. In a GPRS system there are three states: IDLE, STANDBY and READY. In the IDLE mode, a subscriber is not attached to the GPRS network, while in the STANDBY mode the GPRS network knows the routing area location of the mobile station. The mobile station enters the READY state by sending a service request to the network. In this state, the mobile station becomes attached to the GPRS mobility management and is known by the network on the call basis. Once the call is finished, the mobile enters into the STANDBY mode again. Thus, when moving from STANDY to READY, the SGSN receives and processes a GPRS attach request; and when moving from READY to STANDBY, the SGSN receives and processes a GPRS detach request. For movement of data between the MS and the GPRS network, the PDP (packet data protocol) context needs to be activated. Either the MS or the GPRS network can generate the PDP context. These requests are sent and processed by the SGSN. A PDP context generally contains activated information such as addresses (required for the data traffic), QoS-related information, protocol types, etc. MS uses the PDP contexts in the STANDBY and READY states. The number of PDP contexts is one of the factors that have a direct impact on the SGSN capacity. Resource Allocation Radio time-slot allocation also changes in the GPRS air interface. It becomes more dynamic. A GPRS mobile is capable of using the network both for voice (CS) and data (CS and PS). GPRS traffic is managed by the BSC as it does the allocation of resources for the CS and PS data. The time slots that handle the CS traffic fall under CS territory and the time slots that handle PS traffic fall under the GPRS territory. Some of the time slots are in dedicated mode and some in default. Each group of time slots is known as a territory (see Figure 5.5). Consider a base station with two transceivers, TRX1 and TRX2. There are eight radio time slots in each of the two TRXs. In TRX1, two TS are allocated to the signalling (i.e. GPRS NETWORK PLANNING TRX 1 PBCCH Dedicated(fixe