28
6193-3201
Fragmentation Threshold
The maximum transmission unit
(MTU) of data over the radio.
This selects the maximum number of bytes that
will be transmitted in one message. If more than
this number of bytes is input into the RM-90, the
module will transmit more than one message.
The default value is 500 bytes.
If fixed radio rates are configured, this value can
be increased and will reduce radio transmission
overhead. For 200Kbps and 100Kbps, the frag-
mentation threshold can be increased to 2000,
and at 38.4Kbps, to 1000. However if the radio
path is poor, or there is high radio interference,
increasing this value will decrease system per-
formance as the number of re-try messages will
increase.
If Ethernet traffic is only small packets sizes (ie
<300 bytes), an improvement in overall through-
put rate can be achieved by reducing MTU size.
This improvement is achieved through a reduc-
tion in the retry holdoff time required for units
in the system. As packets in the system are small-
er, 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 sustain-
able 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.
