GPRS is the so-called "two-and-a-half generation" of mobile comms. It's called this because it uses the existing underlying GSM network but overlays a packet-switched network over it. Any GSM system can be adapted to GPRS by modifying the phones and the hardware at the base stations of the cells.
Rather than establishing a circuit-switched connection to the base station, the phone just sends a single packet and then stops. This is perfect for 'bursty' traffic such as data transfer, where timing isn't important but accuracy is but is not suitable for something like voice where although accuracy isn't important (the human ear is very good at making up for inaccurate data) timing is very important.

As mentioned in the discussion of GSM, eight conversations are permitted per band on a GSM network, so each conversation can only obtain one eighth of the bandwidth of the whole band. However, with GPRS, a conversation is allowed to use the whole band to send, albeit only for a brief time (the duration of one packet).

Rather than the pitiful 9600bps that GSM is capable of, GPRS can (theoretically) attain data rates of >100Kbps. However, this bandwidth is shared between users of a cell, so in practice, you can expect a sustained data rate equivalent to current generation modems. However, GPRS has a major advantage over using a modem: it gives the appearance of being always connected to the Internet. Because it is a digital network, it doesn't take any time to connect to a remote host, but can send packets on demand, giving the illusion that it is always connected.

Introduction - Modems - ISDN - DSL - cable modems - Mobile comms - Conclusion - Glossary