aximum number of PDP contexts the maximum number of TRXs the maximum number of BTSs the maximum number of PCM lines towards the Abis and towards the Gb interface, as well as the traffic on the Gb interface the maximum number of location areas and routing areas. GPRS: NETWORK PLANNING AND OPTIMISATION Abis-interface G6-interface Figure 5.6 Packet control unit (PCU) 5.5.4 Packet Core Network Planning Owing to the introduction of packet data, core network planning is subdivided into two major parts: planning for the circuit core and for the packet core. Planning for the circuit core remains more or less as discussed in Chapter 3, so will not be repeated here. This section covers planning for the packet core. The most important aspect of packet core network planning is dimensioning of the three interfaces, Gb, Gn and Gj (refer back to Figure 5.3). The Gb interface The interface between the BSS and SGSN, which allows the exchange of both data and signalling information, is called the Gb interface, as shown in Figure 5.7. This interface is more dynamic than the A-interface. It not only allows multiple users to share its resources, but also reallocates the resources once the data transfer is stopped, as compared to the A-interface where the physical resources are dedicated to the user irrespective of their usage. The protocol stack of the Gb interface is shown in Figure 5.8. There are three layers on the top of the physical layer. The physical layer serves the upper layers and transfers the data and signalling information from one end to another along with the overheads that are generated by each of the layers. The interconnection between the BSS and the SGSN can be done by using any of the physical media or by implementing the frame relay network. The advantage of using the frame relay network is that the interfaces at the two ends can be different. Frame Relay Network Figure 5.7 Gb interface GPRS NETWORK PLANNING SNDCP RELAY BSSGP BSSGP GSM RF Figure 5.8 Protocol stack of Gb interface A frame-relay network is basicall