Iphone

I am trying to develop an telemetry system. It consists of ADuC814 embedded system and Siemens MC75
GPRS modem with integrated TCP/IP stack via AT commands.

I have three possible solutions:

1. Direct GPRS connection from MC75 to a central station (PC computer) with static IP address. A computer has
installed software which listens to defined port and stores incoming datagrams.

2. Central station has router which routes user datagrams to PC.

3. Central station also has MC75 modem. A direct GPRS connection between GPRS modems is established and user datagrams are being sent form modem to the PC.

Now, I have few questions about theese three systems. I´m sure it´s a peice of a cake for you :-)

First: Since I use GPRS modem with integrated TCP/IP stack, does also header traffic is being billed?
In the other words, is GSM operater billing only the useful data, or they bill all the informations going out from modem
(including TCP(UDP)/IP headers)?

Second: I have some Siemens datasheets with project proposals. It is said that it is possible to send raw, unformatted data in options 2 and 3. Precisely, it defines:

- Relation (Net data/Gross data) in telegram:
<100% for option 1
100% for options 2 and 3.

and

- GPRS connection costs >100% for option 1, due to overhead through formatted structure.

Since I read on this site that it is impossible to establish a direct PPP connection between
two points in GPRS, I am a little bit confused. What do they mean when they say that it is possible
to send raw data in options 2 and 3?

Third: In option 3, I am aware of that both GPRS modems must have static IP adresses . But, many
sources on the Inetrnet claim that GSM operaters do not offer static IP adresses for mobile device because of security issues. Can somebody give me a little bit more detailed explanation about how security is being affected if mobile station has a static IP adress?

Fourth: Is it possible to create such a system (similar to corporative VPN), in which both GPRS and central station have
static IP adress from private space, and due to that become unreachable from outside Internet world?

Thank you very much for your answers.

Iphone

First: Since I use GPRS modem with integrated TCP/IP stack, does also header traffic is being billed?
Yes, it will be billed. BTW, one reason more to us UDP/IP
> Can somebody give me a little bit more detailed explanation about how security is being affected if mobile station has a static IP adress?
From my side of few, there is no reason based on security. With dymamic IP adresses you can handle more users in the same IP range, because they are never all online.
Regards
Meff
GSM / GPS / GPRS modem and module for vehicle tracking