Operation
RFI-9256 Radio Modem User Manual
Page 33 of 109
5.3 Protocol Operation
The protocol mode of a serial port determines how the serial port data is interpreted and converted into
packets for transmission over the air. There are four basic protocol modes:
Point-to-point Protocol:
Communications occurs between two radios only.
Broadcast Protocol:
Communications occurs between the master and any number of slaves, and
any slave back to the master. Data is broadcast from the master to all slaves, while the slave only
transmits data directly back to the master.
Hayes Dial-up Protocol:
Communications occurs between a master and any number of slaves one
at a time, where Hayes dialling commands are used to create and destroy connections.
SCADA Protocols:
Communications occurs using SCADA communications protocols such as
Modbus, Honeywell, DNP3, or TDE.
All protocol modes support back-to-back repeaters for extending network coverage.
5.3.1 Point-to-point Protocol
A point-to-point network establishes a link between two radio radios, through an optional number of
repeaters. A point-to-point connection can be established on the main, auxiliary, or both serial ports.
A single master unit and a single slave unit are configured such that:
They have the same hopping pattern, network address, and security code.
The master and slave have different local addresses.
Both the master and slave have the point-to-point protocol selected on their main and/or auxiliary
serial port.
The point-to-point destination address on the slave is set to the master’s local address, while the
point-to-point destination address on the master is set to the slave’s local address.
This results in a connection being established between the two units. The network link, carrier detect and
online LED should turn green on both units, and data transmitted by the DTE on the master be received on
the DTE on the slave, and vice versa.
5.3.2 Broadcast Protocol
In a point-to-multipoint broadcast network, data transmitted by the master unit is output by all the slaves,
while data transmitted by each slave is only output by the master.
When using point-to-multipoint broadcast mode, there are no acknowledgments on the master to slave
transactions. This is because multiple slaves may be receiving the data, and if they were to all attempt to
acknowledge the transmission they would interfere with each other.
Instead of acknowledgements, the master will transmit each message a fixed number of times equal to the
maximum retries. For this reason, the number of retries used in a broadcast network should be configured to
between 1 and 5 in order to maintain a reasonable throughput.
Main -> Protocol
Main -> Protocol
Main -> Protocol
