General Packet Radio Service (GPRS) has been introduced as transitional data technologies for the evolution of GSM GPRS is the packet mode extension to GSM, supporting data applications and exploiting the already existing network infrastructure in order to save the operator’s investments.

GPRS needs for a modest adaptation at radio interface level of GSM hardware. However, it adopts new physical channels and mapping into physical resources, as well as new radio resource management. The new physical channel is called 52-multiframe and it is composed of two 26 control multiframes of voice-mode GSM.

High data rates can be provided since the GPRS users can exploit more than one time slot in parallel with the possibility, contrary to the HSCSD technology, to vary the number of time slot assigned to a user (e.g., to reduce them in case of scarcity of resources for the voice service).

The maximum theoretical bit rate of the GPRS is 171.2 Kbps (using eight time slots). Current peak values are 20/30 Kbps. The 52-multiframe is logically divided into 12 radio blocks of four consecutive frames, where a radio block (20 ms) represents the minimum time resource assigned to a user.

If the user is transmitting or receiving big flows of data, more than one radio block can be allocated to it. The whole set of these blocks received/transmitted by a mobile terminal during a reception/transmission phase forms the temporary block flow (TBF), which is maintained only for the duration of the data transfer.

A session can consist of one or more TBFs that are activated during the transmission/reception phase. Each TBF is assigned a temporary flow identity (TFI) by the network, which is unique in both directions.

For instance, during the reception, each mobile terminal listens to all the radio blocks flowing on the generic channel, but collects only the ones with the proper label (e.g., TFI).

This mechanism simplifies the resource management in point-to-multipoint transmissions, like in the downlink (base station-mobile terminal), since each receiving station can pick up the proper blocks.

Contrary to the GSM, GPRS service can flexibly handle asymmetric services by allocating a different number of time slot in uplink and downlink. Time slots can be allocated in two ways:

1. On demand, where the time slots not used by voice calls are allocated, and in case of resource scarcity for voice calls (congestion), time slots already assigned to GPRS service can be de-allocated;

2. Static, in which some time slots are allocated for GPRS and they cannot be exploited by voice calls.

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