 does not utilize radio resources very effectively since the timeslot is blocked for other users, even if the MS is not sending anything. The "bursty" character of data communication cannot be well-served by TDMA systems. The capacity that is needed in the uplink and downlink are also not identical. Often, a mobile datacom user can cope with low capacity on the uplink, but requires higher capacity on the downlink (for accessing HTML and other files). A mobile datacom user also uses his access for considerably longer time per session than the average length of a voice call. The solution to that problem is, of course, to use packet switching in PLMNs, which means that the necessary resources depend on the amount of data that are sent, not on the length of the call. 4.4.2 GPRS Physical Network Level 0 Using the formal notation for physical networks, a GSM physical network on level 0 that includes GPRS functionality looks as shown in Fig. 4.10. A GSM-MS should be able to utilize both circuit-switched services and packet access services. These are used over different physical connections over the radio interface, therefore there are two different network interfaces, 11.0 and i2.0. Net- work interface 11.0 is used for packet access. It can be tailored to actual capacity needs in a cell by allocating from one to eight timeslots on a carrier, together called the packet data channel (PDCH). If eight timeslots are used for the PDCH, the bitrate is between 200-600 kbps, depending on the modulation technique that is 4 Physical Network Modelling used (the higher rate is achieved with EDGE). All MSs that exist in a cell use the same PDCH for packet access. gsm&gprs PDN applications Host. plmn.0 pdn.0 pdn packet data network fxn fixed networks Fig. 4.10 GSM with GPRS on physical network level 0 The role of the GPRS part the PLMN is to connect MSs that access the network over i1.0 to a packet data network (PDN) of their choice. When the PLMN has established a logical connection between an MS and a PDN, the MS communicates with t