Rf Optimizations/Mac Advanced Settings - CalAmp Viper 100 User Manual

4.4.1 RF OPTIMIZATIONS/MAC ADVANCED SETTINGS

Figure 25 – Setup(Advanced)RF Optimizations/MAC Advanced Settings
― Duplicates Detection Period. Enter a value from 1000 to 15000 to specify the time period (in milliseconds) Default
= 5000 ms. Viper will look for a duplicate message being sent, such as control and relay messages. If a duplicate
message is detected it will not be forwarded. Certain protocols such as Modbus cannot tolerate hearing duplicate
messages (echoes). The duplicate messages will not be sent to the Serial ports or forwarded to the Ethernet
connection. Larger values should be used for lower over-the-air (OTA) speeds and longer path networks.
― Retries. Default = 1. Enter a value to specify the number of times the MAC layer will try to resend a packet if the unit
does not receive an acknowledgement reply from the receiving device. Increasing the retries may improve marginal RF
paths. For this field to be active, Viper must be programmed for RF Acknowledgments Enabled as shown in Section
4.4.4.
― RTS Threshold. Default = 128. Viper utilizes the FAMA-NCS (for floor acquisition multiple access with non-persistent
carrier sensing) protocol. The FAMA-NCS protocol tries to assure that a single Viper is able to send data packets free of
collisions to a given receiver at any given time. FAMA-NCS is based on a three-way handshake between the sender and
receiver in which the sender uses non-persistent carrier sensing to transmit a request-to-send (RTS) and the receiver
sends a clear-to-send (CTS). RTS/CTS handshaking protocol enables the Viper SC network to avoid collisions in networks
with multiple coverage areas. Before transmitting an RTS frame, a Viper SC listens to the channel to determine if it is
already in use. If the channel is busy, the unit calculates a random back off period to wait before sensing the channel
again. The RTS threshold parameter specifies how large a packet must be before the unit will use RTS/CTS handshaking
in the over-the-air protocol. A value of 0 means the Viper SC will always use over-the-air RTS/CTS handshaking. A value
equal to the RF_MTU (OTA maximum transmit unit) means the Viper SC will never use RTS/CTS handshaking. A value of
128 means the Viper SC will use RTS/CTS for packets larger than 128 bytes. Note: This value should not be confused
with RTS/CTS for RS232 Serial ports.
― Carrier Sense Level Threshold. Default = -110 dBm. The threshold Viper uses to determine whether a received RF signal
is a valid message or unwanted noise. If RF level above threshold is detected, Viper will not transmit data. Signals are
received and decoded. Outgoing data is buffered until the channel becomes available. Threshold may be raised to
prevent false detection in noisy environments or lowered to gain extra receive sensitivity. Lower thresholds should only
be used when ambient RF noise is very low. Receive sensitivity depends upon the channel bandwidth/speed being
used. Refer to Product Specifications for Carrier Sense by model.
― Listen Before Transmit. Default = Enabled (listen to noise and data).
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