Rainbow Electronics GM862-QUAD-PY - Manual (Page 9)

Easy GPRS User Guide
80000ST10028 Rev. 4 - 16/07/08
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved page 9 of 63
Now there are two possibilities:
• the server application calls on demand the remote units, provided it has stored their phone
numbers in a private database.
• the remote units call the server application modem when needed and eventually retry in the
case they found it busy; this time the phone number to be stored is only one, the server number
which must be stored on the remote units.
In both cases, once connected, the remote unit sends the meteorological data to the server, which
places it in a central database for further reading by anyone who accesses the meteorological internet
site for example.
The drawback of this approach is that the CSD modem needs about 30s to establish the connection
and, depending on the amount of data to be transferred (usually few hundreds bytes), some seconds
to transfer them. So let’s say we pay a 40s call while we need only 10s to transfer data.
1.1.2 GPRS application example
The same application can be preformed with all the Telit modules using the GPRS feature.
The remote unit is always connected to the internet taking advance of the features of the GPRS
system, when it needs to send data to the server application it simply fills the TCP/IP packets for the
server with the meteorological data and gives them to the Telit module to deliver. The central server
has a single modem to connect to the internet, receives the TCP/IP packets from all the remote units
and places the contained data in the central database.
The advantage of using GPRS is that the remote unit is always connected and reachable and it pays
only for the amount of data (small) transferred and not for the connection time as in CSD operations;
in addiction the call billing is equal for devices placed anywhere in the Network Operator State and the
server can be anywhere in the World.
Furthermore, in the CSD operation the server shall have a set of modems and multiple phone lines to
ensure that the calling units will not find it busy, while a single modem is enough for GPRS operation.
The speed at which the packets can be downloaded is up to 57600 bps (class 10 device working at
4+1), 4 times faster than CSD.
In the following paragraphs more detailed information will be given on how to establish GPRS
connection.