default) allows the Access Point to automatically determine the

number of time slots, which it does based on the number of Clients

connected. If there are more than 8 Clients, then more than one Client

is allocated to some time slots.

In a large system where there is inherently little transmission overlap

(such as in a polling system), then manually setting the Contention

Window size to a smaller number than 8 will increase the overall data

rate.

Duty Cycle Alarm

Threshold

Duty cycle alarm

activation point

In CE countries, the 869.4 MHz 500mW band has a regulated transmit

duty factor of 10%. The Access Point calculates the system duty cycle

and will set an internal alarm flag if the actual duty cycle exceeds this

parameter. Refer to more information on Duty Cycle calculations at the

end of this section.

The internal alarm flag can be configured to drop to wireless link or to

set the digital output channel (refer Digital I/O configuration).

Default value is 10%.

Duty Cycle Alarm

Minimum

The internal alarm flag will reset when the actual duty cycle drops

below this value - default value is 9%.

Duty Interval The time period over which the duty cycle is calculated - default is 60

minutes

Current Duty Cycle

Achieved

A display of the current duty cycle value.

Drop Radio Link on Duty

Cycle Alarm

Allows the internal duty cycle alarm to force the Access Point to reduce

radio activity. The Access Point will disassociate from all Client units

and will not allow re-association until the duty cycle alarm resets.

Default value is “not selected”.

Fallback Probation When data rate is reduced automatically due to poor signal, the

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