User Manual

The Packet Switched Data (PSD) connection on GPRS, EDGE, WCDMA and HSDPA
network permits DATA transfers in a completely different way with respect to previous point
to point communications made with Circuit Switch Data (CSD) connection on GSM and
WCDMA network.
In CSD operations the modem establishes a connection with the other party (another modem)
in such a way that all the Network devices in between are transparent to the data exchanged,
simulating a real point to point connection, just as if the other party is directly connected with
the controlling application of the modem. The other party can be either an Internet Service
Provider (ISP) or a private server, but in any case, the arrival point must have a modem to
connect to (Landline, ISDN or GSM/WCDMA CSD). The connection establishment
procedure defines a particular path where all the information exchanged between the two
peers flows and this path is reserved for exclusive use of these 2 peers for all the time the
connection is active.
This approach has the drawbacks of a long time to set-up the link between the two peers (up
to a minute) and a time counting bill which proceeds even if no data is exchanged because the
path resources are reserved anyway; furthermore the speed of the data transfer is limited to
14400 bps.
An example of this kind of operation is shown in the following picture, where the point to
point connection is between the two peers as if all the devices inside the dashed line are not
present:
Wireless Cellular CSD interconnectivity