to the network and not vice versa (a feature that came in the Universal Mobile Telecommunications System, or UMTS). Second Generation Cellular Networks MSC/VLR Network SubSystem (NSS) H/E etc A-bis (EIR) SS7 Network Gr/Gs GPRS backbone IP Network Base Station Subsystem (BSS) GPRS Core Network The Internet (or a corporate) Figure 1.1 GSM and GPRS System Limitations of 2G Networks Low transfer rates. The 2G networks are primarily designed to offer voice services to the subscribers. Thus the transfer rates offered by these networks are low. Though the rates vary across technologies, the average rate is of the order of tens of kilobits per second. Low efficiency for packet switched services. There is a demand for Internet access, not just at home or the office but also while roaming. Wireless Internet access with the 2G networks is not efficiently implemented. Multiple standards. With a multitude of competing standards in place, a user can roam in only those networks that support the same standard. This allows the user only limited roaming. Therefore the 2G network technology was semi-global in this respect. 1.3.4 GPRS (General Packet Radio Service) GPRS is a nonvoice, i.e. data, value added service to the GSM network. This is done by overlaying a packet based air interface on the existing circuit switched GSM network (see Figure 1.1). In infrastructure terms, the operator just needs to add a couple of nodes and some software changes to upgrade the existing voice GSM system to voice plus data GPRS system. The voice traffic is circuit switched while data traffic is packet switched. Packet switching enables the resources to be used only when the subscriber is actually sending and receiving the data. This enables the radio resources to be used concurrently while being shared between multiple users. The amount of data that can be transferred is dependent upon the number of users. Theoretical maximum speeds of up to 171.2 kilobits per second (kbps) are achievable with GPRS using all eight timeslots at the same time. GPRS 