User guide

CS-GPRS Communications Package
10
every 30 minutes or set up another process, e.g. low frequency pinging, to keep
the connection active.
It should be noted that when you download a program to the datalogger via a
TCP/IP connection, the datalogger will reset that connection as part of the process
of compiling the program. This will cause it to drop the PPP connection for some
tens of seconds. This process should not be evident from a user standpoint as
Loggernet should wait long enough for this to take place so should not report an
error in most instances.
7.4 Firewall Issues
When using either of the above call-back methods you need to have the Loggernet
PC either be directly attached to the internet with its own public IP, or be behind a
router that forwards incoming calls to specific ports onto the Loggernet PC. With
some airtime providers you might also be able to setup a private network
connection (or VPN) to the Loggernet PC to avoid it being on the public network.
In addition to allow incoming connections to that PC you will need to open up
“holes” in any firewalls running on the PC or external routers to allow incoming
connections to the call-back sockets and outgoing responses from those sockets.
If using a PC running Windows XP with SP2/SP3 or Vista as the Loggernet server
you will as a minimum need to check the Firewall settings, via the advanced
setting, add Exception rules for the incoming port numbers you wish to allow
dataloggers to call back in on.
If you have a PC that can make connections out to the internet you can test
firewalls by using a PC to make a connection to Loggernet using Start, Run, cmd
<enter> and then type
telnet n.n.n.n port <enter>
Where n.n.n.n is the public IP address of the LN server and port is the callback
port. You can also try this directly from another PC on the public internet. When
you run this a black telnet window should appear on the screen and say connected
in the top bar. You should also see messages in Loggernet’s logfile indicating
something has connected to LN on a particular socket (which it is listening on). It
will eventually timeout (as you cannot emulate logger speak). If the telnet box
flashes on the screen or generates an error message in the top bar it is likely one or
more of the firewall, router or Loggernet are setup incorrectly.
7.5 Minimising call costs and power use
Because the process of keeping the connection alive involves significant data
traffic which will cost money and also power, it may be desirable to shutdown the
PPP connection for periods (and shut off the power to modem too). This can be
done by including the command PPPClose in the datalogger program to prevent it
dialling and PPPOpen to restart dialling. Power control of the modem can be
done in the conventional way after the PPPClose command is executed and a
delay of 10 s allowed letting the shutdown finish cleanly. When shutting down
the modem it is important to deregister the modem from the network before
turning off the power. This is usually done by sending a command AT+CFUN=0
to the modem and waiting at least 2 seconds before turning off the power. Failure
to do this may result in subsequent connections to the network being refused for
prolonged periods or the modem even being barred from the network if this is
done frequently.