8.1 GPRS as Compared to GSM CS Data

The data services provided by the GSM circuit switched (CS) network do not fulfill the needs of service providers and users. GPRS has devised a set of mechanisms to transfer user data packets in an efficient way between the user and external packet data networks.

The GPRS packet switched (PS) technology is designed considering commonly used packet protocols (e.g., IP, PPP, and X.25). Therefore, applications based on these standard data protocols are supported much more efficiently than the GSM CS networks. For instance, unlike the CS data there is no need to perform rate adaptation to 64 Kbps on the network interface.

The GPRS system can provide much higher data rates than the current CS data services on the GSM networks. It can achieve a maximum of up to 171.2 Kbps using all eight time slots on a GSM carrier at the same time. This results in supporting much higher bit rate applications. However, it should be noted that most implementations of mobile devices will support either 3 or 4 timeslots on the downlink and 1 or 2 timeslots on the uplink.

The GPRS radio interface provides spectrum efficiency for packet data transfer. It provides mechanisms to compress the header and payload of a packet before it is transmitted over the radio interface. The resulting bandwidth savings are critical since bandwidth is relatively scarce and should be used as efficiently as possible.

GPRS provides PS radio bearers for bursty traffic. A channel is allocated when needed and released immediately after the transmission of the packets. With this principle, multiple users can share one physical channel (e.g., time slot). This results in highly efficient radio resource utilization compared to the dedicated radio bearers in the CS network.

GPRS offers more options for charging packet data usage than that offered by the CS network. In the CS network, billing is based only on the duration of the connection. In addition to duration-based charging, GPRS provides volume and content-based charging. Volume-based charging is more suitable for bursty traffic. A user can be charged based on the data volume exchanged. Content-based charging provides additional flexibility to the operators to price different types of contents.

GPRS provides session setup with a packet session management protocol. In the GSM CS networks, a modem connection on top of a CS connection has to be established before the MS can exchange data with the network. In GPRS, there is no need for a dial-up modem connection, thus reducing the session setup time. GPRS supports concurrent operation with existing GSM services for CS speech, CS data, and SMS.