User's Manual Part 1

Product Overview — Introduction to GSM and GPRS 5
P/N 9002363 Revision 1.8
Figure 3 GPRS Network Architecture
An interesting aspect of GPRS is how it achieves its high speeds to over 100 kbps when
circuit-switched data today is limited to 9600 (baud rate) or 14.4 kbps. GPRS uses the
same radio channel as voice calls, a channel that is 200 kHz wide. This radio channel
carries a raw digital radio stream of 271 kbps, which for voice calls is divided into 8
separate data streams, each carrying about 34 kbps. After protocol and error correction
13 kbps remains for each voice connection or about 14 kbps for data.
Circuit-switched data today uses one voice channel. GPRS can combine up to 8 of these
channels, and since each of these can deliver up to 14 kbps of data throughput, the net
result is that users will be able to enjoy rates over 100 Kbps. But not all eight-voice
channels have to be used. In fact, most mobile stations (MS) will be ones that are limited
to 56 kbps. The GPRS standard defines a mechanism by which a MS can request the
amount of bandwidth it desires at the time it establishes a data session.