User Manual

In PSD operations instead, the connection is made directly towards internet as if the PSD
modem which support GPRS/EDGE/WCDMA/HSDPA was a network IP socket interface.
There is 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 PSD connection is shown in the following picture, where the PSD connection
is between the PSD modem and the internet as if all the devices inside the dashed line are not
present:
Wireless Cellular PSD interconnectivity
Due to this kind of connection, when activating the PSD connection you must provide the
network parameters to enter through the internet point of the GPRS/EDGE/WCDMA/HSDPA
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 PSD 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
PSD modem directly on the internet, ready to be accessed virtually from anywhere in the
world at the same cost on the GPRS/EDGE/WCDMA/HSDPA network. Actually the billing
of the PSD connection is based on the amount of data exchanged (number of packets
transferred) independently from the time the connection is active or where these packets 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 PSD connection is that the controlling application must have its own
TCP/IP protocol stack embedded to decode the packets that arrive from
GPRS/EDGE/WCDMA/HSDPA network and encode the ones to be sent through the internet.
There are few considerations than must be done on the PSD connections:
 The WCDMA connection speed is symmetrical, 384kbps in reception and
sending.