GSM offers circuit-switched data services at lower rates. As a standard form, it is limited to 9.6 Kbps. This is obviously not enough for many applications. It takes a long time to setup and is too slow. A user occupies one timeslot out of the available 8 timeslots in a frame during the entire duration of a data call. This makes it very expensive. Later, a few enhancements were proposed and implemented to overcome data rate limitations. High speed circuit-switched data (HSCSD), which uses multiple timeslots, offers a maximum data rate up to 57.6 Kbps. It was not a great success. It essentially a circuit-switched technology and hence very expensive and inefficient for data applications. Most of the data applications are bursty and asymmetric in nature. This means that there are periods when little or no data is being transferred. For data applications, packet switching makes more efficient use of network resources than circuit switching, as it allows sharing of a data channel by many users.
General Packet Radio Service (GPRS) is designed to offer high-capacity end-to-end IP packet services over the GSM infrastructure. It is designed as an overlay network to protect the investment already made in GSM networks. It is based on packet switching. This means that scarce radio resources are shared among many users, resulting in much better utilization and hence lower cost. To achieve high data rates, GPRS employs new air interface error coding schemes and multiple timeslots. By using eight timeslots, the maximum data rate of 171.2 Kbps is achieved. In the BSS, the data is processed separately and passed to new serving nodes capable of handling packet data and finally routed to external data networks such as X.25, the Internet, or intranets.
