User`s guide

Modem Operation Explained 4-1
Chapter 4
Modem Operation Explained
This section describes in detail the operation of a number of the radio modem’s
configurable features.
Flow Control
The buffers in the radio modem and its flow control function permit serial
communications even if the speed differs between the computer (DTE) and the
modem DCE or between the radio modems (modem ports).
If there is a speed difference between the serial port and modem port (DTE speed and
radio throughput), the buffers in the radio modem may become full periodically.
Therefore communications speed is controlled so that data transmission and reception
is temporarily halted before the data exceeds the buffer capacity, and that
transmission is resumed when the receiving buffers have room. This is the flow
control function.
The radio modem has two kinds of flow control:
• Serial port flow control
• Modem port flow control
Computer (DTE) Radio Modem (DCE)
Receive
Transmit
Buffer
Buffer
Radio
Interface
Serial port
flow control
DTE<->DCE
Modem port
flow control
modem<->modem
Two kinds of radio modem flow control
- Serial port and Modem port
Serial Port Flow Control
Serial port data flow is controlled by the modem in its communication with a DTE
device.
If the serial port speed is higher than the modem port speed, the flow control function
sends a transmission halt request to the DTE before the buffers in the radio modem
are about to become full. When the buffers have room to receive data again, the
transmission halt request is cancelled and data transmission from the DTE device is
resumed.
User’s Guide