Insys GPRS 4.2 11-02-01-03-10.008 Benutzerhandbuch
Produktcode
11-02-01-03-10.008
Manual Supplement Insys GSM/GPRS 4.0
23
Version 1.0 / 07.03
3. Usage With Own Application
3.1 What To Observe With GPRS
3.1.1 No Point To Point Connection Possible
In contrast to the usual GSM mode, in GPRS mode no point to point connection
is possible between two GPRS devices or between a GPRS device and a
is possible between two GPRS devices or between a GPRS device and a
modem (analog/ISDN).
Because the INSYS GSM/GPRS 4.0 has still GSM functionality, a point to point
connection is possible in GSM operation, but not with the transmission rates
available with GPRS.
After registering (“GPRS attach”) with the GPRS provider, PPP data is available
via the serial interface of the INSYS GSM/GPRS 4.0.
So, the application has to provide a PPP client to complete the dial-up.
The protocols for user data transport and connection management have to be
provided by the application as well (e.g. TCP/IP stack).
Because the INSYS GSM/GPRS 4.0 has still GSM functionality, a point to point
connection is possible in GSM operation, but not with the transmission rates
available with GPRS.
After registering (“GPRS attach”) with the GPRS provider, PPP data is available
via the serial interface of the INSYS GSM/GPRS 4.0.
So, the application has to provide a PPP client to complete the dial-up.
The protocols for user data transport and connection management have to be
provided by the application as well (e.g. TCP/IP stack).
3.1.2 Firewall/NAT At GPRS Provider
The IP address of the GPRS terminal device is dynamically assigned by the
provider and it is temporary, i.e. another IP address will be assigned for the next
dial-up to the provider.
The IP address cannot be addressed from outside, because the providers
manage the addressing at the transition from the GPRS network to the “regular”
internet using a NAT table (Network Address Translation), to be able to manage
the address range limited by IPV4.
Furthermore, this increases the security because the GPRS device is not
provider and it is temporary, i.e. another IP address will be assigned for the next
dial-up to the provider.
The IP address cannot be addressed from outside, because the providers
manage the addressing at the transition from the GPRS network to the “regular”
internet using a NAT table (Network Address Translation), to be able to manage
the address range limited by IPV4.
Furthermore, this increases the security because the GPRS device is not
accessible for “scanner” that way. Unintended data traffic can be prevented
so, because the data amount is accounted for GPRS.
This means that the following functions are not possible for example:
This means that the following functions are not possible for example:
-
“Ping” the device from outside
-
Set-up TCP/ IP connections to the GPRS device from outside
-
Send UDP packets to the GPRS device from outside