Introduction

• Today, the cellular networks are evolving to meet the new requirements of mobile data communications. The target of the mobile communications system development is to create service that is able to offer global coverage with multi-media access speed. Today, satisfactory mobile data communications are possible only via a second generation digital mobile communications network. The world's most advanced and wide spread second generation mobile network is GSM (Global System for Mobile Communications).
• There are two methods how data can be transferred in GSM: Short Message Service (SMS) and GSM data service. Both of them enable 9.6 kbit/s circuit switched connection. However, data transmission capabilities of SMS are much more restricted and thus it is only suitable for transmitting short text messages.
• There are several drawbacks in the second generation GSM being a bearer service for data. For example, the bit rate of the GSM radio access network is very low, thus clearly acting as a bottleneck in the end-to-end system. In addition, a relatively long connection setup time and the typical restrictions of a circuit switched connection method in data transmission limit data applications to be offered.