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GPRS Session Protocol
GPRS follows a protocol when sending self-timed and alarm transmissions that permits
the server to issue commands. This protocol is often referred to as, “Session Type 0”. The
protocol helps support communications to a device which has a non-routable IP address,
as many IP cell modems provide. Session Type 0 does not apply to SSP transmissions.
The following is a description of the protocol:
Course of Events
1. Logger connects to Main or Backup Server
2. Logger sends Session Type Code<cr> (see below)
3. Logger sends StationName<cr>
4. Logger sends Report Type Code<cr> to indicate purpose of connection (see
below)
5. Logger sends scheduled (or alarm) transmission data (if any)
6. Logger sends ETX (0x03) to mark end of data
7. Logger sends a 3 byte pseudobinary encoded CRC16 of previous data and a
shared secret
8. Server sends user login command, !login=username,password<cr> and waits for
logger reply (ETX)
9. If user login matches, logger enters command-line session (see operational details,
below)
10. Server issues pending commands, and Logger processes and responds accordingly
11. When command processing complete, the Server disconnects
Session Type Code
"Session type" defines the processing that occurs on connection. Currently, there is only
one session type, "0". This type is defined by the Course of Events above, and details that
follow.
"0" = defined by Course of Events, above
Report Type Code
“Report Type code” describes the purpose of the transmission:
"0" = self-timed
"2" = entering alarm
"4" = exiting alarm
"6" = no data, command session only
Command-line Session Details
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