Datasheet

INSYS GPRS 5.0 Ethernet GPRS General
Dez-06 53
IP Addresses/Accessibility
The IP address of the GPRS end device is dynamically allocated by the provider and
is temporary, i.e. during the next dialup at the provider a new IP address is allo-
cated.
In many GPRS networks the IP address can not be accessed from outside (routing-
enabled), as the providers perform the addressing for the switch from GPRS net-
works to the “normal Internet” via a NAT table (Network Address Translation).
This also provides a security aspect, as the GPRS device is not accessible by so-
called "scanners" because the IP address can not be accessed. As GPRS is billed by
the amount of data, this prevents unwanted and costly data traffic.
This also means that the following functions may not be possible:
 Pinging the GPRS device from outside
 Establishing TCP/IP connections to the GPRS device from outside
 Sending UDP/IP packets to the GPRS device from outside
All connections (channels) must be opened starting with the GPRS device. This
means that the GPRS device or the Ethernet device behind it can only react as Cli-
ent.
Exceptions to this restriction will be provided by the according provider, if avail-
able. Please also contact your provider to clarify if it is possible to use a VPN (Vir-
tual Private Network) for possibly required server functionality.
The GPRS provider mdex offers a service called “fixed.IP”. This service features a
fixed IP address for each SIM card (at the moment only possible for SIM cards
from T-mobile and Vodafone) and a secure connection to the device over the
internet via a VPN tunnel. For further information contact mdex at
http://www.mdex.eu.