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P800/P802
White Paper, January 2003
97
Technical Explanation of CSD, HSCSD and GPRS
This section provides an overview of the way data communication works in a GSM network
environment. This will help you to understand the characteristics of the different solutions
supported by the P800 and the parameters which govern the data transmission speeds available.
Circuit Switched Data (CSD)
A modem and landline is a common way to connect to the internet and company networks. The modem
establishes a telephone call to the remote server which is ‘circuit-switched’, meaning that a telephone circuit
is maintained for the duration of the connection, irrespective of whether data flows or not. The connection
has a fixed bandwidth and is normally charged on a connected-time basis.
In GSM networks, this facility is widely available and is called Circuit Switched Data (CSD). It is
very similar to using a modem, but is subject to lower data transmission speeds due to the
connection taking place over the GSM wireless network. The standard speed of operation for
CSD is 9.6kbps transmit and receive. 14.4kbps is available in some GSM networks. The P800 will
operate at the higher speed where it is available.
The above diagram shows an end-to-end overview of a circuit switched data call via the GSM
network. When establishing a data call, the P800 will be connected via the GSM network to what
you may think of as a ‘modem’ within the network, rather like the GSM network is acting as a
Circuit-Switched Network Server