Campbell COM110A User Manual Download

Page: 20 / 76

CS-GSM/GPRS Digital Transceiver Kits (including the COM110A modem)

enabled and any 3G compatibility does not slow down the log-on process to the
network (which has been seen on UK O2 networks).

When buying a contract for GPRS the standard offering in Europe is for a
connection where you are allocated a dynamic, private IP address.  This can be
used with Campbell dataloggers and is often the cheapest way to get a system up
and running.  However, when operating in this way you can only have a limited
numbers of PCs or loggers connected to one logger and you lose some of  the ftp
server, http and some other functions as the logger cannot accept unsolicited calls
made to it because it is on a private network behind a firewall.

For full flexibility specialist suppliers provide a service to give individual devices
a fixed IP address, which can either be private (accessed via a VPN connection) or
a public address on the internet.  In the UK the suppliers include Wireless Logic,
Wireless Innovation Ltd and Wyless.net. Such companies are suitable for larger
scale networks and provide additional on-line tools to let you monitor the state of
your GPRS connections, traffic use etc.  Alternative suppliers can be found by
searching for “Fixed IP SIM” on the internet making sure the offering is not a 3G
only card.  Currently Campbell Scientific Ltd only offers SIM cards as part of a
subscription to its Konect data service..

It is important to ensure you are aware of the likely costs of GPRS data transfer.
Prices can range from £0.005 to £10.00 per Megabyte of data transferred.  As it
can require in excess of 50 Kbytes of data per day to check and keep a GPRS
connection open, let alone transfer any data, it is important to find the right tariff
and realise the likely costs.  Where an always on connection is required, a flat-rate
tariff will likely be more economic or you should at least negotiate a volume
discount tariff with your provider.  In the UK it is now possible to buy data only
access for few GBP per month for several tens of MB data transfer.

Before using the system you need to know the APN server name of your provider,
plus your username and password to gain access to the GPRS IP services.

5.3 GPRS Modes of operation

5.3.1 Using systems with fixed IP addresses

If you have a fixed IP service it may be either with routing to a public internet
address or to a private fixed IP address that you connect to via a VPN tunnel.

If it is via a VPN tunnel please seek the advice from the SIM provider on how to
setup and use the VPN tunnel. The tunnel will need to be open and kept open
automatically if you wish to use Loggernet to call the logger automatically.

With a fixed IP address, once connected to the network the logger will be able to
accept incoming connections for the services you have enabled, e.g. Pakbus, ftp,
http. If you connect to the logger for normal datalogger communications (via the
Pakbus/TCP service port) the datalogger will automatically start to send beacon
messages once per minute to the device that called. This will hold the connection
open (which is useful as some GPRS providers will cut-off inactive connections)
and also ensures the connection is working, however this does incur data traffic
charges. (See the help within Loggernet for connecting via an IP port – the port
number must match that set for the Pakbus/TCP Service port set in the logger.)

With a fixed IP address, Loggernet should be able to call out to the logger on
demand so it is possible to setup scheduled data collection. To minimise data
charges you can prevent the extra traffic outside the scheduled calls by unchecking
the box on the Pakbus port that forces it to stay open.