insys icom GPRS 5.1, Руководство пользователя, Страница: 78 / 102

GSM, GPRS, and EDGE General INSYS GPRS 5.1 serial
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8.4 IP Addresses/Accessibility
The IP address of the GPRS terminal is dynamically allocated by the provider and
therefore only temporary. During the next dialin at the provider, a new IP address
is allocated.
In almost all GPRS networks the IP address can not be accessed from outside as
the providers perform the addressing for the switch from GPRS networks to the
“normal Internet” via a NAT table (Network Address Translation) to manage the
address area limited by IPV4.
These firewalls prevent the GPRS device or its IP address from being accessed by
so-called "scanners". As GPRS is billed by the amount of data, this prevents un-
wanted 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 application behind it can only react as CLIENT.
Exceptions to this restriction will be provided by the according provider, if availa-
ble. Please also contact your provider to clarify if it is possible to use a VPN (Virtual
Private Network) for possibly required server functionality.