Telit Wireless Solutions Easy GPRS manual - page 5

Easy GPRS User Guide
80000ST10028 Rev. 0 - 02/01/07
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved page 5 of 35
In GPRS operations instead, the connection is made directly towards internet as if the GPRS modem
was a network IP socket interface. There's no data path reserved for the data exchange between the
two peers, instead the resources are allocated dynamically on demand and the data exchanged is
organized into packets typically TCP/IP, furthermore the maximum transfer speed can be much faster
than GSM CSD.
An example of GPRS connection is shown in the following picture, where the GPRS connection is
between the GPRS modem and the internet as if all the devices inside the dashed line are not
present:
GPRS interconnectivity
Due to this kind of connection, when activating the GPRS connection you must provide the network
parameters to enter through the internet point of the GPRS network ISP (Internet Service Provider)
and not the phone number to be dialed; therefore it is not possible to establish a direct point to point
GPRS connection between two modems as in CSD case, instead an internet tunneling must be done
to achieve a point to point connection between two peers.
This approach as the immediate advantage of projecting the controlling application of the GPRS
modem directly on the internet, ready to be accessed virtually from anywhere in the world at the same
cost on the GPRS; actually the billing of the GPRS connection is based on the amount of data
exchanged (number of packets transferred) independently from the time the connection is active or
where these packet must be delivered. Therefore, it is possible to leave the controlling application
always connected and ready to receive/send data on demand, while paying only for the data really
exchanged.
The drawback of the GPRS connection is that the controlling application must have its own TCP/IP
protocol stack embedded to decode the packets that arrive from GPRS and encode the ones to be
sent through the internet.
There are few considerations than must be done on the GPRS connections:
• the GPRS connection speed with a GPRS class 10 multislot device is asymmetrical, 3 time
slots in reception (43200 bps max) and 2 time slot in sending (28800 bps max) or 4 time slots in
reception (57600 bps max) and 1 time slot in sending (14400 bps max).
• The controlling application of the module must have a TCP/IP - PPP software stack to
interface with the GPRS modems.