TS4000 Radio Modem User’s Manual AirNet Packet Protocol 44
Configuration Parameter Setting
CSMA MAC Setup-Data Pkts-Min Idle Slots Number of slots for an outbound polling
packet
Number of slots for an outbound polling packet = Packet Transmit Time / Slot Time
Packet Transmit Time = [9 * Max Outbound Message Length (in bytes) * Overhead / Air Rate (in
kbps)] + Radio Tx Attack Time (in ms)
Overhead = 1 if Coding (FEC) is Unchecked
Overhead = 1.5 if Coding (FEC) is Checked
Slot Time = 1.5 * Radio Transmit Attack Time
Example:
Max Message Length for Modbus protocol = 255 bytes
Radio Tx Attack Time = 20ms (this value can be read on the Radio Hardware Screen)
Air Rate = 9.6 kbps (this is configured on the Radio tab)
Coding = Unchecked (this is configured on the radio tab)
Slot Time = 1.5 * 20ms = 30ms (this is configured on the Packet General tab)
Packet Transmit Time = [9 * 255 * 1 / 9.6] + 20 = 259ms
Number of slot for an outbound polling packet = 259/30 = 9 (rounded up from 8.6) (this value must
always be round up)
To Next Page