User`s guide

A receiving modem, upon receipt of a connect request, will send a connect
acknowledgement to complete the link establishment phase. Once the
communications link has been set up, data can then be exchanged between the Radio
Modems. After no activity between the Radio Modems for a short period, both
modems send a disconnect request message.
DAck
DAck
DAck
CReq
CAck
DTE RM-232 RM-232 DTE
Lin
k
set-up
Data
transfer
Lin
k
clearing
DReq
Data
Data
Data
Data to
RM-232
Data from
RM-232
Data to
RM-232
Data from
RM-232
Short delay…
CReq = Connection Request Data = Data packet
CAck = Connection ACK DAck = Data ACK
DReq = Disconnect Request
Link connection and data transfer operation
in point-to-point mode
Each packet of data is assembled with a destination address, site code, a sequence
ID and a checksum value. When a Radio Modem receives a data packet the address
and site code are checked, if a match occurs the packet data is further processed. A
received data packet is discarded if there is no match with the unit address and site
code.
Type+hop+seq Unit/site code …Data Bytes… Checksum
Data packet ready for transmission
Before valid received data is sent to the attached host device (via the serial port), the
Radio Modem will validate the checksum and packet sequence number. Provided
these checks are valid, the packet data is sent to the serial output buffer in the Radio
Modem and a packet acknowledgement message (ACK) is transmitted. If the received
data packet is either corrupted or out of sequence the receiving Radio Modem will
ignore the packet.
If the source Radio Modem does not receive an ACK message within a given period of
time, the data packet is resent. The packet will be resent for a user configurable
number of attempts (configuration command word retry). If after exceeding the
User’s Guide Modem Operation Explained 4-6