User guide

CS-GPRS Communications Package
8
7.2 Using systems with dynamic IP addresses
If you have a dynamic IP SIM (as is standard on most networks) you will not be
able to call out to the logger to start up the link for communication using
Loggernet. Instead you need to configure the datalogger to open a connection
back to the Loggernet PC which must have a public IP address (see firewall issues
below).
There are two ways of doing this.
1) using the Device Configuration program you can configure the logger to
automatically establish a socket connection on a remote system. It will do this as
soon as it is powered up and a PPP connection is established. It will try to open
the socket once per second, until successful. This is done by entering the IP
address and socket in the Net Services tab, as a Pakbus/TCP Server settings, as
shown above. This method is easy to setup and does not rely on the datalogger
program.
2) alternatively you can call the TCPOpen/TCPClose command in your program
at regular intervals (the speed determines how quickly the logger will re-establish
a broken link). In the TCPOpen command you need to give the public address of
the Loggernet server and the port you are going to connect on. This method is
only normally used where the logger needs to conserve power so the modem is not
on all of the time or more than four connections to different servers are required.
For either method the port (socket) number must match the call-back port number
entered in the setup screen of Loggernet (see below). You should also enable call-
back for the datalogger on the datalogger hardware tab. In versions of Loggernet
of 3.4 or above there is an extra setting in the setup screen (see below) called
“TCP Listen only”. This should be set when using dynamic, private IP addresses
to prevent Loggernet trying to call back out to the logger in some circumstances,
e.g. loss of a connection. This setting ensures Loggernet returns to a state of
waiting for another call-back as soon as possible.
When filling in this screen the settings for the Internet address and the IPPort on
the IPPort hardware screen are largely irrelevant as Loggernet cannot make new
outgoing calls to the logger as most dynamic IPs (assigned to the datalogger) do
not allow incoming connections. You should still add a valid IP and match the
port number to the Pakbus port number in the datalogger to prevent Loggernet
flagging errors. When a successful connection is made from a remote logger you
will see that Loggernet updates the IP address of the remote logger, as viewed in
the Setup screen. Do not expect to be able to make connections out to this address
though as it is normally the address of an intermediate router that is the barrier
between the private and public networks. If you have several systems with service
from the same airtime provider you will often find the same IP address shown for
several of different loggers.